Nanoalloys as advanced materials

Transcription

European Cost Action MP0903
Nanoalloys as advanced materials:
from structure to properties and applications
http://www.nanoalloy.eu
Action Conference and MC meeting
Kilmurry Lodge, Limerick, Ireland
October 12-14, 2011
Joint Chair of the Meetings:
Dr David Tanner / Dr Tofail Syed
(Materials and Surface Science Institute,
University of Limerick, Ireland)
MSSI
1
Oral Presentation Schedule
Wednesday 12th October 2011
9:00 – 9:30
9:30 – 9:50
9:50 – 10:20
10:20 – 10:40
10:40 – 11:00
11:00 – 11:30
11:30 – 12:00
12:00 – 12:20
12:20 – 12:40
12:40 – 13:00
12:40 – 15:00
Registration
Welcome
Dr David Tanner & Prof. Edmond Magner
Materials and Surface Science Institute, University of Limerick
Action Chair: Prof. Riccardo Ferrando
Session 1 – Structure: Chair Roy L. Johnston
P. Andreazza1,*, Z. Kataya1, H. Kelfane1, C. Andreazza-Vignolle1, C. Mottet2,
H.C.N. Tolentino3, M. De Santis3, R. Felici4, O. Lyon5, A.Y. Ramos3
(1 Orléans, France ;2 Marseille, France ;3 Grenoble, France ;4 Grenoble,
France ; 5Cedex, France)
Structural and morphological probing of core-shell and alloyed nanopaticles
from in situ x-ray scattering methods
B.Zhu1, Y. Wang1,2, I.S. Atanasov1, D. Cheng3, M. Hou1
(1Bruxelles, Belgium ; 2Shanghai, China; 3Beijing, P.R. China)
Ordering and Segregation in Isolated Au-Pd Icosahedral Nanoclusters and
Nanowires and the Consequences of their Encapsulation inside Carbon
Nanotubes
A. Kroupa1,T. Kana1, R. Mishra2, A. Zemanova1, H. Ipser2
(1Brno, Czech Republic; 2 Wien, Austria)
CALPHAD type modeling of phase diagrams of nanomaterials, experimental
preparation of nanoalloys
Coffee Break
Session 2 – Catalysis : Chair Konstantin M. Neyman
Elad Gross2 and Micha Asscher1
(1Jerusalem, Israel ; 2, Berkeley, USA)
The role of reduced oxide sites on the stability, morphology, reactivity and
selectivity of supported bimetallic clusters
D. A. Tanner, S. Belochapkine, F. Laffir and S. Nakahara
(Limerick, Ireland)
TEM analysis of Kirkendall void formation in sputtered aluminium-lithium
films
Alberto Sandoval1, Antonio Aguilar1, Catherine Louis2, Agnès Traverse3 and
Rodolfo Zanella1,*
(1UNAM, México ; 2 Ivry sur Seine, France ; 3Orsay, France)
Bimetallic Au-Ag/TiO2 Catalyst Prepared by Deposition-Precipitation. High
Activity and Stability in CO Oxidation.
J.Vřešťál, J.Pinkas, J.Sopoušek, P.Brož, P.Buršík, A.Zemanová, D.Škoda,
A.Stýskalík
(Brno, Czech Republic)
Preparation, Characterisation, Thermal Analysis and Phase Diagram of SnAg and Cu-Ni Nanoalloys
Lunch Break and Discussions
2
15:00 – 15:30
15:30 – 15:50
15:50 – 16:10
16:10 – 16:40
16:40 – 17:00
17:00 – 17:20
17:20 – 17:40
17:40 – 18:00
18:00 – 18:20
Session 3 – Magnetism : Chair Alessandro Fortunelli
L. E. Diaz-Sanchez1, G. M. Pastor2, F. Tournus3, and Veronique Dupuis3
(1Toluca, Mexico; 2Kassel, Germany; 3Villeurbanne, France)
Ab-intio calculations on CoPt nanoalloys to explain apparent experimental
contradictions
V. Dupuis1, L. Diaz-Sanchez 2, A. Hillion1, S. Rusponi3, A. Tamion1, F.
Tournus1, G. Pastor2, H. Brune3.
(1 Villeurbanne (FR) ;2 Lausanne (CH); 3 Kassel (DE))
Finite size effects on structure and magnetism in mass-selected FeRh and
CoPt nanoparticles
Peter Entel
(Duisburg, Germany)
Tailoring structure and magnetism of free and decorated transition metal
nanoparticles
Coffee Break
Session 4 – Structure: Chair Veronique Dupuis
K. Damianos and R. Ferrando
(Genova, Italy)
Structures of Au and AuPd clusters on stepped MgO
D. Chovan, S. Tofail
(Limerick, Ireland)
Elasticity of Ni(Ti,Pt)
F. Calvo
(Lyon, France)
Roles of size, composition, and chemical disorder on the vibrations of goldsilver nanoalloys
S.Brodacka 1, A. Antusek2, D. Passerone3, J. Janczak-Rusch3, R. Kozubski1
(1 Krakow, Poland; 2Trnava, Slovak Republic; 3Dübendorf, Switzerland)
Simulation of nanostructure interfaces and segregation in nanostructured
filler metals in a multilayer configuration
Ruth Chantry and Ziyou Li
(Birmingham, U.K.)
Metal-Metal Interface in Bimetallic Nanorods at Atomic Scale
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Thursday 13th October 2011
Session 5 – Growth: Chair Ziyou Li
9:30 – 10:00
C. Petit
(Paris, France)
Synthesis of Nano-Alloys: a Colloidal Approach
10:00 – 10:20 Aymen Ben Azouz1,2, Mercedes Vázquez1, C.P. Romero3, Milan Obradovic3,
Didier Grandjean3, Peter Lievens3, Dermot Brabazon 1,2 and Brett Paull4
(1 Dublin, Ireland; 2 Dublin, Ireland; 3Leuven, Belgium; 4Hobart, Australia)
Bimetallic nano-cluster deposition in microfluidic channels for bio-analyte
detection
10:20 – 10:40 Numan Hoda, Leyla Budama, Buçin Acar, Önder Topel
(Antalya, Turkey)
Synthesis of Ag-ZnO nanoparticles within reverse micelles
10:40 – 11:00 Willian G. Menezes1, Volkmar Zielasek1, Christian Kübel2, Dieter Wöhrle1,
and Marcus Bäumer1
(1 Bremen, Germany; 2Eggenstein-Leopoldshafen, Germany)
TEM study of nanoparticle formation in diblock copolymer micelles loaded
with two metal salts: AuAg and Au/Pt
11:00 – 11:30 Coffee Break
Session 6 – Structure: Chair David Tanner
11:30 – 11:50 Roy L. Johnston 1, Andrew J. Logsdail1, Sven Heiles2 and Rolf Schäfer2
(1Birmingham, UK ; 2Darmstadt, Germany)
Global Optimisation of Nanoalloys at the Density Functional Theory Level
11:50 – 12:10 Micha Polak
(Beer-Sheva, ISRAEL)
Prediction of intra-core and inter-particle separation transitions: Towards
the construction of nanoalloy phase-diagrams
12:10 – 12:30 Y. Wang 1,2, M. Hou2
(1Shanghai, China; 2Brussels, Belgium)
Ordering of bimetallic nanoalloys predicted from bulk alloy phase diagrams
12:30 – 12:50 P. Lecante a, MJ. Casanovea, JG. Matteia, C. Amiensb, D. Ciuculescub, F.
Pelletierb
(aToulouse, France ; bToulouse, France)
The complex structural study of bi-metallic Fe-Bi nanocomposites
12:40 – 14:30 Lunch Break and Discussions
14:30 – 16:30 Management Committee meeting
16:30 – 18:30 Poster Session
Social Dinner at Bunratty Castle – Bus leaves from Kilmurry Lodge at 19:30
4
9:10 – 9:40
9:40 – 10:00
10:00 – 10:20
10:20 – 10:40
10:40 – 11:00
11:00 – 11:30
11:30 – 12:00
12:00 – 12:20
12:20 – 12:40
12:40 – 13:00
13:00 – 13:10
Friday 14th October 2011
Session 7 – Growth / Catalysis: Chair Catherine Louis
Stefan Vajda
(New Haven, USA.)
Sub-nanometer Clusters as Building Blocks for (Multi)functional Nanoalloys
Sergey M. Kozlov,1 Lyudmila V. Moskaleva,2 Marcus Bäumer,2 Konstantin M.
Neyman1,3*
(1 Barcelona, Spain; 2 Bremen, Germany; 3 Barcelona, Spain)
Progress in density-functional studies of Pd-Zn and Au-Ag nanostructures
C. Di Paola1, S.M. Kozlov2, K.M. Neyman2 and F. Baletto1
(1 London, UK ; 2Barcelona, Spain)
O2 chemisorption on Pt shell Ni core nanoalloys deposited on MgO(100)
Dmitri A. Bulushev1*, Sergey Beloshapkin1, Pavel E. Plyusnin2, Yurii V.
Shubin2, Valerii I. Bukhtiyarov3, Sergey V. Korenev2, and Julian R.H. Ross1
(1Limerick, Ireland; 2 Novosibirsk, Russia; 3Novosibirsk,Russia)
PdAu/Al2O3 Catalysts for Hydrogen Generation from Formic Acid
Alessandro Fortunelli
(Pisa, Italy)
CO2 reduction by H2 using Ni-Cu oxide-supported catalysts
Coffee Break
Session 8 – Catalysis: Chair H. Polatoglou
Julius Jellinek and Aslihan Sumer
(Argonne, USA)
Theoretical Studies of Structural, Electronic and Chemical Reactivity
Properties of Pt, Mo, and Pt/Mo nanocatalysts
Gordon Armstrong, Tanushree Bala*, Fathima Laffir and Roibeard Thornton
(Limerick, Ireland)
From Microprocessors to Microbes: Versatile synthesis and potential
applications of titania–silver and alumina–silver composite nanoparticles
A. M. Sharif,+ D. N. Buckley,+ M. Buck,* and C. Silien+
(+ Limerick, Ireland; *St. Andrews, U.K.)
Bonding Asymmetry and Adatoms in Low Density Self-assembled
Monolayers of Dithiol on Au (111)
Urszula Salaj-Kosla, Edmond Magner
Materials and Surface Science Institute, University of Limerick, Limerick,
Ireland,
e-mail address: [email protected], [email protected],
tel.:+353 (0)61 202629, fax.:+353 (0)61 203529
Mesoporous gold nanoalloy as a matrix for redox enzymes immobilization
Close of the meeting
5
Poster Session: Thursday 13th October 16:30-18:30
O’Brien Suite, Kilmurry Lodge
Poster presentations
1
2
3
4
5
6
7
8
9
10
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J. Fedotova1, M. Milosavljević2, Cz. Kapusta3
(1Minsk, Belarus; 2Belgrade, Serbia ; 3Krakow, Poland)
Tunneling magnetoresistance in FeCoZr-Al2O3 films containing “metal core-oxide shell”
nanoalloy particles
T. Káňa, A. Kroupa and M. Šob
(Brno, Czech Republic)
Surface tension of Ni−Sn intermetallics
M. Röefzaad, J. Spéder, M. Nesselberger, M.Arenz
(Copenhagen, Denmark)
L. Altmann, M. Bäumer
(Bremen, Germany)
Pt based Nanoalloys for the use in proton exchange membrane fuel cells
R.P. Doherty1,2, C. Thomas1, J.-M. Krafft1, C. Méthivier1, H. Remita2, C. Louis1
(1 Paris, France; 2Orsay, France)
On the promoting effect of Au on CO oxidation kinetics of Au-Pt bimetallic nanoparticles
supported on SiO2: an electronic effect?
N. El Kollia, S. Merad Bedranea,b, S. Giorgioc, L. Delannoya, C. Louisa
(a Paris – France; bAlgérie; cMarseille, France)
A comparative study of The preparation OF SUPPORTED nanosized bimetallic goldpalladium particles
Haydar Arslan* and Roy L. Johnston**
(* Zonguldak, Turkey; ** Birmingham, UK.)
Theoretical Study of 38-Atom Cobalt-Palladium Clusters
Baljit Singh a, Fathima Laffir b, and Eithne Dempsey a
(a Dublin, Ireland; bLimerick, Ireland)
Surface chemistry of bimetallic nanocomposite catalysts as revealed by X-ray
Photoelectron Spectroscopy
Jacek Żegliński1, Michael Nolan2, Damien Thompson2, and Syed A. M. Tofail1
(1 Limerick, Ireland ; 2 Cork, Ireland)
A detailed ab initio investigation of water adsorption on stoichiometric and nonstoichiometric surfaces of hydroxyapatite
K. McNamara, S.A.M Tofail, D. Conroy, J. Butler, A.A Gandhi and W. Redington
(Limerick, Ireland )
X-ray analyses of thermally grown and reactively sputtered tantalum oxide films on NiTi
alloy
M. Byshkin1,2, M. Hou1
(1 Bruxelles, Belgium ; 2 Kharkov 61108, Ukraine)
Phase transformations of Fe-Ni nanoalloys
E. Twohig, P. Tiernan, and S.A.M. Tofail
(Limerick, Ireland)
An Experimental and Numerical Analysis of the Dieless Drawing of Nitinol Alloy
Patrick Cronin, Jacek Zeglinski , Peter Tiernan and Syed A.M. Tofail
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13
14
15
16
17
18
19
(Limerick, Ireland)
Incorporation of nanoparticles with tailored distribution into Polymeric Surfaces and the
Adhesive Strength of such incorporated nanoparticles
G. Pigozzi1, D. Mukherji2, P. Schmutz1
(1 Dübendorf, Switzerland ; 2 Braunschweig, Germany)
The synthesis of intermetallic nanoparticles: COST research project plan and preliminary
results
R. Novakovic, S. Delsante, G. Borzone
(Genoa, Italy)
Coalescence in nano-sized metallic systems
S. Delsantea, G. Ennasb, G. Borzonea, G. Pigozzic , M.Pawelkiewiczc, J. Janczak-Ruschc
(a Genova – Italy; b Monserrato-Italy; c Dübendorf – Switzerland)
Synthesis and characterization of eutectic Ag-Cu alloy nanoparticles
I.S. Atanasov1, M. Hou2
(1Sofia, Bulgaria ; 2Brussels, Belgium)
Powerlaw scaling of the rate toward equilibrium of Au-Pd nanoparticles with the rate of
heating
E.Armstrong and C. O’Dwyer
(Limerick, Ireland)
Three-dimensional Ordered Macroporous LiFePO4 Inverted Opal Thin Film Cathodes for
High Performance, Ultrafast Charging Lithium-ion Batteries
Simon Brodersen
(Lyngby, Denmark)
Understanding the catalytic reactivity of gold nanoparticles through multi-scale
simulations
K.Kumbilieva
(Sofia, Bulgaria)
On modeling the kinetics of processes over poly-functional bi-metallic catalysts
7
Oral Session 1 – Structure
8
1
Structural and morphological probing of core-shell and alloyed
nanopaticles from in situ x-ray scattering methods
P. Andreazza1,*, Z. Kataya1, H. Kelfane1, C. Andreazza-Vignolle1, C. Mottet2, H.C.N.
Tolentino3, M. De Santis3, R. Felici4, O. Lyon5, A.Y. Ramos3
*
Email: [email protected]
Centre de Recherche sur la Matière Divisée - Université d’Orléans – CNRS, 1b rue de la
Férollerie, 45071 Orléans Cedex 2, France.
2
Centre Interdisciplinaire de Nanosciences de Marseille - CINaM – CNRS,Campus de Luminy,
case 913, 13288 Marseille cedex 9, France.
3
Institut Néel - CNRS – Université Joseph Fourier, 25 av des Martyrs, 38042 Grenoble cedex 9,
France.
4
European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble cedex 9, France.
5
Synchrotron Soleil, L'Orme de Merisiers, BP 48, F-91192 Gif-sur-Yvette, Cedex, France.
1
Abstract
Compared to monometallic systems, the addition of one or several metals induces
complex behaviors, not always well understood, which give a larger diversity in the
structure and morphology of nanoparticles (NPs) and offer an additional degree of
freedom to tune their properties for relevant applications - as in magnetic data or
energy storage (fuel cell). Besides the composition effect, finite matter quantity effects
lead to original variations of atom arrangement, such as disordered/ordered,
segregated, core-shell, chemically-induced strained particles. The main challenge is to
understand the origin of rearrangements of atomic species in multicomponent
nanoparticles, which lead to such structures. The most complete thermodynamic
equilibrium description of a nanoalloy is achieved by determining its phase diagram, as
a function of size, composition and temperature. However, the kinetic effects which
occur during the growth or the evolution of nanoalloys can yield out-of-equilibrium
structures, not predicted by thermodynamic considerations alone. In all cases, because
of this complexity, the determination of the atom arrangement at the nanoscale is a
very difficult task, requiring the synergic efforts of experiment [1,2] and computer
modelling [3,4].
Methods that probe local and average features as well as nanometer to micrometersized data, provide highly complementary information about the structure and
morphology of nanostructures and are much powerful when used together. For that,
we have developed combined X-ray scattering and electron microscopy strategy
allowing the determination of the structure at the atomic scale range (small angles)
and the morphology at the particle scale range (wide angles), respectively. Because the
high reactivity of Co-based particles, x-ray experiments: Grazing Incidence Small-Angle
X-ray Scattering (GISAXS) and Grazing Incidence X-ray wide angles scattering (GIWAXS),
are performed in situ in UHV conditions [1,2] during the nanoalloy growth obtained by
vapor deposition or during thermal annealing. The quantitative structural analysis have
been facilitated and consolidated using Monte Carlo (MC) simulations [2,3] of Co-Pt
nanoalloys within a semi-empirical tight-binding potential, to identify the experimental
phase transitions (ordered, disordered fcc, multi-twinned decahedra and icosahedra).
In addition, the combination of GISAXS with the anomalous effect have allowed the
extraction of scattering data from the two kind of metal atoms to identify core-shell
atom arrangement [5].
9
Références
P. Andreazza, in Nanoalloys: Synthesis, Structure and Properties edited by D. Alloyeau,
C. Mottet, C. Ricolleau (Springer-Verlag, London) in press
J. Penuelas, P. Andreazza, C. Andreazza-Vignolle, H. C. N. Tolentino, M. De Santis, C.
Mottet, Phys. Rev. Lett. 100 (2008) 115502. and, J. Penuelas, et al. Eur. Phys. J., ST 168
(2009) 19.
P. Andreazza, C. Mottet, C. Andreazza-Vignolle, J. Penuelas, H.C.N. Tolentino M. De
Santis, N. Bouet and R. Felici, Phys. Rev. B 82, (2010) 15.
F. Calvo and C. Mottet, Phys. Rev. B 84, 035409 (2011)
P. Andreazza, H. Khelfane, O. Lyon, C. Andreazza-Vignolle, A. Ramos, M. Samah, Eur.
Phys. J. (2011) in press
10
2
Ordering and Segregation in Isolated Au-Pd Icosahedral
Nanoclusters and Nanowires and the Consequences of their
Encapsulation inside Carbon Nanotubes
B.Zhu1, Y. Wang1,2, I.S. Atanasov1, D. Cheng3, M. Hou1
1
Physique des Solides Irradiés et des Nanostructures CP234, Université Libre de Bruxelles,
Belgium
2
Applied Ion Beam Physics Laboratory, Institute of Modern Physics, Fudan University, Shanghai
200433, China
3
Division of Molecular and Materials Simulation, State Key Laboratory of Organic-Inorganic
Composites, Beijing University of Chemical Technology, Beijing 100029, P.R. China
Abstract
Metropolis Monte Carlo sampling with empirical potentials is used to predict
equilibrium ordered structures and segregation properties of small icosahedral Au-Pd
nanoclusters and helical nanowire segments over the whole range of compositions at
low temperature. The cases of free standing clusters and wires are compared with the
same systems encapsulated in carbon nanotubes.
A number of chemically ordered structures and segregation states are identified and
found to be consistent with the same interplay of thermodynamic forces as driving
macroscopic binary metal alloys. Encapsulation has the effect to modify the surface
energies of nanoclusters and wires, with considerable consequences on their
thermodynamic states, although the metal-graphite interaction strength is weak as
compared with the metal cohesive energy and the carbon-carbon binding energy.
11
3
CALPHAD type modeling of phase diagrams of nanomaterials,
experimental preparation of nanoalloys
A. Kroupa1,T. Kana1, R. Mishra2, A. Zemanova1, H. Ipser2
1
Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, 616 62
Brno, Czech Republic
2
Institut für Anorganische Chemie/Materialchemie, Universität Wien, Währingerstr. 42, A-1090
Wien, Austria
Abstract
The Ni-Sn nanopowders of various compositions were prepared and studied by means
of XRD, SEM, TEM, WDX, EDX and DSC to obtain as complex description of
experimental properties as possible. This data were consequently used in the
theoretical modelling of Ni-Sn phase diagram for nanosystems by means of
combination of CALPHAD and ab-initio calculations.
CALPHAD approach is a very useful technique for calculation of phase diagrams of bulk
materials based on thermodynamic database containing data such as chemical
potentials of pure substances and excess Gibbs energy of mixtures as a function of
composition, temperature and pressure. In order to extend the use of CALPHAD
approach to small metallic particles on sub-micron and nano scale, due to the surface
effect, the chemical potentials and the excess Gibbs energy should be expressed with
an additional parameter: the particle size. The ab-initio calculations are used to model
theoretically the surface effects by means of surface energy and surface tension
calculations.
This project is supported by the Ministry of Education, Youth and Sport under the
number LD 11024.
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Oral Session 2 – Catalysis
13
4
The role of reduced oxide sites on the stability, morphology,
reactivity and selectivity of supported bimetallic clusters
Elad Gross2 and Micha Asscher1
1
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
Department of Chemistry, University of California, Berkeley CA-94720, USA
Email : [email protected]
2
Abstract:
Morphology and surface elemental composition of Au-Pd bimetallic nano-clusters are
reported to be remarkably sensitive to and affected by the interaction with reduced
silicon defect sites on SiO2/Si(100), generated by argon ion sputter under UHV
conditions. Surface segregation of Pd, deduced from CO-temperature programmed
desorption (TPD) titration measurements, has been stabilized by the surface defects as
meta-stable particles. Acetylene conversion to ethylene and benzene (100:1) was
studied as probe reaction, revealing significant modification of selectivity in addition to
thermal stability on the defect rich substrates. These observations demonstrate the
role and importance of oxide-surface defects in anchoring stable and reactive
conformation of supported bimetallic catalysts.
Chemical reactivity of Pd-Au bimetallic nano-clusters grown via amorphous solid water
as buffer layer, Gross, E., Popov, I., Asscher, M., J. Phys. Chem. C., 113, 18341-18346
(2009).
Structure-Reactivity correlations in Pd-Au nanoclusters, Gross, E., Asscher, M.,
Langmuir, 26 (21), 16226-31 (2010)
14
5
TEM analysis of Kirkendall void formation in sputtered
aluminium-lithium films
D. A. Tanner1,2, S. Belochapkine1, F. Laffir1 and S. Nakahara1,3
1
Materials & Surface Science Institute, 2Department of Design and Manufacturing Technology,
Department of Physics, University of Limerick, Limerick, Ireland
Corresponding Author: [email protected]
3
Abstract
The effect of room-temperature (~20°C) air-oxidation on void formation in sputterdeposited thin films of aluminium and its alloys was investigated using a transmission
electron microscope. It was found that after air-oxidation, only lithium-bearing
aluminium alloy films exhibited a high (~4x1016cm-3) density of small (~2nm) voids,
whereas pure aluminium or lithium-free aluminium alloy films did not contain any
voids. In lithium-bearing aluminium alloy films, both aluminium and lithium atoms
migrate to the surfaces to form their surface oxide during room-temperature aging
after film deposition. In the course of the atom migration, excess vacancies are
generated as a result of the large diffusivity difference existing between aluminium and
lithium atoms (DLi in Al >> DAl) in the alloy matrix. The agglomeration of these excess
vacancies led to the formation of so-called Kirkendall voids inside the alloy [1]. Thus the
presence of both aluminium and lithium in the alloys was a key factor for generating
these Kirkendall voids in the films [2].
References:
1.
Smigelskas, A. D. and Kirkendall, E. O. Zinc diffusion in alpha-brass. Trans. AIME 171,
130-142 (1947).
2.
Nakahara, S., Tanner, D. A., Khan, A. K. and Robinson, J. S. Oxidation-Induced Void
Formation in TEM Specimens of an Aluminium-Lithium-Alloy. Materials Science and Technology
27, 783-788 (2011).
15
6
Bimetallic Au-Ag/TiO2 Catalyst Prepared by DepositionPrecipitation. High Activity and Stability in CO Oxidation.
Alberto Sandoval1, Antonio Aguilar1, Catherine Louis2, Agnès Traverse3 and Rodolfo
Zanella1,*
1
Centro de Ciencias Aplicadas y Desarrollo Tecnológico, UNAM, México
Laboratoire de Réactivité de Surface, UPCM-CNRS, Ivry sur Seine, France
3
Laboratoire de Chimie Physique, Université Paris Sud-CNRS, Orsay, France
*[email protected]
2
Introduction
Gold is catalytically active in CO oxidation at ambient temperature when it is dispersed
as small particles on an oxide support, catalytic activity strongly depends on the
particle size and it is highest in the range of 1-3 nm [1-3]. However it decreases during
the catalytic run, deactivation has been proposed to be due to nanoparticle sintering
[4] or to the formation of carbonates adsorbed on the reactive sites of the catalysts [5].
A way to overcome the deactivation process is to prepare bimetallic catalysts.
Bimetallic combinations such as Au-Ag are known to exhibit significantly improved
stability and improved activity in CO oxidation. It is possible that silver improve the
catalyst capability to activate oxygen because of stronger affinity of O2 with Ag; Note
that silver is also a catalyst for CO oxidation but at higher temperatures than gold.
The goal of this work was to prepare Au-Ag catalysts supported on a reducible TiO2
support by sequential deposition-precipitation method, i.e., different from the
impregnation or the colloids methods, which are commonly used.
Experimental
Ag was first deposited by deposition-precipitation with NaOH followed by Au deposited
by deposition-precipitation with urea. Different samples were prepared with a 4 wt.%
gold loading on the support and various amount of silver to obtain different Au:Ag
atomic ratios from 1:0.15 to 1:1. Monometallic Au and Ag catalysts over TiO2 were also
prepared. Their catalytic activity were tested in the CO oxidation reaction (1% vol. CO
and 1% vol. O2 balanced N2) after in-situ activation in H2 with a heating rate of 2°C/min
up to 550 °C and a plateau of 2 h at the final temperature; stability test were
performed under the same conditions at 20 °C during 24 h. Characterization like
chemical analysis, UV-Visible, XANES (at Au LIII-Edge and Ag K-edge), H2-TPR and TEM
were performed on the samples.
Results/Discussion
Au/TiO2 catalyst is already active at -5°C (CO conversion ≈49 %) whereas at
temperature lower than 60 °C de Ag/TiO2 is completely inactive. Bimetallic catalysts
Au-Ag with different atomic ratios show higher conversion than Au/TiO2 below 60 °C,
which shows a clear evidence of a synergic effect between gold and silver (Fig.1a). The
temperature of activation under H2 has important consequence on the catalytic activity
and in the composition of the nanoparticles. Conversion increases as activation
temperature increases and reached a maximum for the activation temperature of
550 °C (Fig. 1b). The Au-Ag/TiO2 catalysts present a better temporal stability than
monometallic gold catalysts at 20 °C in the reaction of CO oxidation.
16
Figure 1. CO oxidation light-off curves a) Au, Ag and Au-Ag/TiO2 (activation at 550 °C) and b) bimetallic Au-Ag/TiO2
(1:0.76) as a function of the temperature of activation in H2.
XANES and H2-TPR results show that gold in bimetallic Au-Ag/TiO2 was more easily
reduced than in Au/TiO2. The difference of gold reducibility might result from
interaction between Au and Ag. The interaction between Au and Ag in the reduced AuAg/TiO2 samples was confirmed by micro-EDS analysis performed on a series of
individual particles. This technique also showed that when the temperature of
activation under H2 increases, the Au:Ag atomic ratio measured in the particles
becomes closer to the value given by catalyst chemical analysis, indicating the
formation of better alloyed particles as the reduction temperature increases. At 550 °C,
the optimal temperature of activation, 90% of the particles contain both metals and
the average particle size is 3.9 nm.
In conclusion we have developed a new method of preparation of Au-Ag/TiO2 catalysts
based on sequential deposition-precipitation of silver then gold. Au-Ag/TiO2 catalysts
activated in H2 at high temperature (550 °C) exhibit significantly higher activity in CO
oxidation at RT and a better temporal stability than monometallic gold catalysts
containing particles of the same size of 4 nm; These results confirm that there is a
synergetic effect between gold and silver. Several indications were obtained for the
existence of interaction between Au and Ag in the reduced Au-Ag/TiO2 samples.
References.
1. M. Haruta, Chem. Record, 3, 75 (2003)
2. R. Zanella, S. Giorgio, C.-H. Shin, C. R. Henry, C. Louis, J. Catal., 222, 357 (2004)
3. G. C. Bond, C. Louis, D. T. Thompson, Catalysis by Gold, ICP, London, 2006
4. F. Yang, M. S. Chen and D. W. Goodman, J. Phys Chem. C, 113, 254 (2009)
5. M.C. Raphulu, J.McPherson, V. d. Lingen,… M.S. Scurrel, Gold Bull., 43, 21 (2010)
17
7
Preparation, Characterisation, Thermal Analysis and Phase
Diagram of Sn-Ag and Cu-Ni Nanoalloys
J.Vřešťál,a J.Pinkas,a J.Sopoušek,a P.Brož,a P.Buršík,b A.Zemanová,b D.Škoda,a A.Stýskalíka
a
b
Department of Chemistry and CEITEC MU, Masaryk University, Brno, Czech Republic
Institute of Physics of Materials ASCR, Brno, Czech Republic
Abstract
AgSn nanoparticles were prepared by wet synthesis from silver nitrate and stannous
ethylhexanoate by reduction with NaBH4 in a temperature range from 0 to -20 °C in
methanol under a nitrogen atmosphere. 1,10-phenanthrolin was used as a surfactant.
Purification of nanoparticles was done by washing in methanol. The nanoparticles were
separated by evaporation of the solvent and other volatiles under vacuum.
The CuNi nanoalloys were synthesized also by the way of the one-pot thermolysis
under inert nitrogen atmosphere using acetylacetonates of copper and nickel as
precursors. The precursors were dissolved by oleylamine. The solution was transferred
into mixed solvent of oleylamine and 1-octadecene. The reaction mixture was heat up
and the precursors reduced. Nanoparticles were finally separated from the solvent by
centrifugation.
All nano-products were characterized by means of SEM, TEM, DSC, and XRD methods.
Surface energy was incorporated in the CALPHAD method into the expression for Gibbs
energy of phases and phase diagram was calculated.
DSC calorimetry was used for the verification of calculated solid/liquid phase
transformation temperatures.
Acknowledgement: Authors thank MSM0021622410, CZ.1.05/1.1.00/02.0068, and
COST CZ LD11046 for the financial assistance.
18
Oral Session 3 – Magnetism
19
8
Ab-intio calculations on CoPt nanoalloys to explain apparent
experimental contradictions
L. E. Diaz-Sanchez1, G. M. Pastor2, F. Tournus3, and Veronique Dupuis3
1
Facultad de Ciencias, UAEMex, Av. Instituto Literario 100, 50000 Toluca, Mexico.
InsƟtut fur Physik, Universitat Kassel, Heinrich Plett Str. 40, 34132 Kassel, Germany and
3
LPMCN, Univ. Lyon 1, CNRS UMR 5586, 69622 Villeurbanne, France.
2
Abstract
Considering physical routes, recent experiments by the group of Dr. Veronique Dupuis
present the synthesis of CoPt supported nanoalloys under ultra high vacumm and using
mass-selected Low Energy Cluster Beam Deposition. Using this technique, they have
been able to synthesize nanoclusters in disordered A1 and, after annealing, ordered
L10 phase with three narrow size distributions corresponding to a media diameter
equal to 2.0 nm, 3.1 nm and 3.8 nm respectively. In this talk we present ab initio
calculations using a spin-polarized generalized-gradient approximation to densityfunctional theory in which we simulate the above mentioned experiments. We report a
theoretical study addressing magnetic and chemical structural organization in well
selected CoPt nanoparticles smaller than 4 nm. Following available experimental
results from resent Extended X-ray Absorption Fine Structure spectroscopy simulation
on both ordered and disordered materials, it has been possible to estimate the average
distance between neighboring atoms and to compare those directly with our
computational results. After locally relaxing the simulated nanoalloy we did calculate
the average atomic bond length (for Co-Co, Co-Pt, and Pt-Pt) and using a simple
Gaussian distribution equation we found three di_erent and well de_ned interatomic
mean distances.
Assuming a bulk-like L10 structure for the annealed samples, the asymmetry ratio c/a
using these distances is larger than 1 (c/a=1.02) contrary to the value lower than 1 in
the bulk. We will shown that this apparent experimental contradiction with previous Xray di_raction results come from the fact that each Co and Pt layer, in the L10 phase,
relax independently at the size of a few nanometers. In addition, disordered bulk-like
systems are also calculated using a large supercell with 16 and 32 atoms per unit cell
and the results will be also presented.
20
9
Finite size effects on structure and magnetism in mass-selected
FeRh and CoPt nanoparticles
V. Dupuis1, L. Diaz-Sanchez 2, A. Hillion1, S. Rusponi3, A. Tamion1, F. Tournus1, G.
Pastor2, H. Brune3.
1
LPMCN, UMR 5586 CNRS/Université de Lyon, Villeurbanne (FR)
EPFL, Institut de Physique de la Matière Condensée, Lausanne (CH)
3
ITP, Institut für Theoretische Physik, Universität Kassel, Kassel (DE)
2
Abstract:
After decades of systematic studies of the size and structural dependence of pure
transition-metal magnetic clusters, the interest has actually moving progressively
towards investigations on finite-size binary alloys. Indeed, magnetic nanoalloys attract
a lot of attention because they offer the possibility to tune the magnetic moments and
the magnetic anisotropy energy (MAE) probably up to the ultimate density storage
limit. As an example, in one hand, finite spontaneous low-temperature magnetization
has already been observed by Stern and Gerlach deflections measurements on Rh
clusters while interesting metamagnetic transitions is expected in the bulk FeRh alloys.
In the other hand, an extremely high magnetocrystalline anisotropy is expected from
the stacking of pure Co and Pt atomic planes in the (001) direction for CoPt bulk alloys
in the chemically ordered L10 phase.
In this paper, we focus our attention on both non-trivial structure and magnetic
properties obtained on mass-selected FeRh and CoPt nano-clusters prepared by massselected low energy cluster beam deposition (LECBD) co-deposited in inert carbon
matrix.
For both as prepared bimetallic samples, we have put into evidence from HRTEM the
transition from a chemically disordered fcc A1 phase to a chemically ordered B2 CsCl
phase for FeRh and a L10 tetragonal phase for CoPt, upon annealing under vacuum
without particle coalescence. From x ray magnetic circular dichroism (XMCD)
measurements at the respective transition metal L2,3 edge, we have found a significant
increase of the Co, Fe and Rh magnetic moment for both ordered FeRh and CoPt
clusters compared to the bulk phase. Moreover thanks to an accurate “triple fit”
method which consists in adjusting simultaneously three curves (ZFC, FC and m(H))
obtained from SQUID magnetometry measurements, we have put into evidence the
fact that the MAE increase in the ordered phase but not in the same proportion that
what is expected for bulk CoPt alloys. In order to obtain new insights on the correlation
between magnetic properties and short- or long-range chemical order in nanoalloys,
we report the refined quantitative local structure on CoPt samples studied from
extended x-ray absorption fine structure (EXAFS) at the Co-K edge experiments. From
simulations of the as prepared samples signal, we have found a contracted lattice
parameter for the particles in the whole sizes range. Upon annealing, unlike bulk
phase, we have clearly observed an expanded c/a ratio up to 1.05 for the L10 phase in
nanoalloys (compared to 0.97 for the bulk). Finally, thanks to ab-initio theoretical
calculations up to a few hundred of atoms, we explain that this discrepancy is due to
different relaxations in Co-Co and Pt-Pt layers at nanosize.Moreover, Pastor et al.
recently performed first-principles study of magnetism, structure and chemical order in
small FexRh1-x alloy clusters (N<8) where they found a systematic FM-like order in the
optimized structures as a function of concentration and size. SQUID magnetometry
21
measurements on our Larger FeRh nanoclusters (N up to a few hundred of atoms) also
revealed a FM-like order (instead of AF-like order as in the bulk). Once more, to go
further, we plane to perform in 2012, both EXAFS measurements under synchrotron
radiation facilities and theoretical ab-initio calculations up to a few hundred of atoms
to determine the cross over size to the bulk-like limit.
Support is acknowledged from both COST-STSM-MP0903-7318 and 7713
22
10
Tailoring structure and magnetism of free and decorated
transition metal nanoparticles
Peter Entel
Faculty of Physics and Center for Nanointegration, CeNIDE, University of Duisburg-Essen, 47048
Duisburg, Germany
Abstract
Magnetic nanoparticles have become a popular target for fundamental research with
respect to biomedical applications, catalysis or functional devices. For instance, arrays
of L10 ordered Fe-Pt and Co-Pt nanoparticles have been discussed as promising
candidates for ultra-high density recording media. Owed to the large magnetocrystalline anisotropy (MCA) of the bulk alloys, single crystalline particles with
diameters as small as 4 nm were considered. Multiply twinned structures, however,
compromise the hard magnetic properties. Such morphologies are frequently
encountered in gas phase experiments (e.g., [1]) and have been confirmed as potential
ground state structures in recent density functional theory (DFT) calculations [2, 3].
These include a full optimization of the geometry and have been carried out for
nanoparticles with up to 1415 atoms. We find that for diameters below 4 nm, the
favored L10-type layering is energetically superseded by an icosahedral structure with
onion-shell alternation of Fe and Pt atoms in the particle core. This arrangement is
characterized by an effective L11 ordering which is stabilized by the extraordinarily low
surface energy of Pt covered [111] facets [4]. The preference for multiply twinned
structures can be systematically tuned by an exchange of the 3d component, whereas
similar clear trends upon the exchange of the 5d component are not encountered [5].
For deposited clusters, significant modifications of spin and orbital magnetic moments
arise from the interface to the substrate or a possible embedding matrix. The
comparison of nanometer-sized Fe-Pt particles decorated with monolayers of, e.g., Au,
Al, Si or C allows to make predictions concerning the influence of a surrounding matrix
on structural and magnetic properties of Fe-Pt and Co-Pt nanoparticles. Fully relativistic
DFT calculations including spin-orbit interaction provide access to site-resolved orbital
moments and MCA and allow to identify basic design trends tailoring the hard
magnetic properties needed for recording purposes. The calculations are compared to
X-ray absorption spectroscopy offering an element specific approach to MCA and the
orbital magnetism.
References :
[1] R. Wang, O. Dmitrieva, M. Farle, G.\Dumpich, H. Poppa, R. Kilaas, and C. Kisielowski, Phys.
Rev. Lett. 100, 017205
(2008).
[2] M. E. Gruner, G. Rollmann, P. Entel, and M. Farle, Phys. Rev. Lett. 100, 087203 (2008).
[3] M. E. Gruner and P. Entel, J. Phys.: Condens. Matter 21, 293201 (2009).
[4] A. Dannenberg, M. E. Gruner, A. Hucht, and P. Entel, Phys. Rev. B 80, 245438 (2009).
[5] M. E. Gruner, J. Phys. D: Appl. Phys. 43, 474008 (2010).
23
24
11
Structures of Au and AuPd clusters on stepped MgO
K. Damianos and R. Ferrando
Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146, Genova, Italy
Abstract
The struictures of Au and AuPd clusters adsorbed along high-symmetry steps of the
(001) surface of MgO are searched for by computational methods. The energetics of
the system is modelled within the Density Functional Theory framework by using the
PBE gradient-corrected functional. The results are compared to those of the Local
Density approximation. For pure Au clusters, size up to 24 atoms are considered,
whereas for AuPd clusters only small aggregates up to 7 atoms are investigated. The
pure Au clusters adopt non-compact shapes. With increasing size, they assume quasilinear shapes, then they become two-dimensional leaflets, arched leaflets and finally
three-dimensional cages [1]. These structures are significantly different from those
previously found on the flat surface [2], showing the key role of the step in determining
the stability of the different motifs. In the case of mixed AuPd clusters, the best
structural motifs are characterized by Pd atoms occupying positions closer to the
substrate and the step, indicating a stronger bonding of Pd to oxygen atoms compared
to Au. Compact arrangements of Pd atoms are the most stable. Au atoms preferentially
form extended chains enclosing these compact aggregates of Pd atoms. This is in
agreement with the chain structures which are most stable for pure, small Au clusters.
References
[1] K. Damianos and R. Ferrando, Nanoscale, in press
[2] R. Ferrando, G. Barcaro, A. Fortunelli, Phys. Rev. Lett. 102, 216102 (2009); Phys. Rev. B 83,
045418 (2011)
25
12
Elasticity of Ni(Ti,Pt)
Drahomír Chovan∗, Syed Tofail
University of Limerick, Limerick, Ireland
Abstract
Elastic properties of nickel rich platinum doped nickel-titanium (nitinol) alloy were
calculated within density functional theory (DFT) framework. We focus on hightemperature austenitic cubic phase (B2). According to our calculation, Pt dopant
doesn’t prefer location on Ti sites. We also report lattice contraction and increased
bulk modulus magnitude when Pt is located on Ti lattice sites. Furthermore, elastic
constants were calculated using volume conserving orthorhombic and monoclinic
distortions in elastic region (±2%). Our results show, that nickel rich NiTiPt will prefer
orthorhombic transformation path rather than monoclinic, which is reflected in elastic
anisotropy.
Figure 1. Ground state energy and equilibrium cell volume vs. Pt content for Ni(Ti,Pt).
∗
Contact Author: e-mail: [email protected]
26
13
Roles of size, composition, and chemical disorder on the
vibrations of gold-silver nanoalloys
F. Calvo
LASIM, CNRS and University of Lyon
Abstract
The vibrations of a metallic nanoparticle are strongly affected by its size and shape. In
the present work, the respective roles of size, chemical order and composition have
been theoretically examined in the case of gold-silver nanoalloys by means of atomistic
simulations. While the vibrational density of states exhibits some qualitative
differences between alloyed and segregated (core-shell) particles, the breathing
frequency varies smoothly but nonlinearly with composition in all cases considered.
Elasticity theory accounts reasonably well for the size dependencies, with finite size
corrections scaling as powers of the inverse radius. These deviations are found to vary
with composition through a simple quadratic expansion.
27
14
Simulation of nanostructure interfaces and segregation in
nanostructured filler metals in a multilayer configuration
S.Brodacka1, A. Antusek2, D. Passerone3, J. Janczak-Rusch3, R. Kozubski1
1
M.Smoluchowski Institute of Physics, Jagiellonian University In Krakow, Reymonta 4, 30-059
Krakow, Poland
2
Faculty of Material Science and Technology in Trnava, Slovak University of Technology in
Bratislava, Paulinska 16, 917 24 Trnava, Slovak Republic
3
Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129,
8600 Dübendorf, Switzerland
Abstract
Nanostructured metals in a multilayer configuration are promissing materials
for brazing joints as the multilayer configuration is supposed to yield frequently desired
decrease of the braze melting point (Melting-Point-Depression (MPD) effect).
Modelling of such systems involves two basic aspects: (i) interface properties having
major influence on the material character and (ii) the effect of nanometric size of
composites. It is well known, that nanostructured materials have different properties
than the macro- and micro-sized ones.
The present communication reports on the preliminary results of atomistic
simulation of interfaces in multilayered nanostructured material. Universal bindingenergy relaxation (UBER) pair interaction potentials describing interactions for AlN/Ag
interfaces were fitted to ab initio calculations. Quasi-empirical potentials for Ag-Ag
interactions were used. Because of low reactivity and stable structure no-interactions
in AlN slab were applied. Parameters of the AlN/Ag interaction potentials were
evaluated by fitting the energy obtained by means of Molecular Dynamics to the ab
initio estimated one. This approach was applied for specific range of AlN and Ag slab
distances.
Furthermore, Ag-Cu system was analysed. Equilibrium atomic configurations in
thin films with eutectic compositions were studied by means of hybrid Monte Carlo –
Molecular Dynamics simulations. The influence of film thickness and temperature on
the resulting configurations was investigated.
28
15
Metal-Metal Interface in Bimetallic Nanorods at Atomic Scale
Ruth Chantry and Ziyou Li
Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of
Birmingham, Birmingham B15 2TT, U.K.
Abstract
A full characterization of the metal-metal interface in bimetallic nanostructures is key
to the understanding and effective exploitation of the novel properties of these
nanomaterials. Here, we present our recent progress on characterisation of two
bimetallic nanorods, AuPd and AuRh, via an aberration corrected scanning transmission
electron microscope (STEM), equipped with an electron energy loss spectroscope
(EELS). Both AuPd and AuRh systems are largely immiscible in bulk, yet significant
differences in the atomic structure of the metal-metal interface have been found.
While the AuPd displays an atomically sharp interface, no apparent Au-Rh boundary is
observed. Rather, a 4-5 atomic layer thick alloying interface in the AuRh system is
indicated via high-resolution Z-contrast imaging. These different behaviours may be
attributed to the kinetics and energetic characteristics of the systems. The effects of
interfacial structures on the plasmonic behaviours of nanorods are currently being
investigated via single nanorod plasmon mapping. Preliminary results will be
presented and discussed.
29
Oral Session 5 – Growth
30
16
Synthesis of Nano-Alloys: a Colloidal Approach
Christophe Petit
1
Laboratoire des Matériaux Mésoscopiques et Nanométriques (UMR7070), Bâtiment F,
case 52, Université Pierre et Marie Curie –Paris 6, 75252 Paris cedex 05
E-mail : [email protected]
Abstract
Metallic nanoalloys will initiate important development in nanotechnologies due to
their specific chemical and physical properties (i.e. in catalysis, magnetism, optics, etc.).
It is now well known that these properties are mainly controlled by the fine tuning of
structural parameters such as the size, the bimetallic composition and segregation
processes. Concerning their fabrication, the bottom up approach, either physical or
chemical, is ideal to design this specific class of nanomaterials due to its versatility,
facility and low cost. However, the realization of well controlled bimetallic
nanoparticles is not always straightforward from the know-how developed for
monometallic nanoparticles.
Soft chemistry is well-adapted to produce such nanoalloys in large amount. However at
the nanometer scale, as the properties are strongly dependent on the size and the
surface state (raw or passivated), it is crucial to develop method where the
polydispersity in size and composition is finely controlled. These impose to clearly
separate the nucleation step from the growth process and also to control this latter to
limit the size. This can be done by using colloidal assemblies, as the micellar media (1)
or the two phase system (2,3), where both the nucleation and growth process are
clearly separate in space and time. We will illustrate the advantage and disadvantages
of the colloidal approach in case of the synthesis of CoPt nanoalloys.
Nevertheless, depicted the large amount of work made on the synthesis of nanoalloys
by the chemical way, there is still open questions considering the control of
composition and especially the segregation process. For example, in the chemical
approach, the nanoparticles are always passivated by an organic molecule. The role of
this capping agent on shape and segregation control is still under discussion.
Furthermore, in case of the magnetic nanoalloys as CoPt , post synthetic
treatment are needed (4), whatever the synthesis route is, in order to reach the
ordered L10 phase. We will show recent results allowing the structural transition,
keeping their nanometer size and low polydispersity.
References:
1- Petit, C., Rusponi, S., Brune, H. J., Appl. Phys. 95, 4251, (2004).
2- Demortière, A., Petit, C. Langmuir, 23, 8575 (2007).
3- Demortière, A., Losno, R., Petit, C.and Quisefit, J.P., Anal. Bioanal. Chem. 397, 1485 (2010).
4- Demortière, A., Petit, C, J., Appl. Phys 109, 084344 (2011)
31
17
Bimetallic nano-cluster deposition in microfluidic channels for
bio-analyte detection
Aymen Ben azouz1,2, Mercedes Vázquez1, C.P. Romero3, Milan Obradovic3, Didier
Grandjean3, Peter Lievens3, Dermot Brabazon1,2 and Brett Paull4
1. Irish Separation Science Cluster, Dublin City University, Dublin, Ireland
2. School of Mechanical Engineering, Dublin City University, Ireland
3. Solid State Physics and Magnetism Section, Katholieke Universiteit Leuven, Belgium
4. Australian Centre for Research on Separation Science, University of Tasmania, Hobart,
Australia
Abstract
The selective extraction of specific proteins (non-glycosylated, glycosylated or different
glycoforms) from complex sample matrices is of significant interest within the fields of
proteomics and glycoproteomics. One approach to obtain selective extraction is to
utilise solid phase extraction (SPE) whereby the solid phase incorporates a selective
ligand or bio-recognition molecule for efficient trap and release of the target.
This work, describes the deposition of gold-based mono and bimetallic nanoclusters
within micro-fluidic channels for future applications in biochemical sensing. Microfluidic platforms have been fabricated using various micro-fabrication techniques in
Dublin City University, then nano-clusters of gold and bimetallic gold-palladium were
deposited onto the open channels using Low Energy Cluster Beam Deposition (CBD)
facility (KU Leuven). Deposited nano-alloy clusters were characterised using Atomic
Force Microscope (AFM). Successful deposition of average sized three nanometre Gold
and bi-metallic Gold-palladium nano-clusters onto the surface of micro-fluidic channels
were observed.
32
18
Synthesis of Ag-ZnO nanoparticles within reverse micelles
Numan Hoda, Leyla Budama, Buçin Acar, Önder Topel
Akdeniz University Department of Chemistry, 07058, Antalya, Turkey
Abstract
Over the past decades using of nanoparticles has a substantial increase in fabrication of
new materials due to their high catalytic activity and large surface area (100 –3000
m2/g). In order to synthesize such small particles, it is known to use many methods
such as sol-gel technology, vapor deposition, micro emulsion systems and stabilizing
templates like copolymers which might provide to control their size and size
distribution. Block copolymers in a selective solvent, thermodynamically good solvent
for one block and precipitant for the other, may associate reversibly to form micellar
aggregates. By micellization, self-assembly block copolymers having microdomain in
their core offer important advantages for production of nanoparticles within these
microdomains. The nanoreactors can be employed to fabricate nanoparticles having
certain size and size distribution by encapsulating particles such as metal salts. After
collecting the metal ions in the cores of micelles, size controlled nanoparticles can be
produced by chemical reduction or oxidation in them. Moreover, it is also possible to
produce bi-metallic core-shell nanoparticles by loading another metal ion into the
cores. By regarding this phenomena, silver and zincoxide bi-metallic nanoparticles were
synthesized using reverse micelles of polystyrene-block-polyacrylic acid as a
nanoreactor in the present work. In an organic medium, micelles formed in which PAA
and PS blocks constitute cores and coronas, respectively. Preparation of micelle
solution was performed in toluen. AgNO3 and Zn(NO3)2 precursor salts were used for
Ag-ZnO nanoparticles. Ag-ZnO bi-metallic nanoparticles were synthesized by reduction
of Ag+ ions by N2H4 following ZnO nanoparticles synthesis by oxidation of the precursor
salt loaded to the cores of micelles. Formation of bi-metallic nanoparticles within
micelle cores was confirmed by X-ray diffraction and transmission electron microscopy.
Key words: Bimetallic nanoparticles, Ag-ZnO, nanoreactor, PS-b-PAA.
33
19
TEM study of nanoparticle formation in diblock copolymer
micelles loaded with two metal salts: AuAg and Au/Pt
Willian G. Menezes1, Volkmar Zielasek1, Christian Kübel2, Dieter Wöhrle1, and Marcus
Bäumer1
1
University of Bremen, Institute of Applied and Physical Chemistry, Leobener Str. NW2, 28359 Bremen,
Germany
2
Karlsruhe Institute of Technology, Karlsruhe Nano Micro Facility, 76344 Eggenstein-Leopoldshafen,
Germany
Abstract:
We present a facile method for the preparation of bimetallic AuAg nanoparticles (NPs)
with controlled size and composition rendering them ideally suitable for optical and
catalytic applications. In analogy to methods for the generation of monometallic Au
and Ag NPs, AuAg NPs were prepared inside polystyrene-b-poly(4-vinylpyridine) (PSP4VP) block-copolymer micelles formed in toluene, by loading the P4VP cores of the
micelles first with AgNO3 and then with HAuCl4. In contrast to the reverse sequence of
loading, homogenously bimetallic AgAu particle arrays were achieved after reduction
carried out in solution with hydrazine monohydrate as reducing agent. TEM revealed
stable and spherical NPs well separated from another and with a narrow size
distribution with diameters of ~3 nm. The bimetallic NP composition was confirmed by
energy-dispersive x-ray spectroscopy at single NPs. The atomic ratio of Ag and Au
contained in single particles was systematically varied between 3:1 and 1:3. UV-vis
spectra showed a single plasmon band for all atomic ratios. Its wavelength depends
linearly on the relative amount of gold within the range from monometallic silver (415
nm) to gold (538 nm).
We also present an in-situ TEM study at variable temperatures (95-300 K) of the
electron-induced metal reduction and aggregation in PS-P4VP micelles loaded with
HAuCl4 and H2PtCl6. Electron irradiation-induced coagulation of metal and initial
formation of particulates with subnanometer diameters within the P4VP cores was
observed in the entire temperature range for Au as well as for Pt. Particle coarsening
and ripening, however, strongly depended on the metal, the electron dose and, in
particular, on temperature. Counter-intuitively, the dynamics of metal aggregation into
a single nanoparticle within each micelle core was faster at low temperature whereas
at room temperature even high densities of subnanometer particulates remained
stable. A definite, seemingly negative activation barrier can be extracted from a
quantitative evaluation of the dependence of NP formation on temperature, indicating
that metal aggregation may be hindered by a single thermodynamically activated
process within the P4VP matrix. Au- and Pt-loaded micelles show pronounced
differences under electron irradiation although similar metal precursors were used.
Apparently both, the initial reduction of metal ions and particle aggregation proceed
more efficiently for Au. TEM tomography revealed electron-induced separation of Au
and Pt in micelles that were loaded with both metal salts. While, at 300 K, Pt remained
evenly distributed within the P4VP core, Au particulates formed at the interface
between the core and the PS corona of the micelles.
34
35
20
Global Optimisation of Nanoalloys at the Density Functional
Theory Level
Roy L. Johnston1, Andrew J. Logsdail1, Sven Heiles2 and Rolf Schäfer2
1
School of Chemistry, University of Birmingham, Birmingham B15 2TT, UK.
Eduard-Zintl-Institut für Anorganische und Physicalische Chemie, Technische Universität
Darmstadt, 64287 Darmstadt, Germany
2
Abstract
It has been shown that for many nanoalloy systems a two stage approach, namely
performing global optimisation at the empirical potential level, followed by local
minimisation of a variety of candidate structures at a higher level of theory – usually
Density Functional Theory (DFT) – can lead to reliable cluster geometries and chemical
ordering [1]. However, there are limitations to the use of empirical potentials – for
example, they do not reproduce the planar structures of small Au-containing clusters
[2] and there are some systems (e.g. Sn. Pb and Bi) for which no realistic empirical
potentials exist.
In this presentation, I will introduce a novel genetic algorithm based program for the
direct global optimisation of small bimetallic nanoalloys directly at the DFT level (with
DFT calculations performed using the PWscf code within QuantumEspresso) [3].
Example applications will include: the investigation of the 2D-3D transition in small AuAg nanoalloys as a function of size and composition (see Figure 1); and the study of the
effect of Bi doping on the structures of small Sn clusters.
Figure 1. 2D-3D Interconversion in 8-atom Au-Ag clusters as a function of composition.
References
[1]
R. Ferrando, A. Fortunelli and R. L. Johnston, Phys. Chem. Chem. Phys. 2008,
10, 640-649.
[2]
M. Neumaier, F. Wiegend, O. Hampe and M. M. Kappes, Faraday Discuss.
2008, 138, 393-406 (and references therein).
[3]
S. Heiles, A. J. Logsdail, R. Schäfer and R. L. Johnston, Nanoscale (in press).
36
21
Prediction of intra-core and inter-particle separation transitions:
Towards the construction of nanoalloy phase-diagrams
Micha Polak
Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 84105, ISRAEL
Abstract
The equilibrium compositional structures of Pt-Ir and Pd-Ir cuboctahedral (CO)
nanoparticles (NPs) consisting of up to 923 atoms capable of exchange between
particles, are predicted by a recently introduced approach that uses the coordination
dependence of surface bond-energy variations (CBEV) [1] as DFT-based input to the
statistical-mechanical free-energy concentration expansion method (FCEM) [2]. The
high computation efficiency of the CBEV/FCEM approach allows evaluation of the
complete temperature dependence of the compositional structures and the
corresponding heat-capacity curves. Depending on the NP size and overall
composition, two distinct kinds of separation-like sharp “nanophase transitions” are
revealed:
1) Intra-core transition between a pure-Pt inner core stable at low temperatures in
"onion-like" Pt-Ir-Pt NPs and sub-vertex centered Pt-rich small clusters at higher
temperatures. A core-shell Ir-Pd low-temperature structure transforms to a solidsolution-like high temperature nanophase. For both nanoalloys the critical
temperatures decrease significantly below the bulk values with the NP size (923 vs. 561
atom CO), and the sharp transition vanishes for 309 CO.
2) Inter-particle separation into NPs having different compositional magic-numbers, as
reflected by convexity in the corresponding low-temperature mixing free-energy
curves, which disappears at a characteristic temperature signifying transition to a
system of solid-solution like NPs.
The relationship between the two types of separation transitions as well as the role
played by preferential strengthening of surface-subsurface inter-layer bonds are
elucidated. The results furnish partial phase diagrams for the two binary NPs, and are
compared with nanophase transitions predicted for Pt-Pd-Ir NPs.
References:
[1] L. Rubinovich, M. Polak, Phys. Rev. B 80 (2009) 045404.
[2] M. Polak and L. Rubinovich, Surf. Sci. Rep. 38 (2000) 127.
37
22
Ordering of bimetallic nanoalloys predicted from bulk alloy phase
diagrams
Y. Wang1,2, M. Hou2
1
Applied Ion Beam Physics Laboratory, Institute of Modern Physics, Fudan University, Shanghai 200433,
China
2
Physique des Solides Irradi¶es et des nanostructures, CP 234, Universit¶e Libre de Bruxelles, Campus de
la Plaine, Boulevard du Triomphe, B-1050 Brussels, Belgium
Abstract:
The Metropolis Monte Carlo method is used to demonstrate the relationship between
the bulk phase diagram of alloys with limited miscibility and the equilibrium
configurations of nanoparticles. Using the Au-Pt system as a case study, an embedded
atom potential is parameterized so as to match the phase diagram exactly. The smooth
temperature dependence of the short range order parameter is shown correlated with
an onion-like configuration intermediate between solid solution and phase separated
states.
38
23
The complex structural study of bi-metallic Fe-Bi nanocomposites
P. Lecantea, MJ. Casanovea, JG. Matteia, C. Amiensb, D. Ciuculescub, F. Pelletierb
CNRS, CEMES (Centre d’Elaboration des Matériaux et d’Etudes Structurales), Université de
Toulouse, UPS, BP94347, 29 rue J.Marvig, F-31055 Toulouse, France
Université de Toulouse, UPS, LCC (Laboratoire de Chimie de Coordination, UPR CNRS 8241) 205
route de Narbonne 31077 – Toulouse Cedex 04, France
Abstract
Core-shell particles with a magnetic metal core and a non-magnetic functional metal
shell are particularly desirable as they display the largest panel of applications, with
potential interest for catalysis, biology, or physics. In such a view, combine in a single
object metallic Fe and Bi, i.e. a ferromagnet and the most diamagnetic metal, can
indeed bring original properties. Moreover, iron and bismuth being totally immiscible
in the bulk, we can expect sharp interfaces between the respective domains. The
chemical approach to elaborate this highly unusual system largely relies on a one-pot
reaction, however involving distinct steps to produce Fe seeds and then release Bi
atoms to form the FeBi composite.
As for any new system, synthesis is challenging, and structural characterization and
modeling also are: both X-ray based techniques (WAXS, EXAFS) and electron based
ones (HRTEM, EFTEM, EELS) may have, and actually experienced, difficulties to provide
information, especially on the chemical ordering between the relatively light and highly
air sensitive iron component, and the more stable but massive bismuth one. Recent
results on the system will be presented, with emphasis on practical conditions for
sensible measurement, and their careful interpretation.
39
Oral Session 7 – Growth / Catalysis
40
24
Sub-nanometer Clusters as Building Blocks for (Multi)functional
Nanoalloys
Stefan Vajda
Materials Science Division and Center for Nanoscale Materials, Argonne National Laboratory,
Argonne, IL 60439, USA &
Department of Chemical and Environmental Engineering, Yale University, New Haven,
CT 06520, US. Email: [email protected]
Abstract
The elucidation of the size/composition/shape/structure and function correlation, the effect of
support along with the determination of the nature of the catalytic particles under reaction
conditions are instrumental for addressing fundamental aspects of catalysis on the way to the
design of new catalysts. Highly uniform particles on technologically relevant supports are
prerequisites for such studies1.
The experimental studies are based on 1) chemically uniform support fabrication, 2) sizeselected cluster deposition, 3) ex situ and in situ microscopies and 4) in situ synchrotron X-ray
characterization of clusters under working conditions, combined with mass spectroscopy
analysis of the reaction products. The experimental work is complemented with DFT
calculations performed by collaborating groups.
The main part of the lecture will outline, by using examples of selective bond activation, the
applicability of this approach in identifying optimal cluster sizes using model, sub-nanometer
size-selected clusters.2-10 In the second part of the talk perspectives of using sub-nanometer
size clusters as building blocks of larger aggregates and as nanoalloys will be discussed - a joint
experimental and theoretical approach towards the design of mono- and bifunctional catalysts.
References
1. "The Impact of Nanoscience on Heterogeneous Catalysis", A.T. Bell, Science 299, 1688 (2003)
2. “Combined Temperature Programmed Reaction and in-Situ X-ray Scattering Studies of Size Selected Silver
Clusters under Realistic Reaction Conditions in the Epoxidation of Propene”, S. Vajda et al., J. Chem. Phys., 131,
121104 (2009)
3. “Selective Propene Epoxidation on Immobilized Au6-10 Clusters: The Effect of Hydrogen and Water on Selectivity
and Activity”, S. Lee et al, Angew. Chemie. Int. Ed. 48, 1467 (2009)
4. “Subnanometre Platinum Clusters as Highly Active and Selective Catalysts for the Oxidative Dehydrogenation of
Propane”, S. Vajda et al., Nat. Mater. 8, 213 (2009)
5. “Combined TPRx, in situ GISAXS and GIXAS Studies of Model Semiconductor-Supported Platinum Catalysts in the
Hydrogenation of Ethene”, S. Wyrzgol et al, Phys. Chem. Chem. Phys. 12, 5585 (2010)
6. “Increased Silver Activity for Direct Propylene Epoxidation via Subnanometer Size Effects”, Y. Lei et al., Science
328, 224 (2010)
7. “Size-Dependent Selectivity and Activity of Silver Nanoclusters in the Partial Oxidation of Propylene to Propylene
Oxide and Acrolein: A Joint Experimental and Theoretical Study”, L. Molina et al., Catal. Today 160, 116 (2011)
8. “Cleavage of the C-O-C bond on Size-Selected Subnanometer Cobalt Catalysts and on ALD-Cobalt Coated
Nanoporous Membranes”, W. Deng, S. Lee, J. A. Libera, J. W. Elam, S. Vajda, and C. L. Marshall, Appl. Catal. A:
General 393, 29-35 (2011)
9. “Simultaneous Measurement of X-ray Small Angle Scattering, Absorption, and Reactivity: A Continuous Flow
Catalysis Reactor”, S. Lee, B. Lee, S. Seifert, S. Vajda and R. E. Winans, Nucl. Instr. and Meth. A, 649. 200-203 (2011)
10. “Size and Support-Dependent Reactivity of Subnanometer Cobalt Catalysts with CO and H2: A combined GIXAS,
GISAXS and TPRx Study", S. Lee, B. Lee, S. Seifert, R. E. Winans, and S. Vajda
Phys. Chem. Chem. Phys., invited article, submitted
41
25
Progress in density-functional studies of Pd-Zn and Au-Ag
nanostructures
Sergey M. Kozlov,1 Lyudmila V. Moskaleva,2 Marcus Bäumer,2 Konstantin M.
Neyman1,3*
1
Departament de Química Física and Institut de Química Teòrica i Computacional (IQTCUB),
Universitat de Barcelona, c/ Martí i Franquès 1, Barcelona, Spain
2
Institut für Angewandte und Physikalische Chemie, Universität Bremen, Bremen, Germany
3
Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
*presenting author, E-mail: [email protected]
Abstract
The talk mainly aims at providing a progress report related to two short-term scientific
missions (STSM) taken place during the first year of the Action MP0903 and involving
the team of the presenting author at the Universitat de Barcelona (UB), Spain.
The first STSM of a PhD student S. Kozlov (UB) to Vienna University of Technology
(group of Prof. Rupprecter, Vienna, Austria) dealt with studies of Pd-Zn surface alloys
formed on Pd(111) surface and representing novel Pd/ZnO catalysts for methanol
steam reforming (MSR). Recent experiments by Rupprechter et al. suggested that
surface composition of PdZn-based catalysts may change in the presence of CO or
during the MSR reaction. To verify and understand this experimental indications
density-functional model study has been performed in Barcelona addressing CO
adsorption on monolayer and multilayer PdZn surface alloys on Pd(111). It was shown
that monolayer PdZn surface alloy with reconstructed zigzag structure is more stable
on Pd(111) than that with so far commonly accepted row structure and that adsorption
of CO greatly facilitates reconstruction of the PdZn surface, especially at high coverage.
Finally, the calculations predicted that only on the reconstructed surface it is possible
to achieve the highest experimentally observed CO coverage of 0.5 ML.
Another STSM of Dr. L. Moskaleva from the group of Prof. Bäumer (Universität Bremen,
Germany) to the UB team was a part of a cooperative experimental and theoretical
effort directed to unraveling how nanostructured gold catalysts function at an atomic
scale. The focus was on the properties of nanoporous gold (np-Au), a novel
unsupported catalyst, for the performance of which a very small amount of residual
silver has been proposed to be crucial. The density-functional calculations show that Ag
atoms incorporated into rough gold surfaces can facilitate the adsorption and
dissociation of molecular oxygen on them. One of the latest conclusions is that Ag
impurities seem to be not responsible for lowering the energy barrier of the CO + O →
CO2 reaction but rather promote the dissociation of molecular oxygen on np-Au foams,
which is the bottleneck of oxidation reactions on Au with O2 as oxidizing agent. Overall,
the modelling helped to rationalize the role of low coordination and inherently present
Ag impurities as two driving forces of the catalytic activity of np-Au.
42
26
O2 chemisorption on Pt shell Ni core nanoalloys deposited on
MgO(100)
C. Di Paola*1 , S.M. Kozlov2 , K.M. Neyman2 and F. Baletto1
1
Physics Dept., King’s College London, UK
IQTC, Universitat de Barcelona, Spain
*email: [email protected]
2
Abstract
Metal clusters supported on oxide surfaces have been widely investigated due to their
possible applications in most various fields ranging from heterogeneous catalysis to
electronics and magnetic devices. Generally speaking, the structural motif of adsorbed
nanoparticles depends strictly on the mismatch between the metallic interatomic
distance and the oxygen-oxygen bond length of the oxide-substrate [1,2]. Our
attention is focused on the chemisorption of oxygen molecules over two PtNi coreshell nanoalloys, the truncated octahedron at 38 and the icosahedron at 55 atoms,
deposited on a 6x6x3 MgO(100). The choice of PtNi nanoparticles is due to their
enhance catalytic activity for the oxygen reduction reaction, which is still one of the
challenges for a widespread use of fuel cells [3].
First, a geometrical and electronic description of the interface cluster/substrate is
performed after an ionic and electronic relaxation of the system using VASP [4]. Then,
the chemisorption map of an oxygen molecule is presented.
Our preliminary results show that the effect of the oxide substrate is almost negligible
for the chemisorption energy of oxygen on Pt-Pt bridge between neighbouring facets
with respect have been observed for free clusters [5]. The substrate is only relevant
when the truncated octahedron PtcoreNishell is deposited on one of its (111) facet; in this
case the oxygen adsorption energy is lower of about 1 eV with respect to the other
considered cases.
Finally, the magnetic properties of the system with or without the addition of O2 are
also discussed, following a Bader analysis performed using a spin-polarised PWSCF
approach, as released in the Quantum Espresso package [6].
References :
1. Ferrando R. et al, ACS Nano, 2 (2008) 1849
2. Goniakowski J. et al., J. Chem Phys., 130 (2009) 174703
3. Zhang J. et al., Nano Lett., 10 (2010) 638
4. Kresse G. et al., Phys. Rev. B, 49 (1994) 14251
5. Di Paola C. et al., Phys. Chem. Chem. Phys., 13 (2011) 7701
6. Giannozzi P. et al., J. Phys. Condens Matter, 21 (2009) 385502
43
27
PdAu/Al2O3 Catalysts for Hydrogen Generation from Formic Acid
Dmitri A. Bulushev1*, Sergey Beloshapkin1, Pavel E. Plyusnin2, Yurii V. Shubin2, Valerii I.
Bukhtiyarov3, Sergey V. Korenev2, and Julian R.H. Ross1
1
Nikolaev Institute of Inorganic Chemistry, Novosibirsk, 630090, Russia
3
Boreskov Institute of Catalysis, Novosibirsk, 630090, Russia
2
Introduction
Earlier, we have shown [1] that Pd based catalysts were quite active, selective and
stable in formic acid decomposition giving hydrogen at low temperatures (373-473 K).
PdAu catalysts are known to demonstrate catalytic properties better than Pd or Au
catalysts in some reactions like hydrogenation and oxidation. The objective of the
present research was to correlate catalytic properties of the supported PdAu
nanoparticles in the mentioned reaction with their surface and bulk composition.
Experimental
1.8% PdAu/Al2O3 catalysts with different Au/Pd ratios were prepared by incipient
wetness impregnation of a γ-Al2O3 support with [Pd(NH3)4](NO3)2 and HAuCl4 dissolved
in a water-acetone solution followed by reduction in hydrazine at room temperature
and drying. The catalysts were not calcined in air. They were placed in a quartz tubular
reactor, then pretreated in a 1% H2/Ar mixture at 573 K for 1 h and cooled in He to
reaction temperature. The reaction products were analyzed by a GC. AAS, XRD, XPS, CO
chemisorption and STEM/EDS methods were used to characterize the catalysts.
Results/Discussion
Hydrogen selectivities during formic acid decomposition at low conversions were high
(90-97%) for all catalysts. The conversion of formic acid decreased with the Au atomic
fraction. For the Au/Al2O3 catalyst it was negligible as compared to the Pd/Al2O3
catalyst at 403 K. Hence, Au was considered as inactive in the reaction and the activity
was assigned to surface Pd atoms. Turnover frequency (TOF) values were calculated
using concentrations of surface Pd measured by CO chemisorption. It is seen in Fig. 1
that the TOFs for the Pd/Al2O3 sample were 2-3 higher than those for the PdAu
catalysts. This could be explained by the switching off the most active Pd sites by Au.
The TOFs for the PdAu catalysts almost did not depend on the Au atomic fraction in the
range of 0.1 to 0.9. The surface composition measured by XPS was close to the bulk
composition only at the Au fraction about 0.33. At lower fractions the surface was
enriched with Au and at higher - with Pd. The variation of the Au fraction in the
catalysts from 0.3 to 0.9 did not affect the surface composition and electronic
properties of metallic particles corresponding to the Pd2Au alloy. This explains the
catalytic data demonstrating independence of the catalytic properties on the Au
atomic fraction (Fig. 1). Earlier, Baddeley et al. [3] have reported the formation of
ordered surface Pd2Au alloy after deposition of Pd on Au(111) and annealing to 500 K.
This layer behaved as an effective catalyst for ethyne trimerization.
Thus, using the mentioned synthesis procedure the catalysts with quite similar Pd2Au
surface layer and with different bulk composition could be prepared. This Pd2Au layer
determines surface electronic and catalytic properties. The obtained results can be
useful for development of catalysts for reactions were the activity of bimetallic
catalysts is higher than those for single metal catalysts.
44
Figure 1. Turnover frequency in formic acid decomposition at 403 K as a function of Au atomic fraction
-1
(2.2
2.2 vol.% HCOOH/He, 51 ml min ).
Acknowledgments
This work has emanated from research conducted with the financial support of Science
Foundation Ireland under Grant Number 06/CP/E007.
References.
D. A. Bulushev, S. Beloshapkin, and J.R.H. Ross, Catalysis Today 154, 7 (2010).
C.J. Baddeley, C.J. Barnes, A. Wander, R.M. Ormerod, D.A. King, and R.M. Lambert,
Surface Science 314, 1 (1994).
45
28
CO2 reduction by H2 using Ni-Cu oxide-supported catalysts
Alessandro Fortunelli
IPCF-CNR, via G. Moruzzi, 156124 - Pisa -Italy
Abstract
The conversion of CO2 into fuels and chemicals is viewed as an attractive route for
decreasing the atmospheric concentration of this greenhouse gas and recycling it, but
its industrial application is limited by the low selectivity and activity of the current
catalysts.
Density-functional theory (DFT) calculations could provide a powerful and effective tool
to discover chemical reaction mechanisms and design new catalysts to this purpose,
overcoming the repetitious and time/labor consuming trial-and-error processes in the
experiment. In this presentation, we discuss recent advances on the determination by
DFT calculations of the mechanisms of catalytic hydrogenation of CO2 by two model
systems: (1) Ni3/MgO(100) and (2) Ni2Cu/MgO(100). The issues and the opportunities
provided by judicious alloying of a Ni3 sub-nanometer cluster catalyst and the effect of
the support are dealt with by using an original approach consisting of systematic phase
space searches combined with filtering based on reaction energy barriers. If time
allows, a DFT-guided design procedure of new and improved catalysts for the chemical
conversion of CO2, including the design goals and the recommendations for the catalyst
modification, will be briefly discussed, as well as challenges and possible research
directions in the field.
46
Oral Session 8 – Catalysis
47
29
Theoretical Studies of Structural, Electronic and Chemical
Reactivity Properties of Pt, Mo, and Pt/Mo nanocatalysts
Julius Jellinek1,2 and Aslihan Sumer1
1
Institute for Atom-Efficient Chemical Transformations,
Argonne National Laboratory, Argonne, IL 60439, USA
2
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439,
USA
E-mail: [email protected]
Abstract
Results of an extensive density functional theory study on structural, electronic, and
chemical reactivity properties of pure Pt and Mo, and mixed Pt/Mo catalytic clusters
will be presented and discussed. The discussion will include analyses of isomeric forms,
bonding energetics, and electronic features of the pure clusters as a function of their
size, and how these are affected by admixing Mo to Pt clusters and vice versa. The
issue of the energetically preferred homotopic conformations (particular placement of
different types of atoms among the cites of a given isomeric form) and the role of the
stoichiometric composition will be addressed as well. The chemical reactivity of the
nanocatalysts will be analyzed for the case of CO adsorption. The energetic and
electronic aspects of this reaction will be characterized as a function of cluster size,
structure, and composition. The issues of site and coverage dependence will also be
addressed. The implications of our findings for the well-known problem of COpoisoning of Pt catalysts will be pointed out. Finally, we will remark on the role of the
synthesis pathway in defining the structural and, consequently, chemical reactivity
characteristics of mixed Pt/Mo nanocatalysts.
Acknowledgments
This material is based upon work supported as part of the Institute for Atom-efficient
Chemical Transformations (IACT), an Energy Frontier Research Center funded by the
U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and by
the Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and
Biosciences, U.S. Department of Energy under Contract No.DE-AC-02-06CH11357.
48
30
From Microprocessors to Microbes: Versatile synthesis and
potential applications of titania–silver and alumina–silver
composite nanoparticles
Gordon Armstrong, Tanushree Bala*, Fathima Laffir and Roibeard Thornton
Materials & Surface Science Institute, University of Limerick, Limerick, Ireland
Corresponding author: Gordon Armstrong
Fax: +353 61 213529.
* Present address: Department of Chemistry, University of Calcutta, 92 A.P.C. Road,
Kolkata 700 009, India.
Abstract
Titania–silver (TiO2–Ag) and alumina–silver (Al2O3–Ag) composite nanoparticles were
synthesised by a simple, reproducible, wet chemical method under ambient conditions.
The surface of the oxides was modified with oleic acid, which acted as an intermediate
between the oxide surface and the silver nanoparticles. The resulting composite
nanoparticles were thoroughly characterised by XRD, TEM, XPS, FTIR
and TGA to elucidate the mode of assembly of Ag nanoparticles on the oxide surfaces.
Epoxy nanocomposites were formulated with TiO2–Ag and Al2O3–Ag to examine
potential applications for the composite nanoparticles.
Though these epoxy nanocomposites exhibited improved thermal conductivity
according to ASTM method D5470, the cost/performance ratio proved too high for
microelectronics applications. In contrast, preliminary results from disc diffusion
assays against Escherichia coli DH5a and Staphylococcus epidermidis NCIMB 12721
suggest that these TiO2–Ag and Al2O3–Ag composite nanoparticles have potential as
antimicrobial materials.
49
31
Bonding Asymmetry and Adatoms in Low Density Self-assembled
Monolayers of Dithiol on Au (111)
A. M. Sharif,+ D. N. Buckley,+ M. Buck,* and C. Silien+
+
Physics & Energy Department and Materials and Surface Science Institute
*
EaStChem School of Chemistry, University of St. Andrews, St. Andrews, U.K.
[email protected]
Abstract
Self-Assembled Monolayers (SAMs) of organic molecules are widely used to modify the
properties of surfaces and have been extensively studied in the last two decades. Given
that thiol moieties readily bind to Au and that high ordering is often spontaneous,
alkanethiol SAMs on a Au(111) substrate are a prime academic case. The SAMs
potential lies in their ability to carry active chemical groups. For the case of dithiol
molecule, the presence of a second thiol moiety (i.e., α,ω-dithiol) allows the molecule
to connect two metal electrodes forming a molecular wire that could be measured
with reliable contacts. Nanoelectronic devices have been demonstrated using this
principle. Since the device properties ultimately depend on the molecule-electrode
bonding, we present our study of the potential involment of Au adatoms in the
interfacial structure of dithiol on Au (111). We used scanning tunneling microscopy to
characterize the self-assembly of prototypic symmetric dithiols (1,6-hexanedithiol
(HDT), 1,4-benzenedimethanethiol (BDMT) and biphenyl-4,4’-dimethanethiol(BPDMT))
from dilute solutions and correlated their growth with the deconstruction of the
Au(111) herringbone pattern known to produce adatoms. In all cases, we observed an
initial low density monolayers where the molecules are paired by 0.45 Å tall
protrusions, assigned to Au adatoms. The other terminal group is imaged differently
revealing a strong asymmetry in the dithiol bonding. The formation of vacancy islands
and, thus, the extraction of additional adatoms from terraces are detected only after
substantial molecular rearrangement and loss of bonding asymmetry. The bonding
asymmetry is discussed with respect to the final geometry of the interface.
50
32
Mesoporous gold nanoalloy as a matrix for redox enzymes
immobilization
Urszula Salaj-Kosla, Edmond Magner
Materials and Surface Science Institute, University of Limerick, Limerick, Ireland,
e-mail address: [email protected], [email protected],
tel.:+353 (0)61 202629, fax.:+353 (0)61 203529
Abstract
Mesoporous gold (NPG) is obtained by dealloying Ag-Au alloys in concentrated nitric
acid for a certain period of time1. In the NPG layer the gold atoms assemble into a 3Dstructure to form a large surface area material with tunable pore sizes ranging from a
few nanometres to several microns in diameter. The desired pore diameter is achieved
by varying the temperature and the preparation time. The surfaces of the pores can be
easily modified and the NPG films have high electrical conductivity, indicating that NPG
is a suitable material for the immobilization of redox enzymes for applications in
biosensors and in biofuel cells. The creation of an efficient biofuel cell is dependent on
a number of factors: choice of enzyme, mediator, and electrode material. The
mesostructured electrodes enable a 28 fold higher enzyme loading compared to a
polycrystalline gold electrode and can be utilised in the development of membraneless
biofuel cells capable of generating high power densities. Biofuel cells comprised of
glucose oxidise as bioanode and bilirubin oxidise as biocathode are under
development.
1
H. Qiu, C. Xu, X. Huang, Y. Ding, Y. Qu, P. Gao, J. Phys. Chem. C 2009, 113, 2521.
51
Poster Abstracts
52
1
Tunneling magnetoresistance in FeCoZr-Al2O3 films containing
“metal core-oxide shell” nanoalloy particles
J. Fedotova1, M. Milosavljević2, Cz. Kapusta3
1
NC PHEP Belarusian State University, 220040 Minsk, Belarus
VINČA Institute of Nuclear Sciences, Belgrade University, P.O. Box 522, 11001 Belgrade, Serbia
3
AGH University of Science and Technology, Faculty of Physics and Applied Computer Science,
Department of Solid State Physics, 30-059 Krakow, Poland
2
Abstract
Temperature and magnetic field dependencies of electrical conductivity are
systematically studied in granular films (Fe45Co45Zr10)x(Al2O3)100–x (31≤ x ≤ 64) containing
crystalline metallic α-FeCo-based nanoalloy cores encapsulated in an amorphous oxide
shell embedded in an amorphous Al2O3 matrix. Formation of “metallic core-oxide shell”
nanogranules is confirmed by TEM and HRTEM. The structure of core and shell is
governed with the difference in the oxidation states of Fe and Co ions investigated with
EXAFS, XANES and Mössbauer spectroscopy. Tunneling magnetoresistance (TMR) of
spin-dependent nature is observed for granular films with “core-shell” structure in the
whole range of x values. The decrease of TMR with increasing temperature is correlated
with the magnetic saturation of superparamagnetic metallic nanogranules. The
enhanced TMR effect in “core-shell” granular films is discussed with respect to
stabilization of metallic cores sizes as well as the influence of magnetic oxide shell
through spin accumulation and filtering processes. A considerable high field
magnetoresistance appearing for core-shell samples at low temperatures and the
resulting deviation of magnetoresistance and squared magnetization dependences are
attributed to a magnetic randomness and/or strong magnetic anisotropy of the
magnetic oxide shell.
53
2
Surface tension of Ni−Sn intermetallics
T. Káňa1, A. Kroupa1 and M. Šob2,3,1
1
Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 616 62
2
Central European Institute of Technology, CEITEC MU, Masaryk University, Kamenice 5, 625 00
3
Department of Chemistry, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno,
Czech Republic
Abstract
Studying the properties of Ni−Sn intermetallics is auracvve because of their use in
soldering technology and as alternative anode materials in rechargeable Li-ion batteries.
Their cohesive properties have been reported recently [1]. Performing ab initio
calculations in the frame of density functional theory (DFT) with the help of the WIEN2k
code [2] and applying the approach outlined in [3, 4], we determined the surface energy
and tension of Ni, Sn and of selected stable Ni−Sn intermetallics, i.e. Ni3Sn, Ni3Sn2 and
Ni3Sn4. The calculated results will serve as an input for CALPHAD construction of the
phase diagram of Ni−Sn nanoalloys. This research is supported by Ministry of Educavon,
Youth and Sports (Project No. LD11024).
References
[1]
G. Ghosh, Metal. Mater. Trans. A 40, 4 (2009).
[2]
P. Blaha, K. Schwarz, G. K. H. Madsen, D. Kvasnicka, J. Luitz, WIEN2k, An Augmented
Plane Wave Plus Local Orbitals Program for Calculating Crystal Properties (Vienna
University of Technology, 2007).
[3]
L. Vitos, A. V. Ruban, H. L. Skriver and J. Kollár, Surface Science 411, 186 (1998).
[4]
J. Kollár, L. Vitos, J. M. Osorio-Guillén and R. Ahuja, Phys. Rev. B 68, 245417 (2003).
54
3
Pt based Nanoalloys for the use in proton exchange membrane fuel
cells
M. Röefzaad, J. Spéder, M. Nesselberger, M.Arenz
Department of Chemistry, University of Copenhagen, Denmark
Poster presentation of collaborative work; Presenter M.Röefzaad;
L. Altmann, M. Bäumer
Department of Chemistry, University of Bremen, Germany
Abstract
Pt-based Nanoalloys are promising catalysts for proton exchange membrane fuel cells
(PEMFCs) since they provide the facility to reduce the content of Pt in fuel cell catalysts.
Key to the use of nanoalloys, however, is their long term stability, which has been
shown for some nanoalloy catalysts to be diminished in comparison to pure Pt
nanoparticles [1]. A possible reason for this unfavorable behavior is the segregation of
the non-noble component to the surface of the nanoalloy where it is dissolved due to
the low pH of the electrolyte [2].
In collaboration with the WG of M. Bäumer, which has a strong expertise in the
synthesis of Pt nanoalloys in colloidal suspensions [3], first results on activity and
stability of Pt-nanoparticles have been made in electrochemical and electrocatalytical
measurements. Therefore nanoparticles from a colloidal suspension have been
anchored to high surface area carbon (HSAC) material and were tested under
electrochemical conditions concerning their activity and stability to electrocatalytic
reactions, such as the oxygen reduction reaction (ORR) and the oxidation of carbon
monoxide. The ratio between Pt-nanoparticles and HSAC can be tuned to achieve a
catalyst system with high activity and stability where agglomeration during the (ORR)
can be prevented.
Based on the results made for pure Pt-particles it is planned to prepare catalyst systems
containing Pt-Alloys, such as PtIr, PtCo and PtAu. First studies on the catalytic activity for
ORR have been carried out by L. Altmann during a STSM in Copenhagen.
References
[1]
H. R. Haas, M. T. Davis, ECS Transactions 2009, 25 1623-1631.
[2]
K. J. J. Mayrhofer, K. Hartl, V. Juhart, M. Arenz, Journal of the American Chemical
Society 2009, 131, 16348-+.
[3]
B. Jurgens, H. Borchert, K. Ahrenstorf, P. Sonstrom, A. Pretorius, M. Schowalter,
K. Gries, V. Zielasek, A. Rosenauer, H. Weller, M. Baumer, Angew. Chem.-Int. Edit. 2008,
47, 8946-8949.
55
4
On the promoting effect of Au on CO oxidation kinetics of Au-Pt
bimetallic nanoparticles supported on SiO2: an electronic effect?
R.P. Doherty1,2, C. Thomas1, J.-M. Krafft1, C. Méthivier1, H. Remita2, C. Louis1
1
2
Laboratoire de Réactivité de Surface, CNRS/Université Pierre et Marie Curie. Paris – France
Laboratoire de Chimie Physique, CNRS/Université Paris-Sud, Orsay (France)
Abstract
Bimetallic Au-Pt nanoparticles have been reported to exhibit enhanced catalytic
properties for CO oxidation in comparison to their monometallic counterparts [1, 2].
However full understanding of how the two metals interact at the nanoscale has yet to
be achieved. Explanations for the nanoscale behavior of supported Au-Pt nanoparticles
include the presence of geometric [1] and electronic effects [3-4]. Here, we attempt to
add clarity by investigating the catalytic properties and surface composition of SiO2
supported Au-Pt nanoparticles and comparing the results to those of their
monometallic counterparts.
Bimetallic Au-Pt nanoparticles were prepared by radiolytic reduction of H2PtCl6 and
HAuCl4 in the presence of polyvinyl alcohol (PVA) and polyacrylic acid (PAA) in water
[5]. These nanoparticles where then deposited onto a SiO2 support, dried and calcined
forming catalysts Auwt%Ptwt%/SiO2: Au0.45Pt0.25/SiO2 (4.6 nm) and Au0.45Pt0.36/SiO2
(4.6 nm). Monometallic Pt1.96/SiO2 (1.9 nm) and Au0.70/SiO2 (3.5 nm) catalysts were
prepared by IWI (incipient wetness impregnation with NH3 washing [6]). The kinetics of
CO oxidation (0.5 < CO < 1.5 %, 0.3 < O2 < 0.7 % in He with a reacting temperature
ranging from 270 to 300 °C) was measured.
Characterization of the Au-Pt catalysts by XRD, TEM-EDAX and CO-FTIR strongly
supports the view that alloy-type Au-Pt nanoparticles were formed with a Au-rich
shell/Pt-rich core structure. However, restructuration of the bimetallic Au-Pt
nanoparticles occurs when the bimetallic catalysts have been submitted in a CO
atmosphere at 100 °C for several hours. This treatment led to Pt surface enrichment as
also indicated by XPS measurements performed on Au0.45Pt0.36/SiO2 after CO oxidation
reaction.
CO oxidation kinetic data are listed in Table 1. The reaction orders and apparent
activation energy of the oxidation reaction, as well as the turnover rate, obtained on
Pt1.96/SiO2 are in good agreement with literature [7]. Those determined on Au0.70/SiO2
are reported for the first time. From the comparison of the kinetic parameters, it is
clear that CO oxidation proceeds exclusively on the Au surface atoms of
Au0.45Pt0.25/SiO2, whereas the reaction occurs mainly on the Pt atoms of
Au0.45Pt0.36/SiO2. Interestingly, the rate calculated on the basis of surface composition
of a homogeneous alloy, given by the XPS data, and by the C6D6 hydrogenation results
are lower and higher than those measured experimentally on Au0.45Pt0.36/SiO2 and
Au0.45Pt0.25/SiO2, respectively. This and the observed changes in the CO and O2 orders
with respect to Pt1.96/SiO2 can be attributed to a promotional electronic effect in the
Au-Pt bimetallic nanoparticles with an electron transfer from Au to Pt.
56
Table 1: Comparison of CO oxidation kinetic data obtained at 280 °C.
Ea
Catalyst
-1
(kJ mol )
-9
-1
-1
Reaction order
Rate (x 10 mol CO2 s g )
CO
Measured
O2
Calculated*/
Calculated */
XPS
Homog. Alloys
Calculated*/
C6D6 HYD
Pt1.96/SiO2
112
-0.88
1.02
18000**
Au0.45Pt0.36/SiO2
102
-0.62
0.89
6900
1380
692
30
Au0.45Pt0.25/SiO2
55
0.10
0.54
34
965
673
-
Au0.70/SiO2
64
0.09
0.69
7
* CO2 production rate calculated on the basis of the turnover rates estimated using
those of Pt and Au for the monometallic samples, the average size of the nanoparticles
determined by TEM and their surface compositions determined either by assuming a
homogeneous alloy or by using the data obtained by XPS or by C6D6 HYD. ** Note that
the Pt loading is considerably higher on this sample than the others.
Auten, B.J., Lang, H. F., Chandler, B.D., Appl. Catal. B: Environ. 81, 225 (2008).
Mihut, C., Descorme, C., Duprez, D. Amiridis, M.D., J. Catal. 212, 125 (2002).
Luo, M.F., Wang, C.C., Hu, G.R., Lin, W.R., Ho, C.Y., Lin, Y.C., Hsu, Y.J., J. Phys. Chem. C
113, 21054 (2009).
Bus, E., van Bokhoven, J.A. J. Phys. Chem. C 111, 9761 (2007)
Remita, H., Lampre, I., Mostafavi, M., Balanzat, E., Bouffard, S., Radiat. Phys. Chem., 72,
575, (2005).
Delannoy, L., El Hassan, N., Musi, A.; Le To, N. N., Krafft, J. M. Louis, C. J. Phys. Chem. B,
110, 22471, (2006).
Cant, N.W., Hicks, P.C., Lenon, B.S., J. Catal. 54, 372 (1978).
57
5
A comparative study of the preparation of Supported nanosized
bimetallic gold-palladium particles
N. El Kollia, S. Merad Bedranea,b, S. Giorgioc, L. Delannoya, C. Louisa
a
Laboratoire de Réactivité de Surface, CNRS/Université Pierre et Marie Curie. Paris – France
Laboratoire de Catalyse et Synthèse en Chimie Organique, Université de Tlemcen – Algérie
c
CINaM-CNRS, Campus de Luminy, Marseille – France
[email protected]
b
Abstract
Highly dispersed supported gold catalysts present remarkable activity towards various
reactions provided that gold particles are smaller than 5 nm [2]. In the case of goldbased bimetallic catalysts, which may exhibit better catalytic performances, an
additional constraint is to avoid segregation between the two metals. The purpose of
this work is the study and comparison of three preparation routes of bimetallic goldpalladium catalysts. Samples with several Au/Pd atomic ratios (10, 15, 20) and 1 wt %
Au were prepared on alumina, titania or ceria and compared to monometallic gold and
palladium samples.
The first preparation route is deposition-precipitation with urea (DPU) which was
extensively studied for monometallic gold catalysts [1,3]. The same principle was
applied to the preparation of bimetallic catalysts. Both metal precursors (HAuCl4 and
Pd(NH3)4(NO3)2) and urea were added to an aqueous suspension of the support. Urea,
a delay base, gradually decomposes at 80°C, and increases the solution pH, leading to
the precipitation of the metals onto the support surface. The second preparation route
derives from the colloidal method described by Prati et al [4]. HAuCl4 in aqueous
solution was reduced by NaBH4 in the presence of polyvinyl alcohol (PVA), which acts
as colloid stabilizer; the Au0 colloids were then adsorbed on the support. In a second
step Pd(NH3)4(NO3)2 was added to the Au0 catalyst in suspension in water, then
hydrogen was bubbled in the solution to reduce palladium on gold. The third
preparation route is also a colloidal method, and derives from the one reported by
Baiker et al [5]. It is based on the use of tetrakis (hydroxypropyl) phosphonium chloride
(THPC) which acts both as a stabilizer and a reducing agent for bimetallic AuPd particles
that are then adsorbed onto a support.
In order to correlate the physico-chemical features to the preparation methods, the
catalysts were characterized by elemental analysis, TEM, Environmental HR-TEM under
O2 and H2 atmospheres, DRIFTS coupled with CO adsorption at RT and in the reaction
of selective hydrogenation of butadiene.
For the DPU, PVA and THPC Au-Pd samples, the average metal particle sizes are about
3, 4.5 and 4 nm, respectively, whatever the support and the Au/Pd ratio. Elemental
analysis showed a better control of the Au/Pd ratio was obtained for the PVA method.
CO adsorption coupled to DRIFTS after in situ reduction revealed small structural
differences between the various samples. For the PVA catalysts, the absence of bands
Références
2
. G.C. Bond, C. Louis, D.T. Thompson, Catalysis by Gold, Imperial College Press, 2006
. R. Zanella, L. Delannoy, C. Louis, Appl. Catal. A: Gen. 291 (2005) 62
4
. D. Wang, A. Villa, F. Porta, D. Su, L. Prati, Chem. Commun., (2006) 1956; J. Phys. Chem. C., 112 (2008) 8617
5
. D.C. Duff, A. Baiker, P.P. Edwards Langmuir, 9 (1993) 2301; D. C. Duff, A. Baiker, I. Gameson, P.P. Edwards Langmuir 9
(1993) 2310.
3
58
of multi-bonded CO on Pd0 and the exclusive presence of CO linearly adsorbed on Au0
and Pd0 indicate that the Pd0 atoms are isolated from each other on the surface of gold
particles, and that the nanoparticles are bimetallic. For the DPU and THPC samples,
linear adsorption of CO on Pd0 is also favored, but bands of bridged CO on Pd0 are
visible. In the reaction of selective hydrogenation of butadiene, a good correlation was
established between the Au/Pd ratio and the catalytic activity. For instance, when the
Pd loading increases i.e. Au/Pd decreases from 20 to 10, the temperature
corresponding to 100% butadiene conversion decreases from 180 to 80°C. In the range
of temperature studied, the PVA catalysts showed higher selectivity to alkenes than
DPU catalysts, which might be related to their higher proportion of isolated Pd0 sites.
59
6
Theoretical Study of 38-Atom Cobalt-Palladium Clusters
Haydar Arslan* and Roy L. Johnston**
*
Zonguldak Karaelmas University, Department of Physics 67100 Zonguldak, Turkey.
University of Birmingham, School of Chemistry, Edgsbaston B15 2TT, Birmingham, UK.
**
Abstract
The energetic and structures of 38-atom Co-Pd nanoalloys have been investigated for
all compositions using a genetic algorithm global optimization technique with the
Gupta empirical potential. An ab initio approach based on density functional theory
(DFT) has been used to reoptimize the initial empirical potential structures. Structural
distributions are investigated and seven different structures are found as a global
minimum for all compositions of Co-Pd nanoalloys. As a results of the excess energy
analysis, we found that Co6Pd32 (Gupta level) and Co16Pd18 (DFT level) are the most
stable structures.
60
7
Surface chemistry of bimetallic nanocomposite catalysts as
revealed by X-ray Photoelectron Spectroscopy
Baljit Singh a, Fathima Laffir b, and Eithne Dempsey a
a
b
Centre for Research in Electroanalytical Technologies, Institute of Technology Tallaght, Dublin
Materials and Surface Science Institute, University of Limerick, Limerick, Ireland
Abstract
Novel bimetallic nanocomposites of Pt/Au and Co/Ni on activated carbon were
prepared as an alternative to enzymatic bio-sensors for direct electro-oxidation of
glucose and uric acid sensing respectively [1, 2]. X-ray Photoelectron Spectroscopy (XPS)
was used to investigate the chemistry and composition of the surface of these
nanocomposites responsible for their excellent catalytic behaviour.
In the case of Pt/Au electro-catalysts, Pt was found to exist in the metallic and oxidised
forms in all nanocomposites of Pt: Au ratios of 1:1, 1:2, 1:3 and 1:4. Higher valent
oxidised states of Pt corresponded to Pt(OH)2 and PtO/PtO2. As the concentration of Au
increased the relative fraction of oxidised Pt increased from Pt/C to PtAu4/C. In
addition, relative surface composition of Pt was greater than 75% in all bimetallic
nanocomposites compared to their nominal compositions. These results highlight the
synergistic role played by Au in Pt/Au systems in enhancing the catalytic activity.
In CoNi/C based catalysts, the binding energies of the principle peaks of Co 2p3/2 and Ni
2p3/2 were characteristic of divalent states of the metal ions. The relative intensities
and the characteristic chemical shifts of the related satellite peaks were used to resolve
surface hydroxides as dominant species with minor contributions from oxides. A
considerable surface enrichment of Ni was seen, in addition to Ni increasing the overall
surface concentration of metallic species. The combination of metal hydroxides/oxides
and nanoparticles in the carbon supported Co-Ni based materials were found to play a
key role in uric acid determination
B. Singh, F. Laffir, T. McCormac and E. Dempsey, Sensors and Actuators B 150 (2010)
80–92
B. Singh, F. Laffir, C. Dickinson, T. McCormac and E. Dempsey, Electroanalysis (2011),
23, 79 – 89
61
8
A detailed ab initio investigation of water adsorption on
stoichiometric and non-stoichiometric surfaces of hydroxyapatite
Jacek Żegliński1, Michael Nolan2, Damien Thompson2, and Syed A. M. Tofail1
1
Materials and Surface Science Institute, University of Limerick, Ireland, [email protected]
Tyndall National Institute, Ireland
2
INTRODUCTION
Water is a main medium interacting with hydroxyapatite (HA) surfaces in physiological
conditions. Molecules of H2O are known to reversibly physisorb to the surface, but also
to dissociate and irreversibly chemisorb thus creating permanent rearrangement of the
surface.1 Knowledge of such a water-altered surface structure and associated
molecular mechanisms could advance the understanding of bone growth, and its
interactions and stability in body environment.
We use a single molecule of water as a probe of interactions with various surfaces of
HA: stoichiometric (001) and (010), and Ca-exposed (010), and PO4-exposed (010)
surfaces. By systematic probing, the affinity of a water molecule to possible adsorption
sites is quantified by calculating relevant adsorption energies. Based on that, the most
stable termination of a surface can be defined.
COMPUTATIONAL METHODS
The surface structures (periodic slab models) are optimised using a VASP code (Vienna
ab-initio simulation package) based on Density Functional Theory (DFT) with GGA PW91 functional and plane wave basis set. The adsorption energy is calculated as follows:
Eads = Eslab-H2O – (Eslab+ EH2O)
where Eslab-H2O is the energy of the complex: slab + adsorbed H2O molecule, Eslab is the
energy of the slab itself, and EH2O is the energy of a molecule of water.
RESULTS AND DISCUSSION
We observe molecular adsorption of water at all of the investigated surfaces of HA.
After being physisorbed, a H2O molecule can be dissociated and chemically bound to
the stoichiometric (001) and PO4-exposed (010) surfaces. There is, however, certain
energy barrier for dissociation of H2O on the (001) surface (-69.5 kJ mol-1).
Nevertheless, we observe further stabilization of this process, where the created
hydroxyl ion is bound to two surface calcium ions. The surface is thus remodeled
according to the following equation:
H2O(gas) + (PO4)3-(sur) + 2Ca2+(sur) = (HPO4)2-(sur) + (Ca2OH)3+(sur)
The affinity towards water and resulting stability of the (010) surface differs
considerably regarding its termination. Comparing the calculated adsorption energies it
can be concluded that the stoichiometric and Ca-exposed surfaces can adsorb a water
molecule but without dissociating it. The strongest adsorption of H2O is, however,
observed at (010) surface with PO43- ions exposed to interface (Eads = -227.3 kJ mol-1),
indicating a preference for dissociation of water at the surface.
62
Fig. 1 Energy barrier for dissociation of a water molecule on (001) surface of
hydroxyapatite. Oxygen – red, Phosphorus – purple, Calcium – green, Hydrogen –
white.
CONCLUSIONS
Our study indicates that the stoichiometric termination of the (010) surface of
hydroxyapatite, Ca2(PO4)2(OH)2 is the most stable and the least susceptible to the
irreversible remodeling by water. Whereas water can be dissociated at the (001)
surface if certain external energy is provided to overcome the observed energy barrier.
REFERENCES
1. Corno M. et al., Langmuir
angmuir 25:2188-2198,
25:2188
2009
ACKNOWLEDGMENTS
We acknowledge a grant of computer time at the SFI/Higher Education Authority
funded Irish Centre for High End Computing (ICHEC) for the provision of computational
facilities.
63
9
X-ray analyses of thermally grown and reactively sputtered
tantalum oxide films on NiTi alloy
K. McNamara1, S.A.M Tofail1, D. Conroy, J. Butler1, A.A Gandhi1 and W. Redington1
1
Abstract
An equiatomic NiTi alloy, popularly known as Nitinol, exhibits some unique properties
such as shape memory effect and superelasticity. These properties are exploited in
biomedical devices such as self-expandable endovascular and urinary stents, catheters,
wire-guides, tissue-extractors and stone removal baskets. Biomedical applications of
NiTi alloys largely depend on the formation of a spontaneous TiO2 at the surface of the
medical device. The presence of this oxide layer prevents the release of Ni2+ ions, which
is prone to give adverse reaction in the body. One of the issues with NiTi implants is the
possibility of the breakdown of this TiO2 layer in body fluids, which may potentially
result in the release of undesirable Ni2+ ions [1] [2]. Sputter deposition of tantalum (Ta)
on the surface of NiTi alloy is expected to improve the alloy’s corrosion resistance and
biocompatibility. Tantalum is a well-known biomaterial which is not affected by body
fluids and is not irritating to human tissue. Here we compare the oxidation chemistry
crystal structure evolution of tantalum oxide films grown on NiTi by reactive O2
sputtering and by thermal oxidation of sputter deposited Ta films. The effect of
sputtering parameters and post-sputtering treatments on the morphology, oxidation
state and crystal structure of the tantalum oxide layer have been investigated by fieldemission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy
(XPS) and X-ray diffraction (XRD). The study has found that it may be better to avoid
oxidation at and above 600C. The study establishes that reactive sputtering in presence
of low oxygen mixture yields thicker film with better control of the film quality except
that the surface oxidation state of Ta is slightly lower [4].
References :
[1] Nolan M. and Tofail S.A.M (2010) ‘Density functional theory simulation of titanium
migration and reaction with oxygen in the early stages of oxidation of equiatomic NiTi
alloy’ Biomaterials, 31 (13), pp. 3439-3448.
[2] Nolan M. and Tofail S.A.M (2010) ‘The atomic level structure of the TiO2-NiTi
interface’ Physical Chemistry Chemical Physics, 12 (33), pp. 9742-9750.
[3] Zein El Abedin S., Welz-Biermann U. and Endres F. (2005) ‘A study on the
electrodeposition of tantalum on NiTi alloy in an ionic liquid and corrosion behaviour of
the coated alloy’, Electrochemistry communications 7 (9), pp. 941–946.
64
10
Phase transformations of Fe-Ni nanoalloys
M. Byshkin1,2, M. Hou1
1
Physique des Solides Irradiés et des Nanostrucutres CP234, Faculté des Sciences, Université
Libre de Bruxelles, Bd du Triomphe, B-1050 Bruxelles, Belgium
2
Akhieser r Institute for Theoretical Physics within National Science Center, “Kharkov Institute of
Physics and Technology”, 1 Akademicheskaya str, Kharkov 61108, Ukraine
Abstract
Phase transformations and ordering properties of Fe-Ni nanoalloys are studied by
means of semi-grand canonical Metropolis Monte Carlo (MMC) and isothermal
molecular dynamics. The embedded atom potential designed by G. Bonny et. al. [1] is
assessed by MMC on the basis of the phase diagram of the bulk alloy. At low
temperature and at both the alloy and the nanoalloy scales, MMC confirms that the L12
Fe3Ni phase is not stable while the BCC Fe, the L10 FeNi, the L12 FeNi3 and the FCC Ni
phases are.
Surface segregation of Ni is favoured on the Fe-rich side of the phase diagram and of Fe
on the other. In contrast with the bulk BCC/FCC martensitic phase transition which
takes place by a nucleation and growth mechanism, we suggest, using molecular
dynamics, that nanoalloy clusters may transform as a whole provided they are in a solid
solution state. Thermodynamic equilibrium inhibits such a fast transformation.
References:
[1] G. Bonny, R.C. Pasianot, L. Malerba; Phil. Mag. 89 (2009) 711.
65
11
An Experimental and Numerical Analysis of the Dieless Drawing of
Nitinol Alloy
E. Twohig1, 2, P. Tiernan1, 2, and S.A.M. Tofail2
1
Deptartment of Design and Manufacturing Technology, University of Limerick, Ireland.
Email : [email protected]
2
INTRODUCTION
Nitinol is widely used in wire and tube form in the biomedical industry as guidewires
for deploying stents, angioplastic balloons and filters, and as self-expanding stents
which are precision laser-cut from thin walled tubing[1, 2].The traditional process of
metal wire and bar production involves pulling the wire/bar through a conically shaped
orifice called a die to reduce its diameter in successive steps. The considerable die
wear that occurs at the tool-die interface, coupled with the additional lubrication and
pre-cleaning costs, add considerably to the overall cost of the process[3]. A process
known as dieless drawing is under development as an innovative method for the
production of wire, bar and tubing without the use of reduction dies. This process is
best suited to material forms that currently have high production costs and are difficult
to produce using the conventional method. The shape memory material, Nitinol
presents such difficulties during production due to its high toughness and workhardenability[4].
An experimental rig for dieless drawing was previously designed, built and successfully
operated at the University of Limerick[5]. The next step in the development of this
process is to develop an accurate, reliable finite element (FE) model capturing the
heating/cooling rate, applied force, and strain rate characteristics of the process as
applied to the shape memory alloy Nickel Titanium. FE modelling using ABAQUS is
being carried out to optimise the process, and results obtained from experimental runs
using the dieless drawing rig have been used to validate the initial FE model. Good
agreement has been shown between experimental and numerical results.
EXPERIMENTAL METHODS
An initial test of ten NiTi rods of 5mm diameter was carried out on the dieless drawing
machine. Successful rod drawing tests were carried out at temperatures of 800oC. An
initial drawing velocity of 3mm/min and heater/cooler assembly velocity of 12mm/min
was applied to the rod, giving a process ratio of 0.25. As the process ratio determines
the percentage reduction in cross-sectional area of the rod, the drawing velocity was
incrementally increased giving process ratios of 0.33, 0.42 and 0.5.
The percentage reduction per pass was measured over the steady state length of
drawn rod to be 51.8% to a diameter of 3.47mm for a rod drawn with a drawing
velocity of 5mm/min and a heating/cooling velocity of 12mm/min. The final rod length
was extended by 143mm. A smooth, even, oxidized surface resulted from the single
pass dieless draw.
The finite element model developed has accurately predicted the process deformation.
The heating/cooling rate and interaction between the heater, the cooler, the rod
surface and the environment were found to be the main controlling factors on results
obtained from the model. An appropriate material definition is required to capture a
true representation of experimental results.
66
The experimental results have shown the possibility to reduce the number of passes
and subsequent heat treatments required in fabricating Nitinol wire.
CONCLUSION
The cross-section of 5mm diameter NiTi rods were successfully reduced using the
dieless drawing method at temperatures of 800oC. Varying the process ratio i.e. the
ratio between the velocities applied to the top of the rod and the heating/cooling
system of the machine, resulted in varying cross-section reductions. Increasing the
process ratio increased the reduction in cross-sectional area, and decreasing the ratio
resulted in a smaller reduction in area.
Further work is required to define the material behavior under load at elevated
temperature in order to allow accurate predictions to be produced by the finite
element model at various drawing conditions. A more accurate definition of the
interaction between the rod and the heating/cooling environment of the machine is
also required.
REFERENCES
1.
Barras, C.D.J. and K.A. Myers, Nitinol - Its Use in Vascular Surgery and Other
Applications. European Journal of Vascular and Endovascular Surgery, 2000. 19(6): p.
564-569.
2.
Duerig, T.W., A.R. Pelton, and D. Stöckel, An overview of nitinol medical
applications. Materials Science and Engineering A, 1999. 273-275: p. 149-160.
3.
Naughton, M.D. and P. Tiernan, Requirements of a dieless wire drawing system.
Journal of Materials Processing Technology, 2007. 191(1-3): p. 310-313.
4.
Russel, S.M. Nitinol Melting and Fabrication. in Shape Memory and Superelastic
Technologies. 2001. California, USA: SMST, California.
5.
Carolan, R. and P. Tiernan, Computer controlled system for dieless drawing of
tool steel bar. Journal of Materials Processing Technology, 2009. 209(7): p. 3335-3342.
67
12
Incorporation of nanoparticles with tailored distribution into
Polymeric Surfaces and the Adhesive Strength of such
incorporated nanoparticles
Patrick Cronin1, 2, Jacek Zeglinski 3, Peter Tiernan2, 3 and Syed A.M. Tofail1, 3.
1
Deptartment of Physics and Energy, University of Limerick, Limerick, Ireland.
Departement of Manufacturing and Operations Engineering, University of Limerick, Ireland.
3
Materials and Surface Science Institute, University of Limerick, Limerick, Ireland,
[email protected]
2
INTRODUCTION
Nanoparticles are a definite source of antimicrobial activity in the battle to beat health
care associated infections (HCAI). Antimicrobial surfaces allow for the sterilisation of
bacteria through their photocatalytic abilities[1]. Developing an active surface layer with
reliable adherence of nanoparticles is an active area of research.
Dip-coating[2] and thin film preparation by spin-coating[2], are popular methods of
developing active surface layers that exhibit efficient electron hole pair generation. Solgels[2] and plasma treatments[2] have been additionally used within the dip-coating
process to increase the adhesive bond by preparing the polymer surface for coating.
Electroless deposition by immersion coating[3], and electrohydrodynamic spraying[4]
have been investigated for their ability to prepare a stable active surface layer.
Polymers coated by these methods have homogeneous coatings which are a
consequence of chemical interactions between the polymeric surface and
nanoparticles or binders. These preparation techniques can be unreliable, creating
deterioration of the polymer surface, and producing unstable active surfaces [2-4].
Nanoparticles have been added to polymer powders before extrusion[2], resulting in
greater adhesion through physical interaction. This strategy is counterproductive as
many applications require that nanoparticles are exposed to the environment and
remain at the polymer surface.[2].
Here we describe a novel method that exploits the polymers surface properties to
achieve a stronger bonding between nanoparticles and a thermoplastic polymer. A
prototype rig has been designed and constructed for controlled distribution and strong
adherence of such particles. This rig was employed to coat the surface of polyethylene
terephthalate (PET) fabric with a single active surface layer of commercially available
titania nanoparticles. A modified pull-out test was then used to determine the strength
of the adhesion. By controlling the process parameters, it was possible to obtain very
strong bonding between the nanoparticles and the thermoplastic polymer.
EXPERIMENTAL METHODS
The PET surface was heated above its softening temperature, but below its melting
point. Commercially available TiO2 nanoparticles were applied to the surface by a
specially controlled spray technique. Nanoparticles were embedded into this surface
side of the heated PET by a pressing force, which ensured an optimum ingress while
maintaining enough surface area exposed for surface activity for e, g. photocatalysis.
The distribution and the amount of these particles were by FEG-SEM and EDS. Active
surface layer adhesive efficacy was characterised in two ways, 1) using a modified
version of ASTM D4541-09[5] and 2) applying ten color fastness cycles by a conventional
laundering machine.
There was nanoparticle coverage distribution on active PET of 18% for 0.13% TiO2
68
concentration, and 22% for 0.25% TiO2. There was no correlation between the Force
required to pull nanoparticles from PET active surfaces, with varying surface
concentrations of active PET. Nanoparticle surface area in the overall active surface
area is negligible, due to their dispersed state. Therefore the tested area is in greater
contact with the PET surface fabric, than that of the combined surface area of the
nanoparticles embedded.
CONCLUSION
Nanoparticles can be successfully adhered to thermoplastic polymers by embedding
through physical interactions and thermal modification. Nanoparticle dispersion over a
PET fiber can be altered through optimization of its concentration. Color fastness trials
are a substantiate method of determining nanoparticle adhesion to polymer surfaces.
Further work is required to determine the effect of pressing force on the adhesion.
REFERENCES
1.
Fujishima, A., T.N. Rao, and D.A. Tryk,. Journal of Photochemistry and
Photobiology C: Photochemistry Reviews, 2000. 1(1): p. 1-21.
2.
Singh, K.V., et al., in Beltwide Cotton Conference, N.C. Council, Editor. 2006:
Texas.
3.
Yang, F.-C., et al., Materials Science and Engineering: C, 2009. In Press,
Corrected Proof.
4.
Jaworek, A. and A.T. Sobczyk, Journal of Electrostatics, 2008. 66(3-4): p. 197219.
5.
International, A., in Paint and Related Coating Standards. 2009, www.astm.org.:
West Conshohocken, PA,.
ACKNOWLEDGMENTS
European Community for the financial support (BioElectricSurfaces; FP7 no. CP 2125332). This communication reflects the views only of the authors, and the Commission
cannot be held responsible for any use of the information contained therein.
69
13
The synthesis of intermetallic nanoparticles: COST research
project plan and preliminary results
G. Pigozzi1, D. Mukherji2, P. Schmutz1
1
Laboratory of Corrosion and Materials Integrity, EMPA, Swiss Federal Laboratories for
Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
2
Institute of Materials, Technical University, Braunschweig, Germany
Abstract:
The synthesis of nanoalloys with controlled size and composition is of fundamental and
technological interest. Recent advancement in nanotechnology provides the capability
to design physical properties not only by changing the material but also by changing the
particle size into nano-scale. Multifunctional nano-systems are gaining importance and
surface modifications of nano-particles have emerged as an important class of
functional nano-materials. Core-shell nanoparticles have attracted recent attention as
they are finding interesting applications in the field of biomedicine. In the core-shell
nanoparticles, the core and the shell are of different material/structure, having
different properties. In particular, systems with a magnetic core surrounded by an inert
shell material, are modern solutions that are being developed for applications in e.g.,
tumour destruction via hyperthermia, drug and gene delivery and MRI contrast
enhancement. In order to boost the signal, and improve the ability of MRI to detect the
smallest tumours, researchers also try to produce stronger magnetic signal from the
iron oxide nanoparticles. This clearly shows the need for alternate nano-particle
compositions with stronger magnetic properties.
Recently, we have developed an electrochemical selective phase dissolution (ESPD)
method to produce nanoparticles of different intermetallic phases, some of them
cannot be produced with standard nano-crystal synthesis routes. This technique is the
focus of a research project hosted by EMPA that has been recently funded by the SBF
(Swiss Secretariat of Education and Research) in the frame of the present COST Action
to be started on 1st October 2011. By this method, a core-shell structure can be formed
in-situ in a single step. A wide range of nanoparticles can be produced from multicomponent alloys containing precipitates, by an electro-chemical extraction technique.
Many intermetallic compounds, some of which show strong magnetic properties, were
produced (e.g. Ni3Si, Ni3Al, Ni3Fe, Co3Al). An example of one of these particles is shown
in the Figure 1. The core-shell structure could be produced under widely varying
conditions of the electro-chemical extraction processing and from different alloy
compositions. Possible applications of our intermetallic nanoparticles include, medical
treatments (like magnetic drug delivery, hyperthermia and MRI contrast agents),
reinforcement of joining materials (brazing and soldering), improvement of corrosion
resistance of metal coatings, and magnetic fluids. The same ESPD method is very
versatile and allows for other nanostructured materials to be produced, like nonporous
membranes, hollow silica capsules and nano-patterned surfaces.
The project goals, the development rout of the nanoparticles with respect to the
possible applications, and the related COST network will be highlighted. Results will be
presented on the characterization of the structure and magnetic properties of Ni3Si
nanoparticles produced by ESPD.
70
14
Coalescence in nano-sized metallic systems
R. Novakovica, S. Delsanteb, G. Borzoneb
a
National Research Council (CNR) – Institute for Energetics and Interphases (IENI), Genoa, Italy
Dipartimento di Chimica e Chimica Industriale, Genoa University, Via Dodecaneso 31, 16146
Genoa, Italy
b
Abstract
During heating, nanoparticles undergo to specific phenomena such as coalescence,
which affect their phase stability. This aspect is of great importance for the potential
application of nanosized metallic system. The driving force for the coalescence of two
nanoparticles is the surface energy reduction due to lower surface area of the new
nanoparticle. In fact, the process begins with the contact of nanoparticles and is
followed by the alignment of the coalescing planes at the interface and by the
subsequent growth of the neck. The study on coalescence includes three topics, i.e.
surface diffusion, physical and thermodynamic properties and coalescence
mechanisms.
The nanoparticles growth at high temperature by coalescence have been analyzed by
means of the theoretical predictions; an important parameter for predicting the final
particle size is the rate of coalescence. The studies of the coalescence processes involve
nanoparticles diffusion, nanoparticles properties relevant to the diffusion, such as
melting points, volumes and diffusion coefficients as well as overall coalescence
mechanisms. A few examples of coalescence in a “small systems” using the literature
data are presented (i.e. Co, Au); in addition, a modeling of the coalescence of pure Sn
and Bi nano-sized particles will be done to compare the theoretical results with own
experimental data.
71
15
Synthesis and characterization of eutectic Ag-Cu alloy
nanoparticles
S. Delsantea, G. Ennasb, G. Borzonea, G. Pigozzic , M.Pawelkiewiczc, J. Janczak-Ruschc
a
Dipartimento di Chimica e Chimica Industriale, Genoa University, Via Dodecaneso 31, 16146
Genova – Italy
b
Dipartimento di Scienze Chimiche, Cagliari University- Cittadella universitaria di Monserrato,
09042 Monserrato-Italy
c
Empa Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstr. 129- ,
8600 Dübendorf - Switzerland
Abstract
The investigation on lead-free solder materials has received much attention in recent
years due to the toxicity of Pb and the restriction of its use in microelectronics by the
WEEE (Waste from Electrical & Electronic Equipment) and RoHS (Restrictions on the
Use of Certain Hazardous Substances in Electrical and Electronic Equipment) European
Directives.
Lead-free solders currently used, such as Sn-Ag-Cu (SAC) alloys, have a liquidus
temperature of about 220°C, that is 40°C higher than the traditional Sn-37mass% Pb
solder. There is therefore a need for melting point reduction. Nanostructured solder
materials offer very interesting thermal properties and we think that they can be used
to pursue this goal. At the present, only a few literature data and patents on the
development of nano-structured alloys in the form of lead-free pastes are available.
The binary Ag-Cu sub-system shows a simple eutectic phase diagram (L ↔ (Ag) + (Cu))
with a melting temperature of 780°C and the eutectic composition of ~39 at.% Cu, and
we have taken this as a model system for our study. Our preliminary results, that were
presented at the previous COST MP0903 Meeting, showed that the melting point of
this eutectic alloy could be reduced by more than 100°C when a nanomultilayer
configuration [1] is used in which thin Ag-Cu layers are intercalated (confined) with thin
layers of a diffusion barrier material (e.g. AlN). Our work is now aimed at extending the
nano-confinement approach to nanoparticles. It is well known that nano-sized particles
(NPs) can have a melting temperature lower than the bulk material. This nano size
effect can be used to decrease the melting temperature of new lead-free solders.
The experimental approach in our joint research is to synthesize Ag-Cu eutectic
nanoparticles by a low temperature chemical reduction method in aqueous solution
adopting potassium borohydride as a reducing agent. Transmission Electron
Microscopy (TEM) was used to determine the crystalline nature of the samples, the size
and the composition of the particles. The thermal behaviour of the samples will be
investigated by Differential Scanning Calorimetry (DSC).
[1] J. Janczak-Rusch, G. Garzel, S. Delsante, G. Borzone, M.Pawelkiewicz, Experimental
and theoretical determination of the size-dependent phase diagrams, COST Meeting
MP0903, Barcellona, 14-16 April 2011.
72
16
Powerlaw scaling of the rate toward equilibrium of Au-Pd
nanoparticles with the rate of heating
I.S. Atanasov
Institute of Electronics at Bulgarian Academy of Sciences, Sofia, Bulgaria
and
M. Hou
Universite Libre de Bruxelles, Brussels, Belgium
Abstract
It is well established both experimentally and theoretically that at equilibrium Au
segregates at the surface of Au-Pd systems. We try to obtain some quantitative
characteristics of the rate this process develops in Au-Pd nanostructures. As a case
study we use a 1264-atom cluster, cut off from an fcc crystal by a sphere. At its initial
state its whole surface consists of Pd atoms and its core is Au. Using extensive
molecular dynamics simulations, we observe how its configurational energy changes as
the cluster is heated with constant rates between 1 K/ns and 20 K/ns and we fit this
dependence with a simple theoretical model, which includes general rate of transition
toward
equilibrium
and
general
activation
energy.
Within the interval of heating rates examined by us, we cannot obtain characteristics of
the transition process which are independent of the heating rate. However, we
observe a well defined powerlaw scaling behaviour of these quantities with the heating
rate. This allows us to estimate the rates the transition toward equilibrium would occur
at lower heating rates using extrapolation. The question whether this powerlaw scaling
dependance eventually saturates at low heating rates is open. The available data do
not provide any indication about this. If so, then the extrapolation of the scaling
behaviour only provides an upper limit of the rate the transition toward equilibrium
occurs in Au-Pd nanoalloy systems.
73
17
Three-dimensional Ordered Macroporous LiFePO4 Inverted Opal
Thin Film Cathodes for High Performance, Ultrafast Charging
Lithium-ion Batteries
E.Armstrong and C. O’Dwyer
Department of Physics & Energy, and Materials & Surface Science Institute,
Abstract
Active lithium battery material electrodes often suffer performance limitations due to
the brittle and disordered structure of the active material architecture. This project will
concentrate on improving battery performance by developing new lithium battery
cathode materials in the form of three-dimensionally ordered mesoporous and
macroporous (3DOM) electrode architectures. Synthesis and assembly routes will be
developed using self-assembled polymer sphere templates, and forced impregnation
for infilling, to fabricate large-scale 3DOM structures of metal oxides. For a high
capacity cathode material, V2O5 will be infilled into the colloidal crystal templates using
electrodeposition. In parallel, LiFePO4, a favoured cathode material due to its long cycle
life and high stability, will also be studied by developing a LiFePO4 precursor to infill the
self-assembled polymer sphere templates. Electrochemical characterisation will be
carried out, using coin cell arrangements, centering on charge-discharge properties,
cycle-life and tolerance to charging rates. In addition, in situ monitoring of structural
changes during lithium insertion and removal will be accomplished using a nondestructive angle-resolved transmission setup to characterize the photonic band gap of
the inverted opal structures. As the volume of the active material changes non-linearly
during charging and discharging, any decrease in structural order which will affect the
optical stop bands will be monitored and related to ex situ measurements of the
material structure. The synthetic, structural/mechanical, electrochemical and
architectural influences of the cathode materials investigated here may lead to a major
reduction in size and weight, giving reliable, mouldable battery shape adaptability to
portable electronic device designs, with increased performance.
74
18
Understanding the catalytic reactivity of gold nanoparticles
through multi-scale simulations
Simon Brodersen
CINF, DTU Physics, Technical University of Denmark, Department of Physics, Fysikvej, Building
307 2800 Kgs. Lyngby
Abstract
We investigate how the chemical reactivity of gold nanoparticles depends on the
cluster size and shape using a combination of simulation techniques at different length
scales, enabling us to model at the atomic level the shapes of clusters in the size range
relevant for catalysis. The detailed atomic configuration of a nanoparticle with a given
number of atoms is calculated by first finding overall cluster shapes with low energy
and approximately the right size, and then uses Metropolis Monte Carlo simulations to
identify the detailed atomic configuration. The equilibrium number of low-coordinated
active sites is found, and their reactivities are extracted from models based on Density
Functional Theory calculations. This enables us to determine the chemical activity of
clusters in the same range of particle sizes that is accessible experimentally. The
variation of reactivity with particle size is in excellent agreement with experiments, and
we conclude that the experimentally observed trends are mostly explained by the high
reactivity of under-coordinated corner atoms on the gold clusters. Other effects, such
as the effect of the substrate, may influence the reactivities significantly, but the
presence of under-coordinated atoms is sufficient to explain the overall trend.
Introduction from poster:
Although gold is generally considered chemically inert, it has been known that gold
nanoparticles can be active catalysts, once the particle size is reduced below 5 nm.
Recent work based on DFT calculations has shown that low-coordinated gold atoms at
corners and possibly edges of the particle can act as active sites for CO oxidation, and
that this can explain the trend of increased reactivity of particles below 5 nm. Based on
this we are investigating the shape of gold nanoparticles, with particular focus on the
number of under-coordinated atoms as a function of particle size.
75
19
On modeling the kinetics of processes over poly-functional bimetallic catalysts
K.Kumbilieva
a
Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; [email protected]
Abstract
Poly-functional bi-metallyc catalysts are often characterized by nano-alloystructured active surface. This can result in non-uniform properties of the active sites,
which makes questionable the adequacy of the ideal-layer approximation for such
systems. Special models must be derived for processes involving active sites of
different structure, action and accessibility. For avoiding discrepancy with the
Hinshelwood-Langmuir kinetics, the suggested approach considers the surface of polyfunctional catalysts as containing 2 or 3 co-existing ideal adsorbed layers, each of which
is characterized by private individual parameters. Extending the approach of
Beeckman and Froment [J.B.Beeckman, G.F.Froment, Ind.Eng.Chem.Fund. 21 (1982)
243] for the case of multifunctional catalysts with 2 or 3 site types, we define the
overall catalyst activity ϕ (u ) as ϕ (u ) = ∑ ϕ j (u ) = ∑ H j σ j (u ) , where the ϕ j (u ) terms
denote the contribution of each type of sites; σ j (u ) - the working fraction of the jth
site type, H j - the probability that the site is accessible. Defining the deactivation
function φ (u ) as change of the activity ϕ (u ) , for bi-disperse pore structure we get:
φ (u ) = ∂ϕ (u ) ∂u = H 1∂σ 1 (u ) + H 2 {∂σ 2 ∂u + ∂σ 3 ∂u} + σ 1 (u )∂H 1 ∂u + {σ 2 (u ) + σ 3 (u )}(∂
Analysing this relation, various trends in the evolution of the catalytic system may be
prognosed, depending on the quantitative changes of σ 1 , σ 2 , σ 3 , and H j provoked
by changes of u ( u may denote time, conversion, coke, poison concentration, or any
other deactivation-responsible factor). The σ j terms may change in different way for
site types requiring different surface ensembles.
The different site types may be vulnerable in different ways under changes of the
reaction medium. Thus, if u stands for conversion, in the general case
∂σ i ∂u ≠ ∂σ j ∂u , depending on the origin of the deactivating agents. The apparent
evolution of the catalytic system will be ruled by the ( ∂σ j ∂u ) regularity which
satisfies the condition: ∂σ j ∂u > ∂σ m ∂u ≥ ∂σ n ∂u . If the system comes to an
alternative point ∂σ m ∂u ≥ ∂σ j ∂u , a step change in the kinetic law may be observed
in the course of the process. Some factors influence the activity of different site types
in opposite directions: ∂σ j ∂u > 0 , but ∂σ i ∂u < 0 . The dominating effect would be
change of selectivity. As the modules of these changes may vary in the course of the
process, the effect on selectivity may be rather complicated. Geometric factors may be
the essential when types of active sites differ by the number of surface atoms in proper
configuration, what makes them vulnerable in different way in respect of coke ( u
standing for coke coverage).
In case u matches with coke deposits near pore openings, the diffusion-dependent
terms may become dominant.
Examples are disputed.
76

Nanoalloys as advanced materials

Transcription

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