Advanced Oxidation Process based on the Cr(III)/Cr(VI) Redox Cycle

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Advanced Oxidation Process based on the Cr(III)/Cr(VI) Redox Cycle
SUPPORTING INFORMATION (Environ. Sci. Technol.)
Advanced Oxidation Process based on the Cr(III)/Cr(VI)
Redox Cycle
Alok D. Bokare and Wonyong Choi*
School of Environmental Science and Engineering, Pohang University of Science and
Technology (POSTECH), Pohang 790-784, Korea
Figure S1.
Pourbaix diagram illustrating oxidation/reduction stability fields for
mononuclear Cr(III)/Cr(VI) species (depicted in red) and water/H2O2 (depicted in black).
S1
Cr(H2O)63+
OH –
2+
OH –
(H2O)5CrOH
H+
(pKa = 4.23)
(H2O)4Cr(OH)2
H+
OH –
H+
(pKa = 6.1)
(log KSP = -30.3)
k22 = 1.8 M-1s-1
k11 = 2 10-4 M-1s-1
OH –
H+
“Dimer”
Cr(OH)3(H2O)3 (s)
“active monomer hydroxide”
k12 =
3.810-2 M-1s-1
Cr2(µ
µ-OH)2(H2O)84+
+
3+
Cr2(µ
µ-OH)2(H2O)7OH
OH –
H+
Cr2(µ
µ-OH)2(H2O)7(OH)22+
(pKa = 6.04)
+ (H2O)5CrOH2+
Trimer
(different deprotonated forms)
+ deprotonated dimer
Tetramer
(different deprotonated forms)
+ (H2O)5CrOH2+
or
+ (H2O)4Cr(OH)2+
Trimer
(different deprotonated forms)
Figure S2. Schematic representation of individual Cr(III) oligomerization steps in aqueous solution. [Spiccia et al., Inorg. Chem. 26 (1987)
474-482].
S2
Figure S3. Chemical structure of β-cyclodextrin (β-CD). The primary and secondary
hydroxyl groups are located outside the ring and inside the apolar cavity, respectively.
The oxygen atoms on adjacent pyranose rings, which act as a diol ligand for forming
metal-inclusion complexes, are depicted in Red.
S3
Figure S4. Comparative MALDI-TOF spectra of Cr(III) aqueous solutions containing βcyclodextrin under different initial pH conditions. The species A and B correspond to
[Cr2(µ-OH)2(H2O)7(OH)]3+–Na+ and [Cr2(µ-OH)2(H2O)6(OH)2]2+–Na+ respectively.
([Cr(III)]0 = [β-CD]0 = 2 mM).
S4

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