ICS84

Contributed
The roles of bicarbonate/carbonate in catalytic oxidation processes

Dan Meyerstein 1,2 Erzsébet Illés 1 Vered Marks 1 Haya Kornweitz 1 Ariela Burg 3 Amir Mizrahi 4
1Department of Chemical Sciences, Ariel University, Ariel, Israel
2Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel
3Department of Chemical Engineering, Sami Shamoon College of Engineering, Beer-Sheva, Israel
4Department of Chemistry, Nuclear Research Center Negev, Beer-Sheva, Israel

The fact that the redox potential of the couple CO3.-/CO32-, 1.57 V, is considerably lower than that of the OH./H2O suggests that in many catalytic oxidation processes carbonate might be involved. Indeed results point out that the Fenton reaction in the presence of HCO3- proceeds via:

Fe(H2O)62+ + HCO3- ⇌ FeII(CO3)(H2O)3 + H3O+ + 2H2O

FeII(CO3)(H2O)3 + OOH- ⇌ (CO3)FeII(OOH)(H2O)2- + H2O

(CO3)FeII(OOH)(H2O)2- -> (CO3)FeIV(OH)3(H2O)-

(CO3)FeIV(OH)3(H2O)- -> FeIII(OH)3(H2O) + CO3.-

i.e. the active ROS in physiological media and in advanced oxidation processes is CO3.- and not OH..

Furthermore DFT calculations suggest that CO3.- is expected as the active species in photo-catalytic oxidation processes.

The observation that CuII(CO3)n(2n-2)- and NiIIL2+ in the presence of bicarbonate are good electro-catalysts for water oxidation is due to:

  1. The carbonate ligand lowers considerably the redox potential of the central cation.
  2. The carbonate ligand is a non-innocent ligand, i.e. a considerable charge transfer from the central cation to the carbonate occurs. This charge transfer is involved in the water oxidation.

Acknowledgement: This study was supported by a grant from the Pazy Foundation.









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