Review article

Catalysis of Redox Processes by Hydrous Oxide Surfaces

Werner Stumm ; Institute for Environmental Science and Technology (EAWAG), Swiss Federal Institute of Technology (ETH Zürich), CH - 8600 Dübendorf, Switzerland

Abstract

Much progress has been made in the identification, physicochemical charaterization and determination of the quantity of solute species in natural waters. Most chemical processes in natural systems occur at the surface of minerals and inorganic and organic particles. The concept of active surface sites at the solid-water interface, and the characterization of the surface sites (surface speciation) is essential in understanding surface controlled processes. Here the role of hydrous oxide surfaces in catalyzing redox processes in natural waters is illustrated by three case examples:
1) Oxidation of Fe(II) by O2 • Fe(II) and other transition elements adsorbed to hydrous oxide (in inner-sphere surface complexes), as well as their hydrolysis species, are readily oxygenated; it can be shown that outer-sphere electron transfer is rate determining.
2) Reduction of nitroaromatic substances by adsorbed Fe(II). Fe(II) adsorbed to Fe304, y-FeOOH and a-FeOOH and other suitable hydrous oxides is an efficient reductant for nitroaromatic and other organic substances; rate determining step is most likely the formation of a precursor product between the reductant and the nitroaromatic substance.
3) Adsorbed chromate is an efficient oxidant of organic substances, e.g., hydroxy carboxylic acid and their esters. Adsorption enhances the oxidizing power of chromate and increases the lability of the oxogroups at the Cr(VI) center.
Redox processes catalyzed by mineral surfaces play an important
role in the evolution of the earth's surface and its natural waters.

Keywords

Hrčak ID:

135606

URI

https://hrcak.srce.hr/135606

Publication date:

3.4.1997.

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