Metal oxide-water interfaces, reaction mechanisms

Brown Jr., G.E., Parks, G.A., Bargar, J.R., and Towle, S.E., Use of X-ray absorption spectroscopy to study reaction mechanisms at metal oxide-water interfaces, in Mineral-Water Interfacial Reactions Kinetics and Mechanisms, in Sparks, D.L. and Grundl, T.J., Eds., American Chemical Society, Columbus, OH, 1998, p.14. 

Use of X-ray Absorption Spectroscopy To Study Reaction Mechanisms at Metal Oxide-Water Interfaces... 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

Brown GE Jr (1990) Spectroscopic studies of chemisorption reaction mechanisms at oxide/water interfaces. In Mineral-Water Interface Geochemistiy. Hochella MF, White AF (eds), 23 309-63 Brown GE Jr, Parks GA, O Day PA (1995) Sorption at mineral-water interfaces macroscopic and microscopic perspectives. In Mineral Surfaces. Vaughan DJ, Patrick RAD (eds), 5 129-184 Birrgess J (1978) Metal Ions in Solution. Ellis Horwood, New York... 

The general mechanism will be roughly similar to that developed in section 15.2 for the oxidation of metals by oxygen with adsorption of water on the surface of oxide, two interface reactions that create and consume the defect and the diffusion of the defect. With these steps, it will be necessary to add desorption of the formed hydrogen at the external interface. 

Scherer, H.W. Zhang, Y. (1999) Studies on the mechanisms of fixation and release of ammonium in paddy soils after flooding. 1. Effect of iron oxides on ammonium fixation. J. Plant Nutr. Soil Sci. 162 593-597 Scherer, M.M. Balko, B.B. Tratnyek, P.G. (1998) The role of oxides in reduction reactions at the metal-water interface In Sparks, D.L. Gmndl.T.J. (eds.) Mineral-Water Interfacial Reactions, Kinetics and Mechanisms ACS Smposium Series 715, Am. Chem. Soc., 301-322... 

Scherer MM, Balko BA, Tratnyek PG. The role of oxides in reduction reactions at the metal-water interface. In Sparks DL, Grundl TJ, eds. Mineral-Water Interfacial Reactions Kinetics and Mechanisms. Washington, DC American Chemical Society, 1998 ACS Symp. Ser. 715 301-322. 

Two well-known snrface stoichiometric photochemical reactions can be identified (i) the photostimnlated adsorption of O2 (reduction of acceptor molecules), and (ii) the photostimnlated adsorption of H2 (oxidation of donor molecules) on a metal-oxide surface. Both result in a new state of the heterogeneous system with charged species adsorbed on the solid. If these two processes occurred simultaneously they would yield a reaction identifiable as the photocatalysed oxidation of hydrogen to water. Nonetheless, snch a simple mechanism gives bnt a small indication of the real processes that take place on solids and at interfaces of heterogeneous systems. We examine these cases later after a discnssion of the nature of solids and a description of the photochemical/photophysical events taking place in these complex materials. 

The catalytic reactions at solid-liquid interfaces of metal oxides have been of great interest to colloid chemists. The adsorption-desorption phenomena of various metal ions on oxides such as Y-AI2O3 have been extensively investigated since adsorption-desorption is a fundamental step in heterogeneous catalytic reactions. Several mechanisms have been proposed by many investigators . Kinetic studies, however, have scarcely been carried out because the reaction is too fast to be measured by ordinary methods. Only a kinetic study on the proton adsorption-desorption at the Ti02-water interface has been reported using the pressure-jump technique by the present authors. ... 

---