Photocatalytic oxidation of cyanide: kinetic and mechanistic studies

The kinetics and mechanism of the photocatalytic oxidation of cyanide in the presence titanium dioxide catalyst were investigated in this study. By displacing the surface hydroxyl groups on the surface of titanium dioxide with fluoride ions, it was deduced that cyanide is oxidised via a pure heterogeneous pathway, i.e. oxidised by the holes trapped at the surface hydroxyl groups dropTiO(.). The quantum efficiency of the photocatalytic oxidation was found to be low (ca. 0.1-0.2%) and this was mainly due to (1) the low adsorption of cyanide ions onto the titanium dioxide surface, (2) the absence of homogenous reaction between cyanide ions and diffused hydroxyl radicals, and (3) the high electron hole recombination rate within the titanium dioxide photocatalyst. A kinetic model was developed to describe the mechanism involved in the photocatalytic oxidation of cyanide. (C) 2002 Elsevier Science B.V. All rights reserved.