Photosensitized CN− oxidation over TiO2

The oxidation of cyanide catalyzed by TiO2 under UV illumination is investigated. The study was performed by determining the yield of cyanide photo-oxidation using different initial cyanide concentrations, irradiation times, masses of semiconductor in suspension, light intensities, pH values and temperatures. It was observed that during the first minutes of irradiation CNO− was the main product of oxidation, but at long irradiation times all the cyanide was converted to CO32−. From the kinetic analysis performed by using the experimental data, it is deduced that the rate constant of the cyanide oxidation by photogenerated holes is 70% greater than the corresponding rate constant of the water oxidation. Finally, some experiments using a continuous flow photoreactor were carried out. With this system a good yield for the removal of cyanide, which could be maintained for at least 9 h, is reported.