Some observations about the photocatalytic oxidation of cyanate to nitrate over TiO₂

The photocatalytic oxidation of cyanate ions in aqueous solution and in the presence of TiO 2 takes place by two different reaction pathways, depending on the solution pH. For pHs lower than 10, the main oxidation product is nitrate instead of N 2 , as reported previously. The hydrolysis of cyanate seems to be the reason for this change of mechanism with pH. NH +4 is formed by CNO - hydrolysis, and its photo-oxidation gives nitrite and nitrate. The hydrolysis rate controls the speed of the whole process, but the photo-oxidation of CNO - to N 2 appeared to be faster in a strongly basic medium. For values of pH lower than 5, NH +4 is hardly oxidized, remaining stable in solution. © 1994.