SOME OBSERVATIONS ABOUT THE PHOTOCATALYTIC OXIDATION OF CYANATE TO NITRATE OVER TIO2

The photocatalytic oxidation of cyanate ions in aqueous solution and i n the presence of TiO2 takes place by two different reaction pathways, depending on the solution pH. For pHs lower than 10, the main oxidati on product is nitrate instead of N-2, as reported previously. The hydr olysis of cyanate seems to be the reason for this change of mechanism with pH NH4+ is formed by CNO- hydrolysis, and its photo-oxidation giv es 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 f aster in a strongly basic medium. For values of pH lower than 5, NH4is hardly oxidized, remaining stable in solution.