PHOTOCATALYTIC MINERALIZATION OF NITROGEN-CONTAINING BENZENE-DERIVATIVES

The photocatalytic mineralization of nitrobenzene, nitrosobenzene, phe nylhydroxylamine, aniline and 4-nitrosophenol has been investigated in aerated conditions. In slightly acidic TiO2 suspensions, all these co mpounds proved to undergo quantitative formation of carbon dioxide, wh ereas nitrogen is converted into nitrate and ammonium ions. The mechan ism of ammonium ion release is suggested. Ammonium ions are not genera ted by reduction of nitrate or nitrite ions, but directly from partly oxidized and unstable intermediates, such as, for example, quinonemono imine and aliphatic imines. Ammonium ions are formed from nitro-and ni troso-derivatives through reduction of the nitrogen-containing substit uent. The reductive pathway prevents detachment of nitro-and nitroso-g roups as either nitrate or nitrite ion from the organic moiety. Quite specularly, from phenylhydroxylamine, aniline and aminophenol, ammoniu m ions are released by means of a partially oxidative pathway. Thus, t he temporal evolution of the [NO3-]/[NH4+] concentration ratio, beside s other experimental conditions (pH, photon flux, reactant concentrati ons), depends largely on both the initial oxidation state of the nitro gen and the nature of the starting organic substrate (e.g. 4-nitrosoph enol vs. nitrosobenzene). (C) 1997 Elsevier Science B.V.