Photocatalytic reduction of nitro organics over illuminated titanium dioxide:: Role of the TiO2 surface

The present study investigates the mechanism of photocatalytic reduction of nitro organics (aromatic and aliphatic) at the surface of titanium dioxide slurries (Degussa P25) in the absence of oxygen and in the presence of the sacrificial electron donor methanol (MeOH) or isopropanol (i-PrOH). Photocatalytic reduction was verified by identifying reduction products as the reaction progressed. Byproducts were observed to occur in the sequence RNO2 - RNO - RNH2; with the hydroxylamine intermediate present by inference but not detected direct:ly. Mass balances ranged between 90+% and 70+%. Comparison of the reduction kinetics in aqueous i-PrOH vs aqueous MeOH revealed that secondary radicals generated from alcohol oxidation played no role in the observed. reduction kinetics. For the nitroaromatic compounds studied, the values of the experimental reduction rate constants using i-PrOH as the electron donor divided by the rates using MeOH as the donor averaged 1.03 (+/-0.19), indicating that the photocatalyst surface was responsible for the observed chemistry. The nitroaliphatic compounds gave an average value of 1.63, with a wide standard deviation of 1.10.