PHOTOCATALYTIC REDUCTION OF NITRO ORGANICS OVER ILLUMINATED TITANIUM-DIOXIDE - ROLE OF THE TIO2 SURFACE

The present study investigates the mechanism of photocatalytic reducti on of nitro organics (aromatic and aliphatic) at the surface of titani um dioxide slurries (Degussa P25) in the absence of oxygen and in the presence of the sacrificial electron donor methanol (MeOH) or isopropa nol (i-PrOH). Photocatalytic reduction was verified by identifying red uction products as the reaction progressed. Byproducts were observed t o occur in the sequence RNO2 - RNO - RNH2; with the hydroxylamine inte rmediate present by inference but not detected direct:ly. Mass balance s ranged between 90+% and 70+%. Comparison of the reduction kinetics i n aqueous i-PrOH vs aqueous MeOH revealed that secondary radicals gene rated 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 don or divided by the rates using MeOH as the donor averaged 1.03 (+/-0.19 ), indicating that the photocatalyst surface was responsible for the o bserved chemistry. The nitroaliphatic compounds gave an average value of 1.63, with a wide standard deviation of 1.10.