Surface modification of TiO2 nanoparticles for photochemical reduction of nitrobenzene

The effects of surface modification of nanocrystalline titanium dioxide (TiO2) with specific chelating agents on photocatalytic degradation of nitrobenzene (NB) was investigated in order to design a selective and effective catalyst for removal of nitroaromatic compounds from contaminated waste streams. Mechanisms of NE adsorption and photodecomposition were investigated using infrared absorption and electron paramagnetic resonance spectroscopy. Liquid chromatography and gas chromatography/mass spectrometry were used for byproduct analyses. Arginine, lauryl sulfate, and salicylic acid were found to bind to TiO2 via their oxygen-containing functional groups. Modification of the TiO2 surface with arginine resulted in enhanced NE adsorption and photodecomposition, and compared to unmodified TiO2. The initial quantum yield for photodegradation of NE in this system was found to be Phi (init) = 0.31 as compared to the one obtained for Degussa P25 of Phi (init) = 0.18. NE degradation followed a reductive pathway over arginine-modified TiO2 and was enhanced upon addition of methanol. No degradation of arginine was detected under the experimental conditions. Arginine improved the coupling between NE and TiO2 and facilitated the transfer of photogenerated electrons from the TiO2 conduction band to the adsorbed NE. These results indicate that surface modification of nanocrystalline TiO2 with electron-donating chelating agents is an effective route to enhance photodecomposition of nitroaromatic compounds.