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 photocatalyic 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 NB 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 NB adsorption and photodecomposition, and compared to unmodified TiO₂. The initial quantum yield for photodegradation of NB in this system was found to be Φ(init) = 0.31 as compared to the one obtained for Degussa P25 of Φ(init) = 0.18. NB 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 NB and TiO₂ and facilitated the transfer of photogenerated electrons from the TiO₂ conduction band to the adsorbed NB. These results indicate that surface modification of nanocrystalline TiO₂ with electron-donating chelating agents is an effective route to enhance photodecomposition of nitroaromatic compounds.