Selective photocatalytic decomposition of nitrobenzene using surface modified TiO₂ nanoparticles

Adsorption and photocatalytic degradation of nitrobenzene (NB) in the presence and absence of phenol (Ph) over UV-illuminated arginine-modified TiO₂ colloids have been investigated by infrared absorption, electron paramagnetic resonance spectroscopy, and X-ray absorption spectroscopy. High performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry were used for monitoring degradation conversion rates and byproduct identification. It was found that photodegradation of NB and Ph strongly depends on the nature of the TiO₂ surface. Through the use of the HPLC peak area ratio before and after illumination, the photocatalytic decomposition rate of NB and Ph individually using bare TiO₂ is nearly identical (1.7 and 1.5, respectively) and occurs via oxidative mechanism. Through the use of arginine-modified TiO₂ nanoparticles, a three-fold increase in the NB decomposition rate is observed while no Ph decomposition is observed. Furthermore, the degradation pathway using the arginine-modified photocatalyst is completely altered to a reductive mechanism, providing a more efficient means to degrade nitrocompounds that are already in a highly oxidized state and limiting the number of byproduct. These results indicate that a critical parameter in the photocatalytic decomposition of NB and Ph is their specific adsorption and coupling to the TiO₂ surface. Modification of the TiO₂ particle surface with chelating agents demonstrates enhanced interaction with the desired target contaminant to impart selectivity to photocatalysis.