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.