Photocatalytic Degradation of 3,3′-Dimethylbiphenyl-4,4′-diamine (o-Tolidine) over Nanocrystalline TiO₂ Synthesized by Sol−Gel, Solution Combustion, and Hydrothermal Methods

The nanocrystalline titania catalysts were prepared by sol−gel, solution combustion, and hydrothermal methods. The catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectrophotometry (FT-IR), scanning electron microscopy (SEM), and BET surface area analysis for their structural properties and by diffuse reflectance spectrophotometer (DRS) for band-gap studies. The photocatalytic activity of synthesized catalysts was determined by the degradation of 3,3′-dimethylbiphenyl-4,4′-diamine (o-tolidine). Commercially available P-25 Degussa catalyst was used as a reference catalyst to compare the photocatalytic activity. The percent degradation was determined using UV−visible spectrophotometer, while the mineralization was confirmed by total organic carbon analysis (TOC). A detailed degradation pathway has been suggested based on electrospray ionization mass spectrometry (ESI-MS). Comparison of different catalysts showed that degradation was favored with the sol−gel synthesized TiO₂ catalyst, while mineralization was nearly the same using a catalyst synthesized by sol−gel, solution combustion method, and commercial TiO₂ Degussa P25.