Photodegradation of phenol by UV/TiO2 and Vis/N,C-TiO2 processes: Comparative mechanistic and kinetic studies

Photodegradation pathway was compared for two systems: N,C-doped TiO2 under visible light and P-25 under UV irradiation. Degradation efficiency of phenol, phenol intermediates and OH radicals formation was investigated for both systems. The obtained results showed similar efficiency of phenol degradation for doped TiO2 excited by visible light to P-25 irradiated by UV light. 60 min irradiation in the Vis/N,C-TiO2 and UV/P-25 systems resulted in 69 and 76% of phenol degradation, respectively. However, photoactivity under visible light (λ > 400 nm) of N,C-TiO2 was four times higher than photoactivity of P-25 TiO2. Presented data indicated different degradation pathways of pollutants in the presence of nonmetal-doped TiO2 and visible light than in UV/TiO2 system. The HPLC–MS analysis revealed the lack of hydroxyl-by-products after irradiation of phenol in the presence of N,C-TiO2 and visible light, whilst they were found in P-25/UV system. Although the degradation of organic contaminants was efficient, no generation of hydroxyl radical in the N,C-doped TiO2/Vis system was observed.