Solar light-assisted photocatalytic degradation of methylene blue with Mo/TiO2: a comparison with Cr- and Ni-doped TiO2

Highly active Cr-doped, Ni-doped and Mo-doped TiO2 photocatalysts were synthesized by a sol–gel method. The synthesized catalysts were characterized by UV–DRS, BET, XRD, FE-SEM–EDS, TEM and XPS. Metal doping decreased the band gap of TiO2 to 2.83 eV for Mo-doped TiO2 and Ni-doped TiO2. The activity of the synthesized photocatalysts was evaluated by studying the degradation of MB as a model pollutant under both UV and solar irradiation. The Mo/TiO2 catalyst achieved 98% degradation under solar light within 120 min. The activity of the catalysts was in the order Ni-doped TiO2 < Cr-doped TiO2 < TiO2 < Mo-doped TiO2. The optimum activity was found at a loading of 1.5 g/L of Mo-doped TiO2 under both UV and solar irradiation. The degradation was rapid at pH > 7 and followed pseudo-first order kinetics. Degradation by-products were analyzed on HR-LCMS and a mechanism is proposed.