Photodegradation of phenol by zinc oxide, titania and zinc oxide–titania composites: Nanoparticle synthesis, characterization and comparative photocatalytic efficiencies

Nano-ZnO, TiO2 and ZnO–TiO2 composite particles were synthesized by a sol–gel method and were used as catalysts in the photocatalytic degradation. The nanocatalysts were characterized by XRD, SEM, EDX and BET methods. The experimental results showed that the nano-ZnO particles are large agglomerates having a hexagonal wurtzite structure of particle size 17.5±5 nm, nano-TiO2 has uniform particles size of 15±5 nm with spherical morphology. The nano-ZnO–TiO2 composite particles are of large agglomerates being embedded inside with particle size of 11.6±5 nm. The photocatalytic activity of nano-ZnO, TiO2 and ZnO–TiO2 composite particles was evaluated using phenol as a model compound. The effect of initial pH, initial catalyst loading and concentration of phenol under UV light irradiation and direct sun light was studied. The photodegradation of phenol was found to follow pseudo-first order kinetics and the experimental results proved that the nano-ZnO, TiO2 and ZnO–TiO2 composite particles are efficient catalysts for phenol degradation in the presence of UV light. Total organic carbon analysis indicated complete mineralization of phenol in the presence of nano-ZnO, TiO2 and ZnO–TiO2 surface.