Photocatalytic degradation of diazinon with illuminated ZnO–TiO2 composite

• ZnO–TiO2 composite was used as a photocatalyst for the removal of diazinon.
• Hybridization of ZnO and TiO2 nanoparticles was identified by EDX and FT-IR analysis.
• UV/ZnO–TiO2 process was more efficient than UV/ZnO or UV/TiO2 process.
• Photocatalytic degradation process was described by Langmuir–Hinshelwood model.

ZnO–TiO2 composite was used as a photocatalyst for the degradation of diazinon. Effects of various parameters such as composite dosage, pH, initial diazinon concentration, dissolved oxygen concentration, hydrogen peroxide concentration and type of organic compounds on the removal efficiency of diazinon were studied. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used for characterization of the prepared composite. Immobilization of zinc oxide nanoparticles onto TiO2 was identified by EDX, XRD and FT-IR analysis. Photocatalytic degradation efficiency of diazinon was increased as the composite dosage increased up to 0.5 g/L. Neutral pH was selected as an optimal condition due to a photo-corrosion of ZnO in acidic and basic conditions. Photocatalytic degradation efficiency of diazinon was decreased with increasing initial diazinon concentration. Pseudo-first order rate constant (kobs) was decreased from 0.1234 to 0.001 min-1 and electrical energy per order (EEO) was increased from 38.9 to 4800 kWh/m3 with increasing diazinon concentration from 5 to 50 mg/L, respectively. Photocatalytic degradation efficiency of diazinon was increased with oxygen purging and addition of hydrogen peroxide while it was decreased in the presence of organic compounds. Photocatalytic activity was maintained even after five successive cycles.