Photocatalytic removal of diazinon from aqueous solutions: a quantitative systematic review

Diazinon is a widely used pesticide that can be effectively degraded in aqueous solutions via photocatalytic oxidation. This quantitative systematic review was conducted to shed light on the various aspects of photocatalytic diazinon removal based on evidence. A systematic search was performed in Scopus, PubMed, Web of Science, Embase, and Ovid databases with keywords including diazinon, photocatalysis, and their equivalents. The search was limited to original articles in English published between January 1, 2010, and March 25, 2021. The results were expressed by descriptive statistics including mean, SD, median, and percentiles, among others. The initial electronic and manual search retrieved 777 articles, among which 41 studies comprising 49 trials were qualified for data synthesis. The reported diazinon degradation rate ranged from 2 to 100%, with a mean ± SD of 59.17 ± 28.03%. Besides, ZnO/UV, WO₃/UV, TiO₂/UV, and TiO₂/Vis, in sequence, were the most widely used processes with the highest efficacies. Solution pH in the range of 5-8, catalyst dose below 600 mg/L, diazinon initial concentration below 40 mg/L, and contact time of 20-140 min could be the optimum conditions. Diazinon degradation obeyed the first-order kinetic model with k_obs between 0.0042 and 1.86 min^-1 and consumed energy of 38.93-350.36 kWh/m³. Diazoxon and IMP were the most detected by-products of diazinon degradation although bioassay data were scarce. Based on the results, photocatalytic processes are very efficient in removing diazinon from aqueous solutions although more elaborate studies are needed to assess the mineralization rate and effluent toxicity.