A comparison of endosulfan removal by photocatalysis process under UV-A and visible light irradiation: optimization, degradation byproducts and reuse

In this study, the removal efficiency of endosulfan as a persistent organic pollutant and formation of its metabolites were investigated using Ag/TiO₂/Fe₃O₄ photocatalyst under visible and UV-A light. Light intensity, catalyst amount, initial endosulfan concentration, initial pH and time were determined as controllable factors for Taguchi experimental design. The highest removal efficiencies of endosulfan were achieved as 86.14% and 85.46% for visible and UV–A light sources, respectively. According to the greatest best criterion, the level at which the highest S/N ratio was obtained for each parameter was accepted as the optimum value. As a result of the validation experiments, 94.2% and 91.9% efficiency were obtained for visible and UV-A light, respectively. The metabolite formations of endosulfan (endosulfan sulfate, ether, and lactone) remained below 7% in all experiments on a concentration basis. In the reuse experiments of the magnetically recovered photocatalyst, high removal efficiency of around 80% was obtained after four cycles. The removal efficiencies were found to be 86.7% and 84.8%, for real samples taken from the drinking water treatment plant inlet and the spring water network injected with endosulfan under optimal photocatalysis experimental conditions, respectively. It has been shown that nitrate and sulfate anions, which are in significant concentrations in raw water samples, have very little effects on endosulfan removal. The overall results showed that the Ag/TiO₂/Fe₃O₄ photocatalyst was produced successfully, the catalyst was highly effective in the mineralization of endosulfan in synthetic and real water samples under UV and visible light, and effective yields could be obtained even with reuse.