The investigation of endosulfan removal using silver doped magnetic photocatalyst and optimization by Taguchi experimental desing method

In this thesis, the efficiency of the synthesised Ag/TiO2/Fe3O4 catalyst in the removal and metabolite formation of endosulfan selected as a model persistent organic pollutant by the photocatalysis process, the effect and optimization of the ambient conditions, the reusability of the catalysts were investigated under visible LED, UV-C and UV-A LED light sources. XRD, SEM-EDX, TEM-EDS analyzes were carried out to examine the structural properties of the prepared catalyst. In the first stage of the study, the VALLME procedure was used in the analysis of endosulfan isomers and metabolites in aquatic environment, as a fast, convenient, cost-effective and environmentally friendly extraction process. After HPLC analysis, the best recovery rates for α‐endosulfan, β‐endosulfan, endosulfan sulfate, endosulfan ether and endosulfan lactone were respectively; 99.06%, 103.06, 91.1, 96.79 and 115.31 were obtained for n-hexane under the conditions of 200 µL solvent volume, 10 mL sample volume and 3 min vortex time. In the second stage of the study, the experimental design of the photocatalysis process with Taguchi method and optimization with analysis of variance (ANOVA) were performed for endosulfan removal and degradation into its metabolites. The samples prepared according to the experimental design initial conditions were applied photocatalysis experiments first in the dark environment and then under UV-A LED, UV-C and visible LED light sources. Taguchi optimization and variance analysis were performed using Minitab 19 program to determine the effects of light intensity, catalyst amount, initial endosulfan concentration, pH and time parameters on removal efficiency. The highest removal efficiency will be achieved at 27 W light power, pH 4, 0.5 g/L catalyst amount, 60 min reaction time and 4 mg/L initial endosulfan concentration, where the highest S/N ratio is obtained for visible LED light and UV-C light, and the results of the verification experiments were obtained as 94.2% and 93.2%, respectively. It was concluded that the highest S/N ratio for UV-A LED light was 18 W light power, pH 4, 0.1 g/L catalyst amount, 60 min reaction time and 4 mg/L initial endosulfan concentration, resulting in the highest removal efficiency, and 91.9% was found as. In addition, when the effects of parameters on removal efficiency of all light sources were evaluated, it was found that the most effective parameters were initial endosulfan concentration and pH, respectively. Fcritical values showed that the effect of light intensity, catalyst amount and reaction time on endosulfan removal was not statistically significant. The error caused by uncontrollable factors remained well below 50% in all light sources, showing that the errors of the experiments are not important. When the P% values in the variance analysis are examined, it is seen in all light sources that there is a significant difference between the levels of the initial endosulfan concentration and pH factor for endosulfan removal. In addition, the contribution of the parameters to the removal was given as % value, respectively, the initial endosulfan concentration and pH were the highest contributors in all light sources. In the normal probability plot of the linear model for endosulfan removal, the residuals are reasonably close to the straight line, the errors are normally distributed, and the terms specified in the model are important in all light sources. The R2 values of the models created according to the experimental results of endosulfan removal for all light sources showed high suitability, and the R2 value obtained from the visible LED light model is higher than the values obtained from UV-C and UV-A LED models, so it is more suitable for endosulfan removal by photocatalysis process. After the removal efficiencies were found by optimizing the factors that are thought to be effective in endosulfan removal in photocatalysis experiments, metabolite formation was also monitored as a result of endosulfan degradation. While endosulfan was removed from all light sources, high concentrations of endosulfan sulfate, endosulfan ether and endosulfan lactone were not observed, on the contrary, the formations remained below 2% in all experiments on the basis of concentration and supported the endosulfan removal. For the reuse experiments of the synthesiesed Ag/TiO2/Fe3O4 catalyst, it was regenerated with pure water under optimum photocatalysis conditions successively and 77.23% total endosulfan removal was obtained even after 5 repetitions. In the third stage of the study, raw water from the inlet of the drinking water treatment plant and tap water from the fresh water network were obtained as real water samples. Photocatalysis experiments were carried out under visible LED light at 27 W light power, 0.5 g/L catalyst amount, 60 min reaction time and original sample pH, and the total endosulfan removal obtained for raw water and spring water was found to be 86.7% and 84.8%, respectively.