Degradation of furosemide using photocatalytic ozonation in the presence of ZnO/ICLT nanocomposite particles: Experimental, modeling, optimization and mechanism evaluation

The presence of pharmaceutical contaminants in the environment, as the result of incomplete degradation of conventional wastewater treatment processes has created serious environmental concerns. In this study, photocatalytic ozonation of furosemide (FRS) pharmaceutical in aqueous media was investigated using ZnO supported on ion-exchanged clinoptilolite (ZnO/ICLT) nanophotocatalysts. The ZnO/ICLT nanophotocatalysts were synthesized by sonoprecipitation method and characterized by XPS, TEM, BET and FTIR analysis. To investigate the effect of operational factors (catalyst loading, reaction time, initial ozone and pollutant concentration) and also their interactions, the modeling was evaluated using response surface methodology (RSM) by means of central composite design (CCD). Pareto analysis confirmed that all 4 factors were impressive on the FRS degradation efficiency as the model response. Results indicated that the developed model was adequate and satisfactory with the high determination coefficient (R2 = 0.988). The complete FRS degradation (99.8%) was obtained by using 11 mg L−1 O3, 33.18 mg L−1 FRS and 0.27 g L−1 cat in 30 min of process. The kinetic studies at optimum conditions showed a synergism effect between photocatalysis and ozonation for FRS degradation. Reusability experiments validated no decrease in photocatalytic activity after five consecutive runs. The effect of organic and inorganic salts indicated that photoexcited electrons had the most impact in FRS degradation via continuous generation of h+, •OH, O3•- and O2•-. Accordingly, a plausible mechanism for FRS degradation was proposed. The percentage of FRS mineralization increased to 88.7% in photocatalytic ozonation, while it was 40.6% by photocatalytic process. Experimental and economic studies indicated that photocatalytic ozonation by ZnO/ICLT could be an appropriate method for organic pollutant degradation due to highest mineralization rate and lowest energy consumption.