Mechanistic and kinetic insights of synergistic mineralization of ofloxacin using a sono-photo hybrid process

The present study reports an ultrasound-photocatalysis based hybrid method for effective degradation/mineralization of a bio-recalcitrant pharmaceutical pollutant, namely ofloxacin (OFLX). To understand the role of different techniques, individual and various combined ultrasound and ultraviolet along with H2O2, TiO2, and ZnO photo-catalyst were investigated in different protocols to understand synergistic effects and mechanistic insight of the mineralization process. Photocatalysts were characterized by FTIR, FE-SEM, TEM, EDX, BET, and EIS analysis. A significant synergistic index of 3.1 for mineralization of OFLX was obtained during the combined US/UV/H2O2/ZnO method due to higher oxidizing (OH) radical formation as compared to other binary and ternary hybrid methods. OFLX degradation and total organic carbon removal were 94.2% and 45.1%, respectively, using US/UV/H2O2/ZnO method at operating condition of H2O2/OFLX stoichiometric molar ratio = 5, ZnO dosage = 0.40 g L−1, 40 kHz ultrasonic frequency, 125 W UV power, reaction time of 120 min and pH 6.3 (natural pH). Kinetics of the degradation was well-represented by the power-law kinetic model with an order of reaction being 2.2 and 1.9 for US + UV + H2O2 + TiO2 and US + UV + H2O2 + ZnO, respectively. Besides, specific energy consumption (SEC), electrical energy per order (EEO), and the operating cost (OC) of each method employed was determined. A detailed OFLX degradation pathway has been suggested, and possible reasons for synergy are identified and discussed.