Comparison of the performance of Ag-deposited ZnO and TiO2 nanoparticles in levofloxacin degradation under UV/visible radiation

Abstract

This study has shown that the Ag-deposited ZnO and TiO2 nanoparticles can be ideally used to degrade and mineralize levofloxacin under UV radiation and with lower efficiency under visible light. The presence of Ag nanoparticles on the surface of photocatalysts contributes to the activation of the surface even under visible light; moreover, they effectively prevent the recombination of photogenerated electrons and holes by the metal oxides, resulting in higher performance of these modified photocatalysts. The best nominal Ag loading and catalyst dosage were 5 wt% and 1 g/L, respectively, and resulted in 99 and 91% levofloxacin removal for Ag/ZnO and Ag/TiO2 under UV irradiation. These values decreased to 56 and 49% under visible light due to the lower photon energy that can only activate Ag. The total organic carbon removal was also measured under UV irradiation, resulting in 97% and 84%, respectively. The kinetics of photocatalytic degradation followed the pseudo-first order kinetic model, and under all conditions, the kinetic rate constant of the ZnO-based photocatalysts was higher than that of the TiO2-based samples. Considering the contribution of dark adsorption in the first 30 min of the process, the pure photocatalytic performance of Ag-deposited ZnO was much more pronounced than Ag/TiO2. This contribution was 36 and 24% for Ag/ZnO and Ag/TiO2 (with 10 wt% Ag), respectively, when the degradation occurred under visible light. The cyclic performance of the photocatalysts showed reasonable results and no significant loss of performance was observed.