Evaluating the binary Z-scheme Bi2S3/CuWO4 immobilized on FTO as a visible-light-driven photocatalyst for metronidazole degradation-response surface method

Metronidazole (MTZ) is an antibacterial drug, which is frequently detected in wastewater, resulting in pathogen-resistance and mutagenicity. Therefore, MTZ removal is a serious challenge. In this research work, the visible-light-driven Z-scheme CuWO4/Bi2S3 heterojunction with optimized weight percentage (7%wt) was evaluated for MTZ degradation under LED radiation in batch and continues reactor. The effect of operational factors such as MTZ concentration (10–30 ppm), catalyst dose (0.4–1 mg/L), pH (3–9) and illumination time (90–150 min) on MTZ degradation efficiency was investigated through response surface methodology (RSM). The optimum values of the operating parameters were found to be as: irradiation time = 150 min, pH = 3, MTZ concentration of 10 ppm and catalyst dose = 0.7 g/L. The utmost degradation efficiencies were obtained 79% and 84%, respectively, in batch and continues flow mode at the optimum conditions. Thereafter, the effect of immobilization of the binary composite on FTO was studied at the obtained optimum conditions. The effect of temperature and light intensity on photocatalytic performance was also investigated, and the optimal values were found to be 25 °C and 400 W/m2, respectively. The mineralization of MTZ was investigated through TOC removal rates with the maximum value of 61.32%. The gas chromatography-mass spectrometry analysis was used to detect the photodegradation intermediates. The kinetic study of MTZ degradation by the binary composite followed the pseudo-first order by the reaction rate of 2 times greater than pristine Bi2S3. The main active species were found to be hydroxyl radical and superoxide by the trapping test method. The binary heterojunction demonstrated high durability and stability after five cycles. This work recommends a promising heterojunction for MTZ photodegradation.