Excellent performance of a novel dual Z-scheme Cu2S/Ag2S/BiVO4 heterostructure in metronidazole degradation in batch and continuous systems: Immobilization of catalytic particles on α-Al2O3 fiber

A ternary heterojunction of Cu2S/Ag2S/BiVO4 with enhanced charge transfer ability was synthesized via hydrothermal method and stabilized on the alpha-Al2O3 fiber. Catalysts were characterized by XRD, XRF, FT-IR, BET-BJH, FE-SEM, EDS, pH(zpc), UV-is DRS, and PL spectra. Compared with pure BiVO4, at the optimal operational condition with 50 mg/l of metronidazole, 1 g/l of catalyst, irradiation time of 105 min, and at pH = 3, the degradation of contaminant was obtained as 52, 74.7, 85.8, and 94.5% by BiVO4, 5 wt% Ag2S/BiVO4, 15 wt% Cu2S/Ag2S/BiVO4, and 15 wt% Cu2S/Ag2S/BiVO4@alpha-Al2O3 respectively. The significant increment of photocatalytic activity of Cu2S/Ag2S/BiVO4 was related to the higher specific area, synergistic interfacial charge transfers, and promotion of electron-hole pair separation in the dual Z-scheme system. The alpha-Al2O3 acts as a photo-generated charge trapper which restrains the recombination of electron-hole pairs. The presence of alpha-Al2O3 drastically reduced the PL intensity of Cu2S/Ag2S/BiVO4. According to the quenching experiments, a reasonable mechanism of Cu2S/Ag2S/BiVO4 was also proposed. The effects of temperature and light intensity were also tested and the optimal values were determined at 25 degrees C and 400 w/m(2) respectively. In the continuous system, at the optimum flow rate (2.4 ml/min), metronidazole degradation was 96.2% by Cu2S/Ag2S/BiVO4@alpha-Al2O3.