A novel 3D Z-scheme heterojunction photocatalyst: Ag6Si2O7 anchored on flower-like Bi2WO6 and its excellent photocatalytic performance for the degradation of toxic pharmaceutical antibiotics

The massive consumption and discharge of pharmaceutical antibiotics have driven researchers to explore environment-friendly and effective technology to eliminate them. Herein, a novel flower-like Ag6Si2O7/Bi2WO6 Z-scheme heterojunction photocatalyst with strong redox capability was fabricated via a facile in situ precipitation strategy and then applied to degrade pharmaceutical antibiotics. The as-obtained Ag6Si2O7/Bi2WO6 heterojunction with strong interfacial coupling effects exhibited superior photocatalytic property in comparison with pristine Bi2WO6 and Ag6Si2O7 for the degradation of ciprofloxacin (CIP) and tetracycline hydrochloride (TC) under visible light. The optimized Ag6Si2O7/Bi2WO6 (ASO/BWO-3) showed the maximum photocatalytic performance, and its rate constant for the degradation of CIP was as high as 0.0217 min(-1), exceeding that of pristine Bi2WO6 and Ag6Si2O7 by approximately 14.5- and 9.8-fold, respectively. The trapping experiments and ESR analyses revealed that the principal active species responsible for pollutant removal are h(+) and O-2(-) species. The PL analysis and EIS measurements further demonstrated that Ag6Si2O7/Bi2WO6 possesses a high separation rate of photogenerated electrons and holes. Its extraordinary photocatalytic performance is ascribed to the synergistic interactions of the Z-scheme hetero-structure and surface plasmon resonance (SPR) effect of the Ag nanoparticles. Remarkably, a separation reaction system was delicately designed and employed to demonstrate the significance of the direct contact between Ag6Si2O7/Bi2WO6 and contaminants for antibiotic degradation. This research may provide a new design concept for constructing highly efficient and stable Z-scheme heterojunction photocatalysts for treating pharmaceutical wastewater.