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

Abstract

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 ˙O₂⁻ 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.