Double Z-scheme biochar-based g-C3N4/Bi2WO6/Ag3PO4 nanocomposite for efficient removal of antibiotics and synergistic mechanisms

Photocatalysis research has evolved towards increasingly sophisticated structural regulation and material design. The synergistic enhancement of photocatalysis by multi-component semiconductors and biochar warrants detailed investigation. This study introduces an innovative biochar-based g-C₃N₄/Bi₂WO₆/Ag₃PO₄ nanocomposite (CN/Bi/Ag@ACB), which was applied to the efficient removal of antibiotic pollutants represented by tetracycline (TC). Findings reveal that CN/Bi/Ag@ACB forms a double Z-scheme heterojunction, significantly reducing photogenerated carrier recombination. It absorbs light in the 200-800 nm range, with a band gap of 1.91 eV. Under 120 min of illumination, the composite nearly completely removed 50 mg·L^-1 of TC, achieving a removal rate of 0.0351 min^-1, which is 8.56-13.50 times higher than that of the individual semiconductors. In real wastewater, TC removal exceeded 85.95%, with concurrent removal of other antibiotics, and achieved 99% sterilization of E. coli and S. aureus within 48 hours. The catalytic system was predominantly driven by ·O₂^-, h⁺, and ·OH radicals. The unique structure and surface characteristics of the composite, along with the incorporation of heteroatoms, substantially enhance photocatalytic activity. The TC degradation process is associated with the conversion of fulvic and humic acids, with three potential degradation pathways proposed. This study elucidates the synergistic mechanisms of photocatalysis enhancement by multi-component semiconductors and biochar.