Z-scheme Ag3PO4/g-C3N4 photocatalyst: Characterization, active species, reaction pathways and mechanisms for enhanced acetaminophen removal

Abstract Visible-light-induced photocatalytic removal of trace organic contaminants is among the most important technologies of water-quality safety control. However, the activity of the photocatalyst reaction is difficult to regulate and the mechanism of the system has not been clarified. In this study, a nanometer-sized Z-scheme Ag₃PO₄/g-C₃N₄ (AP/CN) photocatalyst with a mesoporous structure was prepared through in-situ chemical precipitation. The 50%AP/CN (w/w = 1:1) composite material exhibited a high visible-light absorption threshold( λ ≤ 558 nm), a narrow band gap (Eg = 2.54 eV) and a strong transient photocurrent response. The photocatalytic performance of 50%AP/CN was systematically investigated under different influencing factors. In the optimised system, the photocatalytic removal rate of trace acetaminophen (ACT) exceeded 80% within 30 minutes. The active species were dynamically traced through inhibition experiments, electron spin resonance analysis and probe experiments. The superoxide anion (·O₂⁻) was identified as a bridge in the conversion between dioxygen (O₂) and singlet oxygen (¹O₂), improving the separation of photoelectrons (e⁻) and vacancies (h⁺). Although the hydroperoxides, oxidative polymerisation and humification of ACT induced by ¹O₂ comply with the ‘double carbon’ strategy, they compete with h⁺-driven mineralisation of organics. These new insights into the silver phosphate-based photocatalytic system can promote the reshaping of low-carbon technology.