Solar-driven dual-functional Z-scheme ZnIn2S4–Sb2O3 supported on activated carbon for simultaneous H2 generation and norfloxacin degradation: Mechanism, analytical characterization, and toxicity assessment

Photocatalysis represents a promising green technology for addressing both environmental remediation and clean energy production by harnessing solar energy to drive redox reactions. The construction of Z-scheme heterojunctions enables efficient utilization of the solar spectrum, spatial separation of photogenerated charge carriers, and preservation of strong oxidative and reductive potentials. Herein, a ZnIn₂S₄–Sb₂O₃ supported on activated carbon (ZISB–AC) composite was synthesized via a multi-step approach and evaluated for simultaneous visible-light-driven H₂ production and norfloxacin degradation. The optimized ZISB–0.2C achieved a high NOR removal efficiency of 97.1% within 120 min and an H₂ generation rate of 732 μmol g⁻¹ h⁻¹. Optical (UV–vis DRS, PL, TRPL) and electrochemical (EIS, transient photocurrent) analyses confirmed suppressed electron–hole recombination and improved charge transport compared to pristine counterparts. Radical trapping and ESR experiments revealed •O₂⁻ and •OH as the primary reactive species, validating the proposed direct Z-scheme charge transfer pathway. The photocatalytic degradation mechanism was further elucidated through LC–MS analysis, which identified transformation intermediates and enabled pathway construction. The toxicity of these intermediates was assessed using the T.E.S.T. software, revealing a significant reduction in both acute and developmental toxicity after photocatalysis. Stability and recyclability assessments demonstrated negligible activity loss over five consecutive cycles, with XPS confirming the preservation of surface composition and chemical states, underscoring the robustness and long-term applicability of the ZISB–AC composite for sustainable environmental and energy applications.