Efficient photodegradation of doxycycline and photoreduction of nitrobenzene via a dual S-scheme WO₃/Cu₂O/Ag₃PO₄ heterojunction

A dual S-scheme-based WO₃/Cu₂O/Ag₃PO₄ (WCA) heterojunction was successfully fabricated via ultrasonication and hydrothermal methods for enhanced photocatalytic applications. Comprehensive characterization confirmed robust interfacial contact and efficient S-scheme charge transfer within the heterojunction. Optical and electrochemical analyses demonstrated superior light absorption and enhanced charge separation capabilities. The WCA heterojunction exhibited remarkable photocatalytic performance, achieving 99% photodegradation of doxycycline (DX) in 80 min at pH 6, and 99% selective photoreduction of nitrobenzene to aniline in 105 min. The hydroxyl and superoxide radicals are identified as primary reactive species in DX degradation, while electrons were crucial for the photoreduction process. The photocatalytic performance was evaluated under various conditions, including the presence of co-existing ions (H₂PO₄⁻, NO₃⁻, HCO₃⁻, and Cl⁻), humic acid, and different water matrices. Intermediate products were identified using LC-MS and GC–MS, providing insights into the degradation and reduction pathways. The WCA heterojunction also demonstrated excellent stability, maintaining consistent performance over six consecutive cycles. This research provides valuable insights into the design of advanced S-scheme heterojunctions for a wide range of photocatalytic applications, offering a promising approach for efficient wastewater treatment and environmental remediation.