Microwave-assisted construction of Fe–SnO2@NiO–Ni foam S-scheme heterojunction for enhanced photocatalytic degradation of ciprofloxacin

Fe–SnO 2 @NiO–NF removed 96.85% CIP within 150 min under solar light. • S-scheme heterojunction promotes charge separation and photocatalytic activity. • 3D NiO–NF support enables easy recovery and abundant active sites. • Over 94% degradation activity was retained after four cycles. • DFT and HPLC–MS reveal charge transfer and CIP degradation pathways. Photocatalysis is effective for antibiotic degradation but limited by poor charge separation and difficult recovery of powder catalysts. In this work, a macroscopic p–n heterojunction photocatalyst (Fe–SnO 2 @NiO–NF) was prepared on pre-oxidized nickel foam through in situ growth and microwave-assisted synthesis. XRD confirmed the coexistence of SnO 2 and NiO phases, while HRTEM and XPS analyses verified the successful construction of the Fe–SnO 2 /NiO heterojunction with intimate interfacial contact and interfacial electronic interaction. UV–vis DRS, PL, TRPL, EIS, and photoelectrochemical measurements demonstrated markedly improved light absorption, charge separation and transfer behavior, with a narrowed band gap of 2.92 eV and a prolonged average carrier lifetime of 1.2226 ns. Owing to the enhanced charge separation and the conductive 3D NiO–NF framework, Fe–SnO 2 @NiO–NF exhibited significantly improved photocatalytic activity for ciprofloxacin degradation under solar irradiation, reaching 96.85% removal within 150 min, while the immobilized catalyst could be readily separated from the aqueous solution. ESR and scavenging test identified •O 2 – and h + as the main reactive species, with •O 2 – playing the dominant role, while HPLC–MS revealed the degradation intermediates and pathways. Band structure analysis and DFT calculations demonstrated that the p–n heterojunction follows an S-scheme charge transfer mechanism, promoting efficient charge separation while preserving strong redox capability. The composite retained over 94% of its initial activity after four cycles, showing excellent stability and recyclability. This study provides a practical way to develop efficient and reusable photocatalysts for antibiotic wastewater treatment. Download: Download high-res image (182KB) Download: Download full-size image