Simultaneous reduction of Cr(VI) and oxidation of As(III) by visible-light-driven Z-scheme NiFe2O4/Bi7O9I3-Bi4O5Br2 heterojunction

Design and construction of a Z-scheme heterojunction to enhance its redox ability for photocatalytic applications requires considerable effort, especially when addressing the critical challenge of the efficient and simultaneous removal of toxic metal ions from wastewater during environmental remediation. To address this issue, a novel, direct Z-scheme heterojunction photocatalyst , NiFe 2 O 4 /Bi 7 O 9 I 3 -Bi 4 O 5 Br 2 (NFO/BOI 0.3 Br 0.7 ), was synthesized using a facile and rapid microwave heating method. By overcoming the challenges in designing Z-scheme system through modification with bismuth-rich species, solid-solution formation, and heterojunction engineering, heterostructures with enhanced redox capabilities were achieved. The optimized composite containing 10 mol% NFO loading (10NFO/BOI 0.3 Br 0.7 ) exhibited superior visible-light-driven photocatalytic activity in Cr(VI) reduction and As(III) oxidation compared to the single-component photocatalysts. Competitive interactions with •O 2 − in the Cr(VI)/As(III) combined system slightly reduced the efficiency of the photocatalyst; however, the heterostructure maintained notable photocatalytic activity . The enhanced photocatalytic performance is attributed to increased light absorption and improved charge separation and migration, as confirmed by UV–visible diffuse reflectance spectroscopy , electrochemical, photoluminescence (PL), and time-resolved PL analyses. The results from the Mott-Schottky and EPR-spin trapping experiments, along with photodeposition of Ag and PbO 2 support a Z-scheme electron transfer pathway. The 10NFO/BOI 0.3 Br 0.7 photocatalyst exhibited magnetic properties , allowing easy recovery and reuse through separation with an external magnet, thereby enhancing its practicality for long-term applications. • Novel Z-scheme NiFe 2 O 4 /Bi 7 O 9 I 3 -Bi 4 O 5 Br 2 composite synthesized via microwave heating. • Combination of bismuth enrichment, solid solution , and heterojunction strategies for enhanced performance. • This photocatalyst enhances Cr(VI) reduction and As(III) oxidation simultaneously. • Magnetic NiFe 2 O 4 /Bi 7 O 9 I 3 -Bi 4 O 5 Br 2 composite enables easy recovery and long-term reuse.