Fabrication of SiW9Co3–Bi4O5Br2 photocatalysts with improved charge separation for visible-light-driven hydrogen evolution and metronidazole degradation: Characterization, mechanism, and toxicity assessment

The rational design of efficient photocatalysts for clean energy generation and environmental remediation remains a significant challenge. In this study, a novel SiW 9 Co 3 –Bi 4 O 5 Br 2 heterostructure photocatalyst was successfully synthesized using a simple hydrothermal–self-assembly method. The structural, morphological, and optical properties were thoroughly investigated using techniques such as XRD, FTIR, Raman, XPS, SEM, TEM, and UV–Vis DRS. SiW 9 Co 3 clusters were uniformly anchored on the surface of Bi 4 O 5 Br 2 nanosheets, forming heterojunction interfaces that facilitated charge transfer and suppressed electron–hole recombination. Under visible light, the optimized SiW 9 Co 3 –Bi 4 O 5 Br 2 (20 wt%) composite exhibited superior photocatalytic performance, achieving H 2 evolution rate of 570 μmol·g −1 ·h −1 , significantly higher than that of pristine Bi 4 O 5 Br 2 . Simultaneously, 98.05 % of metronidazole (25 mg·L −1 ) was degraded within 80 min. Radical scavenging and ESR results confirmed that •O 2 − and •OH were the dominant species responsible for H 2 generation and pollutant degradation. The Z -scheme mechanism was proposed, where photogenerated electrons in SiW 9 Co 3 reduce H + to H 2 , while holes in Bi 4 O 5 Br 2 oxidize metronidazole. Additionally, the photocatalyst demonstrated high stability, with minimal performance degradation after five cycles, and XRD confirmed its structural integrity after cycling, supporting its potential for long-term, sustainable applications in both energy and environmental fields.