Oxygen-vacancy-mediated S-scheme BiOI/TiO2-x hollow spheres: Efficient visible-light photodegradation of tetracycline via synergistic regulation of band structure and morphology

Green synthesis of OV-rich TiO 2- x using L-cysteine, avoiding hazardous H 2 /NaBH 4. • Construction of hollow BiOI/ TiO 2- x S-scheme heterojunction via in-situ assembly. • Hollow structure, OVs, and S-scheme synergistically boost light harvesting & charge separation. • 94.24% TC removal in 120 min; kinetic constant 3.83–7.97 times higher than controls. • •O 2 − and h + as dominant active species; S-scheme mechanism confirmed. Addressing the challenge of tetracycline (TC) contamination in aquatic environments, this work reports a high‑performance S‑scheme photocatalyst fabricated via a green and sustainable strategy. Oxygen vacancy (OV)‑rich TiO 2- x hollow microspheres were prepared by a hard‑template method using L‑cysteine as a green reductant, followed by in‑situ hydrothermal deposition of BiOI nanosheets. The optimized BiOI/TiO 2- x -5% composite exhibits 94.24% TC degradation within 120 min under visible light, with a reaction rate constant 3.83, 3.67, and 7.97 times higher than those of pristine TiO 2 , TiO 2- x , and BiOI, respectively. The boosted performance stems from the synergistic effects of the hollow structure, which enhances light harvesting and mass transfer, and the OV‑mediated S‑scheme heterojunction, which greatly suppresses charge recombination while retaining strong redox potentials. Mechanistic investigations confirm •O 2 − and h + as the dominant active species. This work provides a promising paradigm for designing efficient defect‑mediated hollow heterojunctions toward sustainable antibiotic wastewater remediation. Download: Download high-res image (164KB) Download: Download full-size image