Ultrathin Bismuth-Based Composite Nanosheets with Synergistic Bi2+-VO/VN Dual-Defect Engineering and g-C3N4 Modification for Solar-Driven Photocatalytic Antibiotic Degradation

Synergistically coupling complementary vacancy pairs with an ultrathin framework provides a promising yet underexplored route to robust photocatalysts for water purification. Herein, we report the synthesis of ultrathin SBBC (Bi 12 SiO 20 -Bi 2 O 3 -BiOCl-Bi 2 SiO 5 )/g-C 3 N 4 (CN) nanosheets (SBCN-6) in which surface Bi 2+ –V O defect centers are deliberately paired with nitrogen vacancies (V N ), thereby uniting dual-defect chemistry with an ultrathin framework. Electron-sequestering Bi 2+ –V O clusters introduce deep trap states, which robustly capture photoexcited electrons generated in SBBC. V N sites in CN serve as efficient electron-trapping centers that significantly suppress internal electron-hole recombination within CN, and this combined action accelerates visible-light redox reactions. This synergistic dual-defect network, comprising Bi 2+ –V O in SBBC and V N sites in CN, significantly enhances charge separation. Density Functional Theory (DFT) and X-ray Photoelectron Spectroscopy (XPS) unveil a type-Z/type-II hybrid transfer cascade: SBBC (V B ) → Bi 2+ –V O → SBBC (C B ) → CN (C B ) ← V N ← CN (V B ). Under visible-light irradiation, the photocatalyst exhibits exceptional activity in degrading refractory antibiotics, achieving a high apparent rate constant (k) of 0.129 min -1 for tetracycline (93% degradation in 120 min) and removing 91% of ciprofloxacin in 120 min. Moreover, it rapidly degrades the Rhodamine B dye, with over 99% removal within just 30 min. It also retains excellent recyclability over multiple cycles and outperforms most reported Bi-based photocatalysts. Coupling dual-defect engineering with morphology control, this study advances the mechanistic exploration of defect-mediated catalysis and furnishes a valuable reference for constructing visible-light photocatalysts that simultaneously degrade dyes and antibiotics. Synergistic dual-defect engineering creates surface Bi 2+ -V O and bulk V N defects in ultrathin SBBC/CN nanosheets. This unique structure accelerates charge separation, enabling rapid and efficient visible-light-driven photocatalytic degradation of persistent antibiotic pollutants. • Synergistic Bi 2+ -Vo/V N dual-defect network enhances charge separation under visible light. • CTAC and molten-salt yield ≈14.5 nm SBBC/g-C 3 N 4 nanosheets with abundant heterointerfaces. • Type-Z/Type-II cascade transfer suppresses recombination and boosts reactive species generation.