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.