Structure and surface of Ca10-xBix(PO4)6(OH)2-xOx solid solutions for light-driven photocatalytic degradation of oxytetracycline

This study highlights the effect of oxygen vacancies generated by the substitution of Ca²⁺ with Bi³⁺ in Ca 10-x Bi x (PO 4 ) 6 (OH) 2-x O x apatites for photocatalytic degradation of oxytetracycline (OTC) under UV and visible light. Characterizations reveal that the introduction of Bi³⁺ induces the formation of structural oxygen vacancies and modifies the electronic properties, with a substitution limit fixed at x = 0.3. Photocatalytic tests show that the controlled presence of these vacancies improves charge separation and the generation of reactive species, allowing a complete OTC degradation with x = 0.1. These results demonstrate the key role of Bi substitution and the formed oxygen vacancies in the design of efficient apatite-based photocatalysts. • Ca₁₀₋ₓBiₓ(PO₄)₆(OH)₂₋ₓOₓ solid solutions were synthesized with controlled Bi³ ⁺ doping and oxygen vacancies.. • Oxygen vacancies act as efficient electron traps, suppressing charge carrier recombination under UV and visible light. • Bi incorporation significantly extends light absorption toward the visible region. • A strong synergistic effect between Bi³ ⁺ dopants and oxygen vacancies enhances photocatalytic activity. • The optimized Bi 0.1 HAp catalyst exhibits superior oxytetracycline photodegradation under both UV and visible irradiation.