In-situ synthesis of carbon-doped hydroxyapatite via non-hydrolytic sol-gel method: synergistic adsorption-photocatalysis for enhanced tetracycline degradation under visible light

The development of novel, highly efficient, and stable photocatalysts remains a formidable task. Herein, novel peanut-shaped carbon-doped hydroxyapatite (CHAp) was synthesized via a non-hydrolytic sol-gel method at low temperature, and the revelation of a novel “adsorption-in-situ photosensitization” mechanism. Comprehensive structural characterization revealed that carbon doping modulates the crystalline growth orientation, resulting in a distinct peanut-shaped morphology and optimized textural properties, including an increased specific surface area and a reduced average pore size. These structural alterations endow CHAp with enhanced adsorption capacity for tetracycline (TC). The TC-CHAp complex formed via post-adsorption surface coordination exhibits a narrowed band gap, which enhances its visible-light responsiveness. Furthermore, the established p-n heterojunction between TC-CHAp and CHAp facilitates photoinduced charge separation and transfer, enhancing photocatalytic efficiency. The ESR test results proved that the ·O 2 − radical in the reaction system promoted the degradation of TC. Experimental results demonstrate that under dark conditions, the 100 mg samples achieved 68 % adsorption efficiency for TC (50 mg/L, 100 mL) within 60 min, while exhibiting 93.6 % degradation efficiency after 30 min of visible light irradiation. The material maintained 82.7 % degradation efficiency through six consecutive cycling tests, demonstrating excellent stability and reusability for repeated usage. Therefore, this study has expanded the application scope of non-hydrolysis processes and provided a promising approach for the development of novel green photocatalysts with high adsorption capacity and photocatalytic efficiency.