Preparation of Ag₃PO₄/HAP composite photocatalyst and its efficient degradation of methylene blue

High purity hydroxyapatite (HAP) was synthesized via the precipitation method and hydrothermal method, with oyster shells as raw material. After Ag₃PO₄ particles were loaded on the HAP support, the Ag₃PO₄/HAP photocatalysts show a pronounced photocatalytic activity upon decomposition of methylene blue (MB) dye in aqueous solution under visible light. The as-synthesized samples were characterized by SEM, TEM, XRD, BET, XPS, UV-Vis and electron spin resonance(ESR). The results show that HAP could be synthesized by both methods, but higher purity and nano-sized HAP are synthesized by the hydrothermal method. The addition of Ag₃PO₄ does not change the composition and structure of HAP, but improves its absorption property of visible light. Compared with the precipitation method, hydrothermal prepared HAP has the better adsorption performance, and its specific surface area is 46.63 m²·g^-1. And the specific surface areas of Ag₃PO₄/HAP composites (hydrothermal method) increase gradually with the increase of Ag₃PO₄ content. Therefore, the hydrothermal preparation of Ag₃PO₄/HAP shows higher activity, and the 1:2-Ag₃PO₄/HAP produces the highest photocatalytic activity; its degradation rate of MB is up to 50% within 10 min of irradiation and its complete degradation is almost done at 40 min. The free radical capture experiment confirms that the main active species involved in the degradation reaction are •O₂⁻ and h⁺.