Nd2Sn2O7/Bi2Sn2O7/Ag3PO4 double Z-type heterojunction for antibiotic photodegradation under visible light irradiation: Mechanism, optimization and pathways

A novel visible light response Nd2Sn2O7/Bi2Sn2O7/Ag3PO4 (NSO/BSO/APO) composite photocatalyst with double Z-type heterojunction was successfully synthesized by a one-pot hydrothermal-precipitation method. The addition ratios of Nd2Sn2O7(NSO) and Ag3PO4(APO) during composite photocatalyst preparation were optimized, and the photocatalytic reaction conditions included tetracycline hydrochloride (TC) concentration, catalyst dosage, and initial pH of the solution were screened. The maximum degradation rate of 15 mg/L TC (pH = 8) reached 97.10% exposed to visible light in 120 min by NSO/BSO/APO-30 photocatalyst (dosage: 0.4 g/L), its kinetic constant is about 9.78 times that pure Bi2Sn2O7 (BSO). The morphology, composition, and optical properties of the catalysts were characterized. The f-f transition of Nd3+ in NSO improves the absorption ability of the catalyst to visible light. In addition, h+, O2− and OH participated in the photodegradation of TC in NSO/BSO/APO-30 system. The fitting of the Mott-Schottky curve and Tauc-plot curves confirmed the rationality of the double Z-type electron transfer mechanism. The EIS and PL tests show that the NSO/BSO/APO-30 composite catalyst had the lowest charge transfer resistance and the lowest carrier recombination rate. In addition, three possible degradation pathways of TC during the photodegradation by NSO/BSO/APO-30 were analyzed by High-resolution mass spectrometry (APCI-MS).