A comparison study of the photocatalytic mechanism and performance of Bi 2 S 3 -based binary composite (Cu 2 O/Bi 2 S 3 ) and ternary composite (NH 2 -UiO-66/BiOBr/Bi 2 S 3 ) photocatalyst for tetracycline degradation under visible-light irradiation

To study the degradation of tetracycline by Bi2S3-based binary composite and ternary composite photocatalysts, Cu2O/Bi2S3 and NH2-UiO-66/BiOBr/Bi2S3 was successfully fabricated by the solvothermal method, which can effectively and stably degrade tetracycline (TC). The crystal structure, chemical composition, and microscopic morphology of the as-prepared sample were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic performance of the composite photocatalyst was estimated by degradation of TC under visible-light irradiation. The results showed that the removal ratio of TC by Cu2O/Bi2S3 and NH2-UiO-66/BiOBr/Bi2S3 are 95.2% and 93.2%, respectively. The photoelectric properties of the material were evaluated by PL and EIS analysis, and compared to Bi2S3, the overall visible light absorption capacity, as well as the separation and transfer rates of photogenerated carriers of the composites photocatalyst have been significantly improved. Both Cu2O/Bi2S3 and NH2-UiO-66/BiOBr/Bi2S3 can achieve a good photodegradation performance for TC, but the results of UV–vis DRS spectrum, Mott–Schottky curve, and free radical trapping experiments show that their photodegradation mechanism for TC is different. For Cu2O/Bi2S3, •O2− and h+ are the main active species in the photocatalytic reaction process, among which •O2− plays the most important role, but •OH has almost no effect, and for NH2-UiO-66/BiOBr/Bi2S3, the main active species are •OH and h+. The possible photocatalytic mechanisms for Cu2O/Bi2S3 and NH2-UiO-66/BiOBr/Bi2S3 are Z-scheme and double Z-schemes are proposed, respectively.