2D-Bi4NbO8Cl nanosheet for efficient photocatalytic degradation of tetracycline in synthetic and real wastewater under visible-light: Influencing factors, mechanism and degradation pathway

A 2D-Bi4NbO8Cl nanosheet (BNOCF) photocatalyst was fabricated using molten salt or flux method and was employed to degrade tetracycline (TCH) under visible light irradiation. The as-synthesized photocatalyst was characterized by a wide range of studies and compared with bulk-Bi4NbO8Cl (BNOCS). The BNOCF photocatalyst displayed 2.2 times higher degradation efficiency as compared to BNOCS. The enhanced efficiency could be attributed to the 2D architecture, with increased surface area and reduced charge recombination rate. The effect of various parameters was studied, and the optimal photocatalytic efficiency (96.5%) of BNOCF was obtained at a dosage of 1 g L−1, TCH concentration of 10 mg L−1, pH 4.4, and the light intensity of 10 mW cm−2. The effects of coexisting inorganic salts and real wastewater sources were also studied. A detailed study showed that a complex between BNOCF and TCH led to TCH degradation by inducing strong visible-light absorption. The radical trapping experiments showed that •O2− was primarily responsible for the degradation of TCH. Based on these findings, the photocatalytic mechanism was proposed. The inorganic ions like CO32-, Cl- and SO42- were found to hinder the degradation efficiency of BNOCF slightly. Excellent degradation efficiency (95.9%) was achieved towards TCH present in a real wastewater sample. The catalyst efficiently mineralized 34.6% TCH in 1 h, and after four recycling tests, was found quite stable. The intermediate products of TCH degradation over BNOCF were detected, and plausible degradation pathways were proposed. This study proves that BNOCF possesses tremendous potential as a visible-light-reactive photocatalyst in prospective wastewater treatment applications.