Synthesis of a Z-scheme ternary photocatalyst (Ta3N5/Ag3PO4/AgBr) for the enhanced photocatalytic degradation of tetracycline under visible light

Abstract

Solar photocatalysis is a green and sustainable technology that has been widely studied in the field of wastewater treatment. Herein, a ternary photocatalyst (Ta3N5/Ag3PO4/AgBr) with dual Z-scheme heterojunctions was synthesized by the hydrothermal, chemical precipitation and anion exchange methods. The morphology and structure properties of the photocatalysts were systematically characterized by SEM, TEM, EDS, XRD and XPS. Tetracycline was used as the model pollutant to examine the photocatalytic activity under visible light (>420 nm). The results indicated that the unique micron flower-like structure of Ta3N5 made it to be a good substrate for the deposition of Ag3PO4/AgBr. Over the ternary photocatalyst, tetracycline was efficiently degraded, and 95% of tetracycline could be removed in 30 min. The degradation rate constant over the ternary photocatalyst (0.089 min−1) was 1.98 and 15.89 times that over Ta3N5/Ag3PO4 and Ta3N5, respectively. Meanwhile, the stability of the ternary composite was also significantly improved. Additionally, the trapping experiments verified that ·O2− and h+ played major roles during photocatalysis, while ·OH had relatively little impact on the tetracycline removal. Accordingly, the photocatalytic mechanism with respect to dual Z-scheme heterojunctions was proposed. On one hand, the components of the ternary photocatalyst were all visible light driven semiconductors, which endowed the composite catalyst with good light absorption capacity. On the other hand, facilitated by the dual Z-scheme heterojunctions, the photo-generated charge carriers with stronger redox ability could be separated more efficiently, thus leading to a better photocatalytic performance.