Abstract:

With the rapid development of industrial technology, a large number of organic pollutants are routinely released into the environment, which has caused serious problems. Semiconductor photocatalysis is an environmentally-friendly and effective method to degrade and remove typical pollutants, and photocatalysts play a key role in the application of this technology. Therefore, various semiconductor materials have been tried and used in the field of pollutant removal. Graphite carbon nitride (g-C₃N₄) has attracted great interest because of its two-dimensional layered structure and good visible light response range. Owing to a narrow bandgap, adjustable band structure, and high physicochemical stability, g-C₃N₄ absorbs wavelengths up to 450 nm in the visible spectrum, leading to an opportunity for visible-light photocatalytic performance. Nevertheless, there are still some drawbacks that limit the photocatalytic efficiency of g-C₃N₄ in the removal of antibiotics and dyes under visible light, such as the rapid recombination of photoinduced charges and the weak oxidation capacity of holes. To advance this promising photocatalytic material, multiple methods have been tried to optimize the electronic band structure of g-C₃N₄, such as doping with various elements, morphology control, and functional group modification. Recently, a novel type of Step-scheme (S-scheme) heterojunction composed of two n-type semiconductor photocatalysts has been proposed, which can utilize a more positive valance band and a more negative conduction band. It was demonstrated that the formation of S-scheme heterojunctions is a valid way to increase photocatalytic activity of g-C₃N₄. Herein, novel 0D/2D Bi₄V₂O₁₁/g-C₃N₄ S-scheme heterojunctions were prepared by a simple in situ solvothermal growth method. The Bi₄V₂O₁₁/g-C₃N₄ composites displayed a high photocatalytic activity through the removal of oxytetracycline (OTC) and Reactive Red 2. In particular, the BVCN-50 composite showed the highest degradation efficiency for OTC of 74.1% and for Reactive Red 2 of 84.2% with ·O₂^- as the primary active species. This highly improved photocatalytic performance can be ascribed to the generation of S-scheme heterojunctions, which provides for a high redox capacity of the heterojunction system (strong oxidative ability of Bi₄V₂O₁₁ and strong reductive capacity of g-C₃N₄) and facilitates the space separation of photo-generated charges. Moreover, the surface plasmon resonance effect of metallic Bi⁰ broadens the light utilization range of the heterojunction system. In addition, the possible degradation pathway and intermediates throughout the degradation process of OTC based on liquid chromatograph mass spectrometer (LC-MS) analysis were also studied. This work provides a novel tactic for the design and fabrication of g-C₃N₄-based S-scheme heterojunctions with enhanced photocatalytic performance.

Key words: S-scheme, Photocatalysis, Oxytetracycline, g-C₃N₄