Construction of loading g-C3N4/TiO2 on waste cotton-based activated carbon S-scheme heterojunction for enhanced photocatalytic degradation of microplastics: performance, DFT calculation and mechanism study

Abstract

In order to achieve the degradation of polyethylene microplastics (PE) in wastewater. The g-C3N4/TiO2/WCT-AC composite photocatalytic materials were prepared by mixed high-temperature thermal polymerization method with the g-C3N4 and the waste cotton based activated carbon (WCT-AC) loaded TiO2 as precursors. The phase morphology, elemental composition, morphology and photochemical properties of the g-C3N4/TiO2/WCT-AC were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), ultraviolet-visible diffuse reflectance spectrum (UV-vis DRS) and photo luminescence (PL). The results of UV-vis DRS and PL showed that the combination of the g-C3N4 and the TiO2/WCT-AC improved the absorption in the visible region, broadened the spectral response range, and the formation of heterojunctions enabled efficient photoelectron-hole separation and improved the photocatalytic activity. Under visible light irradiation for 200 hours, catalyst dosage 50 mg, and system pH=7.0, the highest removal rate of the g-C3N4/TiO2/WCT-AC for PE microplastics reached 67.58%, and it still showed excellent stability after 5 cycles. The active groups such as ·O2-, ·OH and h+ produced in the g-C3N4/TiO2/WCT-AC system under visible light excitation realized the degradation of PE microplastics. The whole process is a complex oxidation bond breaking process, and the degradation of PE microplastics by g-C3N4/TiO2/WCT-AC follows the S-type charge transfer mechanism.