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 h, 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.