Synthesis of leek-based N,S self-doped CQDs/TiO2 and its application in the photocatalytic degradation of organic pollutants

Abstract

In this work, N,S self-doped CQDs (N,S-CQDs/TiO2) were synthesized from leeks via a microwave method, and a new leek-based N,S-CQDs/TiO2 composite photocatalytic material was prepared by roasting. The structural characteristics, optical properties, and electrical properties of the N,S-CQDs/TiO2 composites were characterized by Scanning electron microscope (SEM), Transmission electron microscope (TEM), X-ray powder diffraction (XRD), Solid ultraviolet–visible diffuse reflectance (UV–vis-DRS), Fourier transform infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transient photocurrent response, and Electrochemical impedance spectroscopy (EIS). In addition, the catalytic degradation effect of N,S-CQDs/TiO2 was evaluated by the photocatalytic degradation of Rhodamine B (RhB) and ibuprofen (IBU). The experimental results showed that the photocatalytic degradation effect of leek-based N,S-CQDs/TiO2 was significantly better than that of TiO2, and N,S-CQDs/TiO2 with 1.86 wt% N,S-CQDs (1.86-N,S-CQDs/TiO2), which demonstrated optimal photocatalytic degradation. The photocatalytic degradation rate of RhB (20 mg/L) was 94.65 % within 120 min of high-voltage mercury lamp irradiation, which was 41.15 % higher than that of TiO2(53.50 %), and the degradation rate was 80.10 % after four cycles. After 180 min, the photocatalytic degradation rate of IBU (10 mg/L) was 96.92 %, which was 26.39 % higher than that of TiO2 (70.53 %), and the degradation rate could still reach 78.94 % after four cycles. In this work, the photocatalytic degradation mechanisms of RhB and IBU by N,S-CQDs/TiO2 were explored by free radical capture and ESR free radical detection experiments. This study may serve as an important reference for enhancing the photocatalytic degradation effect by using biomass self-doped CQDs/TiO2 composite photocatalytic materials, and as a reference for the photocatalytic treatment of organic pollutants in water.