Mechanism of action of the heterojunction structure of the photocatalyst ZnO-g-C3N4@TiO2 and its application to the degradation of acetaminophen

Acetaminophen, a non-steroidal anti-inflammatory drug, is one of the most abundant drugs and personal care products in natural water bodies, and the amount of acetaminophen (APAP) has increased dramatically during COVID-19. Photocatalysis is an advanced oxidation technology with high degradation and mineralization capacity and is environment-friendly, and it is important to design new photocatalysts to improve APAP removal efficiency and investigate the mechanism of photocatalytic oxidation. In this study, two kinds of photocatalysts, g-C3N4@TiO2 (gT) and g-C3N4@TiO2@ZnO (gTZ) were prepared by the sol–gel method and sol–gel heat condensation method. Secondly, they were systematically characterized by SEM, XRD, BET, XPS, UV–vis DRS, steady-state photoluminescence (PL) spectroscopy, and contact angle, and their energy band structures were analyzed and inferred to be composite type II heterojunction photocatalysts. The photocatalytic efficiency was investigated by degrading the pollutants APAP and azo dyes. The degradation rates of gT and gTZ for APAP were 70.6% and 92.4% under 254 nm UV light, respectively. Finally, the main radicals of gTZ for the degradation of APAP were hydroxyl radicals (•OH), which were investigated by the free radical capture, and then eight intermediates for the photocatalytic degradation of APAP were obtained by HPLC-MS/MS, which led to the photocatalytic degradation pathway.