Construction of Z-scheme heterojunction TiO2-ZnO@Oxygen-doped gC3N4 composite for enhancing H2O2 photoproduction and removal of pharmaceutical pollutants under visible light

In this study, the heterojunction photocatalyst of titanium dioxide-zinc oxide@oxygen-doped graphitic carbon nitride (TiO2-ZnO@OCN (TZ@OCN)) was synthesized using a simple and cost-effective hydrothermal self-assembly process. Characterization of the fabricated materials revealed that the incorporation of TiO2 and ZnO as inherent semiconductors along with the oxygen doping has effectively broadened the absorption spectrum of gC3N4, which can promote the electron generation and provide more active sites for O2 and H+ adsorption. It is noteworthy that the mentioned structure modification resulted in a superior H2O2 production rate among gC3N4-based photocatalysts with up to 3.11 mM.g−1 under visible light irradiation. Moreover, a valence band shifting from 1.57 to 2.91 eV upon doping oxygen atoms also elucidated the participation of active species in the photocatalytic degradation of ciprofloxacin (99.7 %, k = 0.030 min−1) and tetracyline (94.6 %, k = 0.017 min−1), in which superoxide radicals (•O2−) were shown to play a major role in removing the antibiotic. Besides, a Z-scheme heterojunction mechanism is additionally suggested, demonstrating the effectiveness of electron-hole pair splitting in the oxidation of antibiotics. Conclusively, the results show a novel and feasible modification pathway to enhance the photocatalytic activities of gC3N4 and other advanced semiconductor catalysts, especially for eliminating antibiotics and generating H2O2 within aqueous media.