N-TiO2-δ/g-C3N4 Dual Photocatalysts for Efficient Oxytetracycline Hydrochloride Photodegradation and CO2 Photoreduction

A series of x% (wt) N-TiO2-δ/g-C3N4 composites was synthesized by calcination and hydrothermal methods (labeled xTiCN, x: 5, 10, and 15). All composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of these composites was evaluated through oxytetracycline hydrochloride (denoted as OTC) photodegradation and CO2 photoreduction. The xTiCN composites exhibited higher OTC photodegradation than bulk g-C3N4. 10TiCN was slightly more active than 5TiCN and 15TiCN, with a photodegradation yield of 97% after 5 h of light irradiation and constant rate of 0.647 h-1. For CO2 photoreduction, it was observed that 5TiCN exhibited the highest activity among the synthesized composites, with 7.0 ppm CH4 formed. This CH4 concentration was 7.8 times higher than the concentration formed by bulk gC3N4 (0.9 ppm). A Z-scheme mechanism was proposed to explain the enhanced photocatalysis by x% (wt) N-TiO2-δ/g-C3N4 composites. The Z-scheme structure increased redox ability, caused better separation of photogenerated electron-hole pairs, and broadened the light absorption zone of the photocatalysts.