A series of composite γ-Fe2O3/g-C3N4 (denoted as xFeCN with x equal 5, 10, 15, and 20 of γ-Fe2O3 percentage in weight) was prepared by calcination and precipitation-impregnation methods. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectrometry (XPS) characterizations indicated the successful synthesis of Z-scheme FeCN composites. A red shift of the light absorption region was revealed by UV-vis diffuse reflectance spectroscopy (UV-DRS). In addition, photoluminescence spectroscopy (PL) spectra showed an interface interaction of two phases Fe2O3 and g-C3N4 in the synthesized composites that improved the charge transfer capacity. The photocatalytic activity of these materials was studied in the photoreduction of CO2 with H2O as the reductant in the gaseous phase. The composites exhibited excellent photoactivity compared to undoped g-C3N4. The CH4 production rate over 10FeCN and 15FeCN composites (2.8 × 10−2 and 2.9 × 10−2 μmol h−1 g−1, respectively) was ca. 7 times higher than that over pristine g-C3N4 (0.4 × 10−2 μmol h−1 g−1). This outstanding photocatalytic property of these composites was explained by the light absorption expansion and the prevention of photogenerated electron-hole pairs recombination due to its Z-scheme structure.

A series of x % (wt) N-TiO2-δ/g-C3N4 composites was synthesized by calcination and hydrothermal methods (labeled x TiCN, 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 x TiCN 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 g-C3N4 (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.