Photoreduction of CO2 to CH4 over Efficient Z-Scheme γ-Fe2O3/g-C3N4 Composites

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.