Photoreduction of CO 2 to CH 4 over Efficient Z-Scheme γ -Fe 2 O 3 /g-C 3 N 4 Composites.

A series of composite γ -Fe 2 O 3 /g-C 3 N 4 (denoted as xFeCN with x equal 5, 10, 15, and 20 of γ -Fe 2 O 3 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 Fe 2 O 3 and g-C 3 N 4 in the synthesized composites that improved the charge transfer capacity. The photocatalytic activity of these materials was studied in the photoreduction of CO 2 with H 2 O as the reductant in the gaseous phase. The composites exhibited excellent photoactivity compared to undoped g-C 3 N 4 . The CH 4 production rate over 10FeCN and 15FeCN composites (2.8 × 10 -2 and 2.9 × 10 -2   μ mol h -1  g -1 , respectively) was ca. 7 times higher than that over pristine g-C 3 N 4 (0.4 × 10 -2   μ mol 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.