Photocatalytic CO2 reduction of C/ZnO nanofibers enhanced by an Ni-NiS cocatalyst†
The photocatalytic reduction of CO2 into valuable hydrocarbon fuels via solar energy is a promising strategy for carbon utilization. In the present paper, a hierarchical Ni-NiS/C/ZnO photocatalyst was prepared via the in situ photodeposition of compact Ni-NiS nanosheets onto C/ZnO electrospun nanofibers. The existence of metallic Ni and NiS was confirmed by X-ray photoelectron spectroscopy. Photoluminescence (PL) and time-resolved PL spectra revealed that the cocatalyst Ni-NiS enhanced the charge separation efficiency of the C/ZnO nanofibers. The as-prepared Ni-NiS/C/ZnO showed enhanced CO2 reduction activity, with CO and CH4 production rates 10 and 15 times greater than those of pristine C/ZnO under 350 W visible light illumination. The intermediates of CH3O−, HCHO, and HCOO− were detected by in situ Fourier transform infrared spectroscopy, confirming that CO2 reduction is a complex reaction with multiple steps. The 13C isotopic tracer method proved that CH4 and CO were obtained from the reduction of CO2 rather than from other carbon species in the environment. The amorphous carbon in C/ZnO could promote optical absorption, improve conductivity and reduce the interfacial charge transport resistance. Ni-NiS improved the electron–hole-pair separation of the C/ZnO nanofibers. The observed enhancement in photocatalytic activity was largely attributed to higher light utilization and effective electron–hole separation. This work proves that Ni-NiS is a promising cocatalyst to ZnO for photocatalytic CO2 reduction.