Engineering the S-scheme heterojunction between NiO microrods and MgAl-LDH nanoplates for efficient and selective photoreduction of CO2 to CH4

The selective photoreduction of CO2 into hydrocarbon fuels, such as CH4, is highly desirable for sustainable energy but remains a significant challenge due to slow proton-electron transfer processes and competing intermediates. Herein, a novel NiO/MgAl-LDH (NMA-x, LDH represents layered double hydroxide) step-scheme (S-scheme) heterojunction has been engineered via in-situ anchoring MgAl-LDH nanoplates on metal–organic frameworks (MOFs) derived NiO microrods, which improves the CO2 adsorption capability and specific surface area of NiO. The steered internal electric field in the p-n heterointerface promotes charge separation and attracts a high electron density center on the catalyst surface to favor CH4 production. Meanwhile, S-scheme photogenerated charge transfer mechanism is proposed by in-situ X-ray photoelectron spectroscopy (XPS), in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra and density functional theory (DFT) calculation. In this process, photogenerated electrons are transferred from the conduction band (CB) of MgAl-LDH to the valence band (VB) of NiO, facilitating the CHO* species serve as the critical intermediate for producing CH4 through desired photocatalytic CO2 reduction. Using pure water as a proton source, the NMA-2 catalyst achieved a high CH4 selectivity of 91.2% and a yield of 8.98 μmol∙g−1∙h−1, representing significant potential for practical applications. This catalyst outperformed pristine and revitalized NiO by 4.23 and 2.07 times, respectively.