Enhanced CO2 photoreduction via a 3D TiO2/NiAl-LDH aerogel with a novel S-scheme heterojunction enabling charge separation

Developing efficient, stable, and low-cost photocatalysts for solar-driven CO 2 conversion is of great significance for sustainable energy. A flower-like NiAl-LDH structure with a particle size of about 3.0 μm, loaded with TiO 2 nanoparticles, is hydrothermally grown into a porous aerogel featuring an S-scheme heterojunction and an average pore diameter of approximately 13.0 nm. Under full-spectrum irradiation and without any CO-catalysts, the optimized aerogel achieves remarkably high CH 4 and CO production rates of 9.45 and 13.67 μmol·g −1 ·h −1 , representing 2.19- and 5.04-fold enhancements over pristine TiO 2 , respectively, along with excellent long-term cyclic stability. UV–vis diffuse reflectance spectroscopy and photoelectrochemical analysis clearly reveal that the S-scheme heterojunction enhances visible-light absorption and significantly prolongs the photogenerated carrier lifetime from 1.46 ns to 3.02 ns. Density functional theory calculations further reveal that compared to TiO 2 , NiAl-LDH exhibits a stronger CO 2 adsorption energy of −1.28 eV and induces significant structural deformation in the adsorbed CO 2 molecule. Band structure, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy consistently verify that before illumination, electrons spontaneously transfer from NiAl-LDH to TiO 2 , establishing a built-in electric field and inducing interfacial band bending. Upon illumination, this built-in field drives photogenerated electrons to transfer directionally from the conduction band of TiO 2 to the valence band of NiAl-LDH for recombination, thereby enabling efficient spatial charge separation and preserving high redox potentials. In situ infrared spectroscopy further reveals the CO 2 photoreduction pathway, thus supporting the proposed S-scheme-based multi-electron reduction mechanism for efficient solar fuel production