Tailoring Interfacial Charge Transfer via Defect-Mediated Au/Bi4Ti3O12 Heterostructures for Highly Selective Photocatalytic CO2 Reduction to CH4

Defect engineering and metal–support coupling provide an effective route to tune interfacial charge dynamics for selective photocatalytic CO2 reduction. Here, Ti-vacancy-rich Bi4Ti3O12 (BTvO) nanosheets were prepared and decorated with Au nanoparticles (Au NPs) to build Au-BTvO junctions that favor multi-electron/proton transfer toward deep hydrogenation. The optimized 3%Au-BTvO achieved high hydrocarbon productivity under visible light (λ > 420 nm), delivering CH4 and C2H6 formation rates of 92.66 and 17.96 μmol g−1 h−1, respectively, with stable performance over 25 h. Spectroscopic analyses reveal higher CO2 uptake and more effective surface activation, increased water adsorption with a more favorable interfacial hydration environment, and time-dependent formation of key C1 and C2 intermediates. In situ light-irradiation XPS, PL mapping, and KPFM collectively demonstrate directional electron transfer from Bi4Ti3O12 to Au and amplified surface band bending, enabling efficient charge separation and accelerated surface reduction. This work highlights defect–metal synergy as a general strategy to boost activity, selectivity, and durability in visible-light CO2-to-methane conversion.