Hot electron back-Injection from plasmonic Au nanoparticles boosts photocatalytic CO₂ reduction over Boron-doped spherical g-C₃N₄

Converting CO₂ into high-value fuels through the synergistic interplay of donor-acceptor (DA) structure and photothermal effects presents a promising strategy for enhancing the carbon cycle and mitigating greenhouse gas emissions. In this work, a carbon nitride (g-C₃N₄) based photocatalyst, designated Au/BMNS-x, was engineered to integrate both a DA structure and Localized Surface Plasmon Resonance (LSPR) by simultaneously incorporating boron doping and Au nanoparticles (NPs) into g-C₃N₄. The plasmonic Au NPs generate a pronounced photothermal effect under irradiation, significantly elevating the local reaction temperature during CO₂ photoreduction. Real-time infrared thermography demonstrated that Au/BMNS-2 reached a stabilized surface temperature of 148.1℃, which is 1.17 times higher than that of BMNS and 2.06 times greater than pristine g-C₃N₄. Under optimized conditions, Au/BMNS-2 exhibited a CO production rate 5.99 times higher than that of pristine g-C₃N₄, along with excellent structural stability and reusability over multiple cycles. In situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient absorption spectroscopy (fs-TAS) provide direct evidence of hot electron back-injection from plasmonic Au NPs into BMNS, enriching electron density around the catalytic active sites. Crucially, the DA structure, synergistically coupled with the LSPR effect, enables highly efficient separation and ultrafast transfer of photogenerated charge carriers, thereby significantly enhancing overall photocatalytic performance. The reaction mechanism was further elucidated through in situ Fourier transform infrared spectroscopy (FT-IR) spectroscopy and density functional theory (DFT) simulation. This study offers a rational design strategy for multifunctional photocatalysts that harness both plasmonic and photothermal effects, opening new avenues for high-efficiency solar-driven CO₂ conversion technologies.