High-Loading Cu Single-Atom Engineering on g-C₃N₄ for Visible-Light CO₂ Photoreduction

The incorporation of metal single atoms into carbon nitride (CN) has emerged as a promising strategy for photocatalytic CO₂ reduction under visible light. However, achieving high single-atom loading and unraveling the precise role of active metal centers in CO₂ conversion remain formidable challenges. Herein, an ultrasound-assisted coordination exchange strategy is reported that enables the high-loading of Cu single atoms on CN. X-ray absorption near-edge spectroscopy and aberration-corrected electron microscopy confirm that Cu is atomically dispersed and coordinated with nitrogen. The introduction of Cu single atoms modulates the electronic structure of CN, serving as electron accumulation centers that facilitate charge carrier separation and transfer. Theoretical calculations combined with in situ spectroscopic analyses reveal that Cu single atoms act as active sites, enhancing CO₂ adsorption and activation while significantly reducing the energy barrier for ^*COOH formation, thereby optimizing reaction thermodynamics. As a result, under visible-light irradiation, Cu-modified CN achieves a CO production rate of 14.65 µmol g⁻¹ h⁻¹, representing an 11.3-fold enhancement over pristine CN. This work not only establishes an efficient approach for synthesizing high-loading single-atom catalysts but also provides fundamental insights into the mechanistic role of single-atom sites in photocatalytic CO₂ reduction.