Cu-Anchored Keggin Ti–Oxo Cluster/Boron-Doped Carbon Nitride Heterojunction for CO2 Photoreduction

Abstract Efficient and selective photocatalytic CO2 conversion in pure water requires both effective utilization of photogenerated charge carriers and well-defined catalytic active sites. Here, a Cu-functionalized Keggin-type titanium–oxo polyoxometalate/boron-doped carbon nitride photocatalyst (Cu–PT/BCN) was developed to integrate interfacial charge regulation with surface catalysis. Phosphate-centered PT clusters were grown in situ on two-dimensional BCN, followed by solvent-assisted ultrasonication to improve interfacial contact and cluster dispersion. The terminal {PO4} groups of the PT clusters were further used to selectively anchor atomically dispersed Cu species. Under UV–vis irradiation in pure water, the optimized Cu–PT/BCN exhibited markedly enhanced CO2 photoreduction activity, with CO2 conversion rates 7 and 30 times higher than those of BCN and pristine CN, respectively, while maintaining nearly 100% selectivity toward CO. Mechanistic studies revealed that charge transfer between BCN and PT follows a Z-scheme pathway, resulting in substantially improved separation of photogenerated charge carriers. The electrons retained on PT are subsequently transferred to Cu sites, which promote CO2 adsorption and activation and facilitate its selective reduction to CO. In situ microsecond transient absorption spectroscopy revealed an electron transfer efficiency of 80.5% under reaction conditions, while CO2 adsorption measurements and in situ Fourier-transform infrared spectroscopy further confirmed enhanced CO2 adsorption and stabilization of the key COOH* intermediate. This work highlights metal-oxo clusters as versatile components for integrating charge regulation with catalytic-site engineering in photocatalytic CO2 reduction in pure water.