Interfacial Manipulation by Rutile TiO₂ Nanoparticles to Boost CO₂ Reduction into CO on a Metal-Complex/Semiconductor Hybrid Photocatalyst

Metal-complex/semiconductor hybrids have attracted attention as photocatalysts for visible-light CO₂ reduction, and electron transfer from the metal complex to the semiconductor is critically important to improve the performance. Here rutile TiO₂ nanoparticles having 5-10 nm in size were employed as modifiers to improve interfacial charge transfer between semiconducting carbon nitride nanosheets (NS-C₃N₄) and a supramolecular Ru(II)-Re(I) binuclear complex (RuRe). The RuRe/TiO₂/NS-C₃N₄ hybrid was capable of photocatalyzing CO₂ reduction into CO with high selectivity under visible light (λ > 400 nm), outperforming an analogue without TiO₂ by a factor of 4, in terms of both CO formation rate and turnover number (TON). The enhanced photocatalytic activity was attributed primarily to prolonged lifetime of free and/or shallowly trapped electrons generated in TiO₂/NS-C₃N₄ under visible-light irradiation, as revealed by transient absorption spectroscopy. Experimental results also indicated that the TiO₂ modifier served as a good adsorption site for RuRe, which resulted in the suppression of undesirable desorption of the complex, thereby contributing to the improved photocatalytic performance. This study presents the first successful example of interfacial manipulation in a metal-complex/semiconductor hybrid photocatalyst for improved visible-light CO₂ reduction to produce CO.