Metal-semiconductor heterojunction accelerates the plasmonically powered photoregeneration of biological cofactors

Photocatalysis with plasmonic nanoparticles (NPs) is emerging as an attractive strategy to make and break chemical bonds. However, the fast relaxation dynamics of the photoexcited charge carriers in plasmonic NPs often result in poor yields. The separation and extraction of photoexcited hot-charge carriers should be faster than the thermalization process to overcome the limitation of poor yield. This demands the integration of rationally chosen materials to construct hybrid plasmonic photocatalysts. In this work, the enhanced photocatalytic activity of gold nanoparticle-titanium dioxide metal-semiconductor heterostructure (Au-TiO₂) is used for the efficient regeneration of nicotinamide (NADH) cofactors. The modification of plasmonic AuNPs with n-type TiO₂ semiconductor enhanced the charge separation process, because of the Schottky barrier formed at the Au-TiO₂ heterojunction. This led to a 12-fold increment in the photocatalytic activity of plasmonic AuNP in regenerating NADH cofactor. Detailed mechanistic studies revealed that Au-TiO₂ hybrid photocatalyst followed a less-explored light-independent pathway, in comparison to the conventional light-dependent path followed by sole AuNP photocatalyst. NADH regeneration yield reached ~70% in the light-independent pathway, under optimized conditions. Thus, our study emphasizes the rational choice of components in hybrid nanostructures in dictating the photocatalytic activity and the underlying reaction mechanism in plasmon-powered chemical transformations.