Size-Controlled Electron Transfer and Photocatalytic Activity of ZnOAu Nanoparticle Composites

A challenge in the research of solar energy conversion and photocatalysts is the rational design of materials that can efficiently trap solar energy, convert into charges, and allow controlled transfer of those charges. Notable breakthroughs have been realized recently in the development of molecular catalysts capable of controlled photogenerated electron transfer. 3 However, much less progress has been made in nanoparticle catalysts that often exhibit unique size-dependent physical and chemical properties. 7 Combining metal nanoparticles exhibiting quantized charging properties with a lightharvesting unit may lead to nanoparticle composites capable of controlled electron transfer and thereby tunable catalysis.We report here the first quantitative results demonstrating that electron transfer and photocatalytic activity can be controlled by the size of metal nanoparticle in metal semiconductor composites. Thiolate-protected gold nanoparticles (AuNPs) with diameters < 3 nm are stable, structurally well-characterized nanoparticles that exhibit size-dependent electrochemical and optical properties. 10 One of the most interesting properties of these quantum-sized AuNPs is the ability to control the transfer of electrons into and out of the metallic core. The controllability of the electronic charging is a fundamental result of the ultrasmall capacitance (on the order of aF) of AuNPs. The size-dependent capacitance (CAuNP) has been successfully modeled 8 as a capacitance of metallic spheres with insulating dielectric layers