Size-Selective Synthesis and Stabilization of Small Silver Nanoparticles on TiO 2 Partially Masked by SiO 2

Controlling metal nanopartide size is one of the principle challenges in developing new supported catalysts. Typical methods where a metal salt is deposited and reduced can result in a polydisperse mixture of metal nanopartides, especially at higher loading. Polydispersity can exacerbate the already significant challenge of controlling sintering at high temperatures, which decreases catalytic surface area. Here, we demonstrate the size-selective photoreduction of Ag nano-particles on TiO2 whose surface has been partially masked with a thin SiO, layer. To synthesize this layered oxide material, TiO2 particles are grafted with tert-butylcalix[4]arene molecular templates (similar to 2 nm in diameter) at surface densities of 0.05-0.17 templates.nm(-2), overcoated with similar to 2 nm of SiO2 through repeated condensation cycles of limiting amounts of tetraethoxysilane (TEOS), and the templates are removed oxidatively. Ag photodeposition results in uniform nanoparticle diameters <= 3.5 nm (by transmission electron microscopy (TEM)) on the partially masked TiO2 whereas Ag nanopartides deposited on the unmodified TiO2 are larger and more polydisperse (4.7 +/- 2.7 nm by TEM). Furthermore, Ag nanopartides on the partially masked TiO2 do not sinter after heating at 450 degrees C for 3 h, while nanopartides on the control surfaces sinter and grow by at least 30%, as is typical. Overall, this new synthesis approach controls metal nanopartide dispersion and enhances thermal stability, and this facile synthesis procedure is generalizable to other TiO2-supported nanopartides and sizes and may find use in the synthesis of new catalytic materials.