Size-Selective Synthesis and Stabilization of SmallSilver Nanoparticles on TiO2Partially Masked by SiO2.

Controlling metal nanoparticle sizeis one of the principle challengesin developing new supported catalysts. Typical methods where a metalsalt is deposited and reduced can result in a polydisperse mixtureof metal nanoparticles, especially at higher loading. Polydispersitycan exacerbate the already significant challenge of controlling sinteringat high temperatures, which decreases catalytic surface area. Here,we demonstrate the size-selective photoreduction of Ag nanoparticleson TiO2whose surface has been partially masked with athin SiO2layer. To synthesize this layered oxide material,TiO2particles are grafted with tert-butylcalix[4]arenemolecular templates (∼2 nm in diameter) at surface densitiesof 0.05–0.17 templates.nm–2, overcoated with∼2 nm of SiO2through repeated condensation cyclesof limiting amounts of tetraethoxysilane (TEOS), and the templatesare removed oxidatively. Ag photodeposition results in uniform nanoparticlediameters ≤ 3.5 nm (by transmission electron microscopy (TEM))on the partially masked TiO2, whereas Ag nanoparticlesdeposited on the unmodified TiO2are larger and more polydisperse(4.7 ± 2.7 nm by TEM). Furthermore, Ag nanoparticles on the partiallymasked TiO2do not sinter after heating at 450 °Cfor 3 h, while nanoparticles on the control surfaces sinter and growby at least 30%, as is typical. Overall, this new synthesis approachcontrols metal nanoparticle dispersion and enhances thermal stability,and this facile synthesis procedure is generalizable to other TiO2-supported nanoparticles and sizes and may find use in thesynthesis of new catalytic materials. [ABSTRACT FROM AUTHOR]