Template-induced Structuring and Tunable Polymorphism of Three-dimensionally Ordered Mesoporous (3DOm) Titania Materials

摘要

A sacrificial nanotemplating strategy involving the infiltration of colloidal crystalscomposed of size-tunable (ca. 10 nm and larger) silica nanoparticles with titaniaprecursor solutions followed by confined hydrolysis therein enables the fabrication ofthree-dimensionally ordered mesoporous (3DOm) titania structures with controlled porebody size in the range of nanometers to tens of nanometers. The hard silica templateenables calcination-induced improvement in titania crystallinity, with the templated poresrobust to collapse upon template removal. This approach results in 3DOm titaniamaterials with attractive textural properties, including surface areas (ca. 289 m~2/g) andpore volumes that are up to four times and more than an order of magnitude larger,respectively, then commercially available titania. Fundamental insight into titaniapolymorphism (i.e., rutile, anatase, or fraction thereof) has been elucidated as it relatesto its sensitivity to the degree of titania confinement imparted by the template as well asthe template surface chemistry. Specifically, increasing confinement helps to stabilizethe active anatase polymorph, while tuning the degree of surface hydroxylation of thetemplate enables fine control over fractional polymorphism, the latter having implicationson inherent reactivity.