Single‐Crystal‐like Titania Mesocages

Abstract

Titania represents the most widely used oxide semiconductor for photocatalysts and photovoltaics, and its performance is heavily governed by its surface area and the exposed crystal planes. To date, however, as-made TiO2 samples have been limited to the single crystals with low surface area or porous polycrystals exposing their less-active planes. We report herein the synthesis of high-surface-area, singlecrystal-like anatase with controlled mesoporous network and preferential exposure of the highly active (001) planes. This simple solution-growth method is readily extendable to the synthesis of other mesoporous single crystals beyond TiO2, providing a new class of materials for catalysis, energy storage and conversion, and other applications. The photocatalytic activity of TiO2 is generally dependent on its crystallography. For example, the (001) planes of anatase are much more active than the (101) planes, which are the most commonly observed and thermodynamically more stable crystalline planes in the anatase form. Significant effort has therefore been devoted to synthesize TiO2 crystals with preferential (001) plane exposure. As well as crystallographic control, equally important is building networks of pores within the crystals to increase the surface area and provide pore-dependent activity and selectivity. To date, although a large number of porous TiO2 have been made using sol–gel and softor hard-templating approaches, 8, 21,23–25] the current materials are limited to porous TiO2 with amorphous or polycrystalline frameworks that exhibit low photocatalytic activity and charge-transport capability. Herein, using a method of crystal oriented growth, we report the synthesis of highly active mesoporous, singlecrystal-like TiO2 (mesocages) with both preferential (001) plane exposure and controllable mesoporous networks. As illustrated in Figure 1, we started with precursor solutions containing SO4 2 ; solvothermal reactions generate TiO2 building crystals of which the (001) planes are preferably