Abstract
We demonstrate a new design concept where the interaction between silica nanoparticles (about 1.5 nm in diameter) with titania nanoparticles (anatase, about 4 nm or 6 nm in diameter) guides a successful formation of mesoporous titania with crystalline walls and controllable porosity. At an appropriate solution pH (~1.5, depending on the deprotonation tendencies of two types of nanoparticles), the smaller silica nanoparticles, which attach to the surface of the larger titania nanoparticles and provide a portion of inactive surface and reactive surface of titania nanoparticles, dictate the direction and the degree of condensation of the titania nanoparticles, resulting in a porous 3D framework. Further crystallization by a hydrothermal treatment and subsequent removal of silica nanoparticles result in a mesoporous titania with highly crystalline walls and tunable mesopore sizes. A simple control of the Si/Ti ratio verified the versatility of the present method through the successful control of mean pore diameter in the range of 2–35 nm and specific surface area in the ranges of 180–250 m2 g−1. The present synthesis method is successfully extended to other metal oxides, their mixed oxides and analogues with different particle sizes, regarding as a general method for mesoporous metal (or mixed metal) oxides.
Highlights
Mesoporous silica[35] or carbon[32] as a rigid template is proposed and proved to be capable of producing mesoporous metal oxides with crystalline frameworks[36,37,38,39,40,41,42]
Present synthesis concept is inspired by the principles, which we have found from our previous studies on intercluster salt systems, in which polyoxometalate anions and polycations, both about 1 nm in diameter, are packed alternately into single crystals[51]
The Si/Ti ratio is controlled to investigate the performance of SNPs as a new structure directing matter of TNPs for mesoporous titania materials with systematically tuned pore sizes
Summary
Mesoporous silica[35] or carbon[32] as a rigid template is proposed and proved to be capable of producing mesoporous metal oxides with crystalline frameworks[36,37,38,39,40,41,42]. We describe a silica nanoparticle-assisted novel design concept for mesoporous titania that have all of the above-mentioned desirable features, i.e., crystalline framework, well developed controllable 3D mesoporosity and facile process (Fig. 1). In the present study (Fig. 1), we used titania nanoparticle (TNP, about 4 nm in diameter) and silica nanoparticle (SNP, about 1.5 nm in diameter).
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