Preparation Of Nanovoid Core(Tio₂ )/shell(SiO₂ ) Phase-boundary Photocatalyst And Its Specific Interface Adsorption Property

Photocatalysis is an ideal technology for environment pollution control and clean energy, which can directly use sunlight to drive the reaction processes under certain conditions of no extra pollution and mild reactions.Among varieties of photocatalysts, titanium dioxide(TiO₂) appears to be the most promising and suitable material because of its superior photocatalytic activity,chemical stability, low cost and nontoxicity. By and large TiO₂ photocatalysts can be traditionally applied in a suspended phase with relatively high photocatalytic efficiency, however, some pressing problems still remain to be done for the separation and cyclic-utilisation of the prepared photocatalysts, and further the related photocatalytic reactions only can be taken place with the help of mechanical stirring. Besides, when the reaction solution becomes feculent, the number of photons absorbed by the photocatalysts will be significantly reduced, and thereby resulting in the decrease of the photocatalytic reaction rate. Although several routes have been raised to solve the existed problems, for instance, loading photocatalyst particles onto organic or inorganic materials, such as a glass plate, has been proposed to overcome these problems, the transportation of effective chemical species across the plate could be highly restricted.In this paper, a new kind of nanovoid phase-boundary photocatalysts were prepared and employed in the new phase-boundary photocatalytic systerms to deal with the weaknesses asforementioned. And the synthetic approach, structures, properties and reaction mechanism of the as-prepared phase-boundary catalysts were characterized and demonstrated via series of particular experiments and analysises, the experimental results were as follows.The nanovoid core/shell photocatalysts were firstly prepared by a typical hydrothermal and sol–gel method using commercial P25 TiO₂ nanoparticles and tetraethoxysilane(TEOS) as starting materials, and then selected silane coupling agent was used to modify the surface of the as-prepared nanoparticles and thus the desirable phase-boundary photocatalysts(TiO₂@@SiO₂-O) were obtained which could obviously float on the aqueous solution. In addition, the effects of different synthetic temperatures and silane coupling agents for the surface property and photocatalytic activity had also been discussed to determine the optimum conditions of core/shell photocatalysts preparation.The stability and photocatalytic activity of the as-prepared samples were observed by putting them under a long time UV irradiation. The results showed that the organic groups grafted on the surface of unmodified TiO₂ nanoparticles were degraded because of its strong oxidability. However, it can also be derived from the results that the surface organic groups onto the phase-boundary photocatalysts(TiO₂@@SiO₂-O) were effectively maintained and protected, and thus appropriately demonstrated the effectiveness of as externally coated porosity silica shell which in a large extent prevented the direct contacts between organic moleculars and bulk TiO₂, yet, the organic moleculars could enter the nanovoid to react with the TiO₂ interior surface efficiently.Phase-boundary photocatalysis was a new concept of heterogeneous photocatalytic system, in this research, a specific heterogeneous photocatalytic system was constructed and the catalytic activities of the employed photocatalysts in this system were investigated. It can be obtained from the results that the newly established photocatalytic system acquired a superior floating effect at the solid/liquid interface and in comparison with the traditional TiO₂ catalysts, the current photocatalytic reactions occurred without the help of mechanical agitation, and thereby the new reaction system could largely extend the application of TiO₂.In addition, many kinds of dyes were employed to test the adsorptive performance and selectivity of the phase-boundary photocatalysts. The results illustrated that the new photocatalysts had a specific and strong adsorption of cationic dye, in contrast the adsorption of anion dye was relatively weak, which indicated that the special adsorption property could possibly depend on some factors of surface charge and molecular structure. The unique selectivity and adsorption property exhibited in the results could have an important influence for the course of photocatalytic reaction, and have large research value in purification and enrichment, it would provide a new field in the study and application of TiO₂ photocatalysts.