Wan Xiang,Wang Jiafei,Wang Dian,Xu Qin,Xie Fazhi,Qu Qishu
In a mixed solvent composed of acetonitrile and ethanol, tetrabutyl orthotitanate (TBOT) was quickly introduced into the pores of the core–shell silica particles (SiO 2 @ d SiO 2 ) using the coordination bond formed between N and Ti. Since all the hydrolysis reactions of TBOT occurred in the pores, SiO 2 @ d SiO 2 spheres coated with TiO 2 (S@S@TiO 2 ) with an effective loading of TiO 2 as high as 74% were obtained. Because all TiO 2 nanoclusters are located in the pores, their growth is restricted by the pores. So the size of crystalline grains in the pores of the shell slowly increases with the increase in the calcination temperature. Due to the confined growth of TiO 2 nanoclusters, S@S@TiO 2 still maintains the anatase phase when the calcination temperature is as high as 1050 °C, which is significantly higher than the maximum thermal stability temperature of 900 °C reported in the literature. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the catalytic activity of S@S@TiO 2 calcined at 950 °C is 2.1 times higher than that of the commercial P25 TiO 2 photocatalyst. Graphical abstract
Based on a detailed study of the hydrolysis process of tetrabutyl orthotitanate (TBOT), TiO 2 nanoclusters were modified inside the pores of SiO 2 core-shell particles instead of the outside. The pore size distribution of SiO 2 core-shell spheres modified with TiO 2 (SiO 2 @ d SiO 2 @TiO 2 ) was analyzed by Barrett-Joyner-Halenda (BJH) method and density functional theory (DFT) method, respectively. The results of the DFT calculations demonstrate that the TiO 2 nanoclusters are always first formed in bulk solution and then enter the pores. By regulating the rate of hydrolysis of TBOT, almost all of the TiO 2 nanoclusters are modified into the pores and the structure of the original SiO 2 core-shell sphere is hardly affected. The morphology of the particles was characterized by scanning electron microscopy and transmission electron microscopy. The crystal phase of TiO 2 was measured by XRD. SiO 2 @ d SiO 2 @TiO 2 spheres functionalized with C18 were packed into a stainless steel column. The chemical stability of SiO 2 @ d SiO 2 @TiO 2 spheres under alkaline was tested by flushing of a mobile phase at pH 13 for 7 days. The efficiency of the column after the alkali solution treatment still reaches 98,430 plates m −1 , which is only about 1.6% lower than that before the alkali solution treatment. A series of basic and acidic analytes were also separated on the column.
TiO 2 nanocrystals were coated into the pore of core-shell silica spheres. The prepared particles were packed into the column and separation performance up to 98,430 plates per meter was achieved.
Graphene is the most attractive carbon-based material at present and attracting increasing attention as promising candidates for applications in numerous areas, because of its extraordinary chemical, thermal and mechanical properties. In this paper, we discussed an innovative and simple method to synthesize titanium dioxide (TiO 2 ) nanoclusters , using graphene as a mid-step template not as a component of final product. Using this method, the graphene was firstly fully coated with TiO 2 nanoparticles by the thermal decomposition of titanium (IV) isopropoxide in a supercritical carbon dioxide (SC-CO 2 ) at 200 °C; the developed TiO 2 /graphene composites then were heated in an oxygen atmosphere. Eventually the TiO 2 nanoclusters were obtained. The prepared TiO 2 nanoclusters showed irregular features with high surface coverage, providing promises in a wide range of applications, especially for photo-degradation of organic compounds in aqueous solution under the radiation of UV-light.
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