Bhattacharya K, Tripathi A K, Dey G K, Gupta N M
Applied Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400 085, India.
J Nanosci Nanotechnol. 2005 May;5(5):790-6. doi: 10.1166/jnn.2005.113.
Nanosize clusters of titania were dispersed in mesoporous MCM-41 silica matrix with the help of the incipient wet-impregnation route, using an isopropanol solution of titanium isopropoxide as precursor. The clusters thus formed were of pure anatase phase and their size depended upon the titania loading. In the case of low (< 15 wt %) loadings, the TiO2 particles were X-ray and laser-Raman amorphous, confirming very high dispersion. These particles were mostly of < or = 2 nm size. On the other hand, larger size clusters (2-15 nm) were present in a sample with a higher loading of approximately 21 wt %. These particles of titania, irrespective of their size, exhibited an absorbance behavior similar to that of bulk TiO2. Powder X-ray diffraction, N2-adsorption and transmission electron microscopy results showed that while smaller size particles were confined mostly inside the pore system, the larger size particles occupied the external surface of the host matrix. At the same time, the structural integrity of the host was maintained even though some deformation in the pore system was noticed in the case of the sample having highest loading. The core level X-ray photoelectron spectroscopy results revealed a + 4 valence state of Ti in all the samples. A positive binding energy shift and the increase of the width of Ti 2p peaks were observed, however, with the decrease in the particle size of supported titania crystallites, indicative of a microenvironment for surface sites that is different from that of the bulk.
通过初湿浸渍法，以异丙醇钛的异丙醇溶液为前驱体，将纳米尺寸的二氧化钛簇分散在介孔MCM-41二氧化硅基质中。由此形成的簇为纯锐钛矿相，其尺寸取决于二氧化钛的负载量。在低负载量（<15 wt%）情况下，TiO₂颗粒为X射线和激光拉曼非晶态，证实其具有很高的分散性。这些颗粒大多尺寸小于或等于2 nm。另一方面，在负载量约为21 wt%的较高负载样品中存在较大尺寸的簇（2-15 nm）。这些二氧化钛颗粒，无论其尺寸大小，都表现出与块状TiO₂相似的吸光行为。粉末X射线衍射、N₂吸附和透射电子显微镜结果表明，较小尺寸的颗粒大多局限于孔系统内部，而较大尺寸的颗粒占据主体基质的外表面。同时，即使在负载量最高的样品中观察到孔系统有一些变形，但主体的结构完整性仍得以保持。芯能级X射线光电子能谱结果表明，所有样品中Ti的价态均为 +4价。然而，随着负载二氧化钛微晶粒径的减小，观察到正的结合能位移和Ti 2p峰宽的增加，这表明表面位点的微环境与块状不同。
