Preparation, Characterization And Photocatalytic Activities Of Inorganic-Organic Nanohybrid Materials

In recent years, the preparation of nanostructured materials becomes an important challenge of materials science and receives great attention due to a range of designed and unique properties.The development of various approaches to fabricate ultrathin films has attracted considerable interest. Among all of these techniques, layer-by-layer (LBL) self-assembly technique is widely employed. It is proved to be the most suitable, versatile and inexpensive means over the past decade. It permits the sequential assembly of multiple layers of oppositely charged materials on planar substrates. Ultrathin, composite particle-containing films with unique catalytic, magnetic or optical properties have been prepared by the LBL method.In the present study, polyhedral oligomeric silsesquioxane (POSS) has been chosen as building block to form nanocomposite ultrathin silica films. The POSS derivative-ammonium salt of octasilsesquioxane acid (Si₈O₂0⁸-") has an integral structure with high symmetry and has an average diameter of only 1.5 nm. Especially, it has excellent physico-chemical, thermal and mechanical properties. In this current work, we have prepared nanocomposite multilayers (PDDA/(Si₈O₂0⁸-))n by consecutively adsorbing (Si₈₂0⁸-) and poly(diallyldimethylammonium chloride) (PDDA) on CaF₂ substrate. Linear build-up of the LBL films was confirmed by UV-vis spectroscopic measurement. IR spectrum suggests the existence of bothSi₈O₂0⁸- and PDDA in the LBL films. Atomic force microscopic surface topography of the LBL films indicates the Si₈O₂0⁸- covers the entire surface of the topmost layer and shows a granular morphology.In recent years, photocatalysis has been drawing a great deal of attention in order to solve serious environmental problems. Among the metal oxides semiconductors suitable for photocatalytic processes, titanium oxide (TiO₂) is well-known with many applications in such as water photolysis, environmental purification, decomposition of organic contaminants etc. However, the efficiency of photocatalytic reactions islimited by the wide band-gap of anatase TiO2, the high degree of electron-hole recombination inherent in photocatalytic processes, as well as by the limited adsorption capability of photocatalysts. Many efforts have been made to minimize these drawbacks. Usually the addition of hetero-atoms into TiO2 crystal and dye-sensitization were used to narrow the band-gap, thus to benefit it operation effectively on visible light illumination. Other works have been done to make TiO2 microporous or even macroporous structure in order to improve its specific surface area. Some efforts have been carried out to graft titanium onto the SBA-15 inner surface in recent years. Nevertheless, the uniform and content of the titanium in the mesoporous materials is not satisfied by using directly grafting method.In this current work, SAB-15 mesoporous silica was modified with anatase TiO2 on the inner pore surface, by employing layer-by-layer self-assembly and sol-gel method. SBA-15 is firstly functionalized with charged polymers onto the inner pore surface through electrostatic attraction. Then the precursors of titanium species (tetraethoxy titanium, TBOT) are introduced into the functionalized pore surface of SBA-15, through the reaction with pendant -OH groups in polymer. The product is calcined to remove the polymers. The nanostructured anatase T1O2 materials distribute uniformly in the channel of the mesoporous host. For sensitization, the thiazol yellow was further covered onto the surface of TiO2 to get TY-TiO2-SBA-15. All the samples were characterized by FTIR spectroscopy, UV-vis diffused reflectance spectroscopy, powder X-ray diffraction, nitrogen adsorption-desorption measurement. The TY-TiO2-SBA-15 exhibits enhanced photo-catalytic activity for degradation of indigo carmine solution than anatase TiO2 and TiO2-SBA-15 by using visible light irradiation.