Template Synthesis And Characterization Of Silica And Si/Al Composite Hollow Spheres

In recent years, hollow microspheres have attracted much attention and can be used in many fileds because of their special properties, such as low densities, high surface areas, good heat stability and larger inner space. In this paper, we used the template method. Our work consisted of two parts: first, we synthesized the silica hollow microspheres through CaCO₃ template, and then silica and Si/Al composite oxide hollow microspheres were fabricated through octylamine (OA) template. The SEM, TEM, XRD, FTIR and nitrogen adsorption methods have been employed to characterize morphologies and structures of silica hollow microspheres (SHMS), and the factors which have effects on the fabrication of the samples have also been investigated.First we studied the synthesis of the silica hollow microspheres by two different CaCO3 templates (one is nanosized, the other is microsized). By using CaCO3 as template and CTAB as the mesoporous-directing agents, mesoporous SHMS were synthesized via sol-gel method. The SHMS prepared with nanosized CaCO3 have anomaly shapes and higher surface areas (842m²/g). The SHMS prepared with microsized CaCO3 have a good roundness and are well-dispersed, but with lower surface areas (554.01m²/g). At the same time, we also investigated the effects of CTAB contents and temperatures on the structures of SHMS. The results showed that SHMS had integrated structures when prepared with higher CTAB contents and the mesopore structures turn more orderly. The BET areas of SHMS were lager with the increase of the temperatures.Then we studied the preparation of the silica and Si/Al composite oxide hollow microspheres on OA template. By using OA as template and hydrochloric acid as catalyst, silica and Si/Al composite oxide hollow microspheres with a good quality were fabricated rapidly. As-synthesized SHMS were between 10μm and 30μm , with a high surface area of 997.9m²/g, a mean pore diameter of 1.6nm, and a mean pore volume of 0.77m²/g (the BJH results). The particle size of SHMS increased with the reaction temperature, but the samples intended to aggregate when the temperature was above 50℃. A higher stirring speed would improve the degree of homogeneity. The mean diameter of the Si/Al composite oxide hollow microspheres was 10μm and the content of Al was 4.34%. Because of the low content of Al, it resulted that the XRD and FTIR patterns of Si/Al composite oxide hollow microspheres were nearly the same as SHMS.