Abstract
The paper presents the studies of effects of TiO2 amount differentiation on the structural and thermal properties of titania–silica complex oxides prepared by chemical vapor deposition of TiCL4 onto the Si-40, Si-60, and Si-100 silica gels. The mesoporous materials, characterized by a varied pore structure with highly developed surface and large pore volume, were obtained. The porous structure of materials under investigations was characterized by the low-temperature nitrogen adsorption–desorption method as well as by power spectral density calculated from the calorimetric investigations of water confined in the pores. Moreover, the thermodesorption of water using the quasi-isothermal thermogravimetry was used to characterize their thermal and surface properties. The adsorbed water layers and the concentration of weakly and strongly bound water as well as the surface free energy on the adsorbent–water interfaces were calculated. It was stated that the increase of titania content causes a gradual decrease of specific surface area and has a significant effect on the porous structure formation. The water thermodesorption from the surface proceeds in few stages because of the porosity created by TiO2. The decrease in the total surface free energy (Δ GΣ) can be observed with the increasing TiO2 content. The largest Δ GΣ value at the adsorbent/strongly bound water interface is exhibited by the adsorbents of Si-100 series. The lowering of the freezing/melting points of water contained in the pores of the studied materials is strongly connected with their porous structure.
Highlights
Complex oxides, especially those based on silica as the mineral matrix, play a significant role in the adsorption and catalytic processes (Gonzalez et al, 1997; Miller and Ko, 1997; Miller and Lakshmi, 1998; Thoma and Nenoff, 2000)
One of the most common methods used in the process of titania–silica complex oxide (TS) preparation is the chemical vapor deposition (CVD) method
By studying the phase transitions of water bound to the surface of such materials, one can obtain the additional information about their porous structure and surface nature
Summary
Especially those based on silica as the mineral matrix, play a significant role in the adsorption and catalytic processes (Gonzalez et al, 1997; Miller and Ko, 1997; Miller and Lakshmi, 1998; Thoma and Nenoff, 2000). Incorporation of the transition metal (in the form of elements, ions or oxides, titanium) (Corma, 1997; Corma et al, 1997; Tanev et al, 1994) into the silica gel structure can cause changes in the porous structure of the complex oxides and lead to creation of additional, special catalytic properties. These materials are considered as a substitute for pure TiO2, due to the superior mechanical strength and thermal stability of such highly dispersive composites including TiO2. By studying the phase transitions of water bound to the surface of such materials, one can obtain the additional information about their porous structure and surface nature
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