Further insights into the porous structure of TEOS derived silica gels

Abstract

Abstract. The porous structure of TEOS derived silica gels was studied using nitrogen adsorption at 77 K. Silica gels were prepared using TEOS, H20 and ethanol for different molar ratios. No catalyst was used in this study. Silica gels were also heat treated up to 1000~ The nitrogen sorption isotherms were analyzed by two models: Fractal and Percolation Theories. Using the fractal analysis approach, the surface roughness of the porous structure of silica gels was determined. The surface fractal dimension depends on the hydrolysis conditions and heat treatment. The surface fractal dimension decreases with increasing H20/TEOS molar ratio or heating temperature. For the silica gels studied, the surface fractal dimension changed from 2.6 to 2.5 after heating the gels, and from 2.4 to 2.6 with decreasing H20/TEOS ratio.Using the Percolation theory, we have determined the connectivity of the porous structure of silica gels. The extent of sorption hysteresis of the nitrogen isotherms reflects the connectivity of the pore network. The mean coordination number (connectivity) Z, and the linear dimension of the network, L, have been calculated from the hysteresis of the isotherms. For the as-prepared silica gels, Z was about 8 and L close to 2. On heating the gels, Z decreases to 4 and L increases to 7, results which are in accordance with the collapse of the porous network.

Microstructure-Controlled Aerosol–Gel Synthesis of ZnO Quantum Dots Dispersed in SiO2 Nanospheres

“…According to Rubio et al, primary particles become smaller as the H 2 O/TEOS ratio increases. It is postulated that smaller primary particles build up denser networks with smaller void spaces in which Zn(NO 3 ) 2 mainly decomposes.…”

“…This transient growth of silica particles is attributed to the low pH of the solution (3.0), close to the point of zero charge of SiO 2 , at which the silica colloid becomes unstable. 16−18 According to Rubio et al, 19 primary particles become smaller as the H 2 O/TEOS ratio increases. It is postulated that smaller primary particles build up denser networks with smaller void spaces in which Zn(NO 3 ) 2 mainly decomposes.…”

Dynamic Mechanical Relaxation of Poly(2‐Hydroxyethyl Acrylate)‐silica Nanocomposites Obtained by the Sol‐gel Method

“…The silica phase obtained under the polymerization conditions of this work exhibits a porous network structure with nanometer-sized pores (22)(23)(24) that facilitates its physical interpenetration with the organic polymer chains. The initial H2O/TEOS ratio was kept constant and equal to 2.…”

Texture and micro-nanostructure of porous silicon oxycarbide glasses prepared from hybrid materials aged in different solvents

“…The control of the porosity determines the future applications of the new SiOC materials developed. 1,2 In general, designing materials with controlled porosity permits the selective access of determined substances into pores. Moreover, their appropriate surface area allows the occurrence of the catalytic processes.…”