Influence of the synthesis parameters on the mesoporous structure and adsorption behavior of silica xerogels fabricated by sol–gel technique

Abstract

Silicon dioxide xerogels with controlled mesoporosity were produced by sol–gel technique. The mesoporosity and adsorption behavior of methylene blue (MB) were evaluated for the fabricated silica materials. This study is supported by several characterizations, including FTIR, TEM, SEM, and N2 sorption. The adsorption kinetics of MB on the prepared samples was evaluated at room temperature over time. It was demonstrated that the pore structure and adsorption performance of silica are closely dependent on the pH of the sol–gel solution, H2O:TEOS molar ratio, the addition of F127 template, and heat treatment performed. The present study shows that for the adsorption parameters used in this work, the control of sol–gel parameters can give rise to silica xerogels with higher adsorption capacities than SBA-16 silica molecular sieve used as the reference and already recognized as an efficient dye adsorbent. The highest adsorption capacities were measured for silica structures obtained without the use of acidic catalyst, heat treatment or F127 template. As the pore volume of the studied materials is much larger than the amount of MB captured in the adsorption tests, such results seem to be related to the specific surface area and pore size obtained in the sol–gel synthesis. Therefore, it appears that large surface areas and pore sizes accelerate the adsorption kinetic and increase the amount of MB able to stay in equilibrium in the pore structure of silica. As a matter of fact, the work developed here underlines the advantages regarding the simplicity, safety, environmental preservation and cost saving of the synthesis methodology developed herein when compared with the other methodologies commonly used to fabricate silica adsorbents.