Mesoporous silicas functionalized with a high density of carboxylate groups as efficient absorbents for the removal of basic dyestuffs

A novel silane bearing a reactive anhydride group was synthesized. Due to its special structure, the direct co-condensation of this synthesized functional silane with TEOS in the presence of different surfactant templates led to ordered mesoporous silicas with different pore sizes and a high density of carboxylic acid groups, which were used as adsorbents for the removal of three basic dyestuffs (methylene blue, phenosafranine and night blue) from waste water. The performed measurements showed that, probably due to their high surface area, good affinity of carboxylic groups and large number of binding sites, the obtained mesoporous materials exhibit a high adsorption capacity and an extremely rapid adsorption rate. Furthermore, these carboxylic-functionalized adsorbents can be regenerated by simple washing with acid solution to recover both the adsorbents and the adsorbed dyes. The experimental data for the adsorption of all three basic dyes were analyzed using Langmuir and Redlich-Peterson isotherm models. It is found that the Langmuir equation provides an accurate description of these adsorption data, suggesting that monolayer adsorption occurred in all cases of the performed sorption processes. In this work, the influences of the pH values of the treated solutions and the pore sizes of the prepared adsorbents on the adsorption behavior were also discussed.