Hybrid sol–gel silica adsorbent materials synthesized by molecular imprinting for tannin removal

Abstract

This study reports the development of a functional adsorbent synthesized by the molecular imprinting method in a sol–gel matrix. The adsorption capacity of the organic-inorganic hybrid adsorbent material was tested on tannin compounds, i.e., phenolic substances that are among the most difficult compounds to remove in industrial wastewater. The specific surface area obtained by nitrogen porosimetry analysis was between 2 and 579 m2 g−1 due to each sol–gel synthetic route used. Small-angle X-ray scattering analysis revealed that the hybrid silicas were arranged in a multi-level structure consisting of three levels of organization and a surface fractal structure. Diffuse reflectance spectroscopy revealed the interactions between the tannins and the silica matrix, and confirmed the partial removal of tannins after ultrasound-assisted extraction. Zeta potential analysis showed that the values ranged between −37.9 and +27.8 mV, where non-functionalized xerogels were anionic and those functionalized with organosilane were cationic. The structural and textural characteristics of the hybrid materials were found to depend on the sol–gel synthetic route, which in turn affected the adsorption capacity. The adsorbent functionalized with (3-Aminopropyl) triethoxysilane was an effective adsorbent for the tannin compounds tested here, with approximately 90% removal in aqueous solutions.