Adsorption of phenolic compounds on some hybrid xerogels

The ability of some hybrid xerogels (HyXs) to adsorb phenolic compounds from aqueous media was studied. It was shown that by incorporating n-alkylormosils (30–50%, v/v) into the composition of the HyXs the ability to adsorb phenolic compounds was improved. Aging of the HyXs was also shown to have an effect on the adsorptive capacity. Sol–gels dried at room temperature had higher adsorptive capacity compared with the analogous gels aged at 4 °C. All HyXs with an ormosil content between 0 and 80% exhibited a base reaction with the phenolic substances. It was also shown that hydrogen bonding appeared to have a negligible effect on the adsorption of the selected phenolic substances for the HyXs studied. It is proposed that adsorption occurs as a result of non-ionic but strong intermolecular Van der Waals interactions and as a consequence is geometry and weight dependant. Considering the molecular weights of the selected phenolic compounds for this study, it is proposed that phenolic substances with a pKa < 7 and MW > 180 will be adsorbed by the HyXs selected. In addition, the non-ionic-based adsorption of the phenolic compounds did not follow the Langmuir monolayer adsorption model.