Adsorption of Quercetin on Mesoporous Silica Modified with Cationic Surfactants

Ordered mesoporous silica (OMS) is widely investigated as a mineral carrier for bioactive compounds; however, the adsorption of poorly soluble flavonoids such as quercetin on unmodified silica remains limited, and the effect of cationic surfactant modification on adsorption performance is still insufficiently understood. This study evaluates the adsorption of quercetin on OMS modified with tetrabutylammonium bromide (TBA-Br) and hexadecyltrimethylammonium bromide (HDTMA-Br). Batch adsorption experiments were analyzed using various adsorption isotherm models, and the quality of fit was evaluated based on the coefficient of determination (R2) and the reduced chi-square statistic (χ2/DoF). The results indicated that quercetin adsorption followed a physisorption mechanism, predominantly governed by hydrophobic interactions and surface heterogeneity. Silica modified with HDTMA-Br exhibited a significantly higher maximum sorption capacity compared to OMS-TBA-Br, reaching gmax values of up to 5.2 mg·g−1, whereas the maximum adsorption for OMS-TBA-Br did not exceed 4.2 mg·g−1. The best fit of the experimental data was obtained for models accounting for the heterogeneous nature of the adsorbent surface, particularly the Tóth model. The obtained results clearly demonstrate that modification of OMS with a cationic surfactant possessing a long alkyl chain significantly enhances the adsorption capacity of silica toward quercetin, which is of considerable importance for the design of mineral carriers for bioactive compounds.