Mesoporous Silica-Supported Chitosan with Improved Affinity for Diclofenac-Role of Silica on Adsorption Efficiency

The role of silica on enhancing diclofenac (DCF) sodium uptake by SBA-supported chitosan (CN-SBA) from aqueous solutions was investigated. For this purpose, the use of SBA-15 and SBA-16-like mesoporous silica as inorganic supports for CN at different proportions resulted in CN-SBA-15 and CN-SBA-16 adsorbents with improved affinity towards DCF as compared to the starting components. These materials were characterized by powder X-ray diffraction (pXRD), nitrogen sorption measurements (BET, BJH) and thermogravimetric analysis (TGA). Their adsorption features for DCF capture were examined through the effects of the solution pH, adsorbent amount and adsorption time on the adsorption process of diclofenac sodium. UV-Vis spectrophotometry revealed fast adsorption kinetics reaching equilibrium with ca. four times higher DCF removal yield by chitosan-loaded SBA-15 and SBA-16 as compared to their bare counterparts. This improvement was explained in terms of additional interactions with the silica surface. The initial pH was found to strongly influence the adsorption capacity, the higher DCF uptakes being registered under acidic conditions, presumably due to a strong contribution of hydrophobic interaction with siloxy groups. Adsorption turned out to fit Langmuir’s model with maximum adsorption capacity in agreement with experimental data. These results open promising prospects for tailored affinity towards DCF according to the silica content.