Influence of pH on cephalexin adsorption onto SBA-15 mesoporous silica: Theoretical and experimental study

Abstract

tCephalexin adsorption from aqueous solutions using SBA-15 mesoporous silica as adsorbent and theinfluence of pH solution on drug adsorption were studied. In order to have a better knowledge aboutthe way the drug molecules interact with the inorganic matrix, the adsorption process was estimatedby applying the computational chemistry software YAeHMOP (Yet Another extended Hückel Molec-ular Orbital Package). A strong correlation between the theoretical calculations and the experimentalresults was established, showing that the adsorbate?adsorbent interaction is pH dependent. Calculatedcephalexin horizontal adsorption energy was almost 9 eV more stable than the one corresponding tovertical adsorption, and also the lowest enthalpy of contact and the maximum adsorption percent werefound for the cationic cephalexin?silica system. Cephalexin adsorption through the NH3+group is 8 eVstronger than the molecule adsorption through the COO−group. In agreement with these theoreticalpredictions, experimental results indicate that the electrostatic attraction between CPX ions and the sur-face of mesoporous silica is favored at pH values between 2 and 2.56, the maximum being for cephalexinadsorption obtained at pH 2.3.