Adsorption of antibiotics on montmorillonite and site energy distribution analysis

Abstract

• Competitive behavior of CIP and ERY on montmorillonite was investigated. • Adsorption process and molecular arrangement of CIP and ERY was discussed. • Site energy distribution and GL model were used to analyze adsorption mechanism. • Competitive adsorption was explained by the average site energy. The migration and transformation of antibiotics requires further study in geochemical settings. In this study, the removal effect of montmorillonite (Mt) on antibiotics was investigated, using the broad-spectrum antibiotics ciprofloxacin (CIP) and erythromycin (ERY) as subjects. The results of adsorption kinetics and adsorption isotherm experiments showed that the generalized Langmuir model describe the adsorption process well, and the adsorption capacity of CIP was higher. The intercalation and adsorption behaviors of CIP and ERY on Mt surface were analyzed by FT-IR, SEM, TEM, XRD and Molecular simulation. In order to analyze the different adsorption capacity of these antibiotics on Mt, the theory of site energy distribution was employed. By fitting the experimental data with the Generalized-Langmuir model, the site energy distribution and average site energy were calculated, which revealed the competitive adsorption mechanism of CIP and ERY on Mt. Moreover, the adsorption of antibiotics on Mt under different pH conditions was studied, and the competitive adsorption results were also demonstrated by the potential energy distribution.