The enhanced adsorption of Ampicillin and Amoxicillin on modified montmorillonite with dodecyl dimethyl benzyl ammonium chloride: Experimental study and density functional theory calculation

The quaternary ammonium surfactant-dodecyl benzyl ammonium chloride (DDBAC) was applied to modify Ca-montmorillonite (Ca-Mt) to obtain organo D-Mt that was used as the adsorbent for micropollutants-ampicillin (AMP) and amoxicillin (AMX). The XRD characterization indicated that DDBAC intercalated the interlayer space of Ca-Mt. When the amount of modifier was 1.4 CEC, the basal spacing enlarged from 1.53 nm to 2.97 nm, and the arrangement of modifier molecules were sloped in the interlayer of Ca-Mt along the longest axis. The saturated adsorption capacity of D-Mt-1.4 for AMP and AMX was 30.86 mg/g and 13.29 mg/g, respectively, while the saturated adsorption capacity of Ca-Mt for two contaminants was only 0.36 mg/g and 0.16 mg/g, respectively. The adsorption of the two pollutants was more consistent with Freundlich adsorption isotherm second-order kinetic model, and the thermodynamic study suggested that adsorption was more likely to occur at higher temperatures, which means that the adsorption of two pollutants was a spontaneous endothermic process. Moreover, Multiwfn wavefunction program based on Density Functional Theory (DFT) was applied to reveal the microadsorption mechanism of D-Mt to two pollutant molecules. This work confirmed that Ca-Mt functionalized by DDBAC was promising adsorbents for micro-contaminants of antibiotics and the insight of the adsorption mechanism from the atomic level, providing theoretical guidance for architecting high performance adsorbent.