The Adsorption Mechanism of Montmorillonite for Different Tetracycline Species at Different pH Conditions: the Novel Visual Analysis of Intermolecular Interactions

Previous researches investigated the adsorption properties and mechanism of clay minerals on antibiotic pharmaceuticals and personal care products (PPCPs) via batch adsorption experiments and X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) characterization, but many PPCPs exhibit different ionization states under different pH conditions; the research on the microscopic mechanism of different ionized PPCPs species adsorbed by clay minerals is very scarce. In this work, as a typical PPCPs contaminant, the common tetracycline (TC) was chosen as the study target; the adsorption micro mechanism of montmorillonite (MMT) on different TC species in aqueous solution was explored in details. Especially outstanding, for the first time, with the help of Multiwfn wavefunction program, quantitative analysis of molecular surface analysis and basin analysis were applied to quantitatively investigate the electrostatic interaction between MMT and different TC species, the possible positions of lone pair electrons. Independent gradient model (IGM) analysis and Hirshfeld surface analysis including local surface analysis were integrated to visualize the binding sites, interaction types, and relative strength between MMT and TC+/- or TC+/2- species, which can insight into the interaction essence from the microscopic perspective at the atomic level.

Automated summary

This study investigated the adsorption mechanisms of clay minerals on antibiotic PPCPs with different ionization states under varying pH conditions. Various analytical tools were used to quantitatively analyze the electrostatic interactions between MMT and different TC species, providing insights into the microscopic interactions at the atomic level.