Adsorption mechanism of polyacrylamide on kaolinite surface in the presence of Ca2+: Insights from DFT calculation

Abstract

The microscopic adsorption mechanism of polyacrylamide (PAM) on kaolinite surface in the presence of Ca2+ was investigated by using density functional theory (DFT). The PAM model was constructed firstly, and the optimal adsorption configurations and adsorption mechanism were examined, with adsorption configurations, bond populations and adsorption energy analyzed. Calculation results demonstrated that the adsorption of PAM on kaolinite (001) surface was dominated by three strong hydrogen bonds between the amide groups of PAM and hydroxyl groups of kaolinite (001) surface. And the PAM adsorbed on the kaolinite (00–1) surface through non-bonding interaction. Ca2+ was selected to explore the influence of metal cations on the adsorption of PAM on kaolinite surface. The results suggested that the adsorption of PAM on the kaolinite (001) surface was promoted in the presence of Ca2+, while the adsorption of PAM on the kaolinite (00–1) surface was inhibited.