Adsorption mechanism insights into CPAM structural units on kaolinite surfaces: A DFT simulation

Abstract

The adsorption behavior and mechanisms of three CPAM structural units (P-DMDAAC, P-MAPTAC, P-DMC) on kaolinite surfaces were investigated using density functional theory (DFT). Results show that the posture of CPAM structural units exerts more influence on the adsorption interaction than the kaolinite surfaces adsorption position. Through the analysis of the Mulliken population analysis, electron density difference, and electronic density of states on the optimal adsorption system, the bonding nature and interaction types were further discovered. It emerged that the interaction of structural units on the kaolinite surfaces is driven by both hydrogen bonds and electrostatic attraction. The hydrogen bond of P-DMDAAC/kaolinite (001) surface is C-Hm···Osn (C-H1···Os1 and C-H4···Os2). Three hydrogen bonds (C-H1···Os1, O-Hs2···O1, and O-Hs3···O1) are formed when P-MAPTAC is adsorbed on the kaolinite (001) surface. For P-DMC adsorption, there are two hydrogen bonds (C-H1···Os1 and O-Hs1···O1). The hydrogen bond of CPAM structural units and kaolinite (001¯) surface is relatively weak and unstable. The electrostatic attraction dominates the whole adsorption process. The order of the electrostatic attraction of structural units on the kaolinite (001) surface is P-DMDAAC > P-MAPTAC > P-DMC, P-MAPTAC still demonstrates the strongest adsorption capacity on kaolinite surfaces.