Adsorption of alkylamine cations on montmorillonite (001) surface: A density functional theory study

Abstract Hydrophobic aggregation in cationic surfactant dispersion is an effective method for the dewatering of clay-rich tailing. The effect of head groups type and alkyl chain length on the adsorption of alkylamine cations on montmorillonite (001) surface was investigated by density functional theory (DFT), sedimentation and measurement of contact angle and adsorption quantity. The results showed that the strongest active sites were located above the six-membered oxygen ring (SOR) of montmorillonite layer, around the H atoms on N atom in the head group for alkyl primary amine (CnPA+), secondary amine (CnSA+), tertiary amine (CnTA+) cations and around H atoms in the –CH3 groups for quaternary amine (CnQA+) cation. The alkylamine cations interacted with surfaces by electrostatic attraction and hydrogen bonding where PA+, SA+, and TA+ cations formed three, two and one N Hn ⋯ Os hydrogen bonds with the montmorillonite (001) surface, respectively, while QA+ cations formed non-traditional C Hc ⋯ Os hydrogen bonds. The adsorption energies of Cn alkylamine cations decreased with the increasing substitution degree of –CH3 groups to Hn atoms in the head group. Moreover, the adsorption energies increased with the n increasing from 12 to 16, but changed slightly when beyond 16. The experimental results were consistent with the theoretically calculated results.