Sorptive characteristics of organomontmorillonite toward organic compounds: A combined LFERs and molecular dynamics simulation study

Linear free energy relationships (LFER) combined with molecular dynamics (MD) simulations were used to investigate the sorptive characteristics of organic compounds (OCs) on cetyltrimethylammonium (CTMA) intercalated montmorillonite (CTMA-Mont). The LFER for OCs sorption on CTMA-Mont, log K _oc = (1.45 ± 0.20)E - (0.37 ± 0.15)S + (0.56 ± 0.15)A - (1.75 ± 0.25)B + (2.50 ± 0.45)V + (0.19 ± 0.35), was obtained by a multiple linear regression of the sorption coefficients of the OCs against their solvation descriptors. In comparison to water, CTMA-Mont is more polarizable, less polar and cohesive, and has stronger H-bond acceptor and weaker H-bond donor capacities. Using the above equation we calculated that vV and eE were the dominant solvation terms contributing to the sorption for all the OCs. MD simulations provided atomic-level insight into the interlayer structure of CTMA-Mont. Phenol molecules were shown to be sorbed into the nanosized aggregates formed by CTMA alkyl chains. The hydrophobic environment within the aggregates is responsible for the sorbent's more polarizable, less polar and cohesive characteristics. CTMA-Mont has strong H-bond acceptor and weak H-bond donor capacities as oxygen atoms on the siloxane surface act as H-bond acceptors for both water and OC molecules. With the combination of the results of the two methods, we can provide new insights for understanding the sorptive characteristics of organomontmorillonite.