Dharni Vasudevan * Teresa A. Arey Daniel R. Dickstein Mark H. Newman Tina Y. Zhang Heather M. Kinnear and Mohammad M. Bader. Nonlinearity of Cationic Aromatic Amine Sorption to Aluminosilicates and Soils: Role of Intermolecular Cation−π Interactions. Environ. Sci. Technol. 2013 47 (24) pp 14119–14127 DOI: 10.1021-es403389a

Abstract

Through the study of substituted anilines and benzylamines we demonstrated that cooperative cation−π π–π and van der Waals interactions can increase aromatic cationic amine sorption to Na-Ca-montmorillonite well beyond the extent expected by cation exchange alone. Cationic amines exhibiting cooperative interactions displayed nonlinear S-shaped isotherms and increased affinity for the sorbent at low surface coverage; parallel cation exchange and cooperative interactions were noted above a sorption threshold of 0.3–2.3% of exchange sites occupied. Our experiments revealed the predominance of intermolecular cation−π interactions which occurred between the π system of a compound retained on the surface via cation exchange and the cationic amine group of an adjacent molecule. Compounds with greater amine charge-area and electron-donating substituents that allowed for greater electron density at the center of the aromatic ring showed a greater potential for cation−π interactions on montmorillonite surfaces. However benzylamine sorption to nine soils at charge loadings comparable to the experiments with montmorillonite revealed no significant cooperative interactions. It appears that cation−π interactions may be likely in soils with exceptionally high cation exchange capacities (>0.7 mol charge-kg) and low organic matter contents abundant in montmorillonite and other expanding clay minerals.

Steven T. J. Droge *†‡ and Kai-Uwe Goss †§.