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Nonlinearity of Cationic Aromatic Amine Sorption to Aluminosilicates and Soils: Role of Intermolecular Cation−π Interactions

Environmental Science & Technology2013Vol. 47(24), pp. 14119–14127

Citations Over TimeTop 13% of 2013 papers

Dharni Vasudevan, Teresa A. Arey, Daniel R. Dickstein, Mark H. Newman, Tina Zhang, Hadrian M. Kinnear, Mohammad M. Bader

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.

Citations Over TimeTop 13% of 2013 papers

Abstract

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