Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 47, Issue 24, Pages 14119-14127Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es403389a
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Funding
- NSF ADVANCE-PAID [0620101, 0620087]
- Fletcher Family Fund (Bowdoin College)
- Clare Boothe Luce Foundation
- Coles, Freedman, Hughes Family
- Division Of Human Resource Development
- Direct For Education and Human Resources [0620101, 0620087] Funding Source: National Science Foundation
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Through the study of substituted anilines and benzylamines, we demonstrated that cooperative cation-pi, pi-pi, 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-pi interactions, which occurred between the pi 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-pi 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-pi 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.
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