Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 49, Issue 3, Pages 1409-1417Publisher
AMER CHEMICAL SOC
DOI: 10.1021/es504019u
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Funding
- National Science Foundation (NSF) [CBET 1235459]
- U.S. Department of Agriculture National Institute of Food and Agriculture (USDA NIFA) [MAS00475]
- Junta de Andalucia [P07-AGR-03077]
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1235459] Funding Source: National Science Foundation
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We recently proposed that weak acids (AH) adsorb to partially oxidized carbonaceous materials in part by forming strong hydrogen bonds with acidic surface groups, depicted by (A...H....O-surf) (-) , known as negative charge-assisted hydrogen bonds, (-)CAHBs. Here we use competition experiments to show that sorption of AH on carbon nanotubes (CNTs) can be described conceptually by a dual specific/nonspecific domain model, where one domain involves (-)CAHB sites that can become saturated. The trends observed in single-solute adsorption, including the stoichiometric release of hydroxide upon sorption of carboxyate or phenolate anions, were consistent with trends in the previous studies and pointed to the formation of (-)CAHB. 3,4-Dinitrophenolate formed (-)CAHBs more efficiently than did 2,6-dichloro-4-nitrophenolate because of alleviation of steric hindrance to approach by the ortho chlorines. Competition against a (-)CAHB-capable target compound was greater when the competitor was also (-)CAHB-capable than when it was not (e.g., benzoate as target vs 3,4-dinitrophenolate or nitrobenzene as competitor; mono-n-butyl phthalate as target vs methyl benzoate or p-tolyl acetate as competitor). Experiments also revealed competition between the nitroaromatic species for pi-pi electron donor-acceptor sites. The findings will contribute to a better understanding of the adsorption mechanism of ionizable compounds on carbonaceous materials.
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