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Competitive sorption used to probe strong hydrogen bonding sites for weak organic acids on carbon nanotubes

AutorLi, Xiaoyun; Gámiz, B. ; Wang, Yiquan; Pignatello, Joseph J.; Xing, Baoshan
Palabras claveAdsorption
Aromatic compounds
Carbon nanotubes
Organic carbon
Adsorption mechanism
Carbonaceous materials
Competitive sorption
Electron donor acceptors
Hydrogen bonding sites
Ionizable compounds
Single-solute adsorption
Weak organic acids
Fecha de publicación6-ene-2015
EditorAmerican Chemical Society
CitaciónEnvironmental Science and Technology - Columbus 49(3): 1409-1417 (2015)
ResumenWe 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 π-π electron donor-acceptor sites. The findings will contribute to a better understanding of the adsorption mechanism of ionizable compounds on carbonaceous materials.
Descripción9 páginas.-- 3 figuras.-- 31 referencias.-- Supporting Information: characteristics of the three multiwalled CNTs; selected physicochemical properties of sorbates; Freundlich model fits to sorption and competitive sorption data of monaromatics by CNTs; adsorption kinetics of BA, DNP, and NB onto C−CNT at pH 7 and adsorption kinetics of MBPh, MBA, and PTA onto C−CNT at pH 6; comparison of sorption isotherms of a given adsobate on hydroxylated (H−), carboxylated (C−), and graphitized (G−)CNTs at pH 7.0; zeta potential measurements for the three CNTs; pH records of the NB adsorption on CNTs at initial pH 7.0; titration curves of the three CNTs from pH 3−12; consumption of OH− as a function of pH for the three CNTs from the titration curves; sorbed concentration of NB on three CNTs as function of sorbed competitor concentration at pH 7.0 and displacement efficiency (DE %) of BA or DNP as function of sorbed competitor concentration; sorbed concentration of MBPh on C−CNT as function of amount sorbed of competitors, MBA and PTA at pH 4 and pH 6 at fixed initial concentration of MBPh of 0.2 Mm; and solution pH change versus moles BA−/DNP− adsorbed for (A, C, E) H−CNT and (B, D, F) C−CNT without or with cosolute. This material is available free of charge via the Internet at http://pubs.acs.org
Versión del editorhttp://dx.doi.org/10.1021/es504019u
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