title: Competitive sorption used to probe strong hydrogen bonding sites for weak organic acids on carbon nanotubes.
abstract: 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 π-π electron donor-acceptor sites. The findings will contribute to a better understanding of the adsorption mechanism of ionizable compounds on carbonaceous materials.
authors.affiliation: College of Resources and Environment, Northwest A&F University , Yangling, Shaanxi 712100, China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Li
authors.forename: Beatriz
authors.initials: B
authors.lastname: Gámiz
authors.forename: Yiquan
authors.initials: Y
authors.lastname: Wang
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Pignatello
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D000327:Adsorption; D006860:Hydrogen Bonding; D037742:Nanotubes, Carbon / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry; D010084:Oxidation-Reduction
chemical_list: D037742:Nanotubes, Carbon; D009930:Organic Chemicals