ABSTRACT: We recently proposed that weak acids (AH) adsorb to partially-oxidized carbonaceous materials in part by forming very strong hydrogen bonds with acidic surface groups, depicted by (A×××H×××O−surf)^- and known as negative charge-assisted hydrogen bonds, (-)CAHBs. Here we use competition experiments supplemented by other types of experiments to show that sorption of AH on carbon nanotubes (CNTs) can be described conceptually by a dual specific/non-specific domain model, where one domain involves (-)CAHB sites that can become saturated. The CNTs included carboxyl-enriched (C-CNT), hydroxyl-enriched (H-CNT) or graphitized (G-CNT). 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. It was shown that 3,4-dinitrophenolate formed (-)CAHB more efficiently than 2,6-dichloro-4-nitrophenolate due to 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, 3,4-dinitrophenolate ion and nitrobenzene molecule, for p-p electron donor-acceptor sites. The findings will contribute to a better understanding of adsorption mechanism of ionizable compounds on carbonaceous materials in both single- and multi-solute systems.