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- Title
Factors influencing inapplicability of cosolvency-induced model on organic acid sorption onto humic substance from methanol mixture.
- Authors
Kim, Minhee; Kim, Juhee; Kim, Jeong-Gyu; Hyun, Seunghun
- Abstract
Applicability of cosolvency model for describing the sorption of organic acids to humic substance was investigated by analyzing dataset of sorption ( K) and solubility ( S) of selected solutes (benzoic acid, 1-naphthoic acid, 2,4-dichlorophenoxyacetic acid, and 2,4,6-trichlorophenol (2,4,6-TCP)) as a function of pH (apparent pH of liquid phase) and f (methanol volume fractions). For all solutes, the K decreased with f with the K reduction being less than the S-based prediction. The slope of log K- f plot in the three organic carboxylic acids was well correlated with their cosolvency power, whereas the data of organic phenolic acid (2,4,6-TCP) was placed above the trend, indicating the different actions of functional groups. The occurrence of Ca bridge between carboxylate and negatively charged humic surface may explain this phenomenon. Normalizing the K to the corresponding S ( α′ = K/ S) was not in unity over the pH- f range but decreased with f, indicating a possible structural modification of sorption domain favoring extra sorption. For a given solute, the α′ of neutral species was always greater than that of anionic species, showing that extra interaction will be likely at pH <p K − 2 when both solute and sorbent are uncharged. In short, the knowledge of cosolvent-enhanced solubility is incapable of describing sorption of organic acids by humic substance in methanol/water mixtures. Modification of humic structure and hydrophilic interaction (such as Ca bridge and same-charge repulsion) is considered a relevant process that possibly restricts the applicability of the cosolvency model.
- Subjects
ORGANIC acids; HUMUS; METHANOL; CARBOXYLIC acids; ANIONIC surfactants
- Publication
Environmental Science & Pollution Research, 2015, Vol 22, Issue 20, p15745
- ISSN
0944-1344
- Publication type
Article
- DOI
10.1007/s11356-015-4742-x