Factors influencing inapplicability of cosolvency-induced model on organic acid sorption onto humic substance from methanol mixture

Minhee Kim, Juhee Kim, Jeong Gyu Kim, Seunghun Hyun

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Applicability of cosolvency model for describing the sorption of organic acids to humic substance was investigated by analyzing dataset of sorption (Km) and solubility (Sm) 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 pHappCME (apparent pH of liquid phase) and fc (methanol volume fractions). For all solutes, the Km decreased with fc with the Km reduction being less than the Sm-based prediction. The slope of log Km-fc 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 Ca2+ bridge between carboxylate and negatively charged humic surface may explain this phenomenon. Normalizing the Km to the corresponding Sm (α′ = Km/Sm) was not in unity over the pHapp-fc range but decreased with fc, 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 pHapp <pKa − 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 Ca2+ bridge and same-charge repulsion) is considered a relevant process that possibly restricts the applicability of the cosolvency model.

Original languageEnglish
Pages (from-to)15745-15754
Number of pages10
JournalEnvironmental Science and Pollution Research
Volume22
Issue number20
DOIs
Publication statusPublished - 2015 Oct 1

Keywords

  • Cosolvency
  • Humic substance
  • Hydrophobic organic acid
  • Sorption

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Health, Toxicology and Mutagenesis

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