Sorption of organic compounds to activated carbons. Evaluation of isotherm models

I. Pikaar, A.A. Koelmans, P.C.M. van Noort

Research output: Contribution to journalArticleAcademicpeer-review

56 Citations (Scopus)


Sorption to 'hard carbon' (black carbon, coal, kerogen) in soils and sediments is of major importance for risk assessment of organic pollutants. We argue that activated carbon (AC) may be considered a model sorbent for hard carbon. Here, we evaluate six sorption models on a literature dataset for sorption of 12 compounds onto 12 ACs and one charcoal, at different temperatures (79 isotherms in total). A statistical analysis, accounting for differences in the number of fitting parameters, demonstrates that the dual Langmuir equation is in general superior and/or preferable to the single and triple Langmuir equation, the Freundlich equation, a Polanyi-Dubinin-Manes equation, and the Toth equation. Consequently, the analysis suggests the presence of two types of adsorption sites: a high-energy (HE) type of site and a low-energy (LE) type of site. Maximum adsorption capacities for the HE domain decreased with temperature while those for the LE domain increased. Average Gibbs free energies for adsorption from the hypothetical pure liquid state at 298 K were fairly constant at -15 ± 4 and -5 ± 4 kJ mol-1 for the HE and LE domain, respectively
Original languageEnglish
Pages (from-to)2343-2351
Issue number11
Publication statusPublished - 2006


  • soot-like materials
  • maximum adsorption capacities
  • slowly desorbing domains
  • black carbon
  • sediments
  • soils
  • equilibria
  • charcoal
  • toluene
  • pahs

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