Adsorption of organic molecules on carbon surfaces: Experimental data and molecular dynamics simulation considering multiple protonation states

Robin Wagner, Saientan Bag, Tatjana Trunzer, Paula Fraga-García, Wolfgang Wenzel, Sonja Berensmeier, Matthias Franzreb

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Owing to their high specific surface and low production cost, carbon materials are among the most important adsorption materials. Novel usages, for instance in pharmaceutical applications, challenge existing methods because charged and strongly polar substances need to be adsorbed. Here, we systematically investigate the highly complex adsorption equilibria of organic molecules having multiple protonation states as a function of pH. The adsorption behavior depends on intermolecular interactions within the solution (dissociation equilibria) and between adsorbed molecules on the carbon surface (electrostatic forces). For the model substances maleic acid and phenylalanine, we demonstrate that a custom-made genetic algorithm is able to extract up to nine parameters of a multispecies isotherm from experimental data covering a broad pH-range. The parameters, including adsorption affinities, interaction energies, and maximum loadings were also predicted by molecular dynamics simulations. Both approaches obtained a good qualitative and mostly also quantitative description of the adsorption behavior within a pH-range of 2–12. By combining the determined isotherms with mass balances, the final concentrations and pH-shifts of batch adsorption experiments can be predicted. The developed modeling tools can be easily adapted to other types of pH-dependent, multispecies adsorbates and therefore will help to optimize adsorption-based processes in different fields.

Original languageEnglish
Pages (from-to)424-437
Number of pages14
JournalJournal of Colloid and Interface Science
Volume589
DOIs
StatePublished - May 2021

Keywords

  • Activated carbon
  • Aqueous systems
  • Carbon nanotubes
  • Dissociation states
  • Genetic algorithm
  • Molecular dynamics
  • Moreau isotherm
  • Organic acids
  • Surface interaction
  • pH dependence

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