Oxalic Acid Adsorption on Rutile

Experiments and Surface Complexation Modeling to 150 °c

Michael L Machesky, Moira K. Ridley, Denys Biriukov, Ondřej Kroutil, Milan Předota

Research output: Contribution to journalArticle

Abstract

Here, we characterize oxalate adsorption by rutile in NaCl media (0.03 and 0.30 m) and between pH 3 and 10 over a wide temperature range which includes the near hydrothermal regime (10-150 °C). Oxalate adsorption increases with decreasing pH (as is typical for anion binding by metal oxides), but systematic trends with respect to ionic strength or temperature are absent. Surface complexation modeling (SCM) following the CD-MUSIC formalism, and as constrained by molecular modeling simulations and IR spectroscopic results from the literature, is used to interpret the adsorption data. The molecular modeling simulations, which include molecular dynamics simulations supported by free-energy and ab initio calculations, reveal that oxalate binding is outer-sphere, albeit via strong hydrogen bonds. Conversely, previous IR spectroscopic results conclude that various types of inner-sphere complexes often predominate. SCMs constrained by both the molecular modeling results and the IR spectroscopic data were developed, and both fit the adsorption data equally well. We conjecture that the discrepancy between the molecular simulation and IR spectroscopic results is due to the nature of the rutile surfaces investigated, that is, the perfect (110) crystal faces for the molecular simulations and various rutile powders for the IR spectroscopy studies. Although the (110) surface plane is most often dominant for rutile powders, a variety of steps, kinks, and other types of surface defects are also invariably present. Hence, we speculate that surface defect sites may be primarily responsible for inner-sphere oxalate adsorption, although further study is necessary to prove or disprove this hypothesis.

Original languageEnglish (US)
Pages (from-to)7631-7640
Number of pages10
JournalLangmuir
Volume35
Issue number24
DOIs
StatePublished - Jun 18 2019

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Oxalic Acid
oxalic acid
Oxalic acid
Complexation
rutile
Oxalates
oxalates
Molecular modeling
Adsorption
adsorption
Surface defects
surface defects
simulation
Experiments
Powders
Ionic strength
Oxides
Free energy
Anions
metal oxides

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

Cite this

Oxalic Acid Adsorption on Rutile : Experiments and Surface Complexation Modeling to 150 °c. / Machesky, Michael L; Ridley, Moira K.; Biriukov, Denys; Kroutil, Ondřej; Předota, Milan.

In: Langmuir, Vol. 35, No. 24, 18.06.2019, p. 7631-7640.

Research output: Contribution to journalArticle

Machesky, Michael L ; Ridley, Moira K. ; Biriukov, Denys ; Kroutil, Ondřej ; Předota, Milan. / Oxalic Acid Adsorption on Rutile : Experiments and Surface Complexation Modeling to 150 °c. In: Langmuir. 2019 ; Vol. 35, No. 24. pp. 7631-7640.
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