Interaction of aluminum ions with fused silica/water interfaces in the presence of oxalic acid tracked by second harmonic generation

David S. Jordan, Franz M. Geiger*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Second harmonic generation (SHG) and the χ(3) technique are used to investigate the effect of oxalic acid on the adsorption of aluminum [Al(III)] to the fused silica/water interface. Al(III) adsorption isotherms are measured in the presence and absence of oxalic acid and fit with the Diffuse Layer model to quantify thermodynamic binding parameters. The evolution of charge density throughout the adsorption process is analyzed and used to derive binding mechanisms at the molecular level. It is found that 0.5 mM oxalic acid irreversibly binds to and increases the negative surface charge on the fused silica surface -0.003 C/m2, corresponding to 1.9 × 1012 bound oxalate ions per cm2 under those conditions if oxalate were singly charged at the interface. Oxalic acid decreases the strength of the Al(III) adsorption interaction: the binding constant, Kads, decreases from 60 000 ± 10 000 to 1100 (200) M-1, corresponding to a reduction in the apparent adsorption free energy, ΔGads, from -37.2(4) to -27.3(5) kJ/mol, while surface charge densities at maximum metal coverage, σm, increase from 0.004(2) to 0.014(3) C/m2. Evidence is presented for a change in the dominant charge determining adsorption mechanism that corresponds with a change in Al(III) speciation. These results reveal important information about the surface activity and speciation of Al(III) in the presence of oxalic acid that have direct implications for the mobility, toxicity, and ultimate environmental fate of this metal pollutant.

Original languageEnglish (US)
Pages (from-to)28970-28977
Number of pages8
JournalJournal of Physical Chemistry C
Volume118
Issue number50
DOIs
StatePublished - Dec 18 2014

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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