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Co-adsorption of Ga(III) and EDTA at the water/goethite interface: spectroscopic evidence for the formation of ternary surface complexes
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 39, 16547-16555 p.Article in journal (Other academic) Published
Abstract [en]

Co-adsorption reactions between metal ions and anionic ligands play important roles in controlling availability and transport of chemical species in natural aquatic environments as well as in industrial processes. A molecular understanding of the properties of the surface species formed provides means to model these reactions in a predictive manner and to exploit them in synthetic routes of modified surfaces. In this study, we have used EXAFS and infrared spectroscopies in combination with quantitative adsorption measurements to investigate the coadsorption of Ga(III) and EDTA on α-FeOOH (goethite) as a function of pH. The quantitative results showed a 1:1 stoichiometry between adsorbed Ga(III) and EDTA and a maximum in total adsorption around pH 5. EXAFS and infrared data showed that the molecular structures displayed pH-dependent characteristics, and within the studied pH range, these results were concurrent and indicated that Ga(III)EDTA formed ternary surface complexes on goethite. The collective results were fully consistent with the occurrence of both outer sphere Ga(III)EDTA and inner sphere ternary surface complexes of type A (i.e., a surface−Ga(III)−EDTA structure), where the latter was favored by increasing pH. This study showed that despite a macroscopic adsorption behavior that was seemingly ligand-like, a substantial fraction of Ga(III) may bond directly to surface hydroxyl groups.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2010. Vol. 114, no 39, 16547-16555 p.
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-2523DOI: 10.1021/jp1054233ISI: 000282209800062OAI: diva2:140691
Available from: 2007-09-06 Created: 2007-09-06 Last updated: 2012-10-02Bibliographically approved
In thesis
1. Coordination Chemistry of Monocarboxylate and Aminocarboxylate Complexes at the Water/Goethite Interface
Open this publication in new window or tab >>Coordination Chemistry of Monocarboxylate and Aminocarboxylate Complexes at the Water/Goethite Interface
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is a summary of five papers with focus on adsorption processes of various monocarboxylates and aminocarboxylates at the water/goethite interface. Interaction of organic acids at the water/mineral interfaces are of importance in biogeochemical processes, since such processes have potential to alter mobility and bioavailability of the acids and metal ions.

In order to determine the coordination chemistry of acetate, benzoate, cyclohexanecarboxylate, sarcosine, MIDA (methyliminediacetic acid), EDDA (ethylenediamine-N,N’-diacetic acid) and EDTA (ethylenediamine-N,N’-tetraacetic acid) upon adsorption to the goethite (alpha-FeOOH) surface, a combination of quantitative measurements with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was utilized.

Over the pH range studied here (pH 3- 9) all ligands, except for sarcosine, have been found to form surface complexes with goethite. In general, theses were characterized as outer sphere surface complexes i.e. with no direct interaction with surface Fe(III) metal ions. Furthermore, two types of different outer-sphere complexes were identified, the solvent-surface hydration-separated ion pair, and hydration-shared ion pair. For the monocarboxylate surface complexes distinction between these two could be made. At high pH values the solvent-surface hydration-separated ion pair was the predominating complex, while at low pH the surface complex is stabilized through the formation of strong hydrogen bonds with the goethite surface. However, it was not possible to clearly separate between the two outer-sphere complexes for coordination of the aminocarboxylates with the surface of goethite. Additionally, EDDA also formed an inner-sphere surface complex at high pH values. The EDDA molecule was suggested to coordinate to the surface by forming a five membered ring with an iron at the goethite surface, through the amine and carboxylate groups.

Contrary to the other ligands studied, EDTA significantly induced dissolution of goethite. Some of the dissolved iron, in the form of the highly stable FeEDTA- solution complex, was indicated to re-adsorb to the mineral surface as a ternary complex. Similar ternary surface complexes were also found in the Ga(III)EDTA/goethite system, and quantitative and spectroscopic studies on adsorption of Ga(III) in presence and absence of EDTA showed that EDTA considerably effects speciation of gallium at goethite surface.

The collective results in this thesis show that the affinity of these ligands for the surface of goethite is primarily governed by their chemical composition and structure, and especially important are the types, numbers and relative position of functional groups within the molecular structure.

Place, publisher, year, edition, pages
Umeå: Kemi, 2007. 52 p.
Acetate, benzoate, adsorption, surface complex, ternary surface complexes, ATR-FTIR spectroscopy, EXAFS spectroscopy., cyclohexanecarboxylate, sarcosine, MIDA, EDDA, EDTA, gallium(III), goethite, mineral surface
National Category
Other Basic Medicine
urn:nbn:se:umu:diva-1337 (URN)978-91-7264-320-8 (ISBN)
Public defence
2007-09-28, KB3A9, KBC, Umeå Universitet, Umeå, 13:00
Available from: 2007-09-06 Created: 2007-09-06 Last updated: 2012-06-29Bibliographically approved

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