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Coordination Chemistry of Monocarboxylate and Aminocarboxylate Complexes at the Water/Goethite Interface
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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.
Keyword [en]
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
Identifiers
URN: urn:nbn:se:umu:diva-1337ISBN: 978-91-7264-320-8 (print)OAI: oai:DiVA.org:umu-1337DiVA: diva2:140692
Public defence
2007-09-28, KB3A9, KBC, Umeå Universitet, Umeå, 13:00
Opponent
Supervisors
Available from: 2007-09-06 Created: 2007-09-06 Last updated: 2017-05-26Bibliographically approved
List of papers
1. Adsorption of monocarboxylates at the water/goethite interface: The importance of hydrogen bonding
Open this publication in new window or tab >>Adsorption of monocarboxylates at the water/goethite interface: The importance of hydrogen bonding
2007 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 71, no 23, 5717-5730 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption of monocarboxylates (acetate, benzoate and cyclohexanecarboxylate) at the water/goethite interface was studied as a function of pH and ionic strength by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra were obtained of suspensions prepared in both H2O and D2O. In order to identify the number of predominating surface complexes and to improve the resolution of overlapping peaks the ATR-FTIR spectra were subjected to a 2D correlation spectroscopic analysis. The adsorption envelopes of acetate, benzoate and cyclohexanecarboxylate are similar and depend strongly on pH and ionic strength, but the pH dependence is also correlated to the slightly different pKa values of the monocarboxylic acids. At the molecular level, the ATR-FTIR spectroscopic results reveal two surface complexes: one solvent-surface hydration-separated ion pair and one surface hydration-shared ion pair. The former predominates at circumneutral pH values while the latter forms mainly in the acidic pH range. We find no evidence for direct inner-sphere coordination between the carboxylic oxygens and the Fe(III) ions present at the surface. The identification of surface hydration-shared ion pairs emphasizes the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes at the water/goethite interface.

Place, publisher, year, edition, pages
Elsevier, 2007
Keyword
adsorption, surface complexation, acetate, benzoate, cyclohexanecarboxlate
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-16376 (URN)10.1016/j.gca.2007.04.037 (DOI)
Available from: 2008-01-08 Created: 2008-01-08 Last updated: 2017-12-14Bibliographically approved
2. Adsorption of alpha amino acids at the water/goethite interface
Open this publication in new window or tab >>Adsorption of alpha amino acids at the water/goethite interface
2008 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 319, no 2, 416-428 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption of amino acids onto mineral surfaces plays an important role in a wide range of areas, e.g., low-temperature aqueous geochemistry, bone formation and protein-bone interactions. In this work, the adsorption of three alpha aminoacids (sarcosine, MIDA and EDDA) onto goethite (α-FeOOH) was studied as a function of pH and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of ATR-FTIR spectroscopy. The results showed that adsorption of alpha amino acids were strongly dependent on the functionality and structure of the ligands. No adsorption was detected for the zwitterionic sarcosine indicating that simple alpha amino acids without other ionizable and/or functional groups display insignificant affinity for mineral surfaces such as goethite. With respect to the more complex amino acids, which are surface reactive, the number and relative positions of carboxylate and amine groups determine the types of surface interactions. These interactions range from non-specific outer-sphere to specific inner-sphere interactions as shown by the MIDA and EDDA results, respectively. The results presented herein suggest that isomerically-selective adsorption might only occur for amino acids that are capable of specific surface interactions, either through site-specific hydrogen bonding or inner-sphere complexation.

Place, publisher, year, edition, pages
San Diego: Academic Press, 2008
Keyword
Adsorption, Amino acids, water/mineral interface, Goethite, ATR-FTIR spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-6920 (URN)10.1016/j.jcis.2007.11.046 (DOI)000253259100005 ()18155715 (PubMedID)
Available from: 2008-01-31 Created: 2008-01-31 Last updated: 2017-05-26Bibliographically approved
3. ATR-FTIR Spectroscopic Characterization of EDTA at the Water/Goethite Interface: Implications for Dissolution
Open this publication in new window or tab >>ATR-FTIR Spectroscopic Characterization of EDTA at the Water/Goethite Interface: Implications for Dissolution
In: Langmuir, ISSN 0743-7463Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-2521 (URN)
Available from: 2007-09-06 Created: 2007-09-06Bibliographically approved
4. Quantitative adsorption and local structures of gallium(III) at the water-alpha-FeOOH interface
Open this publication in new window or tab >>Quantitative adsorption and local structures of gallium(III) at the water-alpha-FeOOH interface
2006 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 5, 2096-2104 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption of Ga(III) at the water−α-FeOOH (goethite) interface has been investigated by means of quantitative adsorption experiments, extended X-ray absorption fine structure (EXAFS) spectroscopy, and surface complexation modeling. Under the conditions studied, pH range 3−11 and surface coverages of 0.9−3.2 μmol/m2, Ga(III) was found to adsorb strongly to α-FeOOH, and the surface species were more resistant toward hydrolysis and formation of soluble Ga(OH)4- than either solid gallium hydroxides or soluble polynuclear complexes. The EXAFS measurements revealed the presence of octahedral Ga(III) complexes at the water−α-FeOOH interface, with practically no structural variations as a function of pH or total gallium concentration. Analysis of the first coordination shell required an anharmonic model indicating a distorted geometry of the GaO6 octahedra, with mean Ga−O distances at 1.96−1.98 Å. A method based on the continuous Cauchy wavelet transforms (CCWT) was used to identify backscattering atoms in the higher coordination shells. This analysis indicated predominately Fe backscattering, and the quantitative data fitting resulted in three Ga−Fe paths at 3.05, 3.2, and 3.55 Å, which correspond to two edge-sharing and one corner-sharing linkage, respectively. The collective results from EXAFS spectroscopy showed that Ga(III) adsorbs to Fe equivalent sites at the surface α-FeOOH as an extension of the rows of Fe octahedra in the bulk structure. This interpretation was further corroborated by a Ga−Fe−Fe multiple scattering path at 6.13 Å. The quantitative adsorption and proton data were modeled using a surface complexation formalism based on a 1 pKa constant capacitance model. In agreement with the EXAFS results, the model obtained included one predominating surface complex with the stoichiometry FeOGa(OH)2-0.5 and the stability constant log β(intr.) = −2.55 ± 0.04 (FeOH-0.5 + Ga3+ + 2H2O ↔ FeOGa(OH)2-0.5 + 3H+).

Place, publisher, year, edition, pages
Washington: American Chemical Society, 2006
Identifiers
urn:nbn:se:umu:diva-2522 (URN)10.1021/la052555j (DOI)
Available from: 2007-09-06 Created: 2007-09-06 Last updated: 2011-03-17Bibliographically approved
5. Co-adsorption of Ga(III) and EDTA at the water/goethite interface: spectroscopic evidence for the formation of ternary surface complexes
Open this publication in new window or tab >>Co-adsorption of Ga(III) and EDTA at the water/goethite interface: spectroscopic evidence for the formation of ternary surface complexes
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
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-2523 (URN)10.1021/jp1054233 (DOI)000282209800062 ()
Available from: 2007-09-06 Created: 2007-09-06 Last updated: 2012-10-02Bibliographically approved

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