umu.sePublications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Charge Development at Iron Oxyhydroxide Surfaces: The Interplay between Surface Structure, Particle Morphology and Counterion Identity
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Iron (oxyhydr)oxide (FeOOH) minerals play important roles in various natural, technological and societal settings. The widespread abundance of these minerals has prompted numerous studies on their surface reactivity in aqueous media. Surface charge development, one that namely takes place through the adsorption of potential determining ions (p.d.i.; H+, OH-) and coadsorption of counterions (e.g. Cl-, ClO4-, Na+), is particularly interesting in this regard. Mineral surface charge development is determined by numerous factors related to the interplay of mineral surface structure, particle morphology and counterion identity.

In this thesis the interplay between these factors is resolved by monitoring charge development on submicron-sized synthetic iron oxyhydroxide particles of different structures and sizes in aqueous media with counteranions of contrasting charge-to-size ratio (i.e. NaCl, NaClO4). This work, which is summarized in an introductory chapter and detailed in five appendices, is focused on three types of synthetic lepidocrocite (ã- FeOOH) of different shapes and surface roughness, three types of goethite (á-FeOOH) of different levels of surface roughness, and finally akaganéite (â-FeOOH), a mineral representing unique ion exchange properties due to its hollandite-type structure. While charge development was chiefly monitored by high precisition potentiometric titrations, these efforts were supported by a range of techniques including electrolyte ion uptake by cryogenic X-ray photoelectron spectroscopy, particle imaging by (high resolution) transmission electron microscopy, porosity analysis by N2 adsorption/desorption, surface potential development by electrokinetics, as well as thermodynamic adsorption modeling.

These efforts showed that lepidocrocite particles of contrasting morphology and surface roughness acquired highly comparable pH and ionic strength p.d.i. loadings. Equilibriation times required to develop these loadings were however altered when particles became aggregated by aging.

Goethite particles of contrasting surface roughness also acquired incongruent p.d.i. loadings, which were predominantly explained by the different charge-neutralizing capabilities of these surfaces, some of which were related to pore size distributions controlling the entrance of ions of contrasting sizes. Such size exclusion effects were also noted for the case of akaganéite where its bulk 0.4×0.4 nm wide channels permitted chloride diffusion but blocked perchlorate. Charge development at goethite surfaces in binary mixtures of NaCl and NaClO4 solutions also showed that the larger size-to-charge ratio chloride ion exerted a strong effect on these results even when present as a minor species. Many of these aforementioned effects were also modeled using variable, counterion- and loading-specific, Stern layer capacitance values.

The findings summarized in this thesis are providing a better understanding of surface processes occurring at iron oxyhydroxide surfaces. They should impact our ability in designing uses of such particles, for example, effective sorption in aquatic media, as well as to understand how they behave in natural systems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2014. , 90 p.
Keyword [en]
Iron oxyhydroxides, adsorption, mineral-water interface, electrolyte, surface roughness, pores
National Category
Inorganic Chemistry Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-85195ISBN: 978-91-7459-797-4 (print)OAI: oai:DiVA.org:umu-85195DiVA: diva2:692059
Public defence
2014-02-20, KBC-huset, KB3B1, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2014-01-30 Created: 2014-01-29 Last updated: 2014-01-30Bibliographically approved
List of papers
1. Electrolyte Ion Binding at Iron Oxyhydroxide Mineral Surfaces
Open this publication in new window or tab >>Electrolyte Ion Binding at Iron Oxyhydroxide Mineral Surfaces
2013 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 39, 12129-12137 p.Article in journal (Refereed) Published
Abstract [en]

Electrolyte ion loadings at the surfaces of synthetic goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) particles that were pre-equilibrated in aqueous solutions of 10 mM NaCl and NaClO4 at 25 °C were investigated by cryogenic X-ray photoelectron spectroscopy (XPS). Atomic concentrations of Cl(-), ClO4(-), and Na(+) were correlated to potential determining ion (pdi; H(+), OH(-)) loadings obtained by potentiometric titrations. While Cl(-) promoted more pdi adsorption than ClO4(-), due to its greater charge-to-size ratio, both ions followed the same loading dependence on pdi adsorption, in contrast to previous studies supporting the concept for negligible perchlorate adorption. Lepidocrocite particles exhibited a stronger response of electrolyte adsorption to pdi loadings due electrolyte ion adsorption on the proton inactive (010) plane. These particles also acquired greater sodium loadings than goethite. These loadings were moreover considerably enhanced by perchlorate adsorption, possibly due to a thickening of the interfacial region in NaClO4 on the (010) plane. Finally, goethite particles with rougher surfaces acquired greater pdi and ion loadings than on those with smoother surfaces. No strong differences could be discerned between Cl(-) and ClO4(-) loadings on these materials. This work thus identified key aspects underpinning the relationship between pdi and electrolyte loadings at FeOOH mineral surfaces of environmental and technological importance.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-80782 (URN)10.1021/la401318t (DOI)24050677 (PubMedID)
Funder
Swedish Research Council, VR 2012-2976
Available from: 2013-09-25 Created: 2013-09-25 Last updated: 2017-12-06Bibliographically approved
2. Particle Morphological and Roughness Controls on Mineral Surface Charge Development
Open this publication in new window or tab >>Particle Morphological and Roughness Controls on Mineral Surface Charge Development
2014 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 141, no 15 September, 567-578 p.Article in journal (Other academic) Published
Abstract [en]

Effects of mineral particle morphology and roughness on potential determining ion (p.d.i.; H+, OH) loadings achieved at synthetic lepidocrocite (γ-FeOOH) surfaces were predominantly investigated by potentiometry and thermodynamic modeling. Nanosized rod- (RL) and lath-shaped (LL) particles exhibiting different proportions of the same predominant crystallographic faces acquired largely comparable pH, ionic strength and counterion (NaCl, NaClO4) dependencies on p.d.i. loadings. These results supported previous claims that faces ideally containing proton silent sites only, are likely populated by additional proton active sites. This concept was supported further by results of roughened LL-like particles (LLR) also showing highly congruent pH-, ionic strength- and composition-dependent p.d.i. loadings with those of LL and RL. These loadings thereby correspond to maximal levels allowed by net attractive and repulsive forces at each solution composition, irrespective of particle morphology. Contrasting equilibration times required to achieve these loadings revealed considerably slower exchange of p.d.i. and electrolyte ions near the point of zero charge in the rough LLR than in the more idealized LL and RL particles.

Thermodynamic modeling was used to test various concepts accounting for these results. The model made use of a novel framework capable of isolating electrostatic contributions from different faces, and of accounting for ion-specific double-layer properties within a single crystallographic face. These efforts made use of capacitance values for each electrolyte ions within the framework of a recently developed Variable Capacitance Model. Attempts at modeling all three particle types were used to suggest that the (0 1 0) face contains ∼0.9 site nm−2 of proton active sites, a value notably constrained by recently published Na+, Cl, and ClO4 loadings derived by cryogenic X-ray photoelectron spectroscopy. The model presented in this work thus provides a means to predict p.d.i. loadings on multifaceted mineral particle surfaces, and can therefore be used to constrain further our understanding of mineral/water interface reactivity.

Place, publisher, year, edition, pages
Elsevier, 2014
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-85193 (URN)10.1016/j.gca.2014.06.016 (DOI)000341926100034 ()
Funder
Swedish Research Council, VR 2012-2976
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
3. Oriented Aggregation of Lepidocrocite and Its Impact on Surface Charge Development
Open this publication in new window or tab >>Oriented Aggregation of Lepidocrocite and Its Impact on Surface Charge Development
(English)Manuscript (preprint) (Other academic)
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-85194 (URN)
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2014-01-29Bibliographically approved
4. Mineral surface charge development in mixed electrolyte solutions
Open this publication in new window or tab >>Mineral surface charge development in mixed electrolyte solutions
2014 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 418, 246-253 p.Article in journal (Refereed) Published
Abstract [en]

Abstract Effects of competing counterions with different charge-to-size ratios on potential-determining ion (pdi; H+, OH−) adsorption at mineral/water interfaces were resolved in mixtures of aqueous solutions of NaCl and NaClO4 solutions. These effects were monitored on two synthetic goethite (α-FeOOH) particle preparations with distinct charge uptake capacities arising from differences in surface roughness. Charge development at these mineral surfaces was chiefly explored by high precision potentiometric titrations at 25 °C. These measurements confirmed that the greater charge-to-size ratio chloride ion not only promoted greater surface charge, but also had pronounced effects in perchlorate-dominated solutions. Cryogenic X-ray photoelectron spectroscopic measurements confirmed that perchlorate retains significant loadings at the goethite surface, even in the presence of chloride. Molecular dynamics simulations of the (1 1 0) plane of goethite exposed to these mixed solutions showed that chloride compressed the interfacial region containing electrolyte ions. Perchlorate, on the other hand, is not only present over a thicker region of the interface but also promotes an additional outer-sphere sodium species. These findings were used to develop a thermodynamic adsorption model predicting charge development at these mineral surfaces. The model involves a new formulation accounting for coexisting ion-specific regions each with their distinct compact plane capacitance values. The model can predict charge development in any mixtures of NaCl and NaClO4 contacted with goethite particles of contrasting charge uptake capacities without any additional parameters. This model can also be applied to a broader range of material surfaces.

Keyword
Electrolyte, Adsorption, Surface, Charge, Iron (oxy)hydroxides
National Category
Inorganic Chemistry Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-85191 (URN)10.1016/j.jcis.2013.11.056 (DOI)000330748700032 ()
Available from: 2014-01-29 Created: 2014-01-29 Last updated: 2017-12-06Bibliographically approved
5. Proton Binding and Ion Exchange at the Akaganéite/Water Interface
Open this publication in new window or tab >>Proton Binding and Ion Exchange at the Akaganéite/Water Interface
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 12, 6409-6419 p.Article in journal (Refereed) Published
Abstract [en]

Proton exchange in nanosized synthetic akaganéite particles suspended in aqueous media and in ionic strengths of 3–100 mM NaCl and NaClO4 was monitored by high precision potentiometry at 25 °C. Proton budgets in the pH 3–10 range pertain to simultaneously occurring surface complexation and bulk ionic exchange reactions. Surface complexation reactions involve proton binding to (hydr)oxo groups of the dominant crystallographic planes of the particles. These are responsible for the colloidal attributes of the akaganéite particles, as confirmed by electrophoretic mobility measurements. Bulk ionic exchange involves the codiffusion of protons and chloride ions through the tunnel structure of the hollandite-type akaganéite bulk. Chloride ions migrate to bulk complexation sites that are ideally defined by eight surrounding hydroxyl groups, ≡(OH)8. Protons are in turn considered to be bound to neighboring oxo groups, ≡O. Collectively, the complexes are referred as [≡(OH)8···Cl······HO≡]. A thermodynamic model accounting for these two processes was developed to predict the pH (3–9), ionic strength (3–100 mM), and ionic medium (NaCl, NaClO4) dependence of the potentiometric data. This model is supported by new zeta potential data pointing to an isoelectric point of 9.6–10.3 for pristine akaganéite particles and by Fourier transform infrared spectra showing the impact of pH and ionic medium on bulk proton-chloride loadings. Our proposed stoichiometry for a chloride-rich solid of β-FeOOH·(HCl)0.192 corresponds to a maximal occupancy of 75% for chloride ions in the [≡(OH)8···Cl······HO≡] bulk complexation sites. Samples equilibrated in pure aqueous solutions should have a composition of β-FeOOH·(HCl)0.151, corresponding to a 60% occupancy for chloride ions due to a partial exchange of HCl. Our model can be used to predict compositional changes in the akaganéite bulk and surfaces upon any variations in pH and ionic media considered in this work.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-68054 (URN)10.1021/jp3101046 (DOI)
Available from: 2013-04-11 Created: 2013-04-11 Last updated: 2017-12-06Bibliographically approved

Open Access in DiVA

Charge Development at Iron Oxyhydroxide Surfaces(26331 kB)830 downloads
File information
File name FULLTEXT01.pdfFile size 26331 kBChecksum SHA-512
7029929a0de381d62edae0cb734d2536119f3ba6e86881bc5a973bfd761790cc2185ddff0ba75df3de7de07ff095d8ed1b86e8e55ea566b8f9c6eb59577ced8c
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Kozin, Philipp A.
By organisation
Department of Chemistry
Inorganic ChemistryPhysical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 830 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 892 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf