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Nanoscale hydration in layered manganese oxides
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-8615-3029
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0003-3927-6197
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-0118-8207
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2021 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, no 2, p. 666-674Article in journal (Refereed) Published
Abstract [en]

Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021. Vol. 37, no 2, p. 666-674
National Category
Geochemistry
Identifiers
URN: urn:nbn:se:umu:diva-174005DOI: 10.1021/acs.langmuir.0c02592ISI: 000612351800008PubMedID: 33404244Scopus ID: 2-s2.0-85100125350OAI: oai:DiVA.org:umu-174005DiVA, id: diva2:1457778
Note

Originally included in thesis in manuscript form.

Available from: 2020-08-12 Created: 2020-08-12 Last updated: 2023-09-05Bibliographically approved
In thesis
1. Molecular-level controls on water and organics intercalation in layered minerals
Open this publication in new window or tab >>Molecular-level controls on water and organics intercalation in layered minerals
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Layered minerals are naturally abundant and often display a large surface area in relation to their weight. For swelling layered minerals, most of this area is contained between the layers in the interlayer space. Their large surface area makes them interesting in many different fields and applications, such as adsorbents, catalysts or as carriers for other particles that can be intercalated and exchanged. In order for the materials to be used effectively, it is hence necessary to have a fundamental understanding of how these processes occur, and ways to predict them.

To address adsorption of water, an isotherm model was created to describe the hydration process on layered materials. The model decomposed the process of adsorptions into internal and external, adsorption and condensation, and could specifically handle hydration in the expanding interlayer nanopores. Adsorption and desorption isotherms of two different materials, Montmorillonite and Birnessite was successfully modelled, where the former was ion-exchanged with the counter-cations Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, Cu2+, whereas the latter contained K+. This indicated that this isotherm model is applicable to also other layered materials. The adsorption process was also characterized experimentally with vibrational spectroscopy (FTIR) and multivariate statistical techniques (MCR), in order to generate spectral- and concentration profiles of the involved components.

In order to also investigate adsorption of different organic molecules, the intercalation of alcohols and a cationic surfactant was investigated in separate studies. Clay-water-alcohol systems of eight alcohols were characterized experimentally by XRD as well as by molecular dynamics simulations, using different combinations of classical force fields for the clay (ClayFF, ClayFFMod, INTERFACE) and for the alcohols (CGenFF, GAFF, OPLS). It was found that the optimal force field combination varied with the fitting approach. A brute force sensitivity analysis indicated that the comparison with the experimental XRD data was more dependent on the relative interlayer loading than the positions of the atoms, an important result for future similar benchmarking studies.

By intercalating and adsorbing a cationic surfactant (CTAB) to Montmorillonite at increasing concentrations, the effects of solvent polarity and the CTAB interlayer content on the Montmorillonite interlayer swelling was investigated. It was found that moderately polar solvents such as DMSO, in combination with CTAB in a planar bilayer configuration resulted in the greatest adsorption of the lipophilic solute alizarin.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2020. p. 49
Keywords
Minerals, Dynamic Vapor Sorption, montmorillonite, XRD, adsorption model, intercalation
National Category
Geochemistry
Identifiers
urn:nbn:se:umu:diva-174006 (URN)978-91-7855-342-6 (ISBN)978-91-7855-341-9 (ISBN)
Public defence
2020-09-08, Glasburen, KBC 3.05.081, Umeå, 10:00 (English)
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Supervisors
Available from: 2020-08-18 Created: 2020-08-13 Last updated: 2020-08-14Bibliographically approved

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Lindholm, JerryHolmboe, MichaelLuong, N. TanShchukarev, AndreyBoily, Jean-Francois

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