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MgO nanocube hydroxylation by nanometric water films
Umeå University, Faculty of Science and Technology, Department of Chemistry.ORCID iD: 0000-0002-0118-8207
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: 0000-0003-4954-6461
2023 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 15, no 24, p. 10286-10294Article in journal (Refereed) Published
Abstract [en]

Hydrophilic nanosized minerals exposed to air moisture host thin water films that are key drivers of reactions of interest in nature and technology. Water films can trigger irreversible mineralogical transformations, and control chemical fluxes across networks of aggregated nanomaterials. Using X-ray diffraction, vibrational spectroscopy, electron microscopy, and (micro)gravimetry, we tracked water film-driven transformations of periclase (MgO) nanocubes to brucite (Mg(OH)2) nanosheets. We show that three monolayer-thick water films first triggered the nucleation-limited growth of brucite, and that water film loadings continuously increased as newly-formed brucite nanosheets captured air moisture. Small (8 nm-wide) nanocubes were completely converted to brucite under this regime while growth on larger (32 nm-wide) nanocubes transitioned to a diffusion-limited regime when (∼0.9 nm-thick) brucite nanocoatings began hampering the flux of reactive species. We also show that intra- and inter-particle microporosity hosted a hydration network that sustained GPa-level crystallization pressures, compressing interlayer brucite spacing during growth. This was prevalent in aggregated 8 nm wide nanocubes, which formed a maze-like network of slit-shaped pores. By resolving the impact of nanocube size and microporosity on reaction yields and crystallization pressures, this work provides new insight into the study of mineralogical transformations induced by nanometric water films. Our findings can be applied to structurally related minerals important to nature and technology, as well as to advance ideas on crystal growth under nanoconfinement.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2023. Vol. 15, no 24, p. 10286-10294
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-209178DOI: 10.1039/d2nr07140aISI: 000988100900001PubMedID: 37194306Scopus ID: 2-s2.0-85160450592OAI: oai:DiVA.org:umu-209178DiVA, id: diva2:1771430
Part of project
Rust in Ice: The Geochemistry of Iron in Freezing Water, Swedish Research CouncilChemistry within the confines of mineral-bound thin water films, Swedish Research CouncilDirect Mineralization of Atmospheric CO2 by Enhanced Weathering, Swedish Research Council Formas
Funder
Swedish Research Council, 2020-05853Swedish Research Council Formas, 2022-01246Available from: 2023-06-20 Created: 2023-06-20 Last updated: 2023-09-04Bibliographically approved
In thesis
1. Water film-mediated mineralogical transformations and photocatalytic reactions
Open this publication in new window or tab >>Water film-mediated mineralogical transformations and photocatalytic reactions
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Mineral particles capture water vapor in the atmosphere in the form of water films that are only few monolayers thick. Water films form nanoscale hydration environments that mediate a wide range of important reactions in nature and technology. This thesis explored two important phenomena that commonly occur within the confines of water films: mineralogical transformations (Topic 1) and photocatalytic decomposition of organics (Topic 2). These transformations were chiefly identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and (Transmission and Scanning) electron microscopy. Interpretations of reaction mechanisms were partially supported by chemometrics, kinetic and thermodynamic modeling, as well as molecular simulations.

Mineralogical transformations (Topic 1) resolved in this thesis involved the hydroxylation (Papers I, II) and carbonation (Paper III) of periclase (MgO), and the oxidation of rhodochrosite (MnCO3) (Paper IV). Two types of MgO nanocubes with contrasting physical properties were used to resolve nucleation- and diffusion-limited hydroxylation reactions to brucite and carbonation reactions to amorphous magnesium carbonate (AMC). While nucleation-limited reactions completely transformed (8 nm) small and aggregated MgO nanocubes to brucite, the reactions became diffusion-limited in larger (32 nm) monodispersed MgO nanocubes because of brucite surface nanocoatings (Paper I). Additionally, brucite nanosheets grew under (GPa-level) crystallization pressures because of the important volumetric expansion of the reaction, which took place in a complex network of microporosity between the small and within the larger MgO nanocubes. Brucite stacking mechanisms, explored in Paper II, focused on the early stages of MgO-water interaction in water films of different thicknesses. These were suggested to involve the stacking and (epitaxial-like) growth of precursor Mg(OH)2 nanosheets in water films. Carbonation reactions explored in Paper III completely hampered hydroxylation reactions studied in Papers I and II, and produced AMC nanocoatings grown over an unreacted MgO core. Finally, oxidation-driven reactions involving rhodochrosite in Paper IV produced MnO2, Mn3O4, and MnOOH nanocoatings with growth rates being scaled with water loadings.

Photocatalytic decomposition reactions of organics (Topic 2) were focused on the case of oxalate bound to TiO2 nanoparticles (Paper V). Photodecomposition rates scaled with humidity in oxygenated water films, and were explained by the combination of hole transfer (HT), ligand-to-metal charge transfer (LMCT), and the formation of hydroxyl radicals and reactive oxygen species. Decreasing rates in oxygen-free water films were, on the other hand, explained by water-driven charge localization, which eventually limited radical production and charge transfers via HT and LMCT. The reactions involved limited HT and LMCT processes which also competed with a charge recombination process across all humidity ranges.

This thesis provides new insight into two key types of transformations mediated by water films on minerals. This knowledge can be used to understand the reactivity of mineral (nano)particles exposed to variations in atmospheric humidity and oxygen content, which are both highly relevant to a wide range of settings in nature and technology. It can also advance new ideas in the study of mineral growth, especially within the confines of nanometer-thick water films.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2023. p. 70
Keywords
mineral, water films, carbon dioxide, MgO, MnCO3, TiO2, hydroxylation, carbonation, oxidation, transformation, photocatalysis
National Category
Materials Chemistry Inorganic Chemistry Physical Chemistry Geochemistry
Research subject
Inorganic Chemistry; nanomaterials; Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-213817 (URN)9789180701501 (ISBN)9789180701518 (ISBN)
Public defence
2023-09-29, Lilla hörsalen, KB.E3.01, KBC building, Linnaeus väg 10, Umeå, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2016-03808Swedish Research Council, 2020-05853Swedish Research Council Formas, 2022-01246
Available from: 2023-09-08 Created: 2023-09-01 Last updated: 2023-09-04Bibliographically approved

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Luong, N. TanHolmboe, MichaelBoily, Jean-Francois

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