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Holmboe, Michael
Publications (10 of 14) Show all publications
Yeşilbaş, M., Holmboe, M. & Boily, J.-F. (2019). Residence times of nanoconfined CO2 in layered aluminosilicates. Environmental Science: Nano, 6(1), 146-151
Open this publication in new window or tab >>Residence times of nanoconfined CO2 in layered aluminosilicates
2019 (English)In: Environmental Science: Nano, ISSN 2051-8153, Vol. 6, no 1, p. 146-151Article in journal (Refereed) Published
Abstract [en]

Nanoconfinement of CO2 in layered aluminosilicates contributes to the capture and release of this greenhouse gas in soils. In this work, we show that the residence times of CO2 in montmorillonite are lowered by 15 min for each 1 degrees C increment in temperature during venting. Molecular simulations showed that activation energies of release are no more than half of the experimentally derived value of 34 kJ mol(-1). This raised the possibility of additional processes limiting CO2 mobility in real materials, including (chemi)sorption at reactive sites or frayed edges or defects. The residence times (approximate to 1616 min at -50 degrees C to approximate to 6 min at 60 degrees C) for some of the driest (approximate to 1.4 mmol H2O per g) montmorillonites that can be produced at ambient temperatures are readily lowered by inclusion of additional water. They are, in turn, prolonged again as the water content and interlayer spacing become smaller through venting. These efforts showed that soil-building clay minerals will lose their propensity to dynamically exchange CO2 as temperatures continue to rise, yet they may retain CO2 more efficiently in cold seasons as soils will become depleted in moisture content.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Environmental Sciences Geochemistry
Identifiers
urn:nbn:se:umu:diva-157978 (URN)10.1039/c8en01156g (DOI)000461698700010 ()
Available from: 2019-04-10 Created: 2019-04-10 Last updated: 2019-04-10Bibliographically approved
Yeşilbaş, M., Holmboe, M. & Boily, J.-F. (2018). Cohesive vibrational and structural depiction of intercalated water in montmorillonite. ACS Earth and Space Chemistry, 2(1), 38-47
Open this publication in new window or tab >>Cohesive vibrational and structural depiction of intercalated water in montmorillonite
2018 (English)In: ACS Earth and Space Chemistry, E-ISSN 2472-3452, Vol. 2, no 1, p. 38-47Article in journal (Refereed) Published
Abstract [en]

The vibrational spectral profiles of Na- and Ca-montmorillonite (MMT) of controlled water layer populations (nW) was extracted by chemometric analysis of new Fourier transform infrared (FTIR) spectroscopy data and validated by mixed-layer modeling of previously published X-ray diffraction data. These efforts resolved FTIR spectral profiles of 0W, 1W, and 2W interlayers, which can now be used to explore the distinct hydration states of MMT. These spectral profiles reflect water populations organized around interlayer cations (Na+, Ca2+), interacting with siloxane groups of the basal face of the interlayer, and with other bound and “free” water molecules. This cohesive description of water-bearing clays provides the link needed to relate vibrational to structural attributes of these geochemically important materials.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
Keywords
adsorption, montmorillonite, vibration spectroscopy, water vapor, X-ray diffraction
National Category
Geochemistry
Identifiers
urn:nbn:se:umu:diva-143020 (URN)10.1021/acsearthspacechem.7b00103 (DOI)000423141600005 ()
Available from: 2017-12-14 Created: 2017-12-14 Last updated: 2018-06-09Bibliographically approved
Yang, G., Neretnieks, I. & Holmboe, M. (2017). Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores. Journal of Chemical Physics, 147(8), Article ID 084705.
Open this publication in new window or tab >>Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores
2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 8, article id 084705Article in journal (Refereed) Published
Abstract [en]

During the last four decades, numerous studies have been directed to the swelling smectite-rich clays in the context of high-level radioactive waste applications and waste-liners for contaminated sites. The swelling properties of clay mineral particles arise due to hydration of the interlayer cations and the diffuse double layers formed near the negatively charged montmorillonite (MMT) surfaces. To accurately study the cation hydration in the interlayer nanopores of MMT, solvent-solute and solvent-clay surface interactions (i.e., the solvation effects and the shape effects) on the atomic level should be taken into account, in contrast to many recent electric double layer based methodologies using continuum models. Therefore, in this research we employed fully atomistic simulations using classical molecular dynamics (MD) simulations, the software package GROMACS along with the CLAYFF forcefield and the SPC/E water model. We present the ion distributions and the deformation of the hydrated coordination structures, i.e., the hydration shells of Na+ and Ca2+ in the interlayer, respectively, for MMT in the first-layer, the second-layer, the third-layer, the fourth-layer, and the fifth-layer (1W, 2W, 3W, 4W, and 5W) hydrate states. Our MD simulations show that Na+ in Na-MMT nanopores have an affinity to the ditrigonal cavities of the clay layers and form transient inner-sphere complexes at about 3.8 Å from clay midplane at water contents less than the 5W hydration state. However, these phenomena are not observed in Ca-MMT regardless of swelling states. For Na-MMT, each Na+ is coordinated to four water molecules and one oxygen atom of the clay basal-plane in the first hydration shell at the 1W hydration state, and with five to six water molecules in the first hydration shell within a radius of 3.1 Å at all higher water contents. In Ca-MMT, however each Ca2+ is coordinated to approximately seven water molecules in the first hydration shell at the 1W hydration state and about eight water molecules in the first hydration shell within a radius of 3.3 Å at all higher hydration states. Moreover, the MD results show that the complete hydration shells are nearly spherical with an orthogonal coordination sphere. They could only be formed when the basal spacing d001 ≥ 18.7 Å, i.e., approximately, the interlayer separation h ≥ 10 Å. Comparison between DFT and MD simulations shows that DFT failed to reproduce the outer-sphere complexes in the Stern-layer (within ∼5.0 Å from the clay basal-plane), observed in the MD simulations.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-138566 (URN)10.1063/1.4992001 (DOI)000409143100035 ()28863548 (PubMedID)
Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2018-06-09Bibliographically approved
Tinnacher, R. M., Holmboe, M., Tournassat, C., Bourg, I. C. & Davis, J. A. (2016). Ion adsorption and diffusion in smectite: Molecular, pore, and continuum scale views. Geochimica et Cosmochimica Acta, 177, 130-149
Open this publication in new window or tab >>Ion adsorption and diffusion in smectite: Molecular, pore, and continuum scale views
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2016 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 177, p. 130-149Article in journal (Refereed) Published
Abstract [en]

Clay-rich media have been proposed as engineered barrier materials or host rocks for high level radioactive waste repositories in several countries. Hence, a detailed understanding of adsorption and diffusion in these materials is needed, not only for radioactive contaminants, but also for predominant earth metals, which can affect radionuclide speciation and diffusion. The prediction of adsorption and diffusion in clay-rich media, however, is complicated by the similarity between the width of clay nanopores and the thickness of the electrical double layer (EDL) at charged clay mineral-water interfaces. Because of this similarity, the distinction between 'bulk liquid' water and 'surface' water (i.e., EDL water) in clayey media can be ambiguous. Hence, the goal of this study was to examine the ability of existing pore scale conceptual models (single porosity models) to link molecular and macroscopic scale data on adsorption and diffusion in compacted smectite. Macroscopic scale measurements of the adsorption and diffusion of calcium, bromide, and tritiated water in Na-montmorillonite were modeled using a multi-component reactive transport approach while testing a variety of conceptual models of pore scale properties (adsorption and diffusion in individual pores). Molecular dynamics (MD) simulations were carried out under conditions similar to those of our macroscopic scale diffusion experiments to help constrain the pore scale models. Our results indicate that single porosity models cannot be simultaneously consistent with our MD simulation results and our macroscopic scale diffusion data. A dual porosity model, which allows for the existence of a significant fraction of bulk liquid water-even at conditions where the average pore width is only a few nanometers-may be required to describe both pore scale and macroscopic scale data.

National Category
Geochemistry
Identifiers
urn:nbn:se:umu:diva-118381 (URN)10.1016/j.gca.2015.12.010 (DOI)000370969700009 ()
Available from: 2016-04-22 Created: 2016-03-18 Last updated: 2018-06-07Bibliographically approved
Tournassat, C., Bourg, I. C., Holmboe, M., Sposito, G. & Steefel, C. I. (2016). Molecular dynamics simulations of anion exclusion in clay interlayer nanopores. Clays and clay minerals, 64(4), 374-388
Open this publication in new window or tab >>Molecular dynamics simulations of anion exclusion in clay interlayer nanopores
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2016 (English)In: Clays and clay minerals, ISSN 0009-8604, E-ISSN 1552-8367, Vol. 64, no 4, p. 374-388Article in journal (Refereed) Published
Abstract [en]

The aqueous chemistry of water films confined between clay mineral surfaces remains an important unknown in predictions of radioelement migration from radioactive waste repositories. This issue is particularly important in the case of long-lived anionic radioisotopes (129I , 99TcO4 , 36Cl) which interact with clay minerals primarily by anion exclusion. For example, models of ion migration in clayey media do not agree as to whether anions are completely or partially excluded from clay interlayer nanopores. In the present study, this key issue was addressed for Cl using MD simulations for a range of nanopore widths (6 to 15 Å) overlapping the range of average pore widths that exists in engineered clay barriers. The MD simulation results were compared with the predictions of a thermodynamic model (Donnan Equilibrium model) and two pore-scale models based on the Poisson-Boltzmann equation under the assumption that interlayer water behaves as bulk liquid water. The simulations confirmed that anion exclusion from clay interlayers is greater than predicted by the pore-scale models, particularly at the smallest pore size examined. This greater anion exclusion stems from Cl being more weakly solvated in nano-confined water than it is in bulk liquid water. Anion exclusion predictions based on the PoissonBoltzmann equation were consistent with the MD simulation results, however, if the predictions included an ion closest approach distance to the clay mineral surface on the order of 2.0 0.8 Å. These findings suggest that clay interlayers approach a state of complete anion exclusion (hence, ideal semi-permeable membrane properties) at a pore width of 4.2 +/- 1.5 Å. 

Keywords
Anion Exclusion, Clay, Donnan Equilibrium Model, Interlayer, Molecular Dynamics, Nanopores, Poisson-Boltzmann, Semi-Permeable Membrane
National Category
Water Engineering Geophysical Engineering
Identifiers
urn:nbn:se:umu:diva-129246 (URN)10.1346/CCMN.2016.0640403 (DOI)000392707300004 ()
Available from: 2016-12-21 Created: 2016-12-21 Last updated: 2018-06-09Bibliographically approved
Holmboe, M., Larsson, P., Anwar, J. & Bergström, C. A. .. (2016). Partitioning into Colloidal Structures of Fasted State Intestinal Fluid Studied by Molecular Dynamics Simulations. Langmuir, 32(48), 12732-12740
Open this publication in new window or tab >>Partitioning into Colloidal Structures of Fasted State Intestinal Fluid Studied by Molecular Dynamics Simulations
2016 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 48, p. 12732-12740Article in journal (Refereed) Published
Abstract [en]

We performed molecular dynamics (MD) simulations to obtain insights into the structure and molecular interactions of colloidal structures present in fasted state intestinal fluid. Drug partitioning and interaction were studied with a mixed system of the bile salt taurocholate (TCH) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLiPC). Spontaneous aggregation of TCH and DLiPC from unconstrained MD simulations at the united-atom level using the Berger/Gromos54A7 force fields demonstrated that intermolecular hydrogen bonding between TCH molecules was an important factor in determining the overall TCH and DLiPC configuration. In bilayered systems, these intermolecular hydrogen bonds resulted in embedded transmembrane TCH clusters. Free energy simulations using the umbrella sampling technique revealed that the stability of these transmembrane TCH clusters was superior when they consisted of 3 or 4 TCH per bilayer leaflet. All-atom simulations using the Slipids/GAFF force fields showed that the TCH embedded in the bilayer decreased the energy barrier to penetrate the bilayer (ΔGpen) for water, ethanol, and carbamazepine, but not for the more lipophilic felodipine and danazol. This suggests that diffusion of hydrophilic to moderately lipophilic molecules through the bilayer is facilitated by the embedded TCH molecules. However, the effect of embedded TCH on the overall lipid/water partitioning was significant for danazol, indicating that the incorporation of TCH plays a crucial role for the partitioning of lipophilic solutes into e.g. lipidic vesicles existing in fasted state intestinal fluids. To conclude, the MD simulations revealed important intermolecular interactions in lipidic bilayers, both between the bile components themselves and with the drug molecules.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-128942 (URN)10.1021/acs.langmuir.6b03008 (DOI)000389557400019 ()
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-06-09Bibliographically approved
Hellrup, J., Holmboe, M., Nartowski, K. P., Khimyak, Y. Z. & Mahlin, D. (2016). Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites. Langmuir, 32(49), 13214-13225
Open this publication in new window or tab >>Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites
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2016 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 49, p. 13214-13225Article in journal (Refereed) Published
Abstract [en]

This study aims at investigating the molecular level organization and molecular mobility in montmorillonite nanocomposites with the uncharged organic low-molecular-weight compound lactose commonly used in pharmaceutical drug delivery, food technology, and flavoring. Nanocomposites were prepared under slow and fast drying conditions, attained by drying at ambient conditions and by spray-drying, respectively. A detailed structural investigation was performed with modulated differential scanning calorimetry, powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, scanning electron microscopy, microcalorimetry, and molecular dynamics simulations. The lactose was intercalated in the sodium montmorillonite interlayer space regardless of the clay content, drying rate, or humidity exposure. Although, the spray-drying resulted in higher proportion of intercalated lactose compared with the drying under ambient conditions, nonintercalated lactose was present at 20 wt % lactose content and above. This indicates limitations in maximum loading capacity of nonionic organic substances into the montmorillonite interlayer space. Furthermore, a fraction of the intercalated lactose in the co-spray-dried nanocomposites diffused out from the clay interlayer space upon humidity exposure. Also, the lactose in the nanocomposites demonstrated higher molecular mobility than that of neat amorphous lactose. This study provides a foundation for understanding functional properties of lactose/Na-MMT nanocomposites, such as loading capacity and physical stability.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-128939 (URN)10.1021/acs.langmuir.6b01967 (DOI)000389866300029 ()
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-06-09Bibliographically approved
Holmboe, M. & Bourg, I. C. (2014). Molecular Dynamics Simulations of Water and Sodium Diffusion in Smectite Interlayer Nanopores as a Function of Pore Size and Temperature. The Journal of Physical Chemistry C, 118(2), 1001-1013
Open this publication in new window or tab >>Molecular Dynamics Simulations of Water and Sodium Diffusion in Smectite Interlayer Nanopores as a Function of Pore Size and Temperature
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 2, p. 1001-1013Article in journal (Refereed) Published
Abstract [en]

The diffusion coefficients (D) of water and solutes in nanoporousNa-smectite clay barriers have been widely studied because of their importancein high-level radioactive waste (HLRW) management and in the isolation of contaminated sites. However, few measurements have been carried out at the high temperatures that are expected to occur in HLRW repositories. We address this knowledge gap by using molecular dynamics (MD) simulations to predict the temperature dependence of diffusion in clay interlayer nanopores, expressed as a pore scale activation energy of diffusion (Ea). Our sensitivity analysis shows that accurate prediction of pore scale Dand Eavalues requires careful consideration of the influence of pore size, simulation cell size, and clay structure flexibility on MD simulation results. We find that predicted Dvalues in clay interlayer nanopores are insensitive to the size of the simulation cell (contrary to the behavior observed in simulation of bulk liquid water) but sensitive to the vibrational motions of clay atoms (particularly in the smallest pores investigated here, the one-, two-, and three-layer hydrates). Our predicted DandEavalues are consistent with experimental data. They reveal,for both water and Na+, that Eaincreases by∼6 kJ mol−1with increasing confinement, when going from bulk liquid water to theone-layer hydrate of Na-montmorillonite.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-128937 (URN)10.1021/jp408884g (DOI)
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-10-02
Holmboe, M., Jonsson, M. & Wold, S. (2012). Influence of γ-radiation on the reactivity of Montmorillonite towards H2O2. The Journal of Physical Chemistry C, 81:2, s. 190-194, 1001-1013
Open this publication in new window or tab >>Influence of γ-radiation on the reactivity of Montmorillonite towards H2O2
2012 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 81:2, s. 190-194, p. 1001-1013Article in journal (Other academic) Published
Abstract [en]

Compacted and water saturated bentonite will be used as an engineered barrier in deep geological repositories for radioactive waste in many countries. Due to the high dose rate of ionizing radiation outside the canisters holding the nuclear waste, radiolysis of the interlayer and pore water in the compacted bentonite is unavoidable. Upon reaction with the oxidizing and reducing species formed by water radiolysis (OH•, e-(aq), H•, H202, H2, H02•, H30+), the overall redox properties in the bentonite barrier may change. In this study the influence of γ-radiation on the structural Fe(II)/Fe(III) content in montmorillonite and its reactivity towards hydrogen peroxide (H2O2) was investigated in parallel experiments. The results show that under anoxic conditions the structural Fe(II)/FeTot ratio of dispersed montmorillonite are increased from ≤ 3 to 25-30% after γ-doses comparable to repository conditions. Furthermore, a strong correlation between the structural Fe(II)/FeTot ratio and the H2O2 decomposition rate in montmorillonite dispersions was found. This correlation was further verified in experiments with consecutive H2O2 additions, since the structural Fe(II)/FeTot ratio was seen to decrease concordantly. This work shows that the structural iron in montmorillonite could be a sink for one of the major oxidants formed upon water radiolysis in the bentonite barrier, H2O2.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2012
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-128998 (URN)10.1016/j.radphyschem.2011.10.009 (DOI)
Available from: 2016-12-20 Created: 2016-12-20 Last updated: 2018-06-09
Holmboe, M., Wold, S. & Jonsson, M. (2012). Porosity investigation of compacted bentonite using XRD profile modeling. Journal of Contaminant Hydrology, 128(1–4), 19-32
Open this publication in new window or tab >>Porosity investigation of compacted bentonite using XRD profile modeling
2012 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 128, no 1–4, p. 19-32Article in journal (Refereed) Published
Abstract [en]

Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier, fundamental understanding of the microstructure of compacted bentonite is needed. This study examined the interlayer swelling and overall microstructure of Wyoming Bentonite MX-80 and the corresponding homo-ionic Na+ and Ca2 + forms, using XRD with samples saturated under confined swelling conditions and free swelling conditions. For the samples saturated under confined conditions, the interparticle, or so-called free or external porosity was estimated by comparing the experimental interlayer distances obtained from one-dimensional XRD profile fitting against the maximum interlayer distances possible for the corresponding water content. The results showed that interlayer porosity dominated total porosity, irrespective of water content, and that the interparticle porosity was lower than previously reported in the literature. At compactions relevant for the saturated bentonite barrier (1.4–1.8 g/cm3), the interparticle porosity was estimated to ≤ 3%.

Place, publisher, year, edition, pages
Elsevier, 2012
Keywords
Bentonite, Clay swelling, Microstructure, Porosity, Nuclear waste disposal, XRD
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-129230 (URN)10.1016/j.jconhyd.2011.10.005 (DOI)
Available from: 2016-12-21 Created: 2016-12-21 Last updated: 2018-06-09
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