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  • 1.
    Broman, Karolina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Chorell, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Combining Virtual Reality and Zoom to visualize chemical structures in 3D and develop the spatial ability of university chemistry students2021Inngår i: Book of abstracts: 9th European Variety in University Chemistry Education Conference EUROVARIETY 2021, University of Ljubljana , 2021, s. -60Konferansepaper (Fagfellevurdert)
  • 2.
    Broman, Karolina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Chorell, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Virtual Reality and Zoom in combination to visualise chemical structures and develop students' spatial ability during the Corona pandemic2021Inngår i: Den 8:e utvecklingskonferensen för Sveriges ingenjörsutbildningar: Detaljerat program, Karlstads universitet , 2021Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In chemistry education, students need to develop their competence to visualise chemical structures and reaction mechanisms, for example, to be able to predict how chemical compounds react. As a chemistry or biotechnology engineering student, this competence needs to be practiced. In our project, students have since 2018 used Virtual Reality (VR) to learn to “see” chemistry, and to move between 2D and 3D representations, i.e., spatial ability or spatial thinking. During the Corona pandemic, several teaching challenges have had to be handled, and Zoom has become the most common teaching and communication platform in Sweden. When combining VR with Zoom, students had a possibility to develop their spatial ability even though distance teaching, something described in this paper. The combination of VR and Zoom is explored further for future teaching implications even post-Covid.

    Fulltekst (pdf)
    fulltext
  • 3.
    Broman, Karolina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Chorell, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Magkakis, Konstantinos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Virtual Reality to visualise chemistry in higher education: Digital tools to enhance student learning2022Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Visualisation of molecular representations is an important area within chemistry education that has been explored for a long time, from several different perspectives. In the 1950s, Linus Pauling and Robert Koltun defined the CPK-model, describing the colours of the different atoms used in wood or plastic ball-and-stick models, for example, the black carbon, the white hydrogen, and the red oxygen. These analogue ball-and-stick models (e.g., MolyMod) are still used both in schools and at universities to help students “see” chemistry in three dimensions (3D). Today, with digitalisation, new tools are available to represent and visualise chemistry(Bernholt, Broman, Siebert, & Parchmann, 2019). With these modern digital tools, there are less limitations in molecular size to represent molecules, and even large structures and reaction mechanisms can be explored (Won, Mocerino, Tang, Treagust, & Tasker, 2019). In our project, interventions applying Virtual Reality (VR) as the digital tool during organic chemistry workshops and tutorials, have been explored related to cognitive and affective learning.

    VR gives students the possibility to practice spatial ability, i.e., to move between 2D and 3D. In textbooks, chemistry is presented in 2D using, for example, Lewis structures. However, in real life, chemistry is three-dimensional, and the move between 2D and 3D is something students, as novices, need to practice to understand why and how chemicals react. In our project, university students practice their spatial ability through the application of VR. This on-going project started in 2018, and different workshops and tutorials have been implemented in different chemistry courses for bachelor, master, and engineering students. As presented in previous recent research from Brown and colleagues (2021), our students were very positive, enthusiastic and engaged to work with VR to develop their spatial ability and to visualise chemistry. In the presentation, we will give examples on how students can improve their learning and interest with the use of VR to represent chemical structures.

  • 4.
    Broman, Karolina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Chorell, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Magkakis, Konstantinos
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Virtual Reality: visualization of chemical structures to enhance student interest and learning2022Inngår i: ECRICE 2022: chemistry teaching and learning in a global unified world: abstract book, Weizmann Institute of Science , 2022Konferansepaper (Fagfellevurdert)
    Abstract [en]

    One of the fundamental aspects of chemistry learning is to visualize chemical structures. Through the application of Alex Johnstone's (1991) multilevel thought, the submicroscopic level is often a challenge for students, especially the shift between 2D and 3D, i.e., spatial thinking or spatial ability (Harle & Towns, 2011). With small molecules, plastic ball-and-stick models are commonly used, but on university level, the structures are often larger. By applying digital tools and techniques, as Virtual Reality (VR), there are less limitations in size to represent molecules, and even large structures and reaction mechanisms can be explored (Won et al., 2019). In a five-year design-based research project (Anderson & Shattuck, 2012), a collaboration between university chemistry teachers and a chemistry education researcher, has had an aim to develop university chemistry students' spatial thinking.

    Students and teachers have, in workshops and tutorials, applied VR with both simple and more advanced tools, see figures 1 and 2. Empirical data has been collected using surveys, interviews, and observations. Standard ethical considerations have been considered throughout the whole project.

    In this presentation, students' cognitive and affective learning related to spatial thinking will be discussed, as well as students', teachers', and researcher’s perspectives from the application of VR to visualize chemistry will be elaborated further. Implications for chemistry teaching at all levels will also be explored.

  • 5.
    Broman, Karolina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för naturvetenskapernas och matematikens didaktik.
    Chorell, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mårell-Olsson, Eva
    Umeå universitet, Samhällsvetenskapliga fakulteten, Pedagogiska institutionen.
    Zoom combined with Virtual Reality (VR) to visualize chemical structures inorganic chemistry2021Inngår i: Universitetspedagogiskakonferensen 2021: den goda utbildningsmiljön 2.1, Umeå: Universitetspedagogik och lärandestöd (UPL), Umeå universitet , 2021, s. 12-13Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The ability to visualize chemistry and to move between two-dimensional (2D) representations presented in textbooks, and three-dimensional (3D) representations of the real molecular structures and mechanisms, is an important competence to master in university chemistry. In research, this is called spatial thinking or spatial ability (Hegarty, 2014). Through spatial thinking, chemists can predict how and why chemical compounds react. Chemistry experts are used to apply this spatial thinking, i.e., visualization through the move between 2D and 3D, without realizing it, whereas novices as students often find spatial thinking or spatial ability challenging (Harle & Towns, 2011). Spatial ability is a competence that is possible to develop through practice (Kozma & Russel, 2005), and in this project, chemistry students had the possibility to use virtual reality, VR, to visualize organic molecular structures and improve their spatial thinking. VR has a potential as a digital learning tool to explore 3D representation  During the last one and a half years, Covid 19 has influenced teaching strategies at universities, and Zoom has become the most common software to teach students. At a first-cycle chemistry course in biological chemistry within a bachelor programme in life science, students were given the opportunity to visualize 3D representations of chemical structures. Due to the Covid 19 restrictions, the teachers could not help students attending the course to be active VR users. Instead, one teacher applied the VR application, Oculus Rift combined with Nanome software (https://nanome.ai), and streamed the visualization over Zoom. The second university chemistry teacher, and the students, used simple VR glasses with their smartphones to visualize the 3D projected molecules, and the teacher explained what was presented. This design-based research project (Anderson & Shattuck, 2012), where the university chemistry teachers collaborated with a chemistry education researcher and a digitalization researcher, will elaborate further on how Zoom as a digital teaching tool also can be applied to facilitate spatial thinking for students even post-Covid. The chemistry teachers and chemistry education researcher designed an intervention from where examples of the visualizations will be presented together with survey results on students’ responses of the application of digital techniques as a way to practice their visualization competence and spatial ability. Preliminary results show that students find this visualization combining VR and Zoom valuable to practice their spatial thinking, and examples of teaching activities will be presented.

    For more information about the project, see https://www.umu.se/en/feature/vr-glasses-help-students-visualize-molecules-/or https://www.umu.se/reportage/vr-glasogon-hjalper-studenter-visualisera-molekyler/

    Fulltekst (pdf)
    fulltext
  • 6.
    Chaudhary, Himanshu
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Iashchishyn, Igor A.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Romanova, Nina V.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Rambaran, Mark A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Musteikyte, Greta
    Smirnovas, Vytautas
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ohlin, C. André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Svedružić, Željko M.
    Morozova-Roche, Ludmilla A.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Polyoxometalates as Effective Nano-inhibitors of Amyloid Aggregation of Pro-inflammatory S100A9 Protein Involved in Neurodegenerative Diseases2021Inngår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 13, nr 23, s. 26721-26734Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pro-inflammatory and amyloidogenic S100A9 protein is central to the amyloid-neuroinflammatory cascade in neurodegenerative diseases. Polyoxometalates (POMs) constitute a diverse group of nanomaterials, which showed potency in amyloid inhibition. Here, we have demonstrated that two selected nanosized niobium POMs, Nb10 and TiNb9, can act as potent inhibitors of S100A9 amyloid assembly. Kinetics analysis based on ThT fluorescence experiments showed that addition of either Nb10 or TiNb9 reduces the S100A9 amyloid formation rate and amyloid quantity. Atomic force microscopy imaging demonstrated the complete absence of long S100A9 amyloid fibrils at increasing concentrations of either POM and the presence of only round-shaped and slightly elongated aggregates. Molecular dynamics simulation revealed that both Nb10 and TiNb9 bind to native S100A9 homo-dimer by forming ionic interactions with the positively charged Lys residue-rich patches on the protein surface. The acrylamide quenching of intrinsic fluorescence showed that POM binding does not perturb the Trp 88 environment. The far and near UV circular dichroism revealed no large-scale perturbation of S100A9 secondary and tertiary structures upon POM binding. These indicate that POM binding involves only local conformational changes in the binding sites. By using intrinsic and 8-anilino-1-naphthalene sulfonate fluorescence titration experiments, we found that POMs bind to S100A9 with a Kd of ca. 2.5 μM. We suggest that the region, including Lys 50 to Lys 54 and characterized by high amyloid propensity, could be the key sequences involved in S1009 amyloid self-assembly. The inhibition and complete hindering of S100A9 amyloid pathways may be used in the therapeutic applications targeting the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

    Fulltekst (pdf)
    fulltext
  • 7. Cheng, Wei
    et al.
    Lindholm, Jerry
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Luong, N. Tan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ilton, Eugene S.
    Hanna, Khalil
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nanoscale hydration in layered manganese oxides2021Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 37, nr 2, s. 666-674Artikkel i tidsskrift (Fagfellevurdert)
    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.

    Fulltekst (pdf)
    fulltext
  • 8.
    Essalhi, Mohamed
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. African Sustainable Agriculture Research Institute (ASARI), Mohammed VI Polytechnic University (UM6P), Laayoune, 70000, Morocco.
    Afsar, Noor Ul
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Bouyer, Denis
    Institut Européen des Membranes, IEM, UMR 5635, ENSCM, CNRS, Univ Montpellier, Montpellier, France .
    Sundman, Ola
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Khayet, Mohamed
    Department of Structure of Matter, Thermal Physics and Electronics, Faculty of Physics, University Complutense of Madrid, Avda. Complutense s/n, 28040, Madrid, Spain .
    Jonsson, Mats
    Department of Chemistry, KTH Royal Institute of Technology, SE - 100 44, Stockholm, Sweden .
    Tavajohi, Naser
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Gamma-irradiated janus electrospun nanofiber membranes for desalination and nuclear wastewater treatment2024Inngår i: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 700, artikkel-id 122726Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents the fabrication of double-layer electrospun nanofibrous membranes (DL-ENMs) using polyvinylidene fluoride (PVDF) and polyether sulfone (PES) based polymers with different degrees of hydrophilicity (PES, sulfonated PES, and PES with hydroxyl terminals). A comparative analysis was carried out with single-layer electrospun nanofiber membranes (SL-ENM) with a total thickness of about 375 μm. Using feed solutions, including sodium chloride, sodium nitrate, and simulated nuclear wastewater (SNWW), the performance of DL-ENMs was evaluated for desalination and radionuclide decontamination by direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) techniques. The results showed that DL-ENMs, especially those incorporating a sulfonated PES-based hydrophilic layer, exhibited superior permeate fluxes, reaching values of 72.72 kg/m2h and 73.27 kg/m2h in the DCMD using aqueous feed solutions of NaCl and NaNO3, respectively, and 70.80 kg/m2h and 41.96 kg/m2h using aqueous feed solutions of SNWW in DCMD and AGMD, respectively. Both SL-ENMs and DL-ENMs exhibited high rejection efficiencies and decontamination factors for the feed solutions (>99.9%). In addition, the prepared ENMs were exposed to gamma radiation to evaluate their applicability in real-life applications. The result of irradiation revealed the negative impact of gamma radiation on the fluorine content of PVDF which could be a critical point in using PVDF as a hydrophobic material for decontaminating nuclear wastewater by membrane distillation.

    Fulltekst (pdf)
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  • 9. Hellrup, Joel
    et al.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nartowski, Karol P.
    Khimyak, Yaroslav Z.
    Mahlin, Denny
    Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 49, s. 13214-13225Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 10.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    atom: A MATLAB package for manipulation of molecular systems2019Inngår i: Clays and clay minerals, ISSN 0009-8604, E-ISSN 1552-8367, Vol. 67, nr 5, s. 419-426Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents Atomistic Topology Operations in MATLAB (atom), an open source library of modular MATLAB routines which comprise a general and flexible framework for manipulation of atomistic systems. The purpose of the atom library is simply to facilitate common operations performed for construction, manipulation, or structural analysis. Due to the data structure used, atoms and molecules can be operated upon based on different chemical names or attributes, such as atom- or molecule-ID, name, residue name, charge, positions, etc. Furthermore, the Bond Valence Method and a neighbor-distance analysis can be performed to assign many chemical properties of inorganic molecules. Apart from reading and writing common coordinate files (.pdb, .xyz, .gro, .cif) and trajectories (.dcd, .trr, .xtc; binary formats are parsed via third-party packages), the atom library can also be used to generate topology files with bonding and angle information taking the periodic boundary conditions into account, and supports basic Gromacs, NAMD, LAMMPS, and RASPA2 topology file formats. Focusing on clay-mineral systems, the library supports CLAYFF (Cygan, 2004) but can also generate topology files for the INTERFACE forcefield (Heinz, 2005, 2013) for Gromacs and NAMD.

    Fulltekst (pdf)
    fulltext
  • 11.
    Holmboe, Michael
    Skolan för kemivetenskap (CHE), Kemi, Kungliga tekniska högskolan, Stockholm, Sverige.
    The bentonite barrier: microstructural aspects on colloid filtration and radiation effects on bentonite colloid stability2009Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In many countries a multi-barrier concept in a deep geological repository is planned for final disposal of nuclear waste. Many of these different concepts, for example the Swedish KBS-3 model, include an engineered barrier consisting of compacted bentonite. The compacted bentonite barrier will be positioned around copper canisters holding the nuclear waste and act as a transport barrier for various radioactive species. This is due to the compact microstructure as well as the large sorption capacity of compacted water saturated bentonite. During its required lifetime (> 100000 years) a deep geological repository and the bentonite barrier itself will be subjected to changing groundwater composition and flow, geochemistry, temperature, and large doses of ionizing irradiation. The long lifetime and significance of a deep geologic repository mean that it must be regarded as a thermodynamically open system and be assessed in terms of worst case scenarios. In case of water bearing fractures, formed by future movements in the granitic host bedrock, low ionic strength groundwater can endanger the stability of the bentonite barrier. Prolonged erosion of the bentonite barrier might cause significant loss of buffer material and jeopardize its overall functionality. This thesis deals with the microstructure of the water saturated compacted bentonite as a function of compaction, as well as effects of γ-radiation on bentonite dispersions. The microstructure was investigated both indirectly through colloid filtration experiments, as well as using low-angle XRD. Effects of γ-irradiation were investigated in terms of colloid stability and sediment behavior of bentonite (and Na-montmorillonite) dispersions. The colloid filtration experiments, using small gold colloids of different sizes as tracers, shows that the microstructural constraints of bentonite effectively filter even extremely small inorganic colloids. Colloid transport was only observed at very low compactions (i.e. dry density g/cm3) where the average interlayer distances of montmorillonite exceeded the colloid size, indicating interlayer rather than interparticle transport. From the low-angle XRD experiments the free porosity of water saturated compacted bentonite was determined by comparing its basal spacings (interlayer distances + 1 nm) with the hypothetical basal spacings assuming no free porosity. Irrespective of compaction, the maximum free porosity proved to be very low, in line with the colloid filtration experiments. The results showed that existing microstructural models sometimes exaggerate the importance of interparticle voids. The γ-irradiation experiments showed a radiation induced increase in colloid stability. This radiation induced effect also changed the sedimentation behavior of irradiated bentonite dispersions compared to unirradiated samples. The effect is attributed to an increase in surface potential of the bentonite colloids, due to reactions with the short-lived radicals formed upon water radiolysis.

  • 12.
    Holmboe, Michael
    Skolan för kemivetenskap (CHE), Kemi, Kärnkemi, KTH, Stockholm, Sverige.
    The bentonite barrier: microstructural properties and the influence of γ-radiation2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Several countries intend to use a multi-barrier concept for the long-termdisposal of spent nuclear fuel. Many of these concepts, including the Swedish KBS-3 concept, involve an engineered barrier consisting of compacted bentonite which will be positioned around canisters holding the nuclear waste. Due to the compact microstructure, high swelling capacity as well as the large sorption capacity for most cationic radionuclides and fission products,highly compacted and water-saturated bentoniteis favored. During the mandatory lifetime of the deep geological repository (≥100000 years), the bentonite barrier will inevitably be subjected to changing groundwater composition and flow, temperatureand ionizing irradiation. If low ionic strength groundwater intersects the bentonite barrier, the stability of the barriercan be endangereddue to erosion. In this thesis, three different topics are embracedregarding the barrier, namely i)characterization of the microstructure and its properties of saturated compacted bentonite; ii)Effects of γ-radiation on bentonite dispersions, as well as on compacted bentonitein terms of radionuclide retention;iii)The potential effects of irreversible interactions between the proposed injection grout Silica sol (SiO2-colloids) and bentoniteparticles.The microstructure was investigated bycolloid filtration experiments, as well as through a basal spacing analysis using XRD. The colloid filtration experiments, usingsmall gold colloids of different sizes (2, 5 and 15 nm) as tracers, showed that the microstructural constraints of compacted bentonite effectively filter even extremely small inorganic colloids. Colloid transport was only observed at the lowest dry density, i.e. at the highest water content used,where the average interlayer distance in the montmorillonite particles exceeded thesize of the tracer colloids. From the XRD experiments theso-called free porosity of saturated compacted bentonite was determined by comparing the interlayer distances (basal spacings –montmorillonite layer thickness) with the theoretical interlayer distances corresponding tono free porosity. Irrespective of water content for the Na+dominated clays samples investigated at low ionic strength, the free porosity proved to be very low. When highly compacted, as in the bentonite barrier, the free porosity was ≤3%meaning thatthe interlayer voids comprise the major part of the total porosity in the bentonite barrier, in line with the colloid filtration experiments. The γ-radiation experiments showed a radiation-induced increase in colloid stability ofmontmorillonite dispersions. This radiation-induced effect also changed the settlingbehavior of irradiated montmorillonite and bentonite dispersions. Furthermore, γ-radiation was also found to increase the structural Fe(II)/FeTotratio in montmorillonite,resulting in an increased reactivity towards H2O2, one of the major anticipated oxidants under repository conditions. However, although both effects were attributed to reactions with the short-lived radicals formed upon water radiolysis, the change in thestructural Fe(II)/FeTotratio could not explain the radiation-induced increase in colloid stability.The effect of γ-radiation on radionuclide retention in compacted bentonite was examined in diffusion and batch sorption experiments,usingboth137Cs+and 60Co2+. In the batch sorption experiments a general decrease in the radionuclide sorption coefficient Kdwas found for Co2+upon γ-irradiation, but not for Cs+.As expected no difference in apparent diffusivity (Da) of Cs+between irradiated and unirradiated samples were found. As for Co2+, the effect of decreasing sorption to the irradiated clays was unfortunately not large enough to be reflected under these experimental conditions.Effects of SiO2-colloids on bentonite particles were studied in free swelling and settling experiments,as a function SiO2/montmorillonite ratio,after different types of treatmentsrepresentative for different repository scenarios. Results showed that the size and colloidal stability of bentonite and montmorillonite particles can be modified by SiO2-colloids, but only when mixed in comparable amounts (by weight) under high ionic strength (0.3 M NaCl) and especially from dehydration. From an AFM investigation using Na-montmorillonite, the sorption of the SiO2-colloids was found to preferentially occur along the edges of the layers, whereas for Ca-montmorillonite sorption also occurredon the faces. Upon aggregation with the SiO2-colloids, the interlayer distances of montmorillonite were left unchanged as measured with XRD, suggesting that the SiO2-colloids only interact with the extralamellar surface of montmorillonite particles.

  • 13. Holmboe, Michael
    et al.
    Bourg, Ian C.
    Molecular Dynamics Simulations of Water and Sodium Diffusion in Smectite Interlayer Nanopores as a Function of Pore Size and Temperature2014Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 2, s. 1001-1013Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 14. Holmboe, Michael
    et al.
    Jonsson, Mats
    Wold, Susanna
    Influence of γ-radiation on the reactivity of Montmorillonite towards H2O22012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 81:2, s. 190-194, s. 1001-1013Artikkel i tidsskrift (Annet vitenskapelig)
    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.

  • 15. Holmboe, Michael
    et al.
    Karin Norrfors, Knapp
    Jonsson, Mats
    Wold, Susanna
    Effect of γ-radiation on radionuclide retention in compacted bentonite2011Inngår i: Radiation Physics and Chemistry, ISSN 0969-806X, E-ISSN 1879-0895, Vol. 80, nr 12, s. 1371-1377Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Compacted bentonite is proposed as an engineered barrier in many concepts for disposal of high level nuclear waste. After the initial deposition however, the bentonite barrier will inevitably be exposed to ionizing radiation (mainly γ) under anoxic conditions. Because of this, the effects of γ-radiation on the apparent diffusivity values and sorption coefficients in bentonite for Cs+ and Co2+ were tested under different experimental conditions. Radiation induced effects on sorption were in general more noticeable for Co2+ than for Cs+, which generally showed no significant differences between irradiated and unirradiated clay samples. For Co2+ however, the sorption to irradiated MX80 was significantly lower than to the unirradiated clay samples regardless of the experimental conditions. This implies that γ-radiation may alter the surface characteristics contributing to surface complexation of Co2+. With the experimental conditions used, however, the effect of decreasing sorption was not large enough to be reflected on the obtained Da values.

  • 16.
    Holmboe, Michael
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Department of Pharmacy, Uppsala University, Uppsala Biomedical Centre, Uppsala, Sweden.
    Larsson, Per
    Anwar, Jamshed
    Bergström, Christel A.S.
    Partitioning into Colloidal Structures of Fasted State Intestinal Fluid Studied by Molecular Dynamics Simulations2016Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, nr 48, s. 12732-12740Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 17. Holmboe, Michael
    et al.
    Wold, Susanna
    Jonsson, Mats
    COLLOID DIFFUSION IN COMPACTED BENTONITE: MICROSTRUCTURAL CONSTRAINTS2010Inngår i: Clays and clay minerals, ISSN 0009-8604, E-ISSN 1552-8367, Vol. 58, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In Sweden and in many other countries, a bentonite barrier will be used in the repository for spent nuclear fuel. In the event of canister failure, colloidal diffusion is a potential, but scarcely studied mechanism of radionuclide migration through the bentonite barrier. Column and in situ experiments are vital in understanding colloid diffusion and in providing information about the microstructure of compacted bentonite and identifying cut-off limits for colloid filtration. This study examined diffusion of negatively charged 2-, 5-, and 15-nm gold colloids in 4-month diffusion experiments using MX-80 Wyoming bentonite compacted to dry densities of 0.6–2.0 g/cm3. Breakthrough of gold colloids was not observed in any of the three diffusion experiments. In a gold-concentration profile analysis, colloid diffusion was only observed for the smallest gold colloids at the lowest dry density used (estimated apparent diffusivity Da ≈5×10−13 m2/s). The results from a microstructure investigation using low-angle X-ray diffraction suggest that at the lowest dry density used, interlayer transport of the smallest colloids cannot be ruled out as a potential diffusion pathway, in addition to the expected interparticle transport. In all other cases, with either greater dry densities or larger gold colloids, compacted bentonite will effectively prevent diffusion of negatively charged colloids due to filtration.

  • 18. Holmboe, Michael
    et al.
    Wold, Susanna
    Jonsson, Mats
    Porosity investigation of compacted bentonite using XRD profile modeling2012Inngår i: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 128, nr 1–4, s. 19-32Artikkel i tidsskrift (Fagfellevurdert)
    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%.

  • 19. Holmboe, Michael
    et al.
    Wold, Susanna
    Jonsson, Mats
    García-García, Sandra
    Effects ofγ-irradiation on the stability of colloidal Na+-Montmorillonite dispersions2008Inngår i: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 43, s. 86-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In many concepts forfinal storage of spent nuclear fuel bentonite will be used as an engineered barrier,mainly due to its inertness, plasticity and ability to retard transport of radionuclides by adsorption. In theevent of water-bearing fractures making contact with the bentonite barrier, generation and transport ofcolloidal particles will strongly depend on groundwater composition and the surface properties of thecolloidal particles. The bentonite barrier will unavoidably be exposed to ionizing radiation from the spentnuclear fuel but very little is known about effects of ionizing radiation on bentonite concerning colloidalstability. In this work we have studied the effect ofγ-radiation on the stability of dilute colloidal Na+-montmorillonite dispersions using a Cs-137γ-source (doses of 0–53.2 kGy).Aggregation kinetics and sedimentation experiments revealed significant radiation effects, evident asincreased colloid stability. The only rationale for this is aγ-radiation induced increase in surface potential.The effects appeared to depend on the Na+-montmorillonite concentration in the irradiated dispersions,indicating that the change in surface potential is induced by aqueous radiolysis products.

  • 20. Holmboe, Michael
    et al.
    Wold, Susanna
    Petterson, Torbjörn
    Effects of the injection grout Silica sol on bentonite2011Inngår i: Physics and Chemistry of the Earth, ISSN 1474-7065, E-ISSN 1873-5193, Vol. 36, nr 17–18, s. 1580-1589Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Silica sol, i.e., colloidal SiO2, may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO2-colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO2-colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3 M NaCl), as well as dehydration and redispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO2-colloids affect the bulk/macro properties of bentonite. In order to study specific SiO2-colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO2-colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO2-colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO2-colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO2-colloids in Na+ dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca2+ dominated samples not subjected to excess NaCl, SiO2-colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and ungelled Silica sol should preferably be avoided.

  • 21.
    Kanbar, Hussein Jaafar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Olajos, Fredrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Englund, Göran
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Geochemical identification of potential DNA-hotspots and DNA-infrared fingerprints in lake sediments2020Inngår i: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 122, artikkel-id 104728Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    DNA preserved in sedimentary materials can be used to study past ecosystem changes, such as species' colonization and extinction. It is believed that minerals, especially clay minerals, enhance the preservation of DNA. However, the role of minerals, as well as organic matter, on DNA sorption in heterogeneous sediments is still not clear. In this study, we examined the effect of mineral and organic matter on DNA binding in lake sediments. Bulk and size-fractionated sediments (0–4, 4–16, 16–64, and >64 μm), having different mineral and organic composition, were used to test DNA sorption; similar experiments were also run after the removal of sedimentary organic matter. Additionally, diffuse reflectance infrared spectroscopy (DRIFT) was used to determine the chemical changes caused by DNA sorption and subsequently produce a DNA-infrared (IR) fingerprint. Clay minerals were the main minerals to sorb DNA in the different samples. Moreover, mica promoted DNA sorption in all size fractions, while chlorite promoted DNA sorption in size fractions greater than 16 μm; clay-mineral and organo-mineral complexes caused a preference of certain clay minerals over others. Sedimentary organic matter affected DNA sorption by covering as well as by amplifying potential DNA binding sites, yet DNA sorption did not change significantly. DNA sorption showed IR spectral modifications mainly at ~1640, 1416, and 1231 cm−1. Interestingly, the DNA-IR fingerprint in the heterogeneous sediments was evident by those peaks after spectral subtraction. Finally, we proposed a simple model, based on sediment geochemistry, that can be used to determine potential DNA-hotspots in sediments.

    Fulltekst (pdf)
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  • 22.
    Kanbar, Hussein Jaafar
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Tran Le, Thai
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Olajos, Fredrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Englund, Göran
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Tracking mineral and geochemical characteristics of Holocene lake sediments: the case of Hotagen, west-central Sweden2021Inngår i: Journal of Soils and Sediments, ISSN 1439-0108, E-ISSN 1614-7480, Vol. 21, nr 9, s. 3150-3168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose: Intact lake sediments reflect the development of terrestrial ecosystems. This development can be understood by decoding mineral and geochemical information of sedimentary archives. Therefore, we characterized a Holocene lake sediment core and revealed bulk to micro-scale variations via a combination of geochemical techniques and statistical methods.

    Methods: A 2.3 m sediment core was collected from Hotagen, a lake in west-central Sweden; a sediment sample was collected every 5 cm. A part of each sediment sample was kept untreated (named bulk) and another part was size-fractionated into < 4, 4–16, 16–64, and > 64 µm subsamples. Characterization was then made with respect to grain size distribution (GSD), physico-chemical parameters, geochemical properties, organic composition, and mineralogy. The sediments were investigated at bulk, micro-, and elemental scales using powder X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM–EDX).

    Results: The deepest sediment was identified as glacial till dating back to the Late Pleistocene. The bulk sediments showed a clear distinction between 0–195 cm (unit 1, U1) and 200–225 cm (unit 2, U2) depths. Quartz and feldspar minerals decreased and organic matter and clay minerals increased from the till towards the lower limit of U1. The development in the sedimentary properties marked the transformation of the terrestrial ecosystem from glacier-covered land to vegetated areas. This development was also well reflected by the appearance of X-ray amorphous materials and the formation of distinct organo-mineral aggregates; chlorite was the predominant clay mineral in these aggregates. The geochemical variation between U2 and U1 sediments was further established by resolving the DRIFT spectral components through multivariate curve resolution alternating least square (MCR-ALS). The U1 sediments settled over a period of ~ 7500 years and showed comparable mineral, geochemical, and organic composition. However, the size-fractionated sediments, mainly < 4 µm, showed diverse mineral and geochemical composition. Indeed, these sediments were distinct by containing relatively higher amounts of X-ray amorphous materials and clay minerals, the latter had variable Na, Mg, and K contents.

    Conclusion: The combined use of geochemical and statistical approaches used in this study followed the mineral and geochemical development of sediments that had settled during the Late Pleistocene and Early Holocene Epochs. Finally, the U2 sediments marked the terrestrial ecosystem development that occurred during the late glaciation, deglaciation, and post-glaciation periods. Graphical abstract: [Figure not available: see fulltext.]

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  • 23.
    Kim, Junhyung
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lindholm, Jerry
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Solvent and lipophilic solute effects on the swelling behavior of an organoclayManuskript (preprint) (Annet vitenskapelig)
  • 24.
    Lindholm, Jerry
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Deconvolution of Smectite Hydration Isotherms2019Inngår i: ACS Earth and Space Chemistry, E-ISSN 2472-3452, Vol. 3, nr 11, s. 2490-2498Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sorption isotherm models have traditionally served as an invaluable tool to characterize synthesized and natural mineral particles. However, for particles susceptible to substantial hydration, such as the swelling smectite clay minerals and other layered minerals displaying intercalation of discrete water monolayers, traditional isotherm models inadequately describe the total water uptake as a result of the change in available surface sites and area during the hydration process. With the goal of deconvoluting the water uptake behavior of swelling smectite minerals, this research presents a novel composite isotherm model that describes water uptake by surface adsorption, condensation, and stepwise intercalation. A set of eight montmorillonite samples ion-exchanged with different countercations (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, and Cu2+) were used to develop this model, which was based on gravimetric uptake measurements and X-ray diffraction data of basal spacings obtained from relative humidity conditions up to 98% relative humidity.

  • 25.
    Lindholm, Jerry
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Alcohol intercalation into montmorillonite: A combined 1D-XRD and molecular dynamics benchmarking studyManuskript (preprint) (Annet vitenskapelig)
  • 26.
    Luong, N. Tan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    MgO nanocube hydroxylation by nanometric water films2023Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 15, nr 24, s. 10286-10294Artikkel i tidsskrift (Fagfellevurdert)
    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.

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  • 27.
    Luong, N. Tan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Oderstad, Hanna
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Temperature-resolved nanoscale hydration of a layered manganese oxide2023Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 25, nr 26, s. 17352-17359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water films captured in the interlayer region of birnessite (MnO2) nanosheets can play important roles in biogeochemical cycling, catalysis, energy storage, and even atmospheric water harvesting. Understanding the temperature-dependent loadings and properties of these interlayer films is crucial to comprehend birnessite reactivity when exposed to moist air and temperature gradients. Using vibrational spectroscopy we show that birnessite intercalates one water (1W) monolayer at up to ∼40 °C, but that loadings decrease by half at up to 85 °C. Our results also show that the vibrational properties of intercalated water are unaffected by temperature, implying that the hydrogen bonding network of water remains intact. Using molecular simulations, we found that the lowered water storage capacity at high temperatures cannot be explained by variations in hydrogen bond numbers or in the solvation environments of interlayer K+ ions initially present in the interlayer region. It can instead be explained by the compounded effects of larger evolved heat, as inferred from immersion energies, and by the larger temperature-driven mobility of water over that of K+ ions, which are electrostatically bound to birnessite basal oxygens. By shedding new light on the temperature-driven intercalation of water in a nanolayered mineral, this study can guide future efforts to understand the (geo)chemical reactivity of related materials in natural and technological settings.

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  • 28.
    Rambaran, Mark
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Gorzsás, András
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Ohlin, C. André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Polyoxoniobates as molecular building blocks in thin films2021Inngår i: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, nr 44, s. 16030-16038Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb10O28]6−, [TiNb9O28]7− and [Ti2Nb8O28]8− onto silicon wafers, and annealing them. The [Nb10O28]6− cluster yields films of Nb2O5 in the orthorhombic and monoclinic crystal phases when annealed at 800 °C and 1000 °C, respectively, whereas the [TiNb9O28]7− and [Ti2Nb8O28]8− clusters yield the monoclinic crystal phases of Ti2Nb12O29 and TiNb2O7 (titanium–niobium oxides) in different ratios. We also demonstrate a protocol for depositing successive layers of metal oxide films. Finally, we explore factors affecting the roughness of the films.

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  • 29. Tinnacher, Ruth M.
    et al.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
    Tournassat, Christophe
    Bourg, Ian C.
    Davis, James A.
    Ion adsorption and diffusion in smectite: Molecular, pore, and continuum scale views2016Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 177, s. 130-149Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 30. Tournassat, Christophe
    et al.
    Bourg, Ian C.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sposito, Garrison
    Steefel, Carl I.
    Molecular dynamics simulations of anion exclusion in clay interlayer nanopores2016Inngår i: Clays and clay minerals, ISSN 0009-8604, E-ISSN 1552-8367, Vol. 64, nr 4, s. 374-388Artikkel i tidsskrift (Fagfellevurdert)
    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. 

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  • 31. Yang, Guomin
    et al.
    Neretnieks, Ivars
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores2017Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, nr 8, artikkel-id 084705Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 32.
    Yeşilbaş, Merve
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-Francois
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Residence times of nanoconfined CO2 in layered aluminosilicates2019Inngår i: Environmental Science: Nano, ISSN 2051-8153, Vol. 6, nr 1, s. 146-151Artikkel i tidsskrift (Fagfellevurdert)
    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.

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    fulltext
  • 33.
    Yeşilbaş, Merve
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Boily, Jean-François
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Cohesive vibrational and structural depiction of intercalated water in montmorillonite2018Inngår i: ACS Earth and Space Chemistry, E-ISSN 2472-3452, Vol. 2, nr 1, s. 38-47Artikkel i tidsskrift (Fagfellevurdert)
    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.

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