| 1. |
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| 2. |
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| 3. |
- Maurina Morais, Eduardo, 1989, et al.
(författare)
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Solvent-free synthesis of protic ionic liquids. Synthesis, characterization and computational studies of triazolium based ionic liquids
- 2022
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Ingår i: Journal of Molecular Liquids. - : Elsevier BV. - 0167-7322. ; 360
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Tidskriftsartikel (refereegranskat)abstract
- A series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98–99% m/m) and dry (128–553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is constructed of only glass and chemically resistant polymer (PTFE and PVDF) parts, which avoid other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). This process is described in detail in the paper as well as in a video. The resulting ionic liquids were carefully analyzed by spectroscopic and thermal methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.
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| 4. |
- Halldin Stenlid, Joakim, 1987-
(författare)
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Computational Studies of Chemical Interactions: Molecules, Surfaces and Copper Corrosion
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The chemical bond – a corner stone in science and a prerequisite for life – is the focus of this thesis. Fundamental and applied aspects of chemical bonding are covered including the development of new computational methods for the characterization and rationalization of chemical interactions. The thesis also covers the study of corrosion of copper-based materials. The latter is motivated by the proposed use of copper as encapsulating material for spent nuclear fuel in Sweden.In close collaboration with experimental groups, state-of-the-art computational methods were employed for the study of chemistry at the atomic scale. First, oxidation of nanoparticulate copper was examined in anoxic aqueous media in order to better understand the copper-water thermodynamics in relation to the corrosion of copper material under oxygen free conditions. With a similar ambition, the water-cuprite interface was investigated with regards to its chemical composition and reactivity. This was compared to the behavior of methanol and hydrogen sulfide at the cuprite surface.An overall ambition during the development of computational methods for the analysis of chemical bonding was to bridge the gap between molecular and materials chemistry. Theory and results are thus presented and applied in both a molecular and a solid-state framework. A new property, the local electron attachment energy, for the characterization of a compound’s local electrophilicity was introduced. Together with the surface electrostatic potential, the new property predicts and rationalizes regioselectivity and trends of molecular reactions, and interactions on metal and oxide nanoparticles and extended surfaces.Detailed atomistic understanding of chemical processes is a prerequisite for the efficient development of chemistry. We therefore envisage that the results of this thesis will find widespread use in areas such as heterogeneous catalysis, drug discovery, and nanotechnology.
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| 5. |
- Rahm, Martin, et al.
(författare)
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The Molecular Surface Structure of Ammonium and Potassium Dinitramide : A Vibrational Sum Frequency Spectroscopy and Quantum Chemical Study
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:21, s. 10588-10596
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Tidskriftsartikel (refereegranskat)abstract
- Vibrational sum frequency spectroscopy (VSFS) and quantum chemical modeling have been employed to investigate the molecular surface structure of ammonium and potassium dinitramide (ADN and KDN) crystals. Identification of key vibrational modes was made possible by performing density functional theory calculations of molecular clusters. The surface of KDN was found to be partly covered with a thin layer of the decomposition product KNO3, which due to its low thickness was not detectable by infrared and Raman spectroscopy. In contrast, ADN exhibited an extremely inhomogeneous surface, on which polarized dinitramide anions were present, possibly together with a thin layer of NH4NO3. The intertwined use of theoretical and experimental tools proved indispensable in the analysis of these complex surfaces. The experimental verification of polarized and destabilized dinitramide anions stresses the importance of designing surface-active polymer support, stabilizers, and/or coating agents, in order to enable environmentally friendly ADN-based solid-rocket propulsion.
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| 6. |
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| 7. |
- Maurina Morais, Eduardo, 1989
(författare)
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Synthesis of protic ionic liquids. Challenges and solutions for the synthesis of pure compounds.
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The urgent need to diversify our energy matrix is responsible for a renewed interest in fuel cell technology, which can use hydrogen gas, a renewable green fuel, as an energy source. This technology is currently a commercially available option, however, it still requires technological improvements before it can be widely used for different applications. One way this technology could potentially be improved is by increasing its temperature range of operation by developing new, anhydrous proton conducting materials. Protic ionic liquids, which are organic salts with low melting temperatures, are interesting candidates for this application, since they can conduct protons in the operational conditions of fuel cells and without the need of water. These compounds can be synthesized by a simple acid-base neutralization reaction, but certain considerations must be taken in order to obtain high quality (dry and pure) protic ionic liquids. In this thesis, a series of triazolium and imidazolium based protic ionic liquids were synthesized using a solvent-free method designed to address several limitations encountered with other commonly used methods. Using this method, pure (98-99% m/m) and dry (128-553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and base, and for the controlled mixing of both compounds, which is essential to avoid producing impure protic ionic liquids with excess of either acid or base. The system is consists of only glass and chemically resistant polymer(PTFE and PVDF) parts, which avoids other contaminants that can result from unwanted reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). The resulting ionic liquids were carefully analyzed by spectroscopic and thermal analysis methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes.
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| 8. |
- Sauer, Christopher, 1993
(författare)
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Green Aromatics: Catalytic Valorisation of bio-derived 2,5-dimethylfuran over Zeolites and Zeotypes
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis discusses the use of biomass as a potentially green feedstock for the chemical industry in the urgent shift away from fossil resources. I elaborate on reasons why we cannot afford to burn virgin biomass for energy production, among them a variety of ecosystem services that forests and other lands provide. In addition, the utilisation of biomass should be focused on products that sequester and lock away carbon for more extended periods, e.g. timber, materials and chemicals. In particular, biomass can be used as an alternative "carbon neutral" feedstock for the chemical industry, where we can preserve the already existing chemical complexity in the bio-based molecules. One example is the upgrading of furans to benzene, toluene and xylene (BTX) aromatics with the help of zeolite catalysis. These aromatics are important commodity chemicals, where the shift to a bio-based resource could make use of already existing knowledge, catalyst and production infrastructure. However, research is necessary to understand these new feedstock molecules and their interaction with the catalysts and to enable the design of applicable catalysts. In order to study the interaction of the furans, in particular 2,5-dimethylfuran (2,5-dmf), I describe and discuss the development of an analytical methodology that utilises infrared spectroscopy and mass spectrometry for the on-line identification and quantification of product molecules during catalytic reactions. This on-line analysis method is then applied to the catalytic conversion of 2,5-dmf to aromatics over a range of zeolite and zeotype catalysts. In-depth studies with ammonia as a probe molecule of the catalytic active acid sites, as well as temperature programmed experiments with ammonia and 2,5-dmf give insights into product distribution, selectivity changes and deactivation of the catalyst. For example, olefins and aromatics are initially preferred products, while with increasing time on stream, the isomerisation of 2,5-dmf becomes dominant. The incorporation of Ga into the zeotype framework, resulting in a Ga-Silicate, shows how targeted catalyst design can increase overall aromatics production. This catalyst is also suitable for selective isomerisation of 2,5-dmf to 2,4-dimethylfuran, which has a rare substitution pattern. Finally, itwas found that the most valuable of BTX, p -xylene, can be produced more selectively when 2,5-dmf is pre-adsorbed onto zeolite ZSM-5 and then released during a temperature programmed product desorption.
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| 9. |
- Shafeie, Samrand, 1984-, et al.
(författare)
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Phase formation, crystal structures and magnetic properties of perovskite-type phases in the system La2Co1+z(MgxTi1-x)1-zO6
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:1, s. 177-190
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type cobaltates in the system La(2)Co(1+z) (Mg(x)Ti(1-x))(1-z)O(6) were studied for z=0 <= x <= 0.6 and 0 <= x <= 0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 degrees C. The space group symmetry of the structure changes from P2(1)/n via Pbnm to R (3) over barc with both increasing Mg content and increasing Co content. The La(2)Co(Mg(x)Ti(1-x))O(6) (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0 <= x <= 0.5 a linear decrease in the L(3)/(L(3)+ L(2))Co-L(2.3) edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co(2+) ion content.
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| 10. |
- Rzepka, Przemyslaw, et al.
(författare)
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CO2-Induced Displacement of Na+ and K+ in Zeolite INaKI-A
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:30, s. 17211-17220
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption technologies offer opportunities to remove CO2 from gas mixtures, and zeolite A has good properties that include a high capacity for the adsorption of CO2 . It has been argued that its abilities to separate CO2 from N-2 in flue gas and CO2 from CH4 in raw biogas can be further enhanced by replacing Na+ with K+ in the controlling pore window apertures. In this study, several compositions of I Na12-xKxI-A were prepared and studied with respect to the adsorption of CO2 N-2, and CH4, and the detailed structural changes were induced by the adsorption of CO2. The adsorption of CO2 gradually decreased on an increasing content of K+, whereas the adsorption of N-2 and CH4 was completely nulled already at relatively small contents of K. Of the studied samples, INa9K3I-A exhibited the highest CO2 over N-2/CH4 selectivities, with a(CO2/N-2 ) > 21 000 and a(CO2/CH4) > 8000. For samples with and without adsorbed CO2 analyses of powder X-ray diffraction (PXRD) data revealed that K+ preferred to substitute Na+ at the eight-ring sites. The Na(+ )ions at the six-ring sites were gradually replaced by K+ on an increasing content, and these sites split into two positions on both sides of the six-ring mirror plane. It was observed that both the eight-ring and six-ring sites tailored the maximum adsorption capacity for CO2 and possibly also the diffusion of CO2 into the alpha-cavities of INa12-xKxI-A. The adsorption of CH4 and N-2 on the other hand appeared to be controlled by the K+ ions blocking the eight-ring windows. The in situ PXRD study revealed that the positions of the extra-framework cations were displaced into the a-cavities of INa12(_)x,KxI-A on the adsorption of CO2 . For samples with a low content of K+, the repositioning of the cations was consistent with a mutual attraction with the adsorbed CO(2 )molecules.
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| 11. |
- Artemenko, A., et al.
(författare)
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Reference XPS spectra of amino acids
- 2021
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Konferensbidrag (refereegranskat)abstract
- In this report we present XPS data for five amino acids (AAs) (tryptophan, methionine, glutamine, glutamic acid, and arginine) with different side chain groups measured in solid state (powder form). The theoretically and experimentally obtained chemical structure of AAs are compared. Here, we analyse and discuss C 1 s, N 1 s, O 1s and S 2p core level binding energies, FWHMs, atomic concentrations of the functional groups in AAs. The experimentally obtained and theoretically calculated ratio of atomic concentrations are compared. The zwitterionic nature of methionine and glutamine in solid state was determined from protonated amino groups in N 1s peak and deprotonated carboxylic groups in the C 1s spectrum. The obtained XPS results for AAs well correspond with previously reported data.
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| 12. |
- Barišić, Antun, et al.
(författare)
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Experimental Data Contributing to the Elusive Surface Charge of Inert Materials in Contact with Aqueous Media
- 2021
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Ingår i: Colloids and interfaces. - : MDPI. - 2504-5377. ; 5:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We studied the charging of inert surfaces (polytetrafluoroethylene, i.e., PTFE; graphite; graphene; and hydrophobic silica) using classical colloid chemistry approaches. Potentiometric titrations showed that these surfaces acquired less charge from proton-related reactions than oxide minerals. The data from batch-type titrations for PTFE powder did not show an effect of ionic strength, which was also in contrast with results for classical colloids. In agreement with classical colloids, the electrokinetic results for inert surfaces showed the typical salt level dependence. In some cases, the point of zero net proton charge as determined from mass and tentatively from acid–base titration differed from isoelectric points, which has also been previously observed, for example by Chibowski and co-workers for ice electrolyte interfaces. Finally, we found no evidence for surface contaminations of our PTFE particles before and after immersion in aqueous solutions. Only in the presence of NaCl-containing solutions did cryo-XPS detect oxygen from water. We believe that our low isoelectric points for PTFE were not due to impurities. Moreover, the measured buffering at pH 3 could not be explained by sub-micromolar concentrations of contaminants. The most comprehensive explanation for the various sets of data is that hydroxide ion accumulation occurred at the interfaces between inert surfaces and aqueous solutions.
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| 13. |
- Brinck, Tore, et al.
(författare)
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Green Energetic Materials, Chapter 2: "Theoretical Design of Green Energetic Materials: Predicting Stability, Detection, Synthesis and Performance"
- 2014
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Ingår i: Green Energetic Materials. - 9781119941293 ; , s. 15-44
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Since the end of the 20th century it has been increasingly realised that the use, or production, of many energetic materials leads to the release of substances which are harmful to both humans and the environment. To address this, the principles of green chemistry can be applied to the design of new products and their manufacturing processes, to create green energetic materials that are virtually free of environmental hazards and toxicity issues during manufacturing, storage, use and disposal. Active research is underway to develop new ingredients and formulations, green synthetic methods and non-polluting manufacturing processes.Green Energetic Materials provides a detailed account of the most recent research and developments in the field, including green pyrotechnics, explosives and propellants. From theoretical modelling and design of new materials, to the development of sustainable manufacturing processes, this book addresses materials already on the production line, as well as considering future developments in this evolving field.Topics covered include:Theoretical design of green energetic materialsDevelopment of green pyrotechnicsGreen primary and secondary explosivesOxidisers and binder materials for green propellantsEnvironmentally sustainable manufacturing technologies for energetic materialsElectrochemical methods for synthesis of energetic materials and waste remediationGreen Energetic Materials is a valuable resource for academic, industrial and governmental researchers working on the development of energetic materials, for both military and civilian applications.
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| 14. |
- Brinck, T, et al.
(författare)
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Green Energetic Materials, Chapter 7: "Green propellants Based on Dinitramide Salts: Mastering Stability and Chemical Compatibility Issues"
- 2014
-
Ingår i: Green Energetic Materials, kapitel 7. - 9781119941293 ; , s. 179-204
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Since the end of the 20th century it has been increasingly realised that the use, or production, of many energetic materials leads to the release of substances which are harmful to both humans and the environment. To address this, the principles of green chemistry can be applied to the design of new products and their manufacturing processes, to create green energetic materials that are virtually free of environmental hazards and toxicity issues during manufacturing, storage, use and disposal. Active research is underway to develop new ingredients and formulations, green synthetic methods and non-polluting manufacturing processes.Green Energetic Materials provides a detailed account of the most recent research and developments in the field, including green pyrotechnics, explosives and propellants. From theoretical modelling and design of new materials, to the development of sustainable manufacturing processes, this book addresses materials already on the production line, as well as considering future developments in this evolving field.Topics covered include:Theoretical design of green energetic materialsDevelopment of green pyrotechnicsGreen primary and secondary explosivesOxidisers and binder materials for green propellantsEnvironmentally sustainable manufacturing technologies for energetic materialsElectrochemical methods for synthesis of energetic materials and waste remediationGreen Energetic Materials is a valuable resource for academic, industrial and governmental researchers working on the development of energetic materials, for both military and civilian applications.
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| 15. |
- Shafeie, Samrand, 1984-
(författare)
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Structure and Properties Investigations of the La2Co1+z(Ti1-xMgx)1-zO6 Perovskite System
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Perovskite based materials have great potentials for various energy applications and the search for new materials for uses in SOFCs has largely been concentrated to this class of compounds. In this search, we have studied perovskite phases in the system La2Co1+z(Ti1-xMgx)1-zO6, with 0 x 0.9 and z = 0.0, 0.2, 0.4, 0.6. Crystal structures were characterized by XRD and, for selected compositions, also by NPD and SAED. They exhibit with increasing x, as well as increasing z, a progressive increase in symmetry from monoclinic to orthorhombic to rhombohedral. The main focus in this work has been on the investigation of structure-property relations for compositions with 0.0 x 0.5 and z = 0. The nominal oxidation state of Co increases for these with increasing x, from Co2+ for x = 0 to Co3+ for x = 0.5. Magnetic measurements and XANES studies showed that the average spin state of Co changes linearly with increasing x, up to x = 0.5, in accordance with varying proportions of Co with two fixed oxidation states, i.e. Co2+ and Co3+. The data suggests that the Co3+ ions have an IS spin state or a mixture of LS and HS spin states for all compositions with nominally only Co2+ and Co3+ ions, possibly with the exception of the composition with x = 0.1, 0.2 and z = 0, for which the data indicate that the spin state might be HS. The XANES data indicate furthermore that for the perovskite phases with z = 0 and x > 0.5, which in the absence of O atom vacancies contain formally Co4+, the highest oxidation state of Co is Co3+, implying that the substitution of Ti4+ by Mg2+ for x ³ 0.5 effects an oxidation of O2- ions rather than an oxidation of Co3+ ions. The thermal expansion was found to increase nearly linearly with increasing oxidation state of Co. This agrees well with findings in previous studies and is attributable to an increase in the ionic radius of Co3+ ions with increasing temperature, due to a thermal excitation from a LS to IS or LS/HS spin states. High temperature electronic conductivity measurements indicate that the electronic conductivity increases with an increase of both relative and absolute amount of Co3+. The latter can be attributed to an increase in the number of Co-O-Co connections. Additional high temperature magnetic measurements for selected samples, whose susceptibilities did not follow a Curie law behaviour up to room temperature, showed effective magnetic moments that did approach plateaus even at high temperatures (900 K). Interpretations of these data are, however, hindered by the samples losing oxygen during the applied heating-cooling cycle. The present study has shown that the investigated system is suitable for further studies, of more fundamental character, which could provide further insight of the structure-property relationships that depend on the oxidation state of Co.
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| 16. |
- Hedlund, Artur, et al.
(författare)
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Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate : contrasting coagulation mechanisms
- 2019
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:3, s. 1545-1563
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].
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| 17. |
- Moth-Poulsen, Kasper, 1978
(författare)
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Molecular Systems for Solar Thermal Energy Storage and Conversion
- 2013
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Ingår i: Organic Synthesis and Molecular Engineering. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. ; , s. 179-196
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Using a synthetic approach to organic materials chemistry, this book sets forth tested and proven methods and practices that make it possible to engineer organic molecules offering special properties and functions. Throughout the book, plenty of real-world examples demonstrate the countless possibilities of creating one-of-a-kind molecules and supramolecular systems to support a broad range of applications. The book explores applications in both materials and bioorganic chemistry, including molecular electronics, energy storage, sensors, nanomedicine, and enzyme engineering.Organic Synthesis and Molecular Engineering consists of fourteen chapters, each one contributed by one or more leading international experts in the field. The contributions are based on a thorough review and analysis of the current literature as well as the authors' firsthand experience in the lab engineering new organic molecules. Designed as a practical lab reference, the book offers:Tested and proven synthetic approaches to organic materials chemistryMethods and practices to successfully engineer functionality into organic moleculesExplanations of the principles and concepts underlying self-assembly and supramolecular chemistryGuidance in selecting appropriate structural units used in the design and synthesis of functional molecules and materialsCoverage of the full range of applications in materials and bioorganic chemistryA full chapter on graphene, a new topic generating intense researchOrganic Synthesis and Molecular Engineering begins with core concepts, molecular building blocks, and synthetic tools. Next, it explores molecular electronics, supramolecular chemistry and self-assembly, graphene, and photoresponsive materials engineering. In short, it offers everything researchers need to fully grasp the underlying theory and then build new molecules and supramolecular systems.
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| 18. |
- Singh, Shivangi, 1996
(författare)
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Investigating hydrothermal stability and influence of water on the activity of Cu-CHA catalysts for NH3-SCR
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Selective catalytic reduction of nitrogen oxides (NOx) with NH3 as a reducing agent (NH3- SCR) is a leading technology for diesel exhaust emission control. Cu-exchanged zeolites with the chabazite structure (Cu-CHA) have emerged as the preferred catalysts thanks to its high activity and hydrothermal stability. Hydrothermal stability is related to dealumination, i.e. removal of aluminum from the zeolite framework to form extraframework aluminum, at high temperatures in the presence of water vapor. Copperexchanged chabazite (Cu-CHA) zeolites have higher hydrothermal stability compared to H-chabazite (H-CHA). To understand the delayed dealumination of Cu-CHA catalysts, we have investigated the reaction paths for dealumination in H-CHA and Cu-CHA using density functional theory (DFT) calculations combined with microkinetic modeling. We find that Cu-CHA and H-CHA follow similar four-step hydrolysis processes, yet the dealumination of Cu-CHA has higher energy barriers, suggesting stabilization of the CHA structure by Cu ions. Furthermore, the preferred reaction product upon complete dealumination of Cu-CHA is a copper-aluminate like species bound to the zeolite framework. The microkinetic analysis quantifies the increased stability of Cu-CHA as compared to H-CHA. In addition to the high-temperature dealumination, we investigated the role of water on low-temperature SCR by experimentally measuring the activity and reaction order of water. The reaction order of water is found to be increasingly negative with increasing water pressure. DFT calculations reveal that water blocks the active Cu-sites and a DFT-based microkinetic model reproduces the measured change of reaction order with water pressure.
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| 19. |
- Sun, Bing, et al.
(författare)
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Ion transport in polycarbonate based solid polymer electrolytes : experimental and computational investigations
- 2016
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:14, s. 9504-9513
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Tidskriftsartikel (refereegranskat)abstract
- Among the alternative host materials for solid polymer electrolytes (SPEs), polycarbonates have recently shown promising functionality in all-solid-state lithium batteries from ambient to elevated temperatures. While the computational and experimental investigations of ion conduction in conventional polyethers have been extensive, the ion transport in polycarbonates has been much less studied. The present work investigates the ionic transport behavior in SPEs based on poly(trimethylene carbonate) (PTMC) and its co-polymer with epsilon-caprolactone (CL) via both experimental and computational approaches. FTIR spectra indicated a preferential local coordination between Li+ and ester carbonyl oxygen atoms in the P(TMC20CL80) co-polymer SPE. Diffusion NMR revealed that the co-polymer SPE also displays higher ion mobilities than PTMC. For both systems, locally oriented polymer domains, a few hundred nanometers in size and with limited connections between them, were inferred from the NMR spin relaxation and diffusion data. Potentiostatic polarization experiments revealed notably higher cationic transference numbers in the polycarbonate based SPEs as compared to conventional polyether based SPEs. In addition, MD simulations provided atomic-scale insight into the structure-dynamics properties, including confirmation of a preferential Li+-carbonyl oxygen atom coordination, with a preference in coordination to the ester based monomers. A coupling of the Li-ion dynamics to the polymer chain dynamics was indicated by both simulations and experiments.
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| 20. |
- Nedumkandathil, Reji, et al.
(författare)
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Hydrogenation induced structure and property changes in GdGa
- 2016
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 239, s. 184-191
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Tidskriftsartikel (refereegranskat)abstract
- Hydrides GdGaH were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 degrees C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 degrees C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) angstrom, b=12.024(2) angstrom, c=4.1009(6) angstrom) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 degrees C affords a hydride with x approximate to 1.3, which is stable up to 500 degrees C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200 degrees C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300 degrees C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of similar to 8 mu B which is typical for compounds containing Gd3+ ions.
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| 21. |
- Sznitko, L., et al.
(författare)
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Low-threshold stimulated emission from lysozyme amyloid fibrils doped with a blue laser dye
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 106:2
-
Tidskriftsartikel (refereegranskat)abstract
- © 2015 AIP Publishing LLC. Amyloid fibrils are excellent self-assembling nanotemplates for organic molecules such as dyes. Here, we demonstrate that laser dye-doped lysozyme type fibrils exhibit significantly reduced threshold for stimulated emission compared to that observed in usual matrices. Laser action was studied in slab planar waveguides of the amyloids doped with Stilbene 420 laser dye prepared using a film casting technique. The lowering of the threshold of stimulated emission is analyzed in the context of intrinsic structure of the amyloid nanotemplates, electrostatic interaction of different microstructures with dye molecules, as well as material properties of the cast layers. All these factors are considered to be of importance for introducing gain for random laser operation.
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| 22. |
- Börjesson, Karl, 1982, et al.
(författare)
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Conjugated anthracene dendrimers with monomer-like fluorescence
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:38, s. 19846-19850
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Tidskriftsartikel (refereegranskat)abstract
- Two generations of highly emissive conjugated anthracene dendrimers containing up to 9 anthracene units are presented. In these dendrimers, anthracene-like absorption and emission properties are preserved due to the relatively weak electronic coupling between the anthracene units, while evidence of fast crosstalk within the molecular framework is still observed.
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| 23. |
- Zhou, Yu, et al.
(författare)
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Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures
- 2019
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Ingår i: Small. - : Wiley-VCH Verlagsgesellschaft. - 1613-6810 .- 1613-6829. ; 15:19
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Tidskriftsartikel (refereegranskat)abstract
- Using the MoS2-WTe2 heterostructure as a model system combined with electrochemical microreactors and density function theory calculations, it is shown that heterostructured contacts enhance the hydrogen evolution reaction (HER) activity of monolayer MoS2. Two possible mechanisms are suggested to explain this enhancement: efficient charge injection through large-area heterojunctions between MoS2 and WTe2 and effective screening of mirror charges due to the semimetallic nature of WTe2. The dielectric screening effect is proven minor, probed by measuring the HER activity of monolayer MoS2 on various support substrates with dielectric constants ranging from 4 to 300. Thus, the enhanced HER is attributed to the increased charge injection into MoS2 through large-area heterojunctions. Based on this understanding, a MoS2/WTe2 hybrid catalyst is fabricated with an HER overpotential of -140 mV at 10 mA cm(-2), a Tafel slope of 40 mV dec(-1), and long stability. These results demonstrate the importance of interfacial design in transition metal dichalcogenide HER catalysts. The microreactor platform presents an unambiguous approach to probe interfacial effects in various electrocatalytic reactions.
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| 24. |
- Howe, Andrew, 1995-
(författare)
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Immobilisation of Ru-Based Molecular Catalysts for Electrochemical Water Oxidation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Artificial photosynthesis requires catalysts for efficient and selective conversions of small molecules. Molecular catalysts are advantageous to use in these instances as they offer precise control over chemical reactivity. They are synthetically tuneable, and their catalytic mechanisms are often well documented and more readily understood than those of solid-state catalysts. In this thesis, the synthetic incorporation of molecular catalysts into heterogenised molecular anodes for water oxidation are evaluated. The catalysts are incorporated as structural linkers into porous metal-organic framework (MOF) structures, and as coordination oligomers stacked onto graphitic surfaces. The preparation of MOF/molecular catalyst hybrid materials of two topologies, UiO (UiO = Universitet i Oslo) and NU-1000 (NU = Northwestern University), were investigated. Multiple synthetic methods for the incorporation of molecular ruthenium-based catalysts into MOFs were examined in papers I and II. In paper III of this thesis, a Ru-bda type molecular complex was successfully used in the solvothermal synthesis of a new MOF. The resulting material is the first of its kind that is built exclusively from molecular water oxidation catalyst linkers. It is shown that MOF incorporation greatly enhances the structural stability of the catalyst linker in chemical water oxidation experiments, giving rise to higher turnover numbers compared to that of a homogenous reference system. Finally, paper IV describes a stable and inert molecular ruthenium complex, which possesses a flexible adaptative multidentate equatorial (FAME) type equatorial ligand with a carbanion on the equatorial ligand that forms a C-Ru bond. This molecular complex is studied in homogeneous phase, and subsequently incorporated into a coordination oligomer, which can be activated for water oxidation catalysis. This finding broadens the field of molecular catalysis significantly, and proves that supramolecular interactions can be used to promote electrocatalysis in complexes which are otherwise too inert and stable to engage in electrocatalytic reactions.
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| 25. |
- Kersti, Hermansson, et al.
(författare)
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The vibrating hydroxide ion in water
- 2011
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 514:1-3, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- The OH− ion in water is studied using a CPMD/BLYP + QMelectronic + QMvibrational approach. The ion resides in a cage of water molecules, which are H-bonded among each other, and pinned by H-bonding to the ion’s O atom. The water network keeps the ‘on-top’ water in place, despite the fact that this particular ion-water pair interaction is non-binding. The calculated OH− vibrational peak maximum is at ∼3645 cm−1 (experiment ∼3625 cm−1) and the shift with respect to the gas-phase is ∼ +90 cm−1 (experiment +70 cm−1). The waters molecules on each side of the ion (O and H) induce a substantial OH− vibrational blueshift, but the net effect is much smaller than the sum. A parabolic ‘frequency-field’ relation qualitatively explains this non-additivity. The calculated ‘in-liquid’ ν(OH−) anharmonicity is 85 cm−1.
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