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  • 51. Maldonado, P.
    et al.
    Godinho, José
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Evins, L. Z.
    Oppeneeer, P. M.
    Ab Initio Prediction of Surface Stability of Fluorite Materials and Experimental Verification2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 13, p. 6639-6650Article in journal (Refereed)
    Abstract [en]

    Utilizing first-principle simulations [based on density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U)], we develop a model to explain the experimental stability in solution of materials having the fluorite structure, such as CaF2 and CeO2. It is shown that the stability of a surface is mainly dependent on its atomic structure and the presence of sites where atoms are deficiently bonded. Using as reference planes the surfaces with low surface formation energies, viz., (111), (100), and (110), our results reveal the relation between the surface energy of any Miller-indexed plane and the surface energy of those reference planes, being dependent on the fluorite surface structure only. Therefore, they follow the same trend for CaF2 and CeO2. Comparison with experimental results shows a correlation between the trends of dry surface energies and surface stabilities during dissolution of both CaF2 and CeO2, even though the chemical processes of dissolution of CeO2 and CaF2 are different. A deviation between ab initio predictions and experiments for some surfaces highlights the sensitivity of the developed model to the treatment of surface dipolar moments.

  • 52.
    Mayence, Arnaud
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wery, Madeleine
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wetterskog, Erik
    Svedlindh, Peter
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Interfacial strain and defects in asymmetric Fe-Mn oxide hybrid nanoparticles2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 29, p. 14171-14177Article in journal (Refereed)
    Abstract [en]

    Asymmetric Fe-Mn oxide hybrid nanoparticles have been obtained by a seed-mediated thermal decomposition-based synthesis route. The use of benzyl ether as the solvent was found to promote the orientational growth of Mn1-xO onto the iron oxide nanocube seeds yielding mainly dimers and trimers whereas 1-octadecene yields large nanoparticles. HRTEM imaging and HAADF-STEM tomography performed on dimers show that the growth of Mn1-xO occurs preferentially along the edges of iron oxide nanocubes where both oxides share a common crystallographic orientation. Fourier filtering and geometric phase analysis of dimers reveal a lattice mismatch of 5% and a large interfacial strain together with a significant concentration of defects. The saturation magnetization is lower and the coercivity is higher for the Fe-Mn oxide hybrid nanoparticles compared to the iron oxide nanocube seeds.

  • 53. McFarland, Hannah L.
    et al.
    Ahmed, Towfiq
    Zhu, Jian-Xin
    Balatsky, Alexander V.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Los Alamos National Laboratory, New Mexico.
    Haradsen, Jason T.
    First-Principles Investigation of Nanopore Sequencing Using Variable Voltage Bias on Graphene-Based Nanoribbons2015In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 6, no 13, p. 2616-2621Article in journal (Refereed)
    Abstract [en]

    In this study, we examine the mechanism of nanopore-based DNA sequencing using a voltage bias across a graphene nanoribbon. Using density function theory and a nonequilibrium Green's function approach, we determine the transmission spectra and current profile for adenine, guanine, cytosine, thymine, and uracil as a function of bias voltage in an energy minimized configuration. Utilizing the transmission current, we provide a general methodology for the development of a three nanopore graphene-based device that can be used to distinguish between the various nucleobases for DNA/RNA sequencing. From our analysis, we deduce that it is possible to use different transverse currents across a multinanopore device to differentiate between nucleobases using various voltages of 0.5, 1.3, and 1.6 V. Overall, our goal is to improve nanopore design to further DNA/RNA nucleobase sequencing and biomolecule identification techniques.

  • 54. Moskalenko, Sveatoslav A.
    et al.
    Podlesny, Igor V.
    Dumanov, Evgheni V.
    Liberman, Michael A.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Novikov, Boris V.
    Dispersion laws of the two-dimensional cavity magnetoexciton-polaritons2016In: Journal of Nanophotonics, ISSN 1934-2608, Vol. 10, no 3, article id 036006Article in journal (Refereed)
    Abstract [en]

    The energy spectrum of the two-dimensional cavity magnetoexciton-polaritons has been investigated previously, using exact solutions for the Landau quantization (LQ) of conduction electrons and heavy holes (hhs) provided by the Rashba method. Two lowest LQ levels for electrons and three lowest Landau levels for hhs lead to the construction of the six lowest magnetoexciton sates. They consist of two dipole-active, two quadrupole-active, and the two forbidden quantum transitions from the ground state of the crystal to the magnetoexciton states. The interaction of the four optical-active magnetoexciton states with the cavity-mode photons with a given circular polarization and with well-defined incidence direction leads to the creation of five magnetoexciton-polariton branches. The fifth-order dispersion equation is examined by using numerical calculations and the second-order dispersion equation is solved analytically, taking into account only one dipole-active magnetoexciton state in the point of the in-plane wave vector (k) over right arrow || = 0. The effective polariton mass on the lower polariton branch, the Rabi frequency, and the corresponding Hopfield coefficients are determined in dependence on the magnetic-field strength, the Rashba spin-orbit coupling parameters, and the electron and hole g-factors. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).

  • 55. Namanga, Jude E.
    et al.
    Gerlitzki, Niels
    Smetana, Volodymyr
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). U.S. Department of Energy, United States.
    Mudring, Anja-Verena
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Ruhr-Universität Bochum, Germany; U.S. Department of Energy, United States.
    Supramolecularly Caged Green-Emitting Ionic Ir(III)-Based Complex with Fluorinated CN Ligands and Its Application in Light-Emitting Electrochemical Cells2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 13, p. 11026-11036Article in journal (Refereed)
    Abstract [en]

    Ionic Ir(III) complexes are the most promising emitters in light emitting electrochemical cells (LECs), especially in the high energy emission range for which it is difficult to find emitters with sufficient efficiencies and lifetimes. To overcome this challenge, we introduced the concept of intramolecular pi-pi stacking of an ancillary ligand (6-phenyl-2,2'-bipyridine, pbpy) in the design of a new green-emitting iridium ionic transition metal complex with a fluoro-substituted cyclometallated ligand, 2-(4-fluorophenyOpyridinato (4Fppy). [Ir(4Fppy)(2)(pbpy)][PF6] has been synthesized and characterized and its photophysical and electrochemical properties have been studied. The complex emits green light with maxima at 561 and 556 nm under UV excitation from powder and thin film, respectively, and displays a high photoluminescence quantum yield (PLQY) of 78.5%. [Ir(4Fppy)(2)(pbpy)][PF6] based LECs driven under pulsed current conditions showed under an average current density of 100 A m(-2) (at 50% duty cycle) a maximum luminance of 1443 cd m(-2), resulting in 14.4 cd A(-1) and 7.4 lm W-1 current and power efficiencies, respectively. A remarkable long device lifetime of 214 h was observed. Reducing the average current density to 18.5 A m(-2) (at 75% duty cycle) led to an exceptional device performance of 19.3 cd A(-1) and 14.4 lm W1- for current and power efficiencies, an initial maximum luminance of 352 cd m(-2) and a lifetime of 617 h.

  • 56. Nileback, Linnea
    et al.
    Widhe, Mona
    Seijsing, Johan
    Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
    Bysell, Helena
    Sharma, Prashant K.
    Hedhammar, My
    Bioactive Silk Coatings Reduce the Adhesion of Staphylococcus aureus while Supporting Growth of Osteoblast-like Cells2019In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 28, p. 24999-25007Article in journal (Refereed)
    Abstract [en]

    Orthopedic and dental implants are associated with a substantial risk of failure due to biomaterial-associated infections and poor osseointegration. To prevent such outcomes, a coating can be applied on the implant to ideally both reduce the risk of bacterial adhesion and support establishment of osteoblasts. We present a strategy to construct dual-functional silk coatings with such properties. Silk coatings were made from a recombinant partial spider silk protein either alone (silk(wt)) or fused with a cell-binding motif derived from fibronectin (FN-silk). The biofilm-dispersal enzyme Dispersin B (DspB) and two peptidoglycan degrading endolysins, PlySs2 and SAL-1, were produced recombinantly. A sortase recognition tag (SrtTag) was included to allow site-specific conjugation of each enzyme onto silk(wt) and FN-silk coatings using an engineered variant of the transpeptidase Sortase A (SrtA*). To evaluate bacterial adhesion on the samples, Staphylococcus aureus was incubated on the coatings and subsequently subjected to live/dead staining. Fluorescence microscopy revealed a reduced number of bacteria on all silk coatings containing enzymes. Moreover, the bacteria were mobile to a higher degree, indicating a negative influence on the bacterial adhesion. The capability to support mammalian cell interactions was assessed by cultivation of the osteosarcoma cell line U-2 OS on dual-functional surfaces, prepared by conjugating the enzymes onto FN-silk coatings. U-2 OS cells could adhere to silk coatings with enzymes and showed high spreading and viability, demonstrating good cell compatibility.

  • 57.
    Ogonowski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Edlund, Ulrica
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Linde, Margareta
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ek, Karin
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Liewenborg, Birgitta
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Könnecke, Oda K.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Navarro, Julien R. G.
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Multi-level toxicity assessment of engineered cellulose nanofibrils in Daphnia magna2018In: Nanotoxicology, ISSN 1743-5390, E-ISSN 1743-5404, Vol. 12, no 6, p. 509-521Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibril (CNF)-based materials are increasingly used in industrial and commercial applications. However, the impacts of CNF on aquatic life are poorly understood, and there are concerns regarding their potential toxicity. Using a combination of standard ecotoxicological tests and feeding experiments, we assessed the effects of CNF exposure (0.206-20.6 mg/L) on the feeding (food uptake and gut residence time) and life-history traits (growth and reproduction) in the cladoceran Daphnia magna. No mortality was observed in a 48 h acute exposure at 2060 mg/L. Moreover, a 21-day exposure at low food and moderate CNF levels induced a stimulatory effect on growth, likely driven by increased filtration efficiency, and, possibly, partial assimilation of the CNF by the animals. However, at low food levels and the highest CNF concentrations, growth and reproduction were negatively affected. These responses were linked to caloric restriction caused by dilution of the food source, but not an obstruction of the alimentary canal. Finally, no apparent translocation of CNF past the alimentary canal was detected. We conclude that CNF displays a low toxic potential to filter-feeding organisms and the expected environmental risks are low.

  • 58.
    Ojuva, Arto
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Akhtar, Farid
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tomsia, Antoni P.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laminated Adsorbents with Very Rapid CO2 Uptake by Freeze-Casting of Zeolites2013In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 7, p. 2669-2676Article in journal (Refereed)
    Abstract [en]

    Structured zeolite 13X monoliths with a laminated structure and hierarchical macro-/microporosity were prepared by freeze-casting aqueous suspensions of zeolite 13X powder, bentonite, and polyethylene glycol. Colloidally stable suspensions with a low viscosity at both room temperature and near freezing could be prepared at alkaline conditions where both the zeolite 13X powder and bentonite carry a negative surface charge. Slow directional freezing of the suspensions led to the formation of well-defined and thin lamellar pores and pore walls while fast freezing resulted in more cylindrical pores. The wall thickness, which varied between 8 and 35 mu m, increased with increasing solids loading of the suspension. Thermal treatment at 1053 K of the freeze-cast bodies containing between 9 and 17 wt % bentonite resulted in mechanically stable zeolite 13X monoliths. The monoliths displayed a carbon dioxide uptake capacity of 4-5 mmol/g and an uptake kinetics characterized by a very fast initial uptake where more than 50% of the maximum uptake was reached within 15 s. Freeze-cast laminated zeolite monoliths could be used to improve the volumetric efficiency and reduce the cycle time, of importance in, for example, biogas upgrading and CO2 separation from flue gas.

  • 59.
    Ojwang, Dickson O.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svensson, Gunnar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    The adsorption kinetics of CO2 on copper hexacyanoferrate studied by thermogravimetric analysis2018In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 272, p. 70-78Article in journal (Refereed)
    Abstract [en]

    The CO2 adsorption and CO2 adsorption kinetics were evaluated by thermogravimetry on two Prussian blue analogues, K2x/3CuII [Fe-x(II) Fe-1-x(III) (CN)(6)](2/3), with nominally K-free x = 0.0 and K-rich x = 1.0. Differential isosteric heats of adsorption were determined from adsorption isotherms using the Clausius-Clapeyron equation and integral values by differential scanning calorimetry. The average differential heats of CO2 adsorption are 28 kJ/mol for x = 0.0 and 33 kJ/mol for x = 1.0. Both compositions show small maxima in differential heat at similar to 1 mmol/g. The integral adsorption heats were determined to be 26 kJ/mol for both x = 0.0 and x = 1.0. The kinetic CO(2 )adsorption/desorption curves can be modeled by a double exponential function describing two parallel processes with different rate constants. The activation energies for CO2 adsorption on x = 0.0 were 6 (1) kJ/mol for the faster component and 16 (1) kJ/mol for the slower one, while the corresponding values for x = 1.0 were 9 (1) kJ/mol and 7 (1) kJ/mol, respectively. The maximum CO2 uptake for both compositions was found to be similar to 4.5 mmol/g, 19.8 wt%, at 1 bar and 273 K. The materials exhibited fast adsorption kinetics and stable cyclic performance at room temperature. The kinetics were slower for the samples with x = 1.0 than for x = 0.0 which may be attributed to interactions between CO2 molecules and K+ ions.

  • 60. Philippe, Bertrand
    et al.
    Jacobsson, T. Jesper
    Correa-Baena, Juan-Pablo
    Jena, Naresh K.
    Banerjee, Amitava
    Chakraborty, Sudip
    Cappel, Ute B.
    Ahuja, Rajeev
    Hagfeldt, Anders
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rensmo, Håkan
    Valence Level Character in a Mixed Perovskite Material and Determination of the Valence Band Maximum from Photoelectron Spectroscopy: Variation with Photon Energy2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 48, p. 26655-26666Article in journal (Refereed)
    Abstract [en]

    A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron-based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from ultraviolet photoelectron spectroscopy (21.2 eV) to hard X-rays (up to 4000 eV), and by taking the variation of the photoionization cross sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. This work also includes a thorough study of the valence band maximum and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties.

  • 61. Rehnlund, David
    et al.
    Valvo, Mario
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ångström, Jonas
    Sahlberg, Martin
    Edström, Kristina
    Nyholm, Leif
    Electrochemical fabrication and characterization of Cu/Cu2O multi-layered micro and nanorods in Li-ion batteries2015In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 32, p. 13591-13604Article in journal (Refereed)
    Abstract [en]

    Electrodes composed of freestanding nano- and microrods composed of stacked layers of copper and cuprous oxide have been fabricated using a straightforward one-step template-assisted pulsed galvanostatic electrodeposition approach. The approach provided precise control of the thickness of each individual layer of the high-aspect-ratio rods as was verified by SEM, EDS, XRD, TEM and EELS measurements. Rods with diameters of 80, 200 and 1000 nm were deposited and the influence of the template pore size on the structure and electrochemical performance of the conversion reaction based electrodes in lithium-ion batteries was investigated. The multi-layered Cu2O/Cu nano-and microrod electrodes exhibited a potential window of more than 2 V, which was ascribed to the presence of a distribution of Cu2O (and Cu, respectively) nanoparticles with different sizes and redox potentials. As approximately the same areal capacity was obtained independent of the diameter of the multi-layered rods the results demonstrate the presence of an electroactive Cu2O layer with a thickness defined by the time domain of the measurements. It is also demonstrated that while the areal capacity of the electrodes decreased dramatically when the scan rate was increased from 0.1 to 2 mV s(-1), the capacity remained practically constant when the scan rate was further increased to 100 mV s(-1). This behaviour can be explained by assuming that the capacity is limited by the lithium ion diffusion rate though the Cu2O layer generated during the oxidation step. The electrochemical performance of present type of 3-D multi-layered rods provides new insights into the lithiation and delithiation reactions taking place for conversion reaction materials such as Cu2O.

  • 62. Renman, Viktor
    et al.
    Valvo, Mario
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zimmermann, Iwan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gomez, Cesar Pay
    Edström, Kristina
    Investigation of the Structural and Electrochemical Properties of Mn2Sb3O6CI upon Reaction with Li Ions2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 11, p. 5949-5958Article in journal (Refereed)
    Abstract [en]

    The structural and electrochemical properties of a quaternary layered compound with elemental composition Mn2Sb3O6Cl have been investigated upon reaction with lithium in Li half cells. Operando XRD was used to investigate the potential impact of this particular layered structure on the lithiation process. Although the results suggest that the material is primarily reacted through a conventional conversion mechanism, they also provide some hints that the space between the slabs may act as preferential entry points for lithium ions but not for the larger sodium ions. Cyclic voltammetry, galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed to unravel the details of the reaction mechanism with the lithium ions. It is found that two pairs of reactions are mainly responsible for the reversible electrochemical cycling of this compound, namely, the alloying of Li-Sb and the conversion of MnxOy to metallic Mn with concomitant formation of Li2O upon lithium uptake. A moderate cycling stability is achieved with a gravimetric capacity of 467 mAh g(-1) after 100 cycles between 0.05 and 2.2 V vs Li+/Li despite the large particle sizes of the active material and its nonoptimal inclusion into composite coatings. The electrochemical activity of the title compound was also tested in Na half cells between 0.05 and 2 V vs Ne/Na. It was found that a prolonged period of electrochemical milling is required to fully gain access to the active material, after which the cell delivers a capacity of 350 mAh CI. These factors are demonstrated to clearly limit the ultimate performances for these electrodes.

  • 63. Russell, Camilla
    et al.
    Welch, Ken
    Jarvius, Jonas
    Cai, Yixiao
    Brucas, Rimantas
    Nikolajeff, Fredrik
    Svedlindh, Peter
    Nilsson, Mats
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Stockholm University, Science for Life Laboratory (SciLifeLab). Uppsala University, Sweden.
    Gold Nanowire Based Electrical DNA Detection Using Rolling Circle Amplification2014In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 8, no 2, p. 1147-1153Article in journal (Refereed)
    Abstract [en]

    We present an electrical sensor that uses rolling circle amplification (RCA) of DNA to stretch across the gap between two electrodes, interact with metal nanoparticle seeds to generate an electrically conductive nanowire, and produce electrical signals upon detection of specific target DNA sequences. RCA is a highly specific molecular detection mechanism based on DNA probe circularization. With this technique, long single-stranded DNA with simple repetitive sequences are produced. Here we show that stretched RCA products can be metalized using silver or gold solutions to form metal wires. Upon metallization, the resistance drops from T Omega to k Omega for silver and to Omega for gold. Metallization is seeded by gold nanoparticles aligned along the single-stranded DNA product through hybridization of functionalized oligonucleotides. We show that combining RCA with electrical DNA detection produces results in readout with very high signal-to-noise ratio, an essential feature for sensitive and specific detection assays. Finally, we demonstrate detection of 10 ng of Escherichia coli genomic DNA using the sensor concept.

  • 64.
    Rzepka, Przemyslaw
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chalmers University of Technology, Sweden; University of Warsaw, Poland.
    Smeets, Stef
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Müller, Melanie
    Gies, Hermann
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    CO2-Induced Displacement of Na+ and K+ in Zeolite INaKI-A2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 30, p. 17211-17220Article in journal (Refereed)
    Abstract [en]

    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.

  • 65.
    Salamon, David
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Maca, Karel
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Rapid sintering of crack free zirconia ceramics by pressure less spark plasma sintering2012In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 66, no 11, p. 899-902Article in journal (Refereed)
    Abstract [en]

    Heating of a ceramic green body is a key step in sintering. We have created inside a spark plasma sintering apparatus pressure-less sintering conditions that allow homogeneous and extremely rapid heating. Dense and crack-free zirconia ceramic was sintered at heating rates of up to 500 degrees C min(-1) and dwell times of 2 min. This extremely fast sintering process is accompanied by extremely rapid grain growth, indicating a non classical sintering mechanism. No grain size gradients were observed inside the sintered zirconia ceramics.

  • 66.
    Saleemi, Mohsin
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). KTH Royal Institute of Technology, Sweden.
    Vanapalli, S.
    Nikkam, N.
    Toprak, M. S.
    Muhammed, M.
    Classical Behavior of Alumina (Al2O3) Nanofluids in Antifrogen N with Experimental Evidence2015In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, article id 256479Article in journal (Refereed)
    Abstract [en]

    A nanofluid is a suspension containing nanoparticles in conventional heat transfer fluids. This paper reports on an investigation of alumina (Al2O3) nanoparticles in Antifrogen N, also called AFN, which is a popular antifreeze coolant consisting primarily of ethylene glycol and other additives to impede corrosion. The base carrier fluid is 50% by weight of water and 50% by weight of AFN. We systematically measured the nanomaterials and heat transfer data of nanofluids for four different size particles, namely, 20, 40, 150, and 250 nm alumina particles. The pH of all the nanofluids is adjusted to have a stable dispersion. The material characterizations include SEM and DLS particle measurements. We measured thermal conductivity, viscosity, and heat transfer coefficient in developing flow of the nanofluids. We observed that these nanofluids behave as any other classical fluids in thermally developing flow and classical heat transfer correlations can be used to completely describe the characteristics of these nanofluids.

  • 67. Shao, Yinming
    et al.
    Post, Kirk W.
    Wu, Jhih-Sheng
    Dai, Siyuan
    Frenzel, Alex J.
    Richardella, Anthony R.
    Lee, Joon Sue
    Sarnarth, Nitin
    Fogler, Michael M.
    Balatsky, Alexander V.
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Los Alamos National Laboratory, United States.
    Kharzeev, Dmitri E.
    Basov, D. N.
    Faraday Rotation Due to Surface States in the Topological Insulator (Bi1-xSbx)(2)Te-32017In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 17, no 2, p. 980-984Article in journal (Refereed)
    Abstract [en]

    Using magneto-infrared spectroscopy, we have explored the charge dynamics of (Bi,Sb)(2)Te-3 thin films on InP substrates. From the magneto-transmission data we extracted three distinct cyclotron resonance (CR) energies that are all apparent in the broad band Faraday rotation (FR) spectra. This comprehensive FR-CR data set has allowed us to isolate the response of the bulk states from the intrinsic surface states associated with both the top and bottom surfaces of the film. The FR data uncovered that electron- and hole-type Dirac Fermions reside on opposite surfaces of our films, which paves the way for observing many exotic quantum phenomena in topological insulators.

  • 68. Shen, Gulou
    et al.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Lu, Xiaohua
    Ji, Xiaoyan
    Developing Electrolyte Perturbed-Chain Statistical Associating Fluid Theory Density Functional Theory for CO2 Separation by Confined Ionic Liquids2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 27, p. 15464-15473Article in journal (Refereed)
    Abstract [en]

    The electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) classical density functional theory (DFT) was developed to describe the behavior of pure ionic liquid (IL) and CO2/IL mixture confined in nanopores, in which a new ionic functional based on the ionic term from ePC-SAFT was proposed for electrostatic free-energy contribution. The developed model was verified by comparing the model prediction with molecular simulation results for ionic fluids, and the agreement shows that the model is reliable in representing the confined behavior of ionic fluids. The developed model was further used to study the behavior of pure IL and CO2/IL mixture in silica nanopores where the IL ions and CO2 were modeled as chains that consisted of spherical segments with the parameters taken from the bulk ePC-SAFT. The results reveal that the nanoconfinement can lead to an increased CO2 solubility, and the solubility increases with increasing pressure. The averaged density of pure IL and solubility of CO2 are strongly dependent on pore sizes and geometries. In addition, the choice of IL ions is very important for the CO2 solubility. Overall, the modeling results for silica-confined systems are consistent with available molecular simulation and experimental results.

  • 69. Silanteva, I. A.
    et al.
    Yurchenko, A. A.
    Vorontsov-Velyaminov, P. N.
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Equilibrium properties of 3-arm star-shaped polyions: an entropic sampling Monte Carlo study2017In: Nanosystems: Physics, Chemistry, Mathematics, ISSN 2220-8054, Vol. 8, no 1, p. 108-120Article in journal (Refereed)
    Abstract [en]

    The entropic sampling Monte Carlo method within Wang-Landau algorithm is applied to investigate properties of a lattice model of strongly charged flexible 3-arm star-shaped polyelectrolyte. The density of states is calculated, from which the canonical properties of the system in a wide temperature range are obtained by simple integration. The effects of the arm length and the short-range monomer-monomer potential on the thermal and structural properties of star polyions are studied. We calculate such characteristics as mean square radius of gyration and its components, the radius vector of the center of mass, components of the tensor of inertia and parameters characterizing the shape of the polyion. In this work, we focus on how these characteristics are influenced by the change of the reduced temperature which, within the considered model, is a parameter combining the effect of real temperature, linear charge density and solvent dielectric permittivity. The coil-globule transition is observed in most of the considered cases, and for the polyions with the longest length of arms ( 24), the transition from a liquid globule to a solid-like state is observed. Comparison of polyelectrolyte models with neutral ones is given.

  • 70. Srifa, Pemikar
    et al.
    Galkin, Maxim V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Samec, Joseph S. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hermansson, Kersti
    Broqvist, Peter
    Detecting Important Intermediates in Pd Catalyzed Depolymerization of a Lignin Model Compound by a Combination of DFT Calculations and Constrained Minima Hopping2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 41, p. 23469-23479Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations, combined with a constrained minima hopping algorithm (global minimum search while preserving the molecular identity), have been performed to investigate important reaction intermediates for the heterogeneously catalyzed beta-O-4' bond cleavage in lignin derivatives. More specifically, we have studied the adsorption properties of a keto tautomer (1-methoxypropan-2-one) and its enol form on a catalytically active Pd(111) surface. In agreement with experiments, we find that for the gas phase molecules the keto tautomer is the most stable. Interestingly, the enol tautomer has a higher affinity to the Pd catalyst than the keto form, and becomes the most stable molecular form when adsorbed on the catalyst surface. The global minimum complex found on the metal surface corresponds to an enolate structure formed when the enol tautomer chemisorbs onto the surface and donates its pi-electrons from the C=C region to two adjacent palladium atoms. The actual formation of a chemical bond to the surface in the case of the enol molecule could be the key to understanding why the enol derivative is needed for an efficient beta-O-4' bond cleavage.

  • 71. Stoerzinger, Kelsey A.
    et al.
    Diaz-Morales, Oscar
    Stockholm University, Faculty of Science, Department of Physics. Leiden University, The Netherlands.
    Kolb, Manuel
    Rao, Reshma R.
    Frydendal, Rasmus
    Qiao, Liang
    Wang, Xiao Renshaw
    Halck, Niels Bendtsen
    Rossmeisl, Jan
    Hansen, Heine A.
    Vegge, Tejs
    Stephens, Ifan E. L.
    Koper, Marc T. M.
    Shao-Horn, Yang
    Orientation-Dependent Oxygen Evolution on RuO2 without Lattice Exchange2017In: acs energy letters, ISSN 2380-8195, Vol. 2, no 4, p. 876-881Article in journal (Refereed)
    Abstract [en]

    RuO2 catalysts exhibit record activities toward the oxygen evolution reaction (OER), which is crucial to enable efficient and sustainable energy storage. Here we examine the RuO2 OER kinetics on rutile (110), (100), (101), and (111) orientations, finding (100) the most active. We assess the potential involvement of lattice oxygen in the OER mechanism with online electrochemical mass spectrometry, which showed no evidence of oxygen exchange on these oriented facets in acidic or basic electrolytes. Similar results were obtained for polyoriented RuO2 films and particles, in contrast to previous work, suggesting lattice oxygen is not exchanged in catalyzing OER on crystalline RuO2 surfaces. This hypothesis is supported by the correlation of activity with the number of active Ru-sites calculated by density functional theory, where more active facets bind oxygen more weakly. This new understanding of the active sites provides a design strategy to enhance the OER activity of RuO2 nanoparticles by facet engineering.

  • 72.
    Sultan, Sahar
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Siqueira, Gilberto
    Zimmermann, Tanja
    Mathew, Aji P:
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Swiss Federal Laboratories for Materials Science and Technology, Switzerland.
    3D printing of nano-cellulosic biomaterials for medical applications2017In: Current Opinion in Biomedical Engineering, ISSN 2468-4511, Vol. 2, p. 29-34Article, review/survey (Refereed)
    Abstract [en]

    Nanoscaled versions of cellulose viz. cellulose nanofibers (CNF) or cellulose nanocrystals (CNC) isolated from natural resources are being used extensively since the past decade in the biomedical field e.g. for tissue engineering, implants, drug delivery systems, cardiovascular devices, and wound healing due to their remarkable mechanical, chemical and biocompatible properties. In the recent years, 3D printing of nanocellulose in combination with polymers is being studied as a viable route to future regenerative therapy. The printability of nanocellulose hydrogels owing to their shear thinning behavior and the possibility to support living cells allows 3D bioprinting using nanocellulose, a recent development which holds tremendous potential.

  • 73. Sun, Rui
    et al.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Strømme, Maria
    Cheung, Ocean
    Hierarchical Porous Carbon Synthesized from Novel Porous Amorphous Calcium or Magnesium Citrate with Enhanced SF6 Uptake and SF6/N-2 Selectivity2019In: Acs Applied Nano Materials, ISSN 2574-0970, Vol. 2, no 2, p. 778-789Article in journal (Refereed)
    Abstract [en]

    The emission of greenhouse gases such as CO2 and SF6 is believed to contribute significantly toward global warming. One way to reduce their release is by adsorption at point sources using a suitable adsorbent. In this work we present the synthesis of two hierarchical porous carbon materials (referred to as PC-CaCit and PC-MgCit) with a high uptake of SF 6 (5.23 mmol/g, 0 degrees C, 100 kPa) and a reasonable uptake of CO2 (>3 mmol/g). PC-CaCit and PC-MgCit were obtained by pyrolysis of the most porous calcium citrate and magnesium citrate ever reported, which were synthesized by us. The Langmuir specific surface area of PC-CaCit and PC-MgCit was over 2000 m(2)/g (BET surface area also close to 2000 m(2)/g). We characterized PC-CaCit and PC-MgCit using a range of advanced characterization techniques including N-2 adsorption, high-resolution electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. PC-CaCit and PC-MgCit also showed a SF6-over-N-2 selectivity of similar to 33 at 0 degrees C (100 kPa), good cyclic performance, and moderately low heat of adsorption. The porous carbons synthesized in this work are good candidate adsorbents for greenhouse gases.

  • 74. Sun, Rui
    et al.
    Zhang, Peng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Bajnócz, Éva G.
    Neagu, Alexandra
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Persson, Ingmar
    Strømme, Maria
    Cheung, Ocean
    Amorphous Calcium Carbonate Constructed from Nanoparticle Aggregates with Unprecedented Surface Area and Mesoporosity2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 25, p. 21556-21564Article in journal (Refereed)
    Abstract [en]

    Amorphous calcium carbonate (ACC), with the highest reported specific surface area of all current forms of calcium carbonate (over 350 m(2) g(-1)), was synthesized using a surfactant-free, one-pot method. Electron microscopy, helium pycnometry, and nitrogen sorption analysis revealed that this highly mesoporous ACC, with a pore volume of similar to 0.86 cm(3) g(-1) and a pore-size distribution centered at 8-9 nm, is constructed from aggregated ACC nanoparticles with an estimated average diameter of 7.3 nm. The porous ACC remained amorphous and retained its high porosity for over 3 weeks under semi-air-tight storage conditions. Powder X-ray diffraction, large-angle X-ray scattering, infrared spectroscopy, and electron diffraction exposed that the porous ACC did not resemble any of the known CaCO3 structures. The atomic order of porous ACC diminished at interatomic distances over 8 angstrom. Porous ACC was evaluated as a potential drug carrier of poorly soluble substances in vitro. Itraconazole and celecoxib remained stable in their amorphous forms within the pores of the material. Drug release rates were significantly enhanced for both drugs (up to 65 times the dissolution rates for the crystalline forms), and supersaturation release of celecoxib was also demonstrated. Citric acid was used to enhance the stability of the ACC nanoparticles within the aggregates, which increased the surface area of the material to over 600 m(2) g(-1). This porous ACC has potential for use in various applications where surface area is important, including adsorption, catalysis, medication, and bone regeneration.

  • 75. Taborda, Farlán
    et al.
    Wang, Zhengyang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). College of Chemistry, Jilin University, China.
    Willhammar, Tom
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Montes, Consuelo
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Synthesis of Al-Si-beta and Ti-Si-beta by the aging-drying method2012In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 150, no 1, p. 38-46Article in journal (Refereed)
    Abstract [en]

    Al-Si-beta and Ti-Si-beta were synthesized by the aging-drying method in fluoride medium without seeding and using tetraethylammonium hydroxide as organic structure-directing agent (OSDA). In the aging-drying method the gels are allowed to release some volatile species (mainly ethanol and water). Samples with molar batch composition: SiO(2):0.54TEAOH:0.7HF:xH(2)O:yM(n+)F(n)(-) (where x approximate to 10, y = 0.02, M = Al or Ti) were aged and dried during about one week. Organic solvents were added to selected aged-dried gels to determine their role as complementary OSDA. All samples were hydrothermally treated at 140 degrees C during 1-12 days. After crystallization, samples were characterized by PXRD, SEM, TGA-DTG, FTIR, atomic absorption, low temperature nitrogen adsorption, (29)Si MAS NMR and (22)Al MAS NMR. Pure and well-crystallized zeolite beta samples were obtained in all experiments performed. Polymorph A enrichments of about 69% and 64% were reached for Ti and Al loaded samples, respectively. AI-loaded samples exhibited small average crystal sizes compared with Ti-loaded samples. The incorporation of Al in the beta framework was proven by several techniques and the Al/Si ratios were similar to those of the precursor gels. However, Ti incorporation was quite low.

  • 76.
    Thersleff, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schönström, Linus
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Adam, Roman
    Bürgler, Daniel E.
    Schneider, Claus M.
    Muto, Shunsuke
    Rusz, Ján
    Single-pass STEM-EMCD on a zone axis using a patterned aperture: progress in experimental and data treatment methods2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 18170Article in journal (Refereed)
    Abstract [en]

    Measuring magnetic moments in ferromagnetic materials at atomic resolution is theoretically possible using the electron magnetic circular dichroism (EMCD) technique in a (scanning) transmission electron microscope ((S)TEM). However, experimental and data processing hurdles currently hamper the realization of this goal. Experimentally, the sample must be tilted to a zone-axis orientation, yielding a complex distribution of magnetic scattering intensity, and the same sample region must be scanned multiple times with sub-atomic spatial registration necessary at each pass. Furthermore, the weak nature of the EMCD signal requires advanced data processing techniques to reliably detect and quantify the result. In this manuscript, we detail our experimental and data processing progress towards achieving single-pass zone-axis EMCD using a patterned aperture. First, we provide a comprehensive data acquisition and analysis strategy for this and other EMCD experiments that should scale down to atomic resolution experiments. Second, we demonstrate that, at low spatial resolution, promising EMCD candidate signals can be extracted, and that these are sensitive to both crystallographic orientation and momentum transfer.

  • 77. Thormann, Esben
    et al.
    Mizuno, Hiroyasu
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Soledad Fernandez, M.
    Luis Arias, Jose
    Rutland, Mark W.
    Pai, Ranjith Krishna
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Embedded proteins and sacrificial bonds provide the strong adhesive properties of gastroliths2012In: NANOSCALE, ISSN 2040-3364, Vol. 4, no 13, p. 3910-3916Article in journal (Refereed)
    Abstract [en]

    The adhesive properties of gastroliths from a freshwater crayfish (Cherax quadricarinatus) were quantified by colloidal probe atomic force microscopy (AFM) between heavily demineralized gastrolith microparticles and gastrolith substrates of different composition. Combined AFM and transmission electron microscopy studies demonstrated that the sequential detachment and large adhesion energies that characterise the adhesive behaviour of a native gastrolith substrate are dominated by sacrificial bonds between chitin fibres and between chitin fibres and CaCO3. The sacrificial bonds were shown to be strongly related to the gastrolith proteins and when the majority of these proteins were removed by ethylenediaminetetraacetic acid (EDTA), the sequential detachment disappeared and the adhesive energy was reduced by more than two orders of magnitude.

  • 78.
    Tiiman, Ann
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. Tallinn University of Technology, Estonia.
    Krishtal, Jekaterina
    Palumaa, Peep
    Tougu, Vello
    In vitro fibrillization of Alzheimer's amyloid-beta peptide (1-42)2015In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 5, no 9, article id 092401Article in journal (Refereed)
    Abstract [en]

    The amyloid deposition in the form of extracellular fibrillar aggregates of amyloid-beta (A beta) peptide is a critical pathological event in Alzheimer's disease. Here, we report a systematic investigation of the effects of environmental factors on the kinetics of A beta fibrillization in vitro. The effects of A beta 42 peptide concentration, temperature, pH, added solvents and the ratio of A beta 40 and A beta 42 on the peptide fibrillization under agitated conditions was studied. The analysis show that the rate of fibril growth by monomer addition is not limited by diffusion but by rearrangement in the monomer structure, which is enhanced by low concentrations of fluorinated alcohols and characterized by the activation energy of 12 kcal/ mol. Fibrillization rate decreases at pH values below 7.0 where simultaneous protonation of His 13 and 14 inhibits fibril formation. The lag period for A beta 42 was only twofold shorter and the fibril growth rate twofold faster than those of A beta 40. Lag period was shortened and the fibrillization rate was increased only at 90% content of A beta 42.

  • 79. Tissot, Heloise
    et al.
    Wang, Chunlei
    Halldin Stenlid, Joakim
    Stockholm University, Faculty of Science, Department of Physics.
    Brinck, Tore
    Weissenrieder, Jonas
    The Surface Structure of Cu2O(100): Nature of Defects2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 13, p. 7696-7704Article in journal (Refereed)
    Abstract [en]

    The Cu2O(100) surface is most favorably terminated by a (3,0;1,1) reconstruction under ultrahigh-vacuum conditions. As most oxide surfaces, it exhibit defects, and it is these sites that are focus of attention in this study. The surface defects are identified, their properties are investigated, and procedures to accurately control their coverage are demonstrated by a combination of scanning tunneling microscopy (STM) and simulations within the framework of density functional theory (DFT). The most prevalent surface defect was identified as an oxygen vacancy. By comparison of experimental results, formation energies, and simulated STM images, the location of the oxygen vacancies was identified as an oxygen vacancy in position B, located in the valley between the two rows of oxygen atoms terminating the unperturbed surface. The coverage of defects is influenced by the surface preparation parameters and the history of the sample. Furthermore, using low-energy electron beam bombardment, we show that the oxygen vacancy coverage can be accurately controlled and reach a complete surface coverage (1 per unit cell or 1.8 defects per nm(2)) without modification to the periodicity of the surface, highlighting the importance of using local probes when investigating oxide surfaces.

  • 80. Torruella, Pau
    et al.
    Arenal, Raul
    de la Pena, Francisco
    Saghi, Zineb
    Yedra, Lluis
    Eljarrat, Alberto
    Lopez-Conesa, Lluis
    Estrader, Marta
    Lopez-Ortega, Alberto
    Salazar-Alvarez, Germán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nogues, Josep
    Ducati, Caterina
    Midgley, Paul A.
    Peiro, Francesca
    Estrade, Sonia
    3D Visualization of the Iron Oxidation State in FeO/Fe3O4 Core-Shell Nanocubes from Electron Energy Loss Tomography2016In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 16, no 8, p. 5068-5073Article in journal (Refereed)
    Abstract [en]

    The physicochemical properties used in numerous advanced nanostructured devices are directly controlled by the oxidation states of their constituents. In this work we combine electron energy-loss spectroscopy, blind source separation, and computed tomography to reconstruct in three dimensions the distribution of Fe2+ and Fe3+ ions in a FeO/Fe3O4 core/shell cube-shaped nanoparticle with nanometric resolution. The results highlight the sharpness of the interface between both oxides and provide an average shell thickness, core volume, and average cube edge length measurements in agreement with the magnetic characterization of the sample.

  • 81.
    Turdean-Ionescu, Claudia
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Surface Reactions of Mesoporous Bioactive Glasses Monitored by Solid-State NMR: Concentration Effects in Simulated Body Fluid2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 9, p. 4961-4974Article in journal (Refereed)
    Abstract [en]

    A bone-mineral-mimicking layer of hydroxycarbonate apatite (HCA) forms at the surface of a bioactive glass on its contact with body fluids. We report a solid-state Si-29 nuclear magnetic resonance (NMR) spectroscopy study of the surface reactions preceding the HCA formation at three CaO-SiO2-(P2O5) mesoporous bioactive glasses (MBGs) with distinct compositions, surface areas, and mesoporous arrangements, during their immersion in simulated body fluid (SBF) out to 30 days. The evolution of the various populations of coexisting silicate species associated with the bulk-arid surface portions of the pore-walls were monitored. The MBGs revealed drastically different surface alterations between the scenarios of low (0.6 g/L) and high (20 g/L) MBG concentrations in the SBF: for the low MBG dose, which is expected to be more relevant for in vivo conditions, all MBGs follow a universal dissolution mechanism beyond approximate to 24 h of SBF soaking, regardless of their precise compositions and textural properties. The only essential difference among the specimens occurs during the first hour of soaking when their variable Ca2+ reservoirs are depleted. In contrast, for high MBG concentrations, the surface reactions and their associated silicate network degradation retard for Ca-poor MBGs, whereas the reactions are completely quenched for Ca-rich compositions. These findings rationalize previously reported discrepancies in the correlation between the HCA formation and the MBG composition for distinct concentrations during SBF testing, and simplify future MBG design by identifying which compositional and textural factors are relevant for a rapid and substantial HCA formation in vitro.

  • 82.
    Voisin, Hugo
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Peng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nanocellulose-Based Materials for Water Purification2017In: Nanomaterials, ISSN 2079-4991, Vol. 7, no 3, article id 57Article, review/survey (Refereed)
    Abstract [en]

    Nanocellulose is a renewable material that combines a high surface area with high strength, chemical inertness, and versatile surface chemistry. In this review, we will briefly describe how nanocellulose is produced, and present-in particular, how nanocellulose and its surface modified versions affects the adsorption behavior of important water pollutants, e.g., heavy metal species, dyes, microbes, and organic molecules. The processing of nanocellulose-based membranes and filters for water purification will be described in detail, and the uptake capacity, selectivity, and removal efficiency will also be discussed. The processing and performance of nanocellulose-based membranes, which combine a high removal efficiency with anti-fouling properties, will be highlighted.

  • 83.
    Volkov, Nikolai
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). University of Gothenburg, Sweden.
    Lyubartsev, Alexander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Phase transitions and thermodynamic properties of dense assemblies of truncated nanocubes and cuboctahedra2012In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 4, no 15, p. 4765-4771Article in journal (Refereed)
    Abstract [en]

    Inspired by recent advances on the self-assembly of non-spherical nanoparticles, Monte Carlo simulations of the packing and thermodynamic properties of truncated nanocubes and cuboctahedra have been performed. The ergodicity problem was overcome by a modified Wang-Landau entropic sampling algorithm and equilibrium structural and thermodynamic properties were computed over a wide density range for both non-interacting and interacting particles. We found a structural transition from a simple cubic to a rhombohedral order when the degree of truncation exceeds a value of 0.9.

  • 84. Wang, Ling
    et al.
    Hu, Jianfeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cheng, Yao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fu, Zhengyi
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Xiong, Yan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Hubei University of Technology, China.
    Defect formation by order coalescence in vermicular grains during alumina phase transformation2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 107, p. 59-62Article in journal (Refereed)
    Abstract [en]

    Vermicular alpha-Al2O3 grains obtained from gamma- to alpha-phase transformation were investigated. X-ray diffraction patterns showed a left-shifting shoulder in all diffraction peaks of transformed alpha-Al2O3. High-resolution transmission electron microscopy results confirmed large amounts of defects inside the vermicular alpha-Al2O3 single-crystal. Combined with grain-growth discontinuity, the authors proposed that the defects inside vermicular grains resulted from assembly of nanosized alpha-crystallites by an ordered coalescence mechanism directly after phase transformation, by which the orientation alignment was thermodynamically favored in the solid-state sintering.

  • 85. Wang, Tao
    et al.
    Shi, Li
    Tang, Jing
    Malgras, Victor
    Asahina, Shunsuke
    Liu, Guigao
    Zhang, Huabin
    Meng, Xianguang
    Chang, Kun
    He, Jianping
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yamauchi, Yusuke
    Ye, Jinhua
    A Co3O4-embedded porous ZnO rhombic dodecahedron prepared using zeolitic imidazolate frameworks as precursors for CO2 photoreduction2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 12, p. 6712-6720Article in journal (Refereed)
    Abstract [en]

    Metal-organic frameworks (MOFs) are attracting considerable attention for their use as both the precursor and the template to prepare metal oxides or carbon-based materials. For the first time in this paper, the core-shell ZIF-8@ZIF-67 crystals are thermally converted into porous ZnO@Co3O4 composites by combining a seed-mediated growth process with a two-step calcination. The designed porous ZnO@Co3O4 composites exhibited the highest photocatalytic activity with an excellent stability for the reduction of CO2 among the commonly reported composite photocatalysts. Their superior photocatalytic performance is demonstrated to be resulting from the unique porous structure of ZnO@Co3O4 and the co-catalytic function of Co3O4 which can effectively suppress the photocorrosion of ZnO.

  • 86.
    Wang, Yong-Lei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Golets, Mikhail
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Li, Bin
    Sarman, Sten
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Interfacial Structures of Trihexyltetradecylphosphonium-bis(mandelato)borate Ionic Liquid Confined between Gold Electrodes2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 5, p. 4976-4987Article in journal (Refereed)
    Abstract [en]

    Atomistic molecular dynamics simulations have been performed to study microscopic the interfacial ionic structures, molecular arrangements, and orientational preferences of trihexyltetradecylphosphonium-bis(mandelato)borate ([P-6,P-6,P-6,P-14][BM]) ionic liquid confined between neutral and charged gold electrodes. It was found that both [P-6,P-6,P-6,P-14] cations and [BMB] anions are coabsorbed onto neutral electrodes at different temperatures. The hexyl and tetradecyl chains in [P-6,P-6,P-6,P-14] cations lie preferentially flat on neutral electrodes. The oxalato and phenyl rings in [BMB] anions are characterized by alternative parallel perpendicular orientations in the mixed innermost ionic layer adjacent to neutral electrodes. An increase in temperature has a marginal effect on the interfacial ionic structures and molecular orientations of [P-6,P-6,P-6,P-14] [BMB] ionic species in a confined environment. Electrifying gold electrodes leads to peculiar changes in the interfacial ionic structures and molecular orientational arrangements of [p(6,6,414)] cations and [BMB] anions in negatively and positively charged gold electrodes, respectively. As surface charge density increases (but lower than 20 mu C/cm(2)), the layer thickness of the mixed innermost interfacial layer gradually increases due to a consecutive accumulation of [P6,6,614] cations and [BMB] anions at negatively and positively charged electrodes, respectively, before the formation of distinct cationic and anionic innermost layers. Meanwhile, the molecular orientations of two oxalato rings in the same [BMB] anions change gradually from a parallel perpendicular feature to being partially characterized by a tilted arrangement at an angle of 45 from the electrodes and finally to a dominant parallel coordination pattern along positively charged electrodes. Distinctive interfacial distribution patterns are also observed accordingly for phenyl rings that are directly connected to neighboring oxalato rings in [BMB] anions.

  • 87. Wei, Xinyu
    et al.
    Fan, Qikui
    Liu, Hongpo
    Bai, Yaocai
    Zhang, Lei
    Zheng, Haoquan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yin, Yadong
    Gao, Chuanbo
    Holey Au-Ag alloy nanoplates with built-in hotspots for surface-enhanced Raman scattering2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 34, p. 15689-15695Article in journal (Refereed)
    Abstract [en]

    Plasmonic noble metal nanocrystals with interior nanogaps have attracted great attention in surface-enhanced Raman scattering (SERS) applications due to the presence of built-in hotspots. Herein, we report a synthesis route to holey Au-Ag alloy nanoplates by controlled galvanic replacement with Ag nanoplates as the sacrificial template, a sulfite-coordinated Au(I) salt as the Au source, and polyvinylpyrrolidone (PVP) as the capping agent. PVP helps regulate the anisotropic growth of nanopores on the Ag nanoplates to afford a highly holey nanostructure, and the monovalent Au(I) salt plays a critical role in stabilizing these holey nanoplates by rapidly enriching Au in the alloy nanostructures. Numerical simulations and experimental results suggest that these holey Au-Ag alloy nanoplates possess enormous internal hotspots for high sensitivity in the SERS analysis, and high stability for excellent reliability of the analysis under many harsh conditions. We believe that this strategy is potentially applicable to the synthesis of many other types of plasmonic nanostructures with inherent nanogaps for many sensing and imaging applications.

  • 88.
    Wesslén, Carl
    Stockholm University, Faculty of Science, Department of Physics.
    Confinement Sensitivity in Quantum Dot Spin Relaxation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quantum dots, also known as artificial atoms, are created by tightly confining electrons, and thereby quantizing their energies. They are important components in the emerging fields of nanotechnology where their potential uses vary from dyes to quantum computing qubits. Interesting properties to investigate are e.g. the existence of atom-like shell structures and lifetimes of prepared states.

    Stability and controllability are important properties in finding applications to quantum dots. The ability to prepare a state and change it in a controlled manner without it loosing coherence is very useful, and in some semiconductor quantum dots, lifetimes of up to several milliseconds have been realized. Here we focus on dots in semiconductor materials and investigate how the confined electrons are effected by their experienced potential.

    The shape of the dot will effect its properties, and is important when considering a suitable model. Structures elongated in one dimension, often called nanowires, or shaped as rings have more one-dimensional characteristics than completely round or square dots. The two-dimensional dots investigated here are usually modeled as harmonic oscillators, however we will also consider circular well models.

    The effective potential confining the electrons is investigated both in regard to how elliptical it is, as well as how results differ when using a harmonic oscillator or a circular well potential. By mixing spin states through spin-orbit interaction transitioning between singlet and triplet states becomes possible with spin independent processes such as phonon relaxation. We solve the spin-mixing two-electron problem numerically for some confinement, and calculate the phonon transition rate between the lowest energy singlet and triplet states using Fermi's golden rule.

    The strength of the spin-orbit interaction is varied both by changing the coupling constants, and by applying an external, tilted, magnetic field. The relation between magnetic field parameters and dot parameters are used to maximize state lifetimes, and to model experimental results.

  • 89.
    Wesslén, Carl-Johan
    Stockholm University, Faculty of Science, Department of Physics.
    Many-Body effects in Semiconductor Nanostructures2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Low dimensional semiconductor structures are modeled using techniques from the field of many-body atomic physics. B-splines are used to create a one-particle basis, used to solve the more complex many-body problems. Details on methods such as the Configuration Interaction (CI), Many-Body Perturbation Theory (MBPT) and Coupled Cluster (CC) are discussed. Results from the CC singles and doubles method are compared to other high-precision methods for the circular harmonic oscillator quantum dot. The results show a good agreement for the energy of many-body states of up to 12 electrons.

    Properties of elliptical quantum dots, circular quantum dots, quantum rings and concentric quantum rings are all reviewed. The effects of tilted external magnetic fields applied to the elliptical dot are discussed, and the energy splitting between the lowest singlet and triplet states is explored for varying geometrical properties. Results are compared to experimental energy splittings for the same system containing 2 electrons.

  • 90.
    Wesslén, Carl-Johan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Lindroth, Eva
    Stockholm University, Faculty of Science, Department of Physics.
    Confinement sensitivity in quantum dot singlet-triplet relaxationManuscript (preprint) (Other academic)
  • 91.
    Wetterskog, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden.
    Klapper, Alice
    Disch, Sabrina
    Josten, Elisabeth
    Hermann, Raphaël P.
    Rücker, Ulrich
    Brückel, Thomas
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tuning the structure and habit of iron oxide mesocrystals2016In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 8, no 34, p. 15571-15580Article in journal (Refereed)
    Abstract [en]

    A precise control over the meso-and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest for exploiting the collective material properties for potential applications. In this work, we produced evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enabled the structural determination of e.g. multi-domain mesocrystals with complex crystal habits and the quantification of interparticle distances with sub-nm precision. Mesocrystals of small nanocubes (l = 8.6-12.6 nm) are isostructural with a body centred tetragonal (bct) lattice whereas assemblies of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size and shape and the strength of the applied magnetic field. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.

  • 92.
    Wetterskog, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures: Topotaxial Oxidation of Fe1-xO|Fe3-δO4 Core|Shell Nanocubes to Single-Phase Particles2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 8, p. 7132-7144Article in journal (Refereed)
    Abstract [en]

    Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe1–xO|Fe3−δO4 nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of antiphase boundaries. Dark-field transmission electron microscopy and powder X-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe1–xO core is removed but that the antiphase boundaries remain. The antiphase boundaries result in anomalous magnetic behavior, that is, a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic properties of iron oxide nanoparticles.

  • 93. Wicklein, Bernd
    et al.
    Diem, Achim M.
    Knöller, Andrea
    Cavalcante, Manoella S.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bill, Joachim
    Burghard, Zaklina
    Dual-Fiber Approach toward Flexible Multifunctional Hybrid Materials2018In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 28, no 27, article id 1704274Article in journal (Refereed)
    Abstract [en]

    Multifunctional paper-like materials containing metal oxide nanofibers are important for flexible electronics and other redox-based applications, but are often prone to mechanical failure. This work presents the coassembly of V2O5 nanofibers (VNFs) in a dual-fiber approach together with cellulose nanofibers to produce tough (0.26 MJ m(-3)), but strong (250 MPa) flexible hybrid materials. Indeed, nanotensile tests reveal a significant increase in toughness (200%) and strength (85%) of the hybrid films as compared to pristine VNF films. The microstructure of the films shows a transition from an anisotropic texture for the single-component films to an isotropic, entangled network in case of the hybrid films, which facilitates effective fracture resistance mechanisms. The flexible hybrid films display high electrical conductivity (0.2 S cm(-1)) and elastic properties originating from V2O5 nanofibers with excellent toughness and transparency endowed by the cellulose nanofibers. The self-supported hybrid films show reversible electrochromic behavior without the need for common substrates such as conducting indium tin oxide glass. It is conceivable that these self-supported films can be exploited in the future in smart, flexible optoelectronic devices.

  • 94.
    Wicklein, Bernd
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Kocjan, Andraz
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Royal Institute of Technology, Sweden.
    Carosio, Federico
    Camino, Giovanni
    Antonietti, Markus
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide2015In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 10, no 3, p. 277-283Article in journal (Refereed)
    Abstract [en]

    High-performance thermally insulating materials from renewable resources are needed to improve the energy efficiency of buildings. Traditional fossil-fuel-derived insulation materials such as expanded polystyrene and polyurethane have thermal conductivities that are too high for retrofitting or for building new, surface-efficient passive houses. Tailored materials such as aerogels and vacuum insulating panels are fragile and susceptible to perforation. Here, we show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods produces super-insulating, fire-retardant and strong anisotropic foams that perform better than traditional polymer-based insulating materials. The foams are ultralight, show excellent combustion resistance and exhibit a thermal conductivity of 15 mW m(-1) K-1, which is about half that of expanded polystyrene. At 30 degrees C and 85% relative humidity, the foams retained more than half of their initial strength. Our results show that nanoscale engineering is a promising strategy for producing foams with excellent properties using cellulose and other renewable nanosized fibrous materials.

  • 95.
    Willhammar, Tom
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yun, Yifeng
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Structural Determination of Ordered Porous Solids by Electron Crystallography2014In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 24, no 2, p. 182-199Article in journal (Refereed)
    Abstract [en]

    Knowing the structure of porous materials is essential for understanding their properties and exploiting them for applications. Electron crystallography has two main advantages compared to X-ray diffraction for structure determination. Crystals too small or too complicated to be studied by X-ray diffraction can be studied by electron crystallography. The crystallographic structure factor phase information, which is lost in X-ray diffraction, can be obtained from high-resolution transmission electron microscopy (HRTEM) images. Here, different electron microscopic techniques and their applications for structure determination of porous materials are reviewed. The recently developed automated diffraction tomography (ADT), the rotation electron diffraction (RED), and the through-focus structure projection reconstruction (QFcous) methods make the structure determination by electron crystallography more feasible for non-TEM experts and as efficient as that by X-ray diffraction. How the various electron crystallographic methods are chosen are demonstrated and these methods used for solving different structural problems in porous materials. The benefits of combining electron crystallography and X-ray diffraction for studying complex zeolite structures are also shown. A large number of examples are given to demonstrate the use of various electron crystallographic techniques for structure determination of zeolites, metal-organic frameworks and ordered mesoporous materials. These electron crystallographic methods are general and can also be used for structural studies of other functional materials.

  • 96. Zhao, Yang
    et al.
    Luo, Min
    Chu, Shufen
    Peng, Ming
    Liu, Boyang
    Stockholm University, Faculty of Science, Department of Physics.
    Wu, Qiuli
    Liu, Pan
    de Groot, Frank M. F.
    Tan, Yongwen
    3D nanoporous iridium-based alloy microwires for efficient oxygen evolution in acidic media2019In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 59, p. 146-153Article in journal (Refereed)
    Abstract [en]

    Although significant progresses have been achieved recently in developing catalysts for electrochemical oxygen evolution in alkaline electrolytes, high performance catalysts toward oxygen evolution in acidic media have not been realized in spite of the technical importance for the development of promising energy transformation technologies including electrocatalytic water splitting, integrated (photo)electrochemistry cells, rechargeable metal-air batteries, and so on. Here, we synthesized a three-dimensional nanoporous Ir70Ni30-xCox alloy microwires as oxygen evolution reaction electrocatalyst using a dealloying strategy. The three dimensional binder-free np-Ir70Ni15Co15 catalyst in 0.1 M HClO4 shows a low overpotential (220 mV@ eta = 10 mA cm(-2)), low Tafel slope (44.1 mV dec(-1)) and excellent corrosion resistance, significantly outperforming commercial IrO2 catalysts. The excellent performance is attributed to the nanoporous structure and the alloying effect, which promote the permeation of electrolyte, accelerate the transportation of electrons. More importantly, the high valence Ir oxide species with low-coordination structure in np-Ir70Ni15Co15 alloy are identified for the real catalytic sites of OER process by the XAS results acquired on synchrotron radiation. This work not only provides fundamental understandings of the correlation between surface activity and stability for OER catalysts, but also paves a new way to advanced electrocatalysts working in acidic media.

  • 97.
    Zhu, Chuantao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Monti, Susanna
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cellulose Nanofiber-Graphene Oxide Biohybrids: Disclosing the Self-Assembly and Copper-Ion Adsorption Using Advanced Microscopy and ReaxFF Simulations2018In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 7, p. 7028-7038Article in journal (Refereed)
    Abstract [en]

    The self-assembly of nanocellulose and graphene oxide into highly porous biohybrid materials has inspired the design and synthesis of multifunctional membranes for removing water pollutants. The mechanisms of self-assembly, metal ion capture, and cluster formation on the biohybrids at the nano- and molecular scales are quite complex. Their elucidation requires evidence from the synergistic combination of experimental data and computational models. The AFM-based microscopy studies of (2,2,6,6-tetramethylpiperidine-l-oxylradical)-mediated oxidized cellulose nanofibers (TOCNFs), graphene oxide (GO), and their biohybrid membranes provide strong, direct evidence of self-assembly; small GO nanoparticles first attach and accumulate along a single TOCNF fiber, while the long, flexible TOCNF filaments wrap around the flat, wide GO planes, thus forming an amorphous and porous biohybrid network. The layered structure of the TOCNFs and GO membrane, derived from the self-assembly and its surface properties before and after the adsorption of Cu(II), is investigated by advanced microscopy techniques and is further clarified by the ReaxFF molecular dynamics (MD) simulations. The dynamics of the Cu(II)-ion capture by the TOCNF and GO membranes in solution and the ion cluster formation during drying are confirmed by the MD simulations. The results of this multidisciplinary investigation move the research one step forward by disclosing specific aspects of the self-assembly behavior of biospecies and suggesting effective design strategies to control the pore size and robust materials for industrial applications.

  • 98.
    Öberg, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Anniyev, Toyli
    Vojvodic, Aleksandra
    Kaya, Sarp
    Ogasawara, Hirohito
    Friebel, Daniel
    Miller, Daniel J.
    Nordlund, Dennis
    Bergmann, Uwe
    Ljungberg, Mathias P.
    Stockholm University, Faculty of Science, Department of Physics.
    Abild-Pedersen, Frank
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Stability of Pt-Modified Cu(111) in the Presence of Oxygen and Its Implication on the Overall Electronic Structure2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 32, p. 16371-16380Article in journal (Refereed)
    Abstract [en]

    The electronic structure and stability of Cu(111)-hosted Pt overlayers with and without the presence of atomic oxygen have been studied by means of core-level spectroscopy and density functional theory (DFT). Because of lattice mismatch, Pt(111) overlayers grown on Cu(111) are compressively strained, and hard X-ray photoelectron spectroscopy together with Pt L-3-edge X-ray absorption spectroscopy (XAS) reveals a pronounced downshift of the Pt d-band owing to the increased overlap of the d-orbitals, an effect also reproduced theoretically. Exposure to oxygen severely alters the surface composition; the O-Cu binding energy largely exceeds that of O-Pt, and DFT calculations predict surface segregation of Cu atoms. Comparing the adsorbate electronic structure for O on unstrained Pt(111) with that of O on Pt-modified Cu(111) using O K-edge XAS and X-ray emission spectroscopy salient differences are observed and calculations show that Cu-segregation to the topmost layer is required to reproduce the measured spectra. It is proposed that O is binding in a hollow site constituted by at least two Cu atoms and that up to 75% of the Pt atoms migrate below the surface.

  • 99. Österberg, Carin
    et al.
    Fahlquist, Henrik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Brown, Craig M.
    Udovic, Terrence J.
    Karlsson, Maths
    Dynamics of Pyramidal SiH3- Ions in ASiH(3) (A = K and Rb) Investigated with Quasielastic Neutron Scattering2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 12, p. 6369-6376Article in journal (Refereed)
    Abstract [en]

    The two alkali silanides ASiH(3) (A = K and Rb) were investigated by means of quasielastic neutron scattering, both below and above the order-disorder phase transition occurring at around 275-300 K. Measurements upon heating show that there is a large change in the dynamics on going through the phase transition, whereas measurements upon cooling reveal a strong hysteresis due to undercooling of the disordered phase. The results show that the dynamics is associated with rotational diffusion of SiH3- anions, adequately modeled by H-jumps among 24 different jump locations radially distributed around the Si atom. The average relaxation time between successive jumps is of the order of subpicoseconds and exhibits a weak temperature dependence with a small difference in activation energy between the two materials, 39(1) meV for KSiH3 and 33(1) meV for RbSiH3. The pronounced SiH3- dynamics explains the high entropy observed in the disordered phase resulting in the low entropy variation for hydrogen absorption/desorption and hence the origin of these materials' favorable hydrogen storage properties.

12 51 - 99 of 99
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