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  • 1.
    Carson, Fabian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Martínez-Castro, Elisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Marcos, Rocio
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jansson, Kjell
    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).
    Martin-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Effect of the functionalisation route on a Zr-MOF with an Ir-NHC complex for catalysis2015In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 54, p. 10864-10867Article in journal (Refereed)
    Abstract [en]

    A new iridium N-heterocyclic carbene (NHC) metallolinker has been synthesised and introduced into a metal-organic framework (MOF), for the first time, via two different routes: direct synthesis and postsynthetic exchange (PSE). The two materials were compared in terms of the Ir loading and distribution using X-ray energy dispersive spectroscopy (EDS), the local Ir structure using X-ray absorption spectroscopy (XAS) and the catalytic activity. The materials showed good activity and recyclability as catalysts for the isomerisation of an allylic alcohol.

  • 2.
    Carson, Fabian
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Martínez-Castro, Elisa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Marcos, Rocío
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    González Miera, Greco
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Jansson, Kjell
    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).
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Introduction of an N-heterocyclic Carbene Iridium Complex into a Zirconium Metal–Organic Framework for CatalysisManuscript (preprint) (Other academic)
  • 3.
    Christensen, Kirsten E.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bonneau, Charlotte
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Gustafsson, Mikaela
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shi, Lei
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sbille, Isabelle
    Su, Bao-Lian
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    An open-framework silicogermanate with 26-ring channels built from seven-coordinated (Ge,Si)10(O, OH)28 clusters2008In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 130, no 12, p. 3758-3759Article in journal (Refereed)
    Abstract [en]

    We report a new open-framework silicogermanate SU-61 containing 26-ring channels with a low framework density. It can be seen as a crystalline analogue to the mesoporous silica MCM-41. The structure is built from the assembly of (Ge,Si)10(O,OH)28 clusters. It is the first time that silicon has been successfully introduced in the Ge10 cluster in significant amounts (21% of the tetrahedral sites). Five- and six-coordinated Ge10 clusters have previously been observed in other germanate compounds leading to either dense or open structures. In SU-61, the seven-coordinated clusters fall onto yet another underlying net, the osf net. SU-61, along with other Ge10 based frameworks, shows the versatility of the germanate system to adopt defined topologies playing on the connectivity of the clusters following the principles of net decoration and scale chemistry.

  • 4. Corma, Averlino
    et al.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hovmöller, Sven
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Zhang, Daliang
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jordá, José L.
    Díaz Cabañas, María J.
    Cantín, Ángel
    Moliner, Manuel
    Synthesis and structure of polymorph B of zeolite Beta2008In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 20, no 9, p. 3218-3223Article in journal (Refereed)
    Abstract [en]

    It was found that either polymorph B or polymorph C of zeolite beta can be obtained from the same structure directing agent: 4,4-dimethyl-4-azonia-tricyclo[5.2.2.02,6]undec-8-ene hydroxide. The synthesis occurs through a consecutive process where polymorph B is first formed and then transformed into polymorph C. It is possible to produce a zeolite highly enriched in polymorph B, provided that the transformation of this phase into polymorph C is slowed down up to the point where polymorph C is only detected at trace levels. The structure of polymorph B was determined for the first time by electron crystallography with SAED and HRTEM from areas of unfaulted polymorph B crystals.

  • 5.
    Dvinskikh, Sergey V.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Thaning, Johan
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Kumar, Sandeep
    Raman Research Institute, C. V. Raman Avenue, Bangalore 560 080, India.
    Zimmermann, Herbert
    Department of Biomedical Optics, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, D-69120 Heidelberg, Germany.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Mesomorphism in columnar phases studied by solid-state nuclear magnetic resonance2006In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 74, no 2, p. 021703-Article in journal (Refereed)
    Abstract [en]

    In this paper, we present 13C and 1H NMR investigations of 2, 3, 6, 7, 10, 11-hexahexyl-thiotriphenylene (HHTT). The measurements were carried out under both static and magic-angle spinning conditions. The phase diagram of HHTT is K↔H↔Dhd↔I, where H is a helical phase and Dhd is a columnar liquid crystal. The motivation was to characterize the molecular order and dynamics and to investigate differences at the molecular level between the two mesophases: H and Dhd. It is shown that Dhd is a conventional columnar liquid crystal, where the molecular core undergoes fast rotation about the symmetry axis. The orientational order in this mesophase is lower and the temperature dependence of the order parameter is steeper than in other triphenylene-based compounds. On the other hand, in the helical phase the core, similarly to the solid phase, is essentially rigid. The difference between the solid and helical phases is mainly manifested in an increased mobility of the aliphatic chains observed in the latter phase. In addition, the sample exhibits thermal history effects, which are observed in the different behavior upon cooling and heating.

    © 2006 The American Physical Society

  • 6.
    Eden, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Physical Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry, Inorganic Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Al and O substitutions in BaS-phases, Ba2AlxSi12-xN16-xO2+x: A TEM, XRD and solid-state NMR study2008In: Solid State Sciences, ISSN 1293-2558, E-ISSN 1873-3085, Vol. 10, no 1, p. 50-60Article in journal (Refereed)
    Abstract [en]

    In a series of Ba-based oxonitrido-silicate S-phases (Ba2AlxSi12-xN16-xO2+x) spanning a compositional range up to x approximate to 3, we examine the incorporation of Al and O by Si-29 and Al-27 magic-angle spinning (MAS) solid state nuclear magnetic resonance (NMR) and Al-27 triple-quantum MAS (3QMAS). The 3QMAS spectra reveal Al-27 signals from two distinct structural environments, assigned to AlN4 or AlN3O tetrahedra, respectively, and with their relative amounts depending on the S-phase substitution parameter x. Si-29 NMR show variable fractions of SiN4 and SiN3O environments. The NMR results accord overall with a structural substitution model for which O enters at one crystallographic position (occupied according to N4-xOx), in conjunction with a random Al for Si substitution at two distinct crystallographic positions. This leads to S-phase frameworks built from SiN4, SiN3O, AlN4 and AlN3O tetrahedra.

  • 7. Gebauer, Denis
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Oliveberg, Mikael
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Indications that Amorphous Calcium Carbonates Occur in Pathological Mineralisation-A Urinary Stone from a Guinea Pig2018In: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 8, no 3, article id 84Article in journal (Refereed)
    Abstract [en]

    Calcium carbonate is an abundant biomineral that is of great importance in industrial or geological contexts. In recent years, many studies of the precipitation of CaCO3 have shown that amorphous precursors and intermediates are widespread in the biomineralization processes and can also be exploited in bio-inspired materials chemistry. In this work, the thorough investigation of a urinary stone of a guinea pig suggests that amorphous calcium carbonate (ACC) can play a role in pathological mineralization. Importantly, certain analytical techniques that are often applied in the corresponding analyses are sensitive only to crystalline CaCO3 and can misleadingly exclude the relevance of calcium carbonate during the formation of urinary stones. Our analyses suggest that ACC is the major constituent of the particular stone studied, which possibly precipitated on struvite nuclei. Minor amounts of urea, other stable inorganics, and minor organic inclusions are observed as well.

  • 8. Granlund, Moa Z.
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nilsson, Marita
    Dawody, Jazaer
    Pettersson, Lars J.
    Evaluation of Co, La, and Mn promoted Rh catalysts for autothermal reforming of commercial diesel2014In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 154, p. 386-394Article in journal (Refereed)
    Abstract [en]

    The objective of this paper was to study the influence three promoters (Co, La, Mn) had on the catalytic activity of Rh-based catalysts for autothermal reforming of diesel. The catalysts were supported on CeO2ZrO2 and the loading was 1 wt.% Rh and 6 wt.% promoter. The catalytic activity was evaluated in a monolith bench scale reactor with Swedish Environmental diesel, MK1. The process parameters employed at the ATR experiments were; O-2/C similar to 0.45, H2O/C similar to 2.5 and GHSV similar to 50,000h(-1), meanwhile the reactor temperature was ramped from 700 degrees C to 950 degrees C. The catalysts were compared based on their fuel conversion, H-2 yield and the selectivity of different short-chain hydrocarbons. The results showed that all three catalysts had both high fuel conversion and H-2 yield in the optimal ATR operation temperatures. The H-2 yield and fuel conversion were increasing in the order Rh/Mn, Rh/La, Rh/Co. To get further insight in the difference between the materials the fresh and aged catalytic materials were characterized. The characterization methods used were H-2-temperature programmed reduction (H-2-TPR), powder X-ray diffraction (XRD), and BET surface measurements. The BET surface measurements showed that promotion with La gave improved thermal stability of the material. The XRD showed a high dispersion of all metals except Co, which was present as crystals in the size range of the particles of the support.

  • 9. Granlund, Moa Z.
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nilsson, Marita
    Dawody, Jazaer
    Pettersson, Lars J.
    Evaluation of Co, La, and Mn promoted Rh catalysts for autothermal reforming of commercial diesel: Aging and characterization2015In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 172, p. 145-153Article in journal (Refereed)
    Abstract [en]

    In this study, three bimetallic catalysts are evaluated for autothermal reforming (AIR) of fuels (1 wt.% Rh and 6 wt.% X (X= Co, La or Mn) supported on high-surface area CeO2-ZrO2). The catalysts are aged for approximately 35 h and carefully characterized both as fresh and aged materials. The objective is to illuminate the changes in material properties after time on stream as well as the differences among the materials. The changes in material properties are evaluated by H-2-TPR, BET surface area analysis, TEM, SEM, and STEM. The material's tendency to coke is investigated by TPO analysis. The three materials exhibit promising initial activity. However, the Co-promoted sample decreases sharply in activity after 25 h of operation. Meanwhile, the other two materials display a more stable activity throughout the evaluated time. The deactivation of the Co-promoted material could be linked to the high amount of coke deposited during operation. Based on the results from the activity evaluation and characterization, the material promoted with lanthanum displays the most promising results. The addition of lanthanum resulted in a catalyst that was both stable and had high activity, even though a low rhodium loading is used. The material also shows superior thermal resistance compared to the other two materials. In addition, the tendency to coke is significantly lower compered to the other materials, which is especially beneficial when dealing with AIR of complex fuels.

  • 10.
    Grüner, Daniel
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fäldt, Jenny
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Argon Ion Beam Polishing: A Preparation Technique for Evaluating the Interface of Osseointegrated Implants with High Resolution2011In: International Journal of Oral & Maxillofacial Implants, ISSN 0882-2786, E-ISSN 1942-4434, Vol. 26, no 3, p. 547-552Article in journal (Refereed)
    Abstract [en]

    Purpose: The objective of this study was to assess the use of ion beam polishing for preparing cross sections suitable for high-resolution scanning electron microscope (SEM) investigation of dental implants with a brittle porous oxide layer and of bone/implant interfaces. Materials and Methods: Thirteen Nobel Biocare TiUnite implants were placed in minipigs. After 4 weeks, the implant and surrounding bone were removed en bloc and the implant was cut axially into two halves. The cross section was then polished with an argon ion beam. Additionally, ion beam-polished cross sections were prepared from four as-received implants. Ion beam-polished surfaces were studied with a field emission SEM (FE-SEM). Results: With FE-SEM, up to 1 mm along the interface of ion beam-polished implant surfaces can be studied with a resolution of a few nanometers. Filled and unfilled pores of the porous TiUnite coating can be distinguished, providing information on pore accessibility. Implant-bone interfaces can be analyzed using backscattered electron images, where titanium, the oxide layer, mineralized extracellular matrix, and osteocyte lacunae/resin/soft tissue can easily be distinguished as a result of atomic number contrast and the sharp boundaries between the different materials. Filled and unfilled pores can be distinguished. Characterization of local chemistry is possible with energy dispersive X-ray spectrometry, and bone growth into small pores (< 1 mu m) can be unambiguously confirmed. Conclusion: FE-SEM complements the established methods for the characterization of interfaces and bridges the wide gap in accessible length scale and resolution between the observations of mechanically polished interfaces by optical or scanning electron microscopes and the observation of focused ion beam-milled sections in a transmission electron microscope.

  • 11.
    Gunawidjaja, Philips N.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Izquierdo-Barba, Isabel
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Garcia, Ana
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Quantifying apatite formation and cation leaching from mesoporous bioactive glasses in vitro: a SEM, solid-state NMR and powder XRD study2012In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 22, no 15, p. 7214-7223Article in journal (Refereed)
    Abstract [en]

    By employing solid-state nuclear magnetic resonance (NMR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy coupled with energy-dispersive X-ray (EDX) spectroscopy, we compare the biomimetic growth of calcium hydroxyapatite (HA) from an ordered mesoporous bioactive glass (MBG) in simulated body fluid (SBF) and buffered water solutions. For the latter medium, we also examine the effects of using two different MBG concentrations. We evaluate the predicting powers of PXRD and P-31 NMR for directly quantifying the relative amounts of biomimetic amorphous calcium phosphate (ACP) and HA: we observe a very good agreement between the two analytical techniques. Thanks to their mesoporous channel system, fluids readily penetrate throughout sub-mm sized MBG grains, as evidenced by EDX. The latter revealed distinct element-mappings across the material after its exposure to SBF compared to water. Under our in vitro conditions involving relatively high MBG-loadings in the solutions, the HA formation reduces in SBF relative to buffered water, particularly for increasing MBG concentration. These features stem from a high [Ca2+]/[PO43-] ratio resulting in the fluid medium, which retards the HA crystallization by inducing a rapid ACP precipitation and an accompanying depletion of phosphate ions in the solution. This has bearings on the design of bioactivity comparisons of bioglasses exhibiting significantly different cation compositions.

  • 12.
    Hamacher-Barth, Evelyne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    A method for sizing submicrometer particles in air collected on Formvar films and imaged by scanning electron microscopy2013In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 6, no 12, p. 3459-3475Article in journal (Refereed)
    Abstract [en]

    A method was developed to systematically investigate individual aerosol particles collected onto a polyvinyl formal (Formvar)-coated copper grid with scanning electron microscopy. At very mild conditions with a low accelerating voltage of 2 kV and Gentle Beam mode aerosol particles down to 20 nm in diameter can be observed. Subsequent processing of the images with digital image analysis provides size resolved and morphological information (elongation, circularity) on the aerosol particle population. Polystyrene nanospheres in the expected size range of the ambient aerosol particles (20–900 nm in diameter) were used to confirm the accuracy of sizing and determination of morphological parameters. The relative standard deviation of the diameters of the spheres was better than ±10% for sizes larger than 40 nm and ±18% for 21 nm particles compared to the manufacturer's certificate. Atmospheric particles were collected during an icebreaker expedition to the high Arctic (north of 80°) in the summer of 2008. Two samples collected during two different meteorological regimes were analyzed. Their size distributions were compared with simultaneously collected size distributions from a Twin Differential Mobility Particle Sizer, which confirmed that a representative fraction of the aerosol particles was imaged under the electron microscope. The size distributions obtained by scanning electron microscopy showed good agreement with the Twin Differential Mobility Sizer in the Aitken mode, whereas in the accumulation mode the size determination was critically dependent on the contrast of the aerosol with the Formvar-coated copper grid. The morphological properties (elongation, circularity) changed with the number of days the air masses spent over the pack-ice area north of 80° before the aerosol particles were collected at the position of the icebreaker and are thus an appropriate measure to characterize transformation processes of ambient aerosol particles.

  • 13.
    Hamacher-Barth, Evelyne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Size-resolved morphological properties of the high Arctic summer aerosol during ASCOS-20082016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 10, p. 6577-6593Article in journal (Refereed)
    Abstract [en]

    The representation of aerosol properties and processes in climate models is fraught with large uncertainties. Especially at high northern latitudes a strong underprediction of aerosol concentrations and nucleation events is observed and can only be constrained by in situ observations based on the analysis of individual aerosol particles. To further reduce the uncertainties surrounding aerosol properties and their potential role as cloud condensation nuclei this study provides observational data resolved over size on morphological and chemical properties of aerosol particles collected in the summer high Arctic, north of 80A degrees aEuro-N. Aerosol particles were imaged with scanning and transmission electron microscopy and further evaluated with digital image analysis. In total, 3909 aerosol particles were imaged and categorized according to morphological similarities into three gross morphological groups: single particles, gel particles, and halo particles. Single particles were observed between 15 and 800aEuro-nm in diameter and represent the dominating type of particles (82aEuro-%). The majority of particles appeared to be marine gels with a broad Aitken mode peaking at 70aEuro-nm and accompanied by a minor fraction of ammonium (bi)sulfate with a maximum at 170aEuro-nm in number concentration. Gel particles (11aEuro-% of all particles) were observed between 45 and 800aEuro-nm with a maximum at 154aEuro-nm in diameter. Imaging with transmission electron microscopy allowed further morphological discrimination of gel particles in 'aggregate' particles, 'aggregate with film' particles, and 'mucus-like' particles. Halo particles were observed above 75aEuro-nm and appeared to be ammonium (bi)sulfate (59aEuro-% of halo particles), gel matter (19aEuro-%), or decomposed gel matter (22aEuro-%), which were internally mixed with sulfuric acid, methane sulfonic acid, or ammonium (bi)sulfate with a maximum at 161aEuro-nm in diameter. Elemental dispersive X-ray spectroscopy analysis of individual particles revealed a prevalence of the monovalent ions Na+/K+ for single particles and aggregate particles and of the divalent ions Ca2+/Mg2+ for aggregate with film particles and mucus-like particles. According to these results and other model studies, we propose a relationship between the availability of Na+/K+ and Ca2+/Mg2+ and the length of the biopolymer molecules participating in the formation of the three-dimensional gel networks.

  • 14.
    Hedin, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Giovane, Frank
    Waldemarsson, Tomas
    Stockholm University, Faculty of Science, Department of Meteorology . Naval Research Laboratory, USA.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Blum, Jürgen
    Stroud, Rhonda M.
    Marlin, Layne
    Moser, John
    Siskind, David E.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Saunders, Russell W.
    Summers, Michael E.
    Reissaus, Philipp
    Stegman, Jacek
    Stockholm University, Faculty of Science, Department of Meteorology .
    Plane, John M. C.
    Horanyi, Mihaly
    The MAGIC meteoric smoke particle sampler2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 118, p. 127-144Article in journal (Refereed)
    Abstract [en]

    Between a few tons to several hundred tons of meteoric material enters the Earth's atmosphere each day, and most of this material is ablated and vaporized in the 70-120 km altitude region. The subsequent chemical conversion, re-condensation and coagulation of this evaporated material are thought to form nanometre sized meteoric smoke particles (MSPs). These smoke particles are then subject to further coagulation, sedimentation and global transport by the mesospheric circulation. MSPs have been proposed as a key player in the formation and evolution of ice particle layers around the mesopause region, i.e. noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). MSPs have also been implicated in mesospheric heterogeneous chemistry to influence the mesospheric odd oxygen/odd hydrogen (O-x/HOx) chemistry, to play an important role in the mesospheric charge balance, and to be a significant component of stratospheric aerosol and enhance the depletion of O-3. Despite their apparent importance, little is known about the properties of MSPs and none of the hypotheses can be verified without direct evidence of the existence, altitude and size distribution, shape and elemental composition. The aim of the MAGIC project (Mesospheric Aerosol - Genesis, Interaction and Composition) was to develop an instrument and analysis techniques to sample for the first time MSPs in the mesosphere and return them to the ground for detailed analysis in the laboratory. MAGIC meteoric smoke particle samplers have been flown on several sounding rocket payloads between 2005 and 2011. Several of these flights concerned non-summer mesosphere conditions when pure MSP populations can be expected. Other flights concerned high latitude summer conditions when MSPs are expected to be contained in ice particles in the upper mesosphere. In this paper we present the MAGIC project and describe the MAGIC MSP sampler, the measurement procedure and laboratory analysis. We also present the attempts to retrieve MSPs from these flights, the challenges inherent to the sampling of nanometre sized particles and the subsequent analysis of the sampled material, and thoughts for the future. Despite substantial experimental efforts, the MAGIC project has so far failed to provide conclusive results. While particles with elemental composition similar to what is to be expected from MSPs have been found, the analysis has been compromised by challenges with different types of contamination and uncertainties in the sticking efficiency of the particles on the sampling surfaces.

  • 15. Karatzas, Xanthias
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dawody, Jazaer
    Lanza, Roberto
    Pettersson, Lars J.
    Microemulsion and incipient wetness prepared Rh-based catalyst for diesel reforming2011In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 175, no 1, p. 515-523Article in journal (Refereed)
    Abstract [en]

    The role of the catalyst preparation technique was investigated for diesel reforming. Reverse microemulsion (ME) and incipient wetness (IW) techniques were used for the preparation of Rh-based monolithic catalysts that were employed for hydrogen generation of low-sulfur diesel via autothermal reforming (ATR). The washcoat of the tested catalysts consisted of 0.5 wt% Rh, 1 wt% Rh, and 1: 1 wt% Rh: Pt supported on gamma-alumina. All washcoats were deposited on 400 cpsi cordierite monoliths. The reaction condition was T(feed) = 650 degrees C, H(2)O/C similar to 2.5, O(2)/C similar to 0.49, TOS = 3 h, GHSV similar to 13 000 h(-1) and P = 1 atm. Fresh and aged powder samples of the catalyst were characterized by N(2)-BET, H(2) chemisorption, XRD, H(2)-TPR, O(2)-TPO and TEM. The activity results established that Rh and RhPt formulations, prepared by ME and IW, are highly active for ATR of diesel where fuel conversions above 92% were obtained. FTIR and NDIR analysis also showed that the highest formation of ethylene was found in the product gas stream from the bimetallic samples indicating that RhPt/Al(2)O(3) is less resistant towards carbon deposition. The latter observation was confirmed by O(2)-TPO analysis of the aged samples where high loads of coke were found both on the active metals and on the support. Interestingly, these effects were less significant on the ME samples. The characterization results clearly showed differences in morphology between the ME and the IW samples. N(2)-BET analysis showed that higher surface area, similar to 268-285 m(2)/g, was obtained with the ME samples. Also, H(2) chemisorption analysis showed that the rhodium dispersion was similar to 10% higher for the ME samples (H/Rh similar to 60-66%). XRD analysis showed that crystalline phases of gamma-alumina were present on all samples. The diffractograms also showed small traces of metallic Pt (similar to 16-30 nm) in the bimetallic samples. H(2)-TPR analysis, showed peaks ascribed to bulk rhodium oxides and rhodium aluminates. It was also noted that the addition of Pt on the support lowered the reducibility of the different rhodium species. TEM analysis performed on the fresh and aged ME and IW bimetallic samples showed mainly Rh(x)Pt(1-x) alloys with an average particle size of similar to 20-50 nm were present on the alumina support. Also, for the aged samples, no sintering effects were noted. Furthermore, rhodium was found to switch oxidation state from e. g. Rh(3+) to Rh(0) while Pt remained in the metallic state.

  • 16. Karatzas, Xanthias
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gonzalez, Angelica
    Dawody, Jazaer
    Pettersson, Lars J.
    Autothermal reforming of low-sulfur diesel over bimetallic RhPt supported on Al(2)O(3), CeO(2)-ZrO(2), SiO(2) and TiO(2)2011In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 106, no 3-4, p. 476-487Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to study and clarify the role of selected supports (both reducible and non-reducible) on the activity, selectivity and stability of RhPt-based catalyst for diesel reforming. Autothermal reforming (AIR) of low-sulfur diesel (S similar to 6 ppm, C/H similar to 6.43 (w/w)), H(2)O/C similar to 2.5, O(2)/C similar to 0.49, was tested at bench scale to detect differences in activity for catalysts consisting of 1 wt% Rh and 1 wt% Pt supported on alumina, ceria-zirconia (17.5 wt% ceria), silica and titania. Promoters in the form of MgO. Y(2)O(3), La(2)O(3), CeO(2) and ZrO(2), ranging from 4 wt% to 10 wt%, were also added onto the supports to detect differences in catalyst activity in terms of diesel conversion, CO(2) selectivity, and hydrogen and ethylene production. All metals were added sequentially onto the support by the incipient wetness technique and washcoated on 400 cpsi cordierite monolithic carriers with dimensions d = 17.8 mm, l=30.5 mm. The product gas analysis, using FTIR and NDIR, showed that RhPt/CeO(2)-ZrO(2) was found to be most active for AIR of diesel since a fuel conversion close to 98% was obtained. Furthermore, the catalyst activity of the unpromoted samples, in terms of diesel conversion, increased in the following order: RhPt/SiO(2) < RhPt/TiO(2) < RhPt/Al(2)O(3) < RhPt/CeO(2)-ZrO(2). The addition of promoters was found to be insignificant as well as having a negative impact on the catalyst performance in most cases, except for the alumina-promoted sample. The addition of 10 wt% La(2)O(3) on RhPt/Al(2)O(3) was found to enhance diesel conversion, hydrogen productivity as well as lower the ethylene concentration from 3700 ppm to less than half that value. The latter observation was confirmed by O(2)-TPO analysis of aged powder samples where lower loads of coke were present than on the La-promoted sample. The morphology, surface and bulk properties of RhPt/CeO(2)-ZrO(2) were closely examined in order to provide a possible correlation between the activity and characterization results. N(2)-BET analysis showed that the surface area of RhPt/CeO(2)-ZrO(2) was 64 m(2)/g, while the silica samples exhibited the highest area, similar to 137-185 m(2)/g. Hence, the difference in the surface areas was not enough to explain the trends observed in the activity measurements. XRD analysis of RhPt/CeO(2)-ZrO(2) showed crystalline phases characteristic of zirconia, most likely tetragonal. Also, the diffractogram did not reveal any Rh or Pt peaks indicating that the noble metal particles are highly dispersed on the support. In contrast, peaks ascribed to metallic Pt (similar to 30-46 nm) were clearly visible on the XRD patterns taken from all the other supported samples. H(2)-TPR analysis of RhPt/CeO(2)-ZrO(2) showed reduction peaks ascribed to Rh(i)O(x) species as well as a minor hydrogen spillover effect on the support to be present at T=120 degrees C and 450 degrees C, respectively. Also, the hydrogen consumption of the Rh(i)O(x) species was the highest compared to the other supported RhPt samples. TEM analysis performed on fresh RhPt/CeO(2)-ZrO(2) showed that the Rh(i)O(x) and Pt particles were highly dispersed on the support, both with particle sizes in the vicinity of similar to 5-15 nm. Rh species was found on ceria and zirconia, while Pt was present mainly on the ceria layer possibly in the form of Pt-O-Ce bonds. H(2)-chemisorption analysis measured at T similar to 40 degrees C shows similar Rh dispersion results. To summarize, the higher activity results of RhPt/CeO(2)-ZrO(2) for AIR of diesel, compared to other supported catalysts, may be ascribed to the higher reducibility of Rh(i)O(x) species as well as the superior Rh and Pt dispersion. Also, the support contribution, in particular ceria, is believed to promote water gas-shift activities as well as reduce coke deposits on the catalyst surface.

  • 17. Lelis, Martynas
    et al.
    Milcius, Darius
    Wirth, Emmanuel
    Halenius, Ulf
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Kadir, Karim
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Ruan, Juanfang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Sato, Toyoto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Yokosawa, Tadahiro
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Noréus, Dag
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    A mechanically switchable metal-insulator transition in Mg2NiH4 discovers a strain sensitive, nanoscale modulated resistivity connected to a stacking fault2010In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 496, no 02-jan, p. 81-86Article in journal (Refereed)
    Abstract [en]

    The band gap in semiconducting Mg2NiH4 was found to be dependent on subtle structural differences. This was discovered when investigating if thin film samples of Mg2NiH4 could be used in a switchable mirror or window device by utilizing a high to low temperature transition at about 510K. In powder samples; this transition between an FCC high temperature phase, with dynamically disordered NiH4-complexes, and a monoclinic distorted low temperature phase, with ordered Mg2NiH4-complexes, has been demonstrated in a mechanical reversible conductor-insulator transition (Blomqvist and Noreus (2002) [7]). Black monoclinic Mg2NiH4 powders were found to have a band gap of 1.1 eV. Pressed tablets of black monoclinic Mg2NiH4 powders are conductive, probably from doping by impurities or non-stoichiometry. Thin film Mg2NiH4 samples were produced by reacting hydrogen with magnetron sputtered Mg2Ni films on quartz glass or CaF2 substrates. The Mg2NiH4 films on the other hand were orange, transparent with a band gap of 2.2 eV and a cubic unit cell parameter almost identical to the disorder HT phase but with lower symmetry. If black Mg2NiH4 powder is heated above the phase transition at 510K and subsequently cooled down, the conductivity is lost and the powder turns brown. After this heat treatment TEM pictures revealed a multiple stacking fault having a local pseudo-cubic arrangement separating regions of monoclinic symmetry. The loss of conductivity and colour change is attributed to a higher band gap in the strained areas. The structure on each side of the stacking fault is related by a mirror plane as a consequence of the possibility for the NiH4-complexes to order with different orientations. This leads to a mismatch in the long range ordering and strain is probably creating the stacking faults. Strain is important for forming the cubic modification. A severely strained film was revealed with optical microscopy in reflected light, indicating that strain prevents it from relaxing back into the monoclinic structure. This was supported by multiple twinned red translucent Mg2NiH4 crystals grown with cubic symmetry at elevated temperatures in a LiH flux. When cooled to ambient conditions, the ""crystals"" had the same cubic symmetry as the films, probably held together by their neighbours. When they were ground to a fine powder to prepare TEM samples, they relaxed and reverted back to the conventional monoclinic unit cell. This interesting nanoscale modulated resistance could possibly be developed into novel memory devices if properly controllable.

  • 18.
    Leonova, Ekaterina
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hakeem, Abbas S.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Esmaeilzadeh, Saeid
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Nitrogenrich La-Si-Al-O-N oxynitride glass structures probed by solid state NMR2008In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 354, no 1, p. 49-60Article in journal (Refereed)
    Abstract [en]

    We investigate the local structures of oxynitride La–Si–(Al)–O–N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si–N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La–Si–Al–O glasses and are discussed in relation to the glass compositions and their proposed structures.

  • 19.
    Lidin, Sven
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Christensen, J
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Fredrickson, D
    Incommensurate Stistaite-Order Made to Order2009In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 48, no 12, p. 5497-5503Article in journal (Refereed)
    Abstract [en]

    The stistaite SbSn phase contg. 40-57 at.% Sb was investigated by using single crystal x-ray diffraction and EDX to yield a simple relation between the modulated structure and compn.  Stistaite is incommensurately ordered over its entire stability region.

  • 20.
    Mathew, Renny
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Gunawidjaja, Philips N.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Izquierdo-Barba, Isabel
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Garcia, Ana
    Arcos, Daniel
    Vallet-Regi, Maria
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Solid-State (31)P and (1)H NMR Investigations of Amorphous and Crystalline Calcium Phosphates Grown Biomimetically From a Mesoporous Bioactive Glass2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 42, p. 20572-20582Article in journal (Refereed)
    Abstract [en]

    By exploiting (1)H and (31)P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we explore the proton and orthophosphate environments in biomimetic amorphous calcium phosphate (ACP) and hydroxyapatite (HA), as grown in vitro at the surface of a 10CaO-85SiO(2)-5P(2)O(5) mesoporous bioactive glass (MBG) in either a simulated body fluid or buffered water. Transmission electron microscopy confirmed the presence of a calcium phosphate layer comprising nanocrystalline HA Two-dimensional (1)H-(31)P heteronudear correlation NMR established predominantly (1)H(2)O <->(31)PO(4)(3-) and O(1)H <->(31)PO(4)(3-) contacts in the amorphous and crystalline component, respectively, of the MBG surface-layer; these two pairs exhibit distinctly different (1)H <->(31)P cross-polarization dynamics, revealing a twice as large squared effective (1)H-(31)P dipolar coupling constant in ACP compared with HA. These respective observations are mirrored in synthetic (well-crystalline) HA, and the amorphous calcium orthophosphate (CaP) clusters that are present in the pristine MBG pore walls: besides highlighting very similar local (1)H and (31)P environments in synthetic and biomimetic HA, our findings evidence closely related NMR characteristics, and thereby similar local structures, of the CaP clusters in the pristine MBG relative to biomimetic ACP.

  • 21.
    Ng, Jovice BoonSing
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Using differential scanning calorimetry to follow how gelcasting proceeds2007In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 90, no 3, p. 999-1001Article in journal (Refereed)
    Abstract [en]

    Differential scanning calorimetry studies on aqueous low-toxicity monomer–crosslinker gelcasting systems loaded with zirconia powder provided information on the onset and kinetics of the polymerization reaction. A simple procedure was developed to determine the relative importance of the individual components on the gelation process. It was found that the thermal stability and dissociation of the initiator control the gelation rate and that the zirconia particles accelerate the gelation.

  • 22. Nilsson, Marita
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jozsa, Peter
    Pettersson, Lars J.
    Catalytic properties of Pd supported on ZnO/ZnAl2O4/Al2O3 mixtures in dimethyl ether autothermal reforming2009In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 86, no 02-jan, p. 18-26Article in journal (Refereed)
    Abstract [en]

    The catalytic properties of Pd supported on mixtures of zinc oxide, zinc aluminate, and alumina, prepared from gamma-alumina and zinc nitrate, were studied for autothermal reforming (ATR) of dimethyl ether (DME). The performance of the catalysts was tested in a small-scale reactor, using cordierite monoliths as substrate. The catalysts exhibited high activity and generated hydrogen-rich product gases with CO concentrations below 5 vol.% in the temperature range between 350 and 450 degrees C (at O-2:DME = 0.7, H2O:DME = 2.5, and GHSV = 15000 h(-1)). The highest DME conversion was obtained for a catalyst in which the support comprised mainly ZnAl2O4. Physical mixing of the catalysts with gamma-Al2O3 resulted in increased DME conversion but a lowering of the CO2 selectivity. The catalysts were characterized by CO chemisorption, liquid nitrogen adsorption, temperature-programmed desorption of ammonia, temperature-programmed reduction, transmission electron microscopy, and X-ray diffraction. It was found that decreasing surface area and decreasing number of acid sites, caused by thermal treatment during generation of the supports, did not affect the activity negatively. The high CO2 selectivity of the catalysts was correlated with PdZn alloy formation. 

  • 23.
    Pahari, Bholanath
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Iftekhar, Shahriar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jaworski, Aleksander
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Okhotnikov, Kirill
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jansson, Kjell
    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).
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Composition-property-structure correlations of scandium aluminosilicate glasses revealed by multinuclear 45Sc, 27Al and 29Si solid-state NMR2012In: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 95, no 8, p. 2545-1553Article in journal (Refereed)
    Abstract [en]

    Many features of aluminosilicate glasses incorporating a rare-earth (RE) ion are dictated by its mass and cation field strength (CFS). ScAlSiO glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass-transition temperature (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3Al2O3SiO2 system. The glasses exhibit uniform and unexpectedly low Tg-values (similar to 875 degrees C), but a high microhardness (approximate to 9.3 GPa) that correlates with the Sc2O3 content. 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass-network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%35%) and AlO6 (approximate to 5%) polyhedra are present in all ScAlSiO glass structures. 45Sc isotropic chemical shifts (similar to 92 ppm) derived from MAS and 3QMAS (triple-quantum MAS) NMR experiments are consistent with ScO6 environments.

  • 24. Pai, Ranjith Krishna
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Transport-Mediated Control of Particles of Calcium Carbonate.      2009In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 9, no 11, p. 4581-4583Article in journal (Refereed)
    Abstract [en]

    Micrometer-sized particles of calcium carbonate were formed by adding NaHCO3 (aq) to a buffered aq. soln. of CaCl2 (aq) and polyelectrolytes.  Particle morphol. and crystal polymorphol. were tuned by varying the stirring rate.  Vigorous stirring led to the formation of micrometer-sized spherical particles of nanocryst. vaterite; slow stirring formed rhombohedral nanostructured particles of calcite.

  • 25. Pai, RK
    et al.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Transport control during the formation of particles of calcium carbonate2009In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 9, no 11, p. 4581-4583Article in journal (Refereed)
    Abstract [en]

    : Micrometer-sized particles of calcium carbonate were formed by adding NaHCO3 (aq) to a buffered aqueous solution of CaCl2 (aq) and polyelectrolytes. Particle morphology and crystal polymorphology were tuned by varying the stirring rate. Vigorous stirring led to the formation of micrometer-sized spherical particles of nanocrystalline vaterite; slow stirring formed rhombohedral nanostructured particles of calcite.

  • 26. Ren, Tie-zhen
    et al.
    Christensen, Kirsten Elvira
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grins, Jekabs
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Shi, Lei
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Zou, Xiaodong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    SU-57 – An aluminosilicogermanate with a DFT topology and variable compositions2009In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 117, no 1-2, p. 285-291Article in journal (Refereed)
    Abstract [en]

    An aluminosilicogermanate with a DFT zeotype framework (denoted as SU-57) was synthesized for the first time by ethanol-assisted hydrothermal synthesis at 160 and 170 °C. The compound was characterized by single crystal and powder X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy (EDS), thermogravimetry (TG) and solid state nuclear magnetic resonance (NMR) spectroscopy. SU-57 crystallizes in space group P42/n with estimated a ≈ 10.38–10.46 Å, c ≈ 8.88–8.91 Å, V ≈ 957–975 Å3. It has variable Al–Si–Ge composition with an approximate formula |C2H10N2| [Al(SixGe1−x)O4]2 (x ≈ 0.3–0.9), which results in a super-structure originated from different cation occupancies of the two unique tetrahedral (T) sites. Single crystal X-ray structure refinements, together with results from X-ray powder diffraction (XRPD) and EDS analysis, showed that (i) the AlO4 and (Si, Ge)O4 tetrahedra are only partially ordered over the DFT framework and do not follow a strict alternating manner. (ii) Al resides predominantly on one T site and Si and Ge predominantly on the other. (iii) The Al cation concentration (Al/(Al + Si + Ge)) is nearly constant and slightly less than 50 at%, while the Si and Ge cation concentrations vary over a large range. (iv) Al and Ge occupy both T sites. The cation disorder was confirmed by 27Al and 29Si solid state NMR. TG analysis and in situ XRPD showed that SU-57 was stable up to 375 °C in N2 atmosphere.

  • 27.
    Stevens, Sam M
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Cubillas, Pablo
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Anderson, Michael W
     Nanoscale Electron Beam Damage Studied by Atomic Force Microscopy2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 43, p. 18441-18443Article in journal (Refereed)
    Abstract [en]

    High-resoln. SEM (HRSEM) has recently been added to the arsenal of characterization tools for material scientists to observe nanoscale surface features on both conducting and insulating materials.  It is now therefore crucial to understand whether the intense electron beam will damage the features of interest.  The authors were able, for the 1st time, to measure and quantify this damage using a combination of HRSEM and at. force microscopy (AFM), and as a consequence, the bulk of the damage, expressed as a depression on the crystal surface, is confined primarily to a subsurface vol.  Simulations demonstrate that the depth of the depression is proportional to the interaction vol. of impact electrons below the crystal surface.  More importantly, the nanometer surface features are conserved, and there is negligible assocd. loss of the crit. information in nanoscopic surface topog.  These results confirm the usefulness of HRSEM as a tool for surface anal. not only for scientists studying crystal growth but also for materials scientists analyzing any surface at the nanoscale.

  • 28. Stevens, Sam M.
    et al.
    Cubillas, Pablo
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Anderson, Michael W.
    Wright, Paul A.
    Castro, Maria
    Nanometre resolution using high-resolution scanning electron microscopy corroborated by atomic force microscopy2008In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 33, p. 3894-3896Article in journal (Refereed)
    Abstract [en]

    The resolving power of high-resolution scanning electron microscopy was judged using topographical height data from atomic force microscopy in order to assess the technique as a tool for understanding nanoporous crystal growth.

  • 29.
    Stevens, Sam M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Klingstedt, Miia
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Grüner, Daniel
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    An Appraisal of High Resolution Scanning Electron Microscopy Applied To Porous Materials2009In: JEOL News, Vol. 44, no 1, p. 17-22Article in journal (Refereed)
    Abstract [en]

    Nanoporous materials such as zeolites and mesoporous silica crystals have attracted a lot of attention in recent years. In particular, the incorporation of various materials such as organic molecules, or metal nanoparticles and other inorganic compounds within their pores which give rise to fascinating new functions. For such materials, it is essential to determine their structure, composition and mechanisms of growth in order to maximize their utility in future applications.

    Recent progress in the performance of SEM is enormous, especially in low energy imaging where we can now directly observe fine surface structures of porous materials even those that are electrical insulators. Furthermore, by precise filtration and detection of emitted electrons by their energy, we can selectively obtain different types of information such as material composition, location of particles inside or outside the pores etc. The physical processes and technologies behind this precise tuning of landing and detection energies for both impact and emitted electrons, respectively, are explained and illustrated using a number of porous materials including zeolite LTA, SBA-15, SBA-16, zeolite LTL, FDU-16 and Au@TiO2 ' rattle spheres,' along with comparisons with other techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM). We conclude that, by using extremely low landing energies, advanced sample preparation techniques and through a thorough understanding of the physical processes involved, HRSEM is providing new and unique information and perspectives on these industrially important materials.

  • 30.
    Svengren, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jansson, Kjell
    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).
    Wan, Wei
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Torapava, Natallia
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Direct Synthesis of Two Inorganic Catalysts on Carbon Fibres for the Electrocatalytic Oxidation of Water2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 3, p. 568-575Article in journal (Refereed)
    Abstract [en]

    Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3Sb4O6F6 and the new compound CoSbO4. The compounds express large differences in their morphology: CoSbO4 grows as thin needles whereas Co3Sb4O6F6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co3Sb4O6F6 was used it gave a low increase of +0.028 mV h(-1) at an overpotential of eta = 472 mV after 10 h and a stability of +0.48 mV h(-1) at an overpotential of eta = 488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at% Co and approximately 0.02 at% Sb were detected in the electrolyte.

  • 31.
    Thomas, Annu
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Andersson, Johanna
    Grüner, Daniel
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Osla, Fredrik
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fäldt, Jenny
    Shen, Zhijian
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Direct observation of bone coherence with dental implants2012In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, no 11, p. 2607-2612Article in journal (Refereed)
    Abstract [en]

    A newly developed gentle ion beam polishing technique was established for preparing of cross sections of dental implants feasible for high resolution scanning electron microscope investigation. This approach was applied to investigate the interfacial microstructure between newly formed bone and dental implants with modified surfaces extracted after in vivo test in adult miniature pigs. The results obtained so far reveal that it has become possible to analyze the bone coherence to implants besides measuring the bone coverage. The amount and density of the mineralized extra cellular matrix has found to be different in different sub-microscopic regions around the implant. From our observations, it can be seen that new bone grows from the existing bone and advances towards the implant surface by in growth mechanism. The images also reveal that new bone is formed directly at the implant surface; we propose a deposition mechanism to explain this. Eventually the in grown and the deposited bone connect to give a good anchorage of the implant. This achievement bears implication for understanding osseointegration at microscopic level.

  • 32. 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.

  • 33. Westin, Gunnar
    et al.
    Leideborg, Michael
    Lashgari, Koroush
    Coleman, Victoria A
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Pohl, Annika
    Solution processing of conducting dense and porous films; doped ZnO and TiO2, and perovskites2009In: International Journal of Nanotechnology, Vol. 6, no 9, p. 828-849Article in journal (Refereed)
    Abstract [en]

    Soln. based processing of porous and dense films by all-alkoxide based precursor systems have been investigated and compared, with a focus on the connection between the precursors and heat-treatment, and the product oxide quality and structure.  Three systems were investigated typically with TGA, DSC, XPS, IR spectroscopy, X-ray diffraction, TEM-EDS and SEM-EDS, but also with other advanced characterization techniques: (i) manganate and cobaltate perovskites of the LCMO (La0.67Ca0.33MnO3), LSMO (La0.75Sr0.25MnO3), LNCMO (La0.33Nd0.33Ca0.33MnO3), LBSM (La0.75Ba0.125Sr0.125MnO3) and LSCO (La0.50Sr0.50CoO3) compns. were investigated.  Highly epitaxial films of LCMO and LSCO were prepd., and the CMR properties of the LCMO were comparable to those of PVD derived films.  Polycryst. films were prepd. for all perovskites.  (ii) Three routes to ZnO : Co/Al were investigated and compared; an acetate based route and two alkoxide based routes with different heat-treatments.  With the acetate based and the alkoxide based route using hydrolysis in air, a max. Co doping of 6% was obtained, while in absence of CO2 and O2, the doping range could be extended to 20%Co.  Both dense films and porous nano-structured films were prepd.  The magnetic properties of the Co-doped films did not show any room-temp. ferro-magnetism.  (iii) ZrO2 and NbO2.5 doped anatase TiO2 were prepd. by heat-treatment or hydrothermal routes.  Alio-valent doping of up to more than 35% of NbO2.5 could be achieved in the anatase.  It is believed that the pentavalent metal doping is compensated by metal vacancies, and as expected from this assumption, the materials have a low d.  ZrO2 doping in titania led to an increase in the dye-sensitized solar cell efficiency and highly active and stable photo-catalysts.

  • 34. Wiinikka, Henrik
    et al.
    Toth, Pal
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molinder, Roger
    Broström, Markus
    Sandström, Linda
    Lighty, JoAnn S.
    Weiland, Fredrik
    Particle formation during pressurized entrained flow gasification of wood powder: Effects of process conditions on chemical composition, nanostructure, and reactivity2018In: Combustion and Flame, ISSN 0010-2180, E-ISSN 1556-2921, Vol. 189, p. 240-256Article in journal (Refereed)
    Abstract [en]

    The influence of operating condition on particle formation during pressurized, oxygen blown gasification of wood powder with an ash content of 0.4 wt% was investigated. The investigation was performed with a pilot scale gasifier operated at 7 bar(a). Two loads, 400 and 600 kW were tested, with the oxygen equivalence ratio (A) varied between 0.25 and 0.50. Particle concentration and mass size distribution was analyzed with a low pressure cascade impactor and the collected particles were characterized for morphology, elemental composition, nanostructure, and reactivity using scanning electron microscopy/high resolution transmission electron microscopy energy dispersive spectroscopy, and thermogravimetric analysis. In order to quantify the nanostructure of the particles and identify prevalent sub-structures, a novel image analysis framework was used. It was found that the process temperature, affected both by A and the load of the gasifier, had a significant influence on the particle formation processes. At low temperature (1060 degrees C), the formed soot particles seemed to be resistant to the oxidation process; however, when the oxidation process started at 1119 degrees C, the internal burning of the more reactive particle core began. A further increase in temperature ( > 1313 degrees C) lead to the oxidation of the less reactive particle shell. When the shell finally collapsed due to severe oxidation, the original soot particle shape and nanostructure also disappeared and the resulting particle could not be considered as a soot anymore. Instead, the particle shape and nanostructure at the highest temperatures ( > 1430 degrees C) were a function of the inorganic content and of the inorganic elements the individual particle consisted of. All of these effects together lead to the soot particles in the real gasifier environment having less and less ordered nanostructure and higher and higher reactivity as the temperature increased; i.e., they followed the opposite trend of what is observed during laboratory-scale studies with fuels not containing any ash-forming elements and where the temperature was not controlled by A.

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