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  • 1.
    Abebe, Mihret
    et al.
    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).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Spherical and Porous Particles of Calcium Carbonate Synthesized with Food Friendly Polymer Additives2015In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 15, no 8, p. 3609-3616Article in journal (Refereed)
    Abstract [en]

    Porous calcium carbonate particles were synthesized by adding solutions of Ca2+ to solutions of CO32- containing polymeric additives. Under optimized conditions well-defined aggregates of the anhydrous polymorph vaterite formed. A typical sample of these micrometer-sized aggregates had: a pore volume of 0.1 cm(3)/g, a pore width of similar to 10 nm, and a specific surface area of similar to 25-30 m(2)/ g. Only one mixing Order (calcium to carbonate) allowed the formation of vaterite, which was ascribed to the buffering capacity and relatively high pH of the CO32- solution. Rapid addition of the calcium chloride solution and rapid stirring promoted the formation of vaterite, due to the high supersaturation levels achieved. With xanthan gum, porous and micrometer-sized vaterite aggregates could be synthesized over a wide range of synthetic conditions. For the Other food grade polymers, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and sodium carboxyl methylcellulose, several intensive and extensive synthetic parameters had to be optimized to obtain pure vaterite and porous aggregates. HPMC and MC allowed well-defined spherical micrometer-sited particles to form. We expect that these spherical and porous particles of vaterite could be relevant to model studies as well as a controlled delivery of particularly large molecules.

  • 2.
    Akhtar, Farid
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Andersson, Linnea
    Ogunwumi, Steven
    Hedin, Niklas
    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).
    Structuring adsorbents and catalysts by processing of porous powders2014In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 34, no 7, p. 1643-1666Article in journal (Refereed)
    Abstract [en]

    Microporous materials such as zeolites, metal organic frameworks, activated carbons and aluminum phosphates are suitable for catalysis and separation applications. These high surface area materials are invariably produced in particulate forms and need to be transformed into hierarchically porous structures for high performance adsorbents or catalysts. Structuring of porous powders enables an optimized structure with high mass transfer, low pressure drop, good heat management, and high mechanical and chemical stability. The requirements and important properties of hierarchically porous structures are reviewed with a focus on applications in gas separation and catalysis. Versatile powder processing routes to process porous powders into hierarchically porous structures like extrusion, coatings of scaffolds and honeycombs, colloidal processing and direct casting, and sacrificial approaches are presented and discussed. The use and limitations of the use of inorganic binders for increasing the mechanical strength is reviewed, and the most important binder systems, e.g. clays and silica, are described in detail. Recent advances to produce binder-free and complex shaped hierarchically porous monoliths are described and their performance is compared with traditional binder-containing structured adsorbents. Needs related to better thermal management and improved kinetics and volume efficiency are discussed and an outlook on future research is also given.

  • 3.
    Akhtar, Farid
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Keshavarzi, Neda
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shakarova, Dilshod
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cheung, Ocean
    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).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Aluminophosphate monoliths with high CO2-over-N2 selectivity and CO2 capture capacity2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 99, p. 55877-55883Article in journal (Refereed)
    Abstract [en]

    Monoliths of microporous aluminophosphates (AlPO4-17 and AlPO4-53) were structured by binder-freepulsed current processing. Such monoliths could be important for carbon capture from flue gas. TheAlPO4-17 and AlPO4-53 monoliths exhibited a tensile strength of 1.0 MPa and a CO2 adsorption capacityof 2.5 mmol g1 and 1.6 mmol g1, respectively at 101 kPa and 0 C. Analyses of single component CO2and N2 adsorption data indicated that the AlPO4-53 monoliths had an extraordinarily high CO2-over-N2selectivity from a binary gas mixture of 15 mol% CO2 and 85 mol% N2. The estimated CO2 capturecapacity of AlPO4-17 and AlPO4-53 monoliths in a typical pressure swing adsorption (PSA) process at 20C was higher than that of the commonly used zeolite 13X granules. Under cyclic sorption conditions,AlPO4-17 and AlPO4-53 monoliths were regenerated by lowering the pressure of CO2. Regeneration wasdone without application of heat, which would regenerate them to their full capacity for CO2 adsorption.

  • 4.
    Akhtar, Farid
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Qingling
    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).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Strong and binder free structured zeolite sorbents with very high CO2-over-N-2 selectivities and high capacities to adsorb CO2 rapidly2012In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 5, no 6, p. 7664-7673Article in journal (Refereed)
    Abstract [en]

    Mechanically strong monoliths of zeolite NaKA with a hierarchy of pores displayed very high CO2-over-N-2 selectivity. The zeolite monoliths were produced by pulsed current processing (PCP) without the use of added binders and with a preserved microporous crystal structure. Adsorption isotherms of CO2 and N-2 were determined and used to predict the co-adsorption of CO2 and N-2 using ideal adsorbed solution theory (IAST). The IAST predictions showed that monolithic adsorbents of NaKA could reach an extraordinarily high CO2-over-N-2 selectivity in a binary mixture with a composition similar to flue gas (15 mol% CO2 and 85 mol% N2 at 25 degrees C and 101 kPa). Structured NaKA monoliths with a K+ content of 9.9 at% combined a CO2-over-N-2 selectivity of >1100 with a high CO2 adsorption capacity (4 mmol g(-1)) and a fast adsorption kinetics (on the order of one minute). Estimates of a figure of merit (F) based on IAST CO2-over-N-2 selectivity, and time-dependent CO2 uptake capacity, suggest that PCP-produced structured NaKA with a K+ content of 9.9 at% offers a performance far superior to 13X adsorbents, in particular at short cycle times.

  • 5.
    Atluri, Rambabu
    et al.
    Uppsala universitet.
    Bacsik, Zoltan
    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).
    Garcia-Bennett, Alfonso E.
    Uppsala universitet.
    Structural variations in mesoporous materials with cubic Pm(3)over-barn symmetry2010In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 133, no 1-3, p. 27-35Article in journal (Refereed)
    Abstract [en]

    The fine structural details of mesoporous materials possessing Pmn symmetry prepared with varying amphiphilic surfactants under acid and alkaline conditions are investigated using electron crystallography and sorption studies. The structural data derived is used to understand the parameters that govern the formation of cavity–windows and to propose synthetic strategies in order to control independently the size of the cavities and cavity–windows. Results support that whilst attainment of Pmn cubic packing is due to the overall surfactant geometry, the formation of cavity–windows is associated with the hydration layer formed at the interphase between the surfactant and the silica wall. The charge density at the micelle surface may be tailored using two strategies: (i) using dicationic gemini surfactants at low pHs resulting in an increase in the hydration layer; or (ii) by using co-structure directing agents such as organoalkoxysilanes which reduce the hydration layer surrounding the micelles. The latter leads to the formation of higher cavity sizes and may be useful for tuning fine structural details of mesoporous materials when considering their use in important applications such as gas separation.

  • 6.
    Atluri, Rambabu
    et al.
    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.
    Garcia-Bennett, Alfonso E.
    Non-Surfactant Supramolecular Templating Synthesis of Ordered Mesoporous Silica2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 9, p. 3189-3191Article in journal (Refereed)
    Abstract [en]

    Hoogsteen-bonded tetrads and pentamers are formed by a large variety of organic molecules through H-donor and acceptor groups capable of inducing self-organization to form columnar and hexagonal mesophases. The biological importance of such macromolecular structures is exemplified by the assembly of guanosine-rich groups of telomere units and their implication in chromosomal replication. Folic acid is composed of a pterin group, chemically and structurally similar to guanine, conjugated to an l-glutamate moiety via a p-amino benzoic acid. Our aim has been to develop a delivery vehicle for folic acid and at the same time provide a novel synthetic route for ordered mesoporous materials without the use of amphiphilic surfactants. We present a new nonsurfactant route for the synthesis of highly ordered mesoporous materials, based on the supramolecular templating of stacked arrays of the tetramer-forming pterin groups of folic acid under a variety of synthetic conditions. This method leads to hexagonally ordered mesoporous structures with gyroid, spherical, and chiral morphologies with pores on the order of 25−30 Å in diameter and surface areas above 1000 m2/g. More importantly circular dichroism studies reveal that the folate template possesses a chiral signature within the pores in the as-synthesized solid and that chirality is transferred from the folate template to the pore surface via the aminopropyl triethoxysilane costructure directing agent used in the supramolecular assembly. This novel templating approach for ordered mesoporous materials breaks the hegemony of surfactant micellar systems for the preparation of these exciting high surface area solids and opens new opportunities for structural control, design of pore geometry, and novel applications.

  • 7. Atluri, Rambabu
    et al.
    Iqbal, Muhammad Naeem
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Villaescusa, Luis Angel
    Garcia-Bennett, Alfonso E.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry. alfonso@mmk.su.se.
    Self-Assembly Mechanism of Folate-Templated Mesoporous Silica2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 38, p. 12003-12012Article in journal (Refereed)
    Abstract [en]

    A method to form ordered mesoporous silica based on the use of folate supramolecular templates has been developed. Evidence based on in situ small-angle X-ray scattering (SAXS), electron microscopy, infrared spectroscopy, and in situ conductivity measurements are used to investigate the organic inorganic interactions and synthesis mechanism. The behavior of folate molecules in solution differs distinctively from that of surfactants commonly used for the preparation of ordered mesoporous silica phases, notably with the absence of a critical micellar concentration. In situ SAXS studies reveal fluctuations in X-ray scattering intensities consistent with the condensation of the silica precursor surrounding the folate template and the growth of the silica mesostructure in the initial stages. High-angle X-ray diffraction shows that the folate template is well-ordered within the pores even after a few minutes of synthesis. Direct structural data for the self-assembly of folates into chiral tetramers within the pores of mesoporous silica provide evidence for the in register stacking of folate tetramers, resulting in a chiral surface of rotated tetramers, with a rotation angle of 30 degrees. Additionally, the self-assembled folates within pores were capable of adsorbing a considerable amount of CO2 gas through the cavity space of the tetramers. The study demonstrates the validity of using a naturally occurring template to produce relevant and functional mesoporous materials.

  • 8.
    Aziz, Baroz
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gebauer, Denis
    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).
    Kinetic control of particle-mediated calcium carbonate crystallization2011In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 13, no 14, p. 4641-4645Article in journal (Refereed)
    Abstract [en]

    By changing the temperature, pH, stirring rate, or time for calcium carbonate crystallization, complex shapes of aggregated calcium carbonates formed. Such shapes have earlier been ascribed to specific interactions with specialized additives. Without polymeric additives, aggregates of vaterite transformed more rapidly into calcite aggregates under slow than under fast stirring. With an anionic polyelectrolyte added, vaterite was stabilized. Larger polycrystalline aggregates of vaterite formed under rapid than under slow stirring, indicative of a particle mediated growth of aggregates controlled by convective currents. The size of the underlying nanoparticles was temperature dependent, with grain sizes of similar to 20 to 50 nm at 20 degrees C and similar to 350 nm at 90 degrees C. The small differences in free energy between the anhydrous polymorphs of calcium carbonate made both kinetic and equilibrium dependencies important.

  • 9.
    Aziz, Baroz
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Bacsik, Zoltán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Quantification of chemisorption and physisorption of carbon dioxide on porous silica modified by propylamines: Effect of amine density2012In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 159, p. 42-49Article in journal (Refereed)
    Abstract [en]

    Detailed molecular aspects of carbon dioxide sorption on porous silica with different amounts of tethered and cross-linked n-propylamine groups were investigated. Infrared spectroscopy was applied to directly quantify physisorbed and chemisorbed CO2 on the amine modified silicas. The fractions of physisorbed CO2 and various chemisorbed species were determined as functions of CO2 pressure and the amine density on the modified silica. Physisorbed CO2 was a minor portion of the total CO2 uptake at low pressures, but it’s contribution increased to ∼35% at 1 bar of CO2 when the propylamine surface density was low or medium (0.87-1.67 NH2/nm2). Chemisorption of CO2 dominated when the propylamine content was high (2.74 NH2/nm2). The quantities of propylammonium propylcarbamate ion pairs increased with increasing propylamine content. At low or medium amine surface densities (0.87-1.67 NH2/nm2) this increase was approximately proportional to the amine density, but the quantity of ion pairs increased very significantly when the propylamine content was high (2.74 NH2/nm2). This dependency on amine density is consistent with the idea that a sufficiently close proximity of propylamine groups allows a formation of ion pairs. The relative fractions of carbamic acid and silylpropylcarbamate were significant for materials on which ion pairs could not form. Furthermore, the quantities of carbamic acid increased with increasing amine densities suggesting that the ion pairs have a role to stabilize the labile carbamic acid through hydrogen bonds.

  • 10.
    Aziz, Baroz
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhao, Guoying
    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).
    Carbon Dioxide Sorbents with Propylamine Groups-Silica Functionalized with a Fractional Factorial Design Approach2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 7, p. 3822-3834Article in journal (Refereed)
    Abstract [en]

    Mesoporous silica particles (Davisil) were functionalized with aminopropyltriethoxysilane (APTES) in a fractional factorial design with 19 different synthesis and uptake experiments. The number of amino groups and the uptake of CO(2) were optimized in a 2(V)(5-1) design. Most important to functionalizationwas the amount of water present during synthesis, the reaction time, and pretreating the silica with a mineral acid; certain two-way interactions were shown to be statistically significant as well. Modifications performed at 110 or 80 degrees C showed no significant differences concerning amine content or uptake of CO(2). Properly choosing center points for the discrete variables is problematic and is somewhat related to the lack of fit with respect to CO(2) uptake; the regression was good. Solid-state (29)Si NMR showed that the APTES was mainly fully condensed. Specific surface areas did not correlate with the number of n-propylamine groups on the silica, which is indicative of differential levels of heterogeneity in the coverage of propylamines. The uptake of CO(2) and N(2) was measured from -20 to 70 degrees C and from 0 to 1 bar and parametrized by the Freundlich isotherm. Amine-modified silica adsorbed significant amounts of CO(2), especially at the low partial pressure, which is important for CO(2) capture from flue gas. At such pressures, samples with a high density of amine (4 amines/nm(2)) showed a much higher uptake of CO(2) than did those with densities of similar to 2-3 amines/nm(2), reflecting differential tendencies to form propylammonium-propylcarbamate ion pairs; these require close proximity among amine groups to form. Water affected the uptake of carbon dioxide in different ways. Certain samples took up more moist CO(2) gas than dry CO(2), and others took up less moist CO(2) than dry CO(2), which is indicative of differential tendencies toward water adsorption. We conclude that experimental design is a time-efficient approach to the functionalization of silica with propylamine groups.

  • 11. Azuara, Manuel
    et al.
    Baguer, Barbara
    Villacampa, Jose I.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Manya, Joan J.
    Influence of pressure and temperature on key physicochemical properties of corn stover-derived biochar2016In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 186, p. 525-533Article in journal (Refereed)
    Abstract [en]

    This study focuses on analyzing the effect of both the peak temperature and pressure on the properties of biochar produced through slow pyrolysis of corn stover, which is a common agricultural waste that currently has little or no value. The pyrolysis experiments were carried out in a fixed-bed reactor at different peak temperatures (400, 525 and 650 degrees C) and absolute pressures (0.1, 0.85 and 1.6 MPa). The inert mass flow rate (at NTP conditions) was adjusted in each test to keep the gas residence time constant within the reactor. The as-received corn stover was pyrolyzed into a biochar without any physical pre-treatment as a way to reduce the operating costs. The properties of biochars showed that high peak temperature led to high fixed-carbon contents, high aromaticity and low molar H:C and O:C ratios; whereas a high pressure only resulted in a further decrease in the O:C ratio and a further increase in the fixed-carbon content. Increasing the operating pressure also resulted in a higher production of pyrolysis gas at the expense of water formation.

  • 12.
    Bacsik, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ahlsten, Nanna
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ziadi, Asraa
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhao, Guoying
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Garcia-Bennett, Alfonso E.
    Uppsala universitet.
    Martin-Matute, Belen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mechanisms and Kinetics for Sorption of CO(2) on Bicontinuous Mesoporous Silica Modified with n-Propylamine2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 17, p. 11118-11128Article in journal (Refereed)
    Abstract [en]

    We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.

  • 13.
    Bacsik, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Atluri, Rambabu
    Uppsala universitet.
    Garcia-Bennett, Alfonso E.
    Uppsala universitet.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Temperature-Induced Uptake of CO2 and Formation of Carbamates in Mesocaged Silica Modified with n-Propylamines2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 12, p. 10013-10024Article in journal (Refereed)
    Abstract [en]

    Adsorption-mediated CO2 separation can reduce the cost of carbon capture and storage. The reduction in cost requires adsorbents with high capacities for CO2 sorption and high CO2-over-N2 selectivity. Amine-modified sorbents are promising candidates for carbon capture. To investigate the details of CO2 adsorption in such materials, we studied mesocaged (cubic, Pmn symmetry) silica adsorbents with tethered propylamines using Fourier transform infrared (FTIR) spectroscopy and volumetric uptake experiments. The degree of heterogeneity in these coatings was varied by either cosynthesizing or postsynthetically introducing the propylamine modification. In situ FTIR spectroscopy revealed the presence of both physisorbed and chemisorbed CO2 in the materials. We present direct molecular evidence for physisorption using FTIR spectroscopy in mesoporous silica sorbents modified with propylamines. Physisorption reduced the CO2-over-N2 selectivity in amine-rich sorbents. Samples with homogeneous coatings showed typical CO2 adsorption trends and large quantities of IR-observable physisorbed CO2. The uptake of CO2 in mesocaged materials with heterogeneous propylamine coatings was higher at high temperatures than at low temperatures. At higher temperatures and low pressures, the postsynthetically modified materials adsorbed more CO2 than did the extracted ones, even though the surface area after modification was clearly reduced and the coverage of primary amine groups was lower. The principal mode of CO2 uptake in postsynthetically modified mesoporous silica was chemisorption. The chemisorbed moieties were present mainly as carbamate−ammonium ion pairs, resulting from the quantitative transformation of primary amine groups during CO2 adsorption as established by NIR spectroscopy. The heterogeneity in the coatings promoted the formation of these ion pairs. The average propylamine−propylamine distance must be small to allow the formation of carbamate−propylammonium ion pairs.

  • 14.
    Bacsik, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Cheung, Ocean
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vasiliev, Petr
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Selective separation of CO2 and CH4 for biogas upgrading on zeolite NaKA and SAPO-562016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 162, p. 613-621Article in journal (Refereed)
    Abstract [en]

    Several commercial and potential adsorbents were investigated for the separation of CO2 from CH4, which is relevant for the upgrading of raw biogas. The main focus of the paper was on the working capacities and selectivities of the adsorbents for a generic vacuum swing adsorption (VSA) process. Zeolites 4A and 13X had good estimated CO2-over-CH4 selectivities and reasonably high working capacities for the removal of CO2. A variant of zeolite A - vertical bar Na12-Kx vertical bar-LTA (with 1.8 <= x <= 3.2), had at least the same working capacity as zeolite 4A but with a significantly improved selectivity. Hence, the environmentally important CH4 slip can be minimized with this vertical bar Na12-Kx vertical bar-LTA sorbent. If a high working capacity for CO2 removal is the most important characteristic for a VSA process, then silicoaluminum phosphate, specifically SAPO-56, appeared to be the best candidate among the studied sorbents. In addition, SAPO-56 had a substantially high estimated CO2-over-CH4 selectivity with a value between similar to 20 and 30.

  • 15.
    Bacsik, Zoltan
    et al.
    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).
    Effects of carbon dioxide captured from ambient air on the infrared spectra of supported amines2016In: Vibrational Spectroscopy, ISSN 0924-2031, E-ISSN 1873-3697, Vol. 87, p. 215-221Article in journal (Refereed)
    Abstract [en]

    Amino groups in highly dense coatings of amines on solid supports react with CO2 of ambient air and form ammonium-carbamate ion pairs. These ion pairs change the properties of the amine-modified supports. In numerous studies, the corresponding infrared (IR) spectra have been misinterpreted. The presumption has been that such ion pairs would not form in ambient air, and therefore IR bands have been assigned to moieties of the support and the amines. Here, we discuss common misunderstandings of the IR spectra of amine-modified supports and highlight that proper sample handling is necessary before employing different characterization techniques. We exemplify by performing an IR spectroscopic study of a propylamine-modified porous silica. Such amine-modified supports are relevant to applications in gas separation, catalysis, controlled drug delivery and adsorption of pollutants from water.

  • 16.
    Bacsik, Zoltan
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Peng
    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).
    Ammonium-Carbamate-Rich Organogels for the Preparation of Amorphous Calcium Carbonates2017In: Minerals, ISSN 2075-163X, E-ISSN 2075-163X, Vol. 7, no 7, article id 110Article in journal (Refereed)
    Abstract [en]

    Amine-CO2 chemistry is important for a range of different chemical processes, including carbon dioxide capture. Here, we studied how aspects of this chemistry could be used to prepare calcium carbonates. Chemically crosslinked organogels were first prepared by reacting hyperbranched polyethylene imine (PEI) dissolved in DMSO with carbon dioxide. The crosslinks of the organogel consisted of ammonium-carbamate ion pairs as was shown by IR spectroscopy. These carbamate-rich organogels were subsequently subjected to aqueous solutions of calcium acetate, and amorphous calcium carbonate (ACC) precipitated. The ACC did not crystalize during the mixing for up to 20 h, as was shown by a combination of IR spectroscopy, X-ray diffraction, scanning electron microscopy, and thermal analysis. Some PEI had been included or adsorbed on the ACC particles. Traces of calcite were observed in one sample that had been subjected to water in a work-up procedure.

  • 17.
    Bacsik, Zoltán
    et al.
    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).
    Adsorption of Carbonyl Sulfide on Propylamine Tethered to Porous Silica2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 26, p. 7708-7713Article in journal (Refereed)
    Abstract [en]

    Carbonyl sulfide (COS) reacts slowly with amines in the aqueous solutions used to absorb CO2 from natural gas and flue gas and can also deactivate certain aqueous amines. The effects of COS on amines tethered to porous silica, however, have not been investigated before. Hence, the adsorption of COS on aminopropyl groups tethered to porous silica was studied using in situ IR spectroscopy. COS chemisorbed mainly and reversibly as propylammonium propylthiocarbamate ion pairs [R-NH(C= O)S- +H3N-R] under dry conditions. In addition, a small amount of another chemisorbed species formed slowly and irreversibly. Nevertheless, the CO2 capacities of the adsorbents were fully retained after COS was desorbed.

  • 18.
    Bernin, Diana
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). University of Gothenburg, Sweden.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Perspectives on NMR studies of CO2 adsorption2018In: Current Opinion in Colloid & Interface Science, ISSN 1359-0294, E-ISSN 1879-0399, Vol. 33, p. 53-62Article, review/survey (Refereed)
    Abstract [en]

    There is a consensus about a long-term goal of a carbon-neutral energy cycle, but the CO2 emissions to the atmosphere are currently very large. Carbon Capture and Storage (CCS) technologies could allow a transformation of the global energy system into a carbon-neutral one and simultaneously keeping the temperature rises within agreed bounds. The CO2 separation step of CCS is, however, very expensive, and adsorption-driven technologies have been put forward as alternatives. Hence, a recent focus has been on studying solid adsorbents for CO2, which include activated carbons, zeolites, metal-organic frameworks, and amine-modified silica. In this context, we summarize the literature concerning CO2 sorption studied with Nuclear Magnetic Resonance (NMR), outline selected NMR methods, and present an outlook for further studies.

  • 19.
    Björnerbäck, Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bernin, Diana
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chalmers University of Technology, Sweden.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Microporous Humins Synthesized in Concentrated Sulfuric Acid Using 5-Hydroxymethyl Furfural2018In: ACS omega, ISSN 2470-1343, Vol. 3, no 8, p. 8537-8545Article in journal (Refereed)
    Abstract [en]

    A new class of highly porous organic sorbents called microporous humins is presented. These microporous humins are derived from sustainable and industrially abundant resources, have high heat of CO2 sorption, and could potentially be useful for the separation of carbon dioxide from gas mixtures. Their synthesis involves the polymerization of 5-hydroxymethyl furfural (HMF) in concentrated sulfuric acid and treatment with diethyl ether and heat. In particular, the porosities were tuned by the heat treatment. HMF is a potential platform chemical from biorefineries and a common intermediate in carbohydrate chemistry. A high uptake of CO2 (up to 5.27 mmol/g at 0 degrees C and 1 bar) and high CO2-over-N-2 and CO2-over-CH4 selectivities were observed. The microporous humins were aromatic and structurally amorphous, which was shown in a multipronged approach using C-13 nuclear magnetic resonance and Fourier transform infrared spectroscopies, elemental analysis, and wide-angle X-ray scattering.

  • 20.
    Björnerbäck, Fredrik
    et al.
    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).
    Highly Porous Hypercrosslinked Polymers Derived from Biobased Molecules2019In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 12, no 4, p. 839-847Article in journal (Refereed)
    Abstract [en]

    Highly porous and hyper-cross-linked polymers (HCPs) have a range of applications and are typically synthesized in an unsustainable manner. Herein, HCPs were synthesized from abundant biobased or biorelated compounds in sulfolane with iron(III) chloride as Lewis acid catalyst. As reactants, quercetin, tannic acid, phenol, 1,4-dimethoxybenzene, glucose, and a commercial bark extract were used. The HCPs had high CO2 uptake (up to 3.94 mmol g(-1) at 0 degrees C and 1 bar), total pore volumes (up to 1.86 cm(3) g(-1)), and specific surface areas (up to 1440 m(2) g(-1)). H-1 NMR, C-13 NMR, and IR spectroscopy, wide-angle X-ray scattering, elemental analysis, and SEM revealed, for example, that the HCPs consisted of amorphous and cross-linked aromatic and phenolic structures with significant contents of aliphatics, oxygen, and sulfur.

  • 21.
    Björnerbäck, Fredrik
    et al.
    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).
    Microporous Humins Prepared from Sugars and Bio-Based Polymers in Concentrated Sulfuric Acid2019In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 7, no 1, p. 1018-1027Article in journal (Refereed)
    Abstract [en]

    Highly microporous humins were synthesized from readily available sugars and bio-based polymers (monosaccharides, disaccharides, and polysaccharides) in sulfuric acid followed by a diethyl ether wash and heat treatment at 400 degrees C. The relative sustainability, costs of production, and availability of the starting materials were improved significantly as compared with the 5-hydroxymethyl-furfural-based microporous humins recently studied by us. A multipronged approach was used to study the detailed characteristics of the adsorbents. Results from H-1 NMR, C-13 NMR, FTIR, WAXS, and elemental analysis were combined and showed that the adsorbents predominantly consisted of amorphous and aromatic carbon structures being rich in oxygen. They were highly porous, and the micropore volumes varied among the compositions as could be observed by analyzing CO2 and N-2 gas adsorption data. Comparably high CO2 uptakes of 4.25 and 1.94 mmol/g at 0 degrees C and 1 and 0.15 bar were observed. With the synthesis of microporous humins with varying porosities, the domain of potential applications of this class of materials could be expanded.

  • 22.
    Bogár, Krisztián
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Krumlinde, Patrik
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bacsik, Zoltán
    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).
    Bäckvall, Jan E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Heterogenized Wilkinson's Catalyst for Transfer Hydrogenation of Carbonyl Compounds2011In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 23, p. 4409-4414Article in journal (Refereed)
    Abstract [en]

    Wilkinson’s catalyst [RhCl(PPh3)3] was heterogenized on common silica by the use of a grafting/anchoring technique. The immobilized catalyst showed high activity and selectivity in transfer hydrogenation reactions of a range of carbonyl compounds in 2-propanol. Reactions carried out in 2-propanol at reflux afforded the corresponding alcohols in high yields in short reaction times. The heterogeneous feature ofthe catalyst allows for easy recovery and efficient reuse in the same reaction up to 5 times without any detectible loss of catalytic activity.

  • 23. Cadars, S
    et al.
    Lesage, A
    Hedin, N
    Stockholm University.
    Chmelka, BF
    Emsley, L
    Selective NMR measurements of homonuclear scalar couplings in isotopically enriched solids2006In: Journal of Physical Chemistry B, Vol. 110, p. 16982-16991Article in journal (Refereed)
  • 24.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Qingling
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mace, Amber
    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).
    Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, p. 1326-1336Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide removal from flue gas via swing adsorption processes requires adsorbents with a high CO2 selectivity and capacity. These properties are particularly valuable to reduce the cost of carbon capture and storage (CCS). Zeolite NaKA was studied for its ability to selectively adsorb CO2 from flue gas, as we previously observed that zeolite NaKA, with a K+/(K+ + Na+) ratio of 17 atomic%, was highly selective towards CO2 over N-2 adsorption by tuning the size of the pore window apertures [1]. The reduced pore apertures may, however, retard the adsorption rate of CO2. Here, we studied the kinetics of CO2 adsorption on regularly sized zeolite NaKA and on nano-sized zeolite NaKA. We used in situ infrared (IR) spectroscopy and observed that CO2 physisorbed relatively rapidly. Density functional theory (DFT) was used for quantum chemical calculations, and the results indicated that CO2 molecules bridged across two or three Na+ ions in the samples with no or very small amount of K. When more K+ ions are present the CO2 molecules no longer bridged across multiple metal ions and adopted an end-on configuration. The calculation showed a shift in the stretching vibration frequency of physisorbed CO2 as observed by IR spectroscopy. Nano-sized zeolite NaKA were synthesised and studied to improve the rate of CO2 adsorption, as the diffusion rate typically increases quadratically with decreasing particle size. Still, the CO2 adsorption rate on nano-sized zeolites NaA and NaKA did not increase significantly. For nano-sized zeolite NaA, we speculate that the absence of such an increased rate is an effect from a skin layer that had formed on the nano-sized zeolite NaA, a layer that was possibly related to intergrowths with extremely small crystals on the surface. The apparently slow adsorption kinetics of CO2 on nano-sized zeolite NaKA was more difficult to explain because it could relate to imperfections within the small crystals, remaining water, or other effects. Overall, the CO2 adsorption rates on zeolite NaKA crystals of different sizes were fast and relevant for the time scales required for adsorption based CCS processes, such as vacuum and temperature swing adsorption (VSA/TSA).

  • 25.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Bacsik, Zoltán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Krokidas, Panagiotis
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO22014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 32, p. 9682-9690Article in journal (Refereed)
    Abstract [en]

    Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N-2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al similar to 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na+ form. When approximately 26 at % of the extraframework cations were exchanged for K+ (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N-2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K+ exchanged zeolite K-ZK-4 upon adsorption of CO2 and N-2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 23:1 restricted the diffusion of CO2 and N-2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N-2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (similar to 4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N-2 selectivity.

  • 26.
    Cheung, Ocean
    et al.
    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).
    Zeolites and related sorbents with narrow pores for CO2 separation from flue gas2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 28, p. 14480-14494Article, review/survey (Refereed)
    Abstract [en]

    Adsorbents with small pores are especially relevant for capturing carbon dioxide at large emission sources. Such sorbents could be used potentially to reduce the energy demands for separating carbon dioxide from flue gas as compared with today's technologies. Here, we review the literature for crystalline, inorganic, and potentially inexpensive adsorbents. A number of different adsorbents with narrow pore openings are compared.

  • 27.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Jie, Su
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zoltán, Bacsik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jing, Li
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Samain, Louise
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Xiaodong, Zou
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Niklas, Hedin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    CO2 selective NaMg-CTS-1 and its structural formation from the titanium silicate based molecule sieve NaMg-ETS-4 upon dehydration2014In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 198, p. 63-73Article in journal (Other academic)
    Abstract [en]

    A range of titanium silicates (ETS-4 and CTS-1) with interesting gas separation properties were studied as CO2 adsorbents. Some of these adsorbents, in particular NaMg-CTS-1, showed the ability to selectively adsorb CO2-over-N2. Partially exchanged NaM-ETS-4 (M = Mg, Ca, Sr and Ba) were synthesised in the Na+ form and ion exchanged with group 2 cations. All but NaBa-ETS-4 transformed into their CTS-1 counterparts, when these partially exchanged Na-ETS-4 were dehydrated. The transformation from ETS-4 to CTS-1 was monitored and studied extensively using diffraction and spectroscopic techniques. Powder X-ray diffraction allowed us to follow the changes of the unit cell parameters occurred at different temperatures. We combined high energy X-ray total scattering (analysed by pair distribution functions – PDF analysis), electron diffraction, infrared, Raman and Nuclear Magnetic Resonance (NMR) spectroscopy to study the transformation of ETS-4 to CTS-1. We understood that under dehydration steps, there was significant disruption to the Ti–O–Ti chain along the b-axis, which occurred concurrently with the distortion of the double 3-rings alongside of these chains. These changes were partly responsible for the contraction of the ETS-4 framework (and successive transformation to CTS-1). The new information allowed us to understand the interesting structures and sorption properties of these adsorbents

  • 28.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Qingling
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    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).
    Silicoaluminophosphates as CO2 sorbents2012In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 156, p. 90-96Article in journal (Refereed)
    Abstract [en]

    Silicoaluminophosphates (SAPO-17, SAPO-35, SAPO-56 and SAPO-RHO) synthesised via hydrothermal means are tested for their abilities to adsorb carbon dioxide. These 8-ring microporous phosphates show high capacities to adsorb CO2. SAPO-RHO has a high uptake of CO2 and a very low uptake of N-2 due to its narrow pore window aperture at 273 K. Its significant uptake of N-2 at 77 K is rationalised by a temperature induced shrinkage effect. SAPO-56 has a slightly higher CO2 capacity (5.42 mmol/g, 273 K, 101 kPa) and is less water sensitive than zeolite 13X. Cyclic adsorption and in situ infrared spectroscopy (IR) reveal that SAPOs retain 95% of their original CO2 capacity after six cycles and that adsorption occurs via physisorption. The calculated heat of adsorption for CO2 (at 0.2-0.7 mmol/g loading) on SAPO-56 and SAPO-RHO lies in the physisorption range (similar to 35 kJ/mol). SAPOs, in particular SAPO-56 and SAPO-RHO, possess many desirable properties and are potentially good adsorbents for CO2 capture in swing adsorption processes.

  • 29.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden .
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vasiliev, Petr
    McCusker, Lynne B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). ETH Zürich, Switzerland.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Highly selective uptake of carbon dioxide on the zeolite vertical bar Na10.2KCs0.8 vertical bar-LTA - a possible sorbent for biogas upgrading2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 24, p. 16080-16083Article in journal (Refereed)
    Abstract [en]

    The vertical bar Na10.2KCs0.8 vertical bar(8)[Al12Si12O48](8)(Fm3c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.

  • 30.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Zoltán, Bacsik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Panagiotis, Krokidas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Niklas, Hedin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    CO2 separation properties of high silicon zeolite NaK-ZK-4 with Si:Al up to 2.8:1Manuscript (preprint) (Other academic)
  • 31.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Zoltán, Bacsik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Petr, Vasiliev
    Niklas, Hedin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Carbon dioxide separation from methane on highly selective ion exchanged zeolite NaKCsA – a possible sorbent for biogas upgradingManuscript (preprint) (Other academic)
  • 32. Christiansen, SC
    et al.
    Hedin, N
    Stockholm University.
    Epping, JD
    Janicke, MT
    del Amo, Y
    Demarest, M
    Brzezinski, M
    Chmelka, BF
    Sensitivity considerations in polarization transfer and filtering using dipole-dipole couplings: Implications for biomineral systems2006In: Solid State Nuclear Magnetic Resonance, Vol. 29, p. 170-182Article in journal (Refereed)
  • 33.
    Church, Tamara L.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bernin, Diana
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). University of Gothenburg, Sweden.
    Garcia-Bennett, Alfonso E.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Dispersed Uniform Nanoparticles from a Macroscopic Organosilica Powder2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 6, p. 2274-2281Article in journal (Refereed)
    Abstract [en]

    A colloidal dispersion of uniform organosilica nanoparticles could be produced via the disassembly of the non-surfactant-templated organosilica powder nanostructured folate material (NFM-1). This unusual reaction pathway was available because the folate and silica-containing moieties in NFM-1 are held together by noncovalent interactions. No precipitation was observed from the colloidal dispersion after a week, though particle growth occurred at a solvent-dependent rate that could be described by the Lifshitz-Slyozov-Wagner equation. An organosilica film that was prepared from the colloidal dispersion adsorbed folate-binding protein from solution but adsorbed ions from a phosphate -buffered saline solution to a larger degree. To our knowledge, this is the first instance of a colloidal dispersion of organosilica nanoparticles being derived from a macroscopic material rather than from molecular precursors.

  • 34.
    Church, Tamara L.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Jasso-Salcedo, Alma Berenice
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björnerbäck, Fredrik
    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).
    Sustainability of microporous polymers and their applications2017In: Science in China Series B: Chemistry, ISSN 1674-7291, E-ISSN 1869-1870, Vol. 60, no 8, p. 1033-1055Article, review/survey (Refereed)
    Abstract [en]

    Microporous polymers (MPs) are studied for their intriguing chemistry and physics as well as their potential application in catalytic transformations, gas-separation processes, water purification and so on. Here, we critically review MPs with respect to the sustainability aspects of their synthesis as well as their applications that have sustainable character. Some MPs have been synthesized from monomers derived from biomass resources, but there is certainly a large potential for further developments. There are also opportunities to improve the sustainability of MP synthesis in terms of the use of solvents, catalysts, and related aspects. The applications of MPs in processes related to sustainability depend upon multiple properties. A rich and flexible chemistry is important to applications as catalysts for, among other useful reactions, the photoreduction of CO2 and selective oxidation. The (ultra) micropore volume of MPs are crucial in gas-separation applications such as CO2 capture, and the chemisorption of CO2 on MP-tethered alkylamines could offer a means to remove that gas from dilute mixtures. When it comes to the storage of H-2 and CH4 in MPs for onboard use in fuel cell or biogas cars, volumetric capacity is paramount, meaning that the density of the MPs must be considered. Finally, for use in separation and purifications from liquid mixtures (aqueous or hydrocarbon-based), crosslinked MPs are more limited than the solution-processable MPs that can be more easily processed into films and membranes.

  • 35. Debatin, Franziska
    et al.
    Behrens, Karsten
    Weber, Jens
    Baburin, Igor A.
    Thomas, Arne
    Schmidt, Johannes
    Senkovska, Irena
    Kaskel, Stefan
    Kelling, Alexandra
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Leoni, Stefano
    Seifert, Gotthard
    Jaeger, Christian
    Guenter, Christina
    Schilde, Uwe
    Friedrich, Alwin
    Holdt, Hans-Juergen
    An Isoreticular Family of Microporous Metal-Organic Frameworks Based on Zinc and 2-Substituted Imidazolate-4-amide-5-imidate: Syntheses, Structures and Properties2012In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 18, no 37, p. 11630-11640Article in journal (Refereed)
    Abstract [en]

    We report on a new series of isoreticular frameworks based on zinc and 2-substituted imidazolate-4-amide-5-imidate (IFP-14, IFP=imidazolate framework Potsdam) that form one-dimensional, microporous hexagonal channels. Varying R in the 2-substitued linker (R=Me (IFP-1), Cl (IFP-2), Br (IFP-3), Et (IFP-4)) allowed the channel diameter (4.01.7 angstrom), the polarisability and functionality of the channel walls to be tuned. Frameworks IFP-2, IFP-3 and IFP-4 are isostructural to previously reported IFP-1. The structures of IFP-2 and IFP-3 were solved by X-ray crystallographic analyses. The structure of IFP-4 was determined by a combination of PXRD and structure modelling and was confirmed by IR spectroscopy and 1H MAS and 13C CP-MAS NMR spectroscopy. All IFPs showed high thermal stability (345400?degrees C); IFP-1 and IFP-4 were stable in boiling water for 7 d. A detailed porosity analysis was performed on the basis of adsorption measurements by using various gases. The potential of the materials to undergo specific interactions with CO2 was investigated by measuring the isosteric heats of adsorption. The capacity to adsorb CH4 (at 298 K), CO2 (at 298 K) and H2 (at 77 K) at high pressure were also investigated. In situ IR spectroscopy showed that CO2 is physisorbed on IFP-14 under dry conditions and that both CO2 and H2O are physisorbed on IFP-1 under moist conditions.

  • 36.
    Debatin, Franziska
    et al.
    Universität Potsdam.
    Thomas, Arne
    Technische Universität Berlin.
    Kelling, Alexandra
    Universität Potsdam.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Senkovska, Irena
    Technische Universität Dresden.
    Kaskel, Stefan
    Technische Universität Dresden.
    Junginger, Matthias
    Universität Potsdam.
    Mueller, Holger
    Universität Potsdam.
    Schilde, Uwe
    Universität Potsdam.
    Jaeger, Christian
    Federal Institute for Materials Research and Testing, Berlin.
    Friedrich, Alwin
    Universität Potsdam.
    Holdt, Hans-Juergen
    Universität Potsdam.
    In Situ Synthesis of an Imidazolate-4-amide-5-imidate Ligand and Formation of a Microporous Zinc-Organic Framework with H-2-and CO2-Storage Ability2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 7, p. 1258-1262Article in journal (Refereed)
  • 37.
    Deiana, Luca
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ghisu, Lorenza
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Afewerki, Samson
    Verho, Oscar
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Mid-Sweden University, Sweden.
    Enantioselective Heterogeneous Synergistic Catalysis for Asymmetric Cascade Transformations2014In: Advanced Synthesis and Catalysis, ISSN 1615-4150, E-ISSN 1615-4169, Vol. 356, no 11-12, p. 2485-2492Article in journal (Refereed)
    Abstract [en]

    A modular design for a novel heterogeneous synergistic catalytic system, which simultaneously activates the electrophile and nucleophile by the combined activation modes of a separate metal and non-metal catalyst, for asymmetric cascade transformations on a solid surface is disclosed. This modular catalysis strategy generates carbocycles (up to 97.5: 2.5 er) as well as spirocyclic oxindoles (97.5: 2.5 to > 99: 0.5 er), containing all-carbon quaternary centers, in a highly enantioselective fashion via a one-pot dynamic relay process.

  • 38.
    Etman, Ahmed S.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Alexandria University, Egypt.
    Pell, Andrew J.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Svedlindh, Peter
    Hedin, Niklas
    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).
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Peking University, China.
    Bernin, Diana
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chalmers University of Technology, Sweden.
    Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR2019In: Acs Omega, ISSN 2470-1343, Vol. 4, no 6, p. 10899-10905Article in journal (Refereed)
    Abstract [en]

    Nanostructured hydrated vanadium oxides (V2O5 center dot nH(2)O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5 center dot nH(2)O nano-sheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5 center dot nH(2)O nanosheets from the V2O5 and VO2 precursors in real using solution- and solid-state V-51 NMR. Solution-state V-51 NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28](4-) and the hydrated dioxova-nadate cation [VO2 center dot 4H(2)O](+), and during the exfoliation process, decavanadate was formed, while the amount of [VO2 center dot 4H(2)O](+) remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state V-51 NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5 center dot nH(2)O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state V-51 signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.

  • 39. Farhadi-Khouzani, Masoud
    et al.
    Chevrier, Daniel M.
    Zhang, Peng
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gebauer, Denis
    Water as the Key to Proto-Aragonite Amorphous CaCO32016In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 55, no 28, p. 8117-8120Article in journal (Refereed)
    Abstract [en]

    Temperature and pH value can affect the short-range order of proto-structured and additive-free amorphous calcium carbonates (ACCs). Whereas a distinct change occurs in proto-vaterite (pv) ACC above 45 degrees C at pH 9.80, proto-calcite (pc) ACC (pH 8.75) is unaffected within the investigated range of temperatures (7-65 degrees C). IR and NMR spectroscopic studies together with EXAFS analysis showed that the temperature-induced change is related to the formation of proto-aragonite (pa) ACC. The data strongly suggest that the binding of water molecules induces dipole moments across the carbonate ions in pa-ACC as in aragonite, where the dipole moments are due to the symmetry of the crystal structure. Altogether, a (pseudo-)phase diagram of the CaCO3 polyamorphism in which water plays a key role can be formulated based on variables of state, such as the temperature, and solution parameters, such as the pH value.

  • 40.
    Gebauer, Denis
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Gunawidjaja, Philips N.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Ko, J. Y. Peter
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Aziz, Baroz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Liu, Lijia
    Hu, Yongfeng
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Tai, Cheuk-Wai
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Sham, Tsun-Kong
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Proto-Calcite and Proto-Vaterite in Amorphous Calcium Carbonates2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 47, p. 8889-8891Article in journal (Refereed)
    Abstract [en]

    Amorphous order: Amorphous calcium carbonates (ACC) have an intrinsic structure relating to the crystalline polymorphs of calcite and vaterite. The proto-crystalline structures of calcite and vaterite (pc-ACC and pv-ACC) are analyzed by NMR (see picture), IR, and EXAFS spectroscopy, which shows that the structuring of ACC relates to the underlying pH-dependent equilibria.

  • 41. 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.

  • 42.
    Gebauer, Denis
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Xingmin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Aziz, Baroz
    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).
    Zhao, Zhe
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Porous tablets of crystalline calcium carbonate via sintering of amorphous nanoparticles2013In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, no 6, p. 1257-1263Article in journal (Refereed)
    Abstract [en]

    Porous tablets of crystalline calcium carbonate were formed upon sintering of a precursor powder of amorphous calcium carbonate (ACC) under compressive stress (20 MPa) at relatively low temperatures (120-400 degrees C), induced by pulsed direct currents. Infrared spectroscopy ascertained the amorphous nature of the precursor powders. At temperatures of 120-350 degrees C and rates of temperature increase of 20-100 degrees C min(-1), the nanoparticles of ACC transformed into crystallites of mainly aragonite, which is generally difficult to achieve using wet-chemicals under kinetic control. The amorphous precursor particles (similar to 10 nm) transformed into crystallites (similar to 30-50 nm) during sintering. Consistently, the specific surface areas of 140-160 m(2) g(-1) for the precursor particles were reduced to 10-20 m(2) g(-1) for the porous tablets. The porous network within the tablets consisted of fused aragonite and vaterite particles in a ratio of similar to 80 : 20. The fraction of aragonite to vaterite was invariant to the temperature and rate of temperature change used. The particle size increased only to a small amount on an increased rate of temperature change. At temperatures above 400 degrees C, porous tablets of calcite formed. The later transformation was under thermodynamic control, and led to a minor reduction of the specific surface area. The size of the crystallites remained small and the transformation to calcite appeared to be a solid-state transformation. Porous, template-and binder-free tablets of calcium carbonate could find applications in for example, biology or water treatment.

  • 43.
    Georgieva, Elka R.
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Narvaez, Ana Julia
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Gräslund, Astrid
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Secondary structure conversions of Mycobacterium tuberculosis ribonucleotide reductase protein R2 under varying pH and temperature conditions2008In: Biophysical Chemistry, Vol. 137, no 43-48Article in journal (Refereed)
    Abstract [en]

    The structural properties of Mycobacterium tuberculosis (Mtb) ribonucleotide reductase R2 protein were studied under varying pH and temperature conditions by circular dichroism (CD) spectroscopy as well as dynamic light scattering (DLS). Under physiological conditions this protein has a high alpha-helical content, similar to the corresponding protein from other species, e.g. mouse. Decreasing the pH induced significant structure conversions. When pH was below 6.5 an aggregated structure was observed and reached a maximum at pH 4. The aggregated state of this protein was verified by DLS and was found to be rich in beta-structure. This amyloid-like structure transformed into a molten globule state with high temperature stability (between 25 and 80 degrees C) at pH below 3. The corresponding mouse protein R2 under similar conditions showed no evidence of an aggregated state around pH 4.

  • 44.
    Gordeyeva, Korneliya
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Voisin, Hugo
    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).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lavoine, Nathalie
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lightweight foams of amine-rich organosilica and cellulose nanofibrils by foaming and controlled condensation of aminosilane2018In: Materials Chemistry Frontiers, ISSN 2052-1537, Vol. 2, no 12, p. 2220-2229Article in journal (Refereed)
    Abstract [en]

    Organosilica foams are commonly formed by a multistep process involving hydrolysis and condensationof organosilanes followed by solvent exchange and e.g. supercritical CO2 drying. Here, we propose astraightforward route to synthesize lightweight hybrid foams from aqueous dispersions of a surfaceactiveaminosilane (AS) and TEMPO-oxidized cellulose nanofibrils (TCNFs). Air bubbles were introducedin the TCNF/AS dispersion by mechanical blending, and the foam was solidified by oven-drying.Evaporative drying at mild temperature (60 1C) resulted in dry foams with low densities (25–50 kg m3),high porosities (96–99%) and macropores of 150–300 mm in diameter. The foaming and foam stabilizationwere successful for a pH range of 10.4–10.8 for foams containing 55–65 wt% of organosilica inthe dry state. The protonation of AS increased the ionic strength of the dispersion and enhanced theinterparticle interactions with TCNFs and, in turn, the foam viscosity and foam stability upon drying. Theevaporation of water catalyzed the condensation of the AS to form low-molecular linear polymers,which resulted in an increased stiffness and strength of the foam lamella. The crosslinking of the ASpolymeric network with the TCNF matrix allowed lightweight and homogeneous macroporous foams tobe obtained with controlled densities and high amine content (amine content 44.5 mmol g1) using anenvironmentally friendly technique.

  • 45. Guleryuz, Hasan
    et al.
    Kaus, Ingeborg
    Buron, Cedric C.
    Filiatre, Claudine
    Hedin, Niklas
    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).
    Einarsrud, Mari-Ann
    Deposition of silica nanoparticles onto alumina measured by optical reflectometry and quartz crystal microbalance with dissipation techniques2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 443, p. 384-390Article in journal (Refereed)
    Abstract [en]

    Understanding of the interactions between particles and the substrate is important for successful sol-gel deposition of thin films. We have studied the deposition of silica nanoparticles on alumina coated surfaces in aqueous electrolytes by optical reflectometry (OR) and a quartz crystal microbalance with dissipation (QCM-D). The deposition of negatively charged silica nanoparticles on positively charged alumina was primarily controlled by the electric diffuse double layer interactions between the substrate and the deposited particles, modulated by the counter-ion release. The build-up of a negative charge on the positively charged substrate resulted in a decrease in the deposition rate with increasing surface coverage. Higher surface coverage of silica nanoparticles was obtained at low pH than at high pH conditions, due to reduced electric diffuse double layer repulsion between the silica nanoparticles. The deposition was enhanced at high pH by increasing the concentration of NaCl due to compression of the electric diffuse double layer. In particular, the repulsion between the silica nanoparticles was efficiently screened at a concentration of NaCl higher than 100 mM and thick silica layers could be deposited at pH = 6 and 8.

  • 46.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björkman, Eva
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Biokol Lilliestråle & Co KB, Sweden.
    Lilliestråle, Malte
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Activated carbons for water treatment prepared by phosphoric acid activation of hydrothermally treated beer waste2014In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 40, p. 15389-15397Article in journal (Refereed)
    Abstract [en]

    Activated carbons were produced by chemical activation of hydrothermally carbonized (HTC) beer waste, withphosphoric acid as the activation agent. The activation was optimized within a full factorial design, using the outcome of 19different experiments. Four different parameters (concentration of the acid, activation time, activation temperature, flow rate)were analyzed with respect to their influence on the median pore size. The concentration of H3PO4 had a strong positive effecton the median pore size. The specific surface areas of these activated carbons were ∼1000 m2/g, which compared wellcommercially available activated carbons. The activated carbons had mostly large pores with a size of ∼4 nm, and a significantamount of acid surface groups. Scanning electron microscopy (SEM) revealed that the morphology of the HTC beer wastechanged significantly after the chemical activation. The capacity to adsorb methylene blue from aqueous solutions was 341 mg/g,for one of the activated carbons at pH 7. A Langmuir model described the uptake of the dye quite well, which suggested ahomogeneous adsorption of Methylene Blue (MB).

  • 47.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björkman, Eva
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lilliestråle, Malte
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Activated carbons prepared from hydrothermally carbonized waste biomass used as adsorbents for CO22013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, p. 526-532Article in journal (Refereed)
    Abstract [en]

    Activated carbons prepared from hydrothermally carbonized (HTC) waste biomass were studied with respect to the adsorption of carbon dioxide. The physically activated carbons (PAC) exhibited a large adsorption of CO2 of 1.45 mmol/g at a small partial pressure of CO2 (10 kPa and a temperature of 0 degrees C). These PACs were prepared by activation in a stream of CO2 and had significant amounts of ultramicropores, which were established by analyzing the adsorption of CO2 with a density functional theory. The uptake at such low pressures of CO2 is of most importance for an adsorption-driven CO2 capture from flue gas at large power stations, as it is difficult to imagine a pressurization of the flue gas. The capacities to adsorb CO2 of the different activated carbons were compared with both the micropore volumes as established by N-2 adsorption, and the ultramicropore volumes as established by CO2 adsorption. The ultramicropore volume is of crucial importance for the capture of CO2 from flue gas. PAC from HTC grass cuttings and from horse manure had the largest ultramicropore volumes. In general, the PAC showed excellent cyclability of adsorption/desorption of CO2 and a minimal capacity loss after subsequent cycles. In addition, the PAC showed a rapid adsorption of CO2. Both characteristics are essential for the eventual use of such PACs in the adsorption driven separation of CO2 from flue gas. A chemically activated carbon (CAC) was prepared by treating hydrothermally carbonized beer waste with H3PO4 and a heat treatment in a flow of N-2. This CAC showed a significant amount of mesopores in the range of 5 nm, in addition to micropores. The apparent selectivity for the activated carbons for CO2-over-N-2 adsorption was determined at 0 degrees C and 10 kPa.

  • 48.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björkman, Eva
    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).
    Lilliestråle, Malte
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Iron Oxide Nanoparticles Embedded in Activated Carbons Prepared from Hydrothermally Treated Waste Biomass2014In: ChemSusChem, ISSN 1864-5631, E-ISSN 1864-564X, Vol. 7, no 3, p. 875-882Article in journal (Refereed)
    Abstract [en]

    Particles of iron oxide (Fe3O4; 20-40nm) were embedded within activated carbons during the activation of hydrothermally carbonized (HTC) biomasses in a flow of CO2. Four different HTC biomass samples (horse manure, grass cuttings, beer production waste, and biosludge) were used as precursors for the activated carbons. Nanoparticles of iron oxide formed from iron catalyst included in the HTC biomasses. After systematic optimization, the activated carbons had specific surface areas of about 800m(2)g(-1). The pore size distributions of the activated carbons depended strongly on the degree of carbonization of the precursors. Activated carbons prepared from highly carbonized precursors had mainly micropores, whereas those prepared from less carbonized precursors contained mainly mesopores. Given the strong magnetism of the activated carbon-nano-Fe3O4 composites, they could be particularly useful for water purification.

  • 49.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Björnerbäck, Fredrik
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Trushkina, Yulia
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bengoechea, Mikel Oregui
    Salazar-Alvarez, German
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Barth, Tanja
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 1. Their Use As Adsorbents for CO22017In: Acs Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 5, no 4, p. 3087-3095Article in journal (Refereed)
    Abstract [en]

    Lignin is naturally abundant and a renewable [GRAPHICS] precursor with the potential to be used in the production of both chemicals and materials. As many lignin conversion processes suffer from a significant production of solid wastes in the form of hydrochars, this study focused on transforming hydrochars into magnetic activated carbons (MAC). The hydrochars were produced via hydrothermal treatment of lignins together with formic acid. The activation of the hydrochars was performed chemically with KOH with a focus on the optimization of the MACs as adsorbents for CO2. MACs are potentially relevant to carbon capture and storage (CCS) and gas purification processes. In general, the MACs had high specific surface areas (up to 2875 m(2)/g), high specific pore volumes, and CO2 adsorption capacities of up to 6.0 mmol/g (I atm, 0 degrees C). The textual properties of the MACs depended on the temperature of the activation. MACs activated at a temperature of 700 degrees C had very high ultramicropore volumes, which are relevant for potential adsorption-driven separation of CO2 from N-2. Activation at 800 degrees C led to MACs with larger pores and very high specific surface areas. This temperature-dependent optimization option, combined with the magnetic properties, provided numerous potential applications of the MACs besides those of CCS. The hydrochar was derived from eucalyptus lignin, and the corresponding MACs displayed soft magnetic behavior with coercivities of <100 Oe and saturation magnetization values of 1-10 emu/g.

  • 50.
    Hao, Wenming
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Keshavarzi, Neda
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Branger, Adrien
    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).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Strong discs of activated carbons from hydrothermally carbonized beer waste2014In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 78, p. 521-531Article in journal (Refereed)
    Abstract [en]

    Strong and dense activated carbon discs (ACDs) were synthesized and studied. The discs were produced in a multistep manner from a precursor based on hydrothermally treated beer waste (HTC-BW). The precursor was processed by pulsed current processing (PCP) into ACDs. These discs were activated by physical activation in CO2 at an elevated temperature. The ACDs had surface areas of ∼500 m2/g and contained significant amounts of micro-, meso-, and macropores. The effect on the temperature during the PCP and the presence of tar in the precursor were studied with respect to the properties of the discs. The ACDs had strengths up to 7.2 MPa with densities up to 1.4 g/cm3. The density is the highest reported for discs of activated carbon.

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