| 1. |
- Afewerki, Samson, 1985-, et al.
(författare)
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Sustainable Design for the Direct Fabrication and Highly Versatile Functionalization of Nanocelluloses
- 2017
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Ingår i: Global Challenges. - Weinheim : Wiley. - 2056-6646. ; 1:7
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Tidskriftsartikel (refereegranskat)abstract
- This study describes a novel sustainable concept for the scalable direct fabrication and functionalization of nanocellulose from wood pulp with reduced energy consumption. A central concept is the use of metal-free small organic molecules as mediators and catalysts for the production and subsequent versatile surface engineering of the cellulosic nanomaterials via organocatalysis and click chemistry. Here, organoclick chemistry enables the selective functionalization of nanocelluloses with different organic molecules as well as the binding of palladium ions or nanoparticles. The nanocellulosic material is also shown to function as a sustainable support for heterogeneous catalysis in modern organic synthesis (e.g., Suzuki cross-coupling transformations in water). The reported strategy not only addresses obstacles and challenges for the future utilization of nanocellulose (e.g., low moisture resistance, the need for green chemistry, and energy-intensive production) but also enables new applications for nanocellulosic materials in different areas.
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| 2. |
- Akansel, Serkan, et al.
(författare)
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Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
- 2018
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 51:30
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Tidskriftsartikel (refereegranskat)abstract
- Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.
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| 3. |
- Asfaw, Habtom D., et al.
(författare)
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Boosting the thermal stability of emulsion–templated polymers via sulfonation : an efficient synthetic route to hierarchically porous carbon foams
- 2016
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Ingår i: ChemistrySelect. - : Wiley. - 2365-6549. ; 1:4, s. 784-792
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchically porous carbon foams with specific surface areas exceeding 600 m2 g−1 can be derived from polystyrene foams that are synthesized via water-in-oil emulsion templating. However, most styrene-based polymers lack strong crosslinks and are degraded to volatile products when heated above 400 oC. A common strategy employed to avert depolymerization is to introduce potential crosslinking sites such as sulfonic acids by sulfonating the polymers. This article unravels the thermal and chemical processes leading up to the conversion of sulfonated high internal phase emulsion polystyrenes (polyHIPEs) to sulfur containing carbon foams. During pyrolysis, the sulfonic acid groups (-SO3H) are transformed to sulfone (-C-SO2-C-) and then to thioether (-C−S-C-) crosslinks. These chemical transformations have been monitored using spectroscopic techniques: in situ IR, Raman, X-ray photoelectron and X-ray absorption near edge structure spectroscopy. Based on thermal analyses, the formation of thioether links is associated with increased thermal stability and thus a substantial decrease in volatilization of the polymers.
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| 4. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
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Over-Stoichiometric NbO2 Nanoparticles for a High Energy and Power Density Lithium Microbattery
- 2017
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Ingår i: ChemNanoMat. - : Wiley. - 2199-692X. ; 3:9, s. 646-655
-
Tidskriftsartikel (refereegranskat)abstract
- Effective utilization of active materials in microbatteries can be enhanced by rational design of the electrodes. There is an increasing trend of using 3D electrodes that are coated in nanosized active materials to boost both energy and power densities. This article focuses on the fabrication of 3D electrodes based on monolithic carbon foams coated in over-stoichiometric NbO2 nanoparticles. The electrodes exhibit remarkable energy and power densities at various current densities when tested in lithium microbatteries. An areal capacity of around 0.7mAhcm(-2) and energy density up to 45mWhcm(-3) have been achieved. More than half of the areal capacity can be accessed at a current density of about 11mAcm(-2), with the corresponding energy and power densities being 21mWhcm(-3) and 1349mWcm(-3). These values are comparable to those of microsupercapacitors containing carbon and MnO2 nanomaterials. Furthermore, the electrochemical reversibility improves progressively upon cycling along with substantial increase in the charge transfer kinetics of the electrode. Based on impedance analyses almost a fourfold decrease in the charge transfer resistance has been observed over 25 cycles. Such enhancement of the electronic properties of NbO2 can account for the high electrochemical rate performance of the 3D electrodes.
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| 5. |
- Asfaw, Habtom Desta, Dr. 1986-, et al.
(författare)
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Tailoring the Microstructure and Electrochemical Performance of 3D Microbattery Electrodes Based on Carbon Foams
- 2019
-
Ingår i: Energy Technology. - : Wiley. - 2194-4288 .- 2194-4296.
-
Tidskriftsartikel (refereegranskat)abstract
- Three-dimensional (3D) carbon electrodes with suitable microstructural features and stable electrochemical performance are required for practical applications in 3D lithium (Li)-ion batteries. Herein, the optimization of the microstructures and electrochemical performances of carbon electrodes derived from emulsion-templated polymer foams are dealt with. Exploiting the rheological properties of the emulsion precursors, carbon foams with variable void sizes and specific surface areas are obtained. Carbon foams with an average void size of around 3.8 mu m are produced, and improvements are observed both in the coulombic efficiency and the cyclability of the carbon foam electrodes synthesized at 2200 degrees C. A stable areal capacity of up to 1.22 mAh cm(-2) (108 mAh g(-1)) is achieved at a current density of 50 mu A cm(-2). In addition, the areal capacity remains almost unaltered, i.e., 1.03 mAh cm(-2) (91 mAh g(-1)), although the cycling current density increases to 500 mu A cm(-2) indicating that the materials are promising for power demanding applications.
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| 6. |
- Bazuev, Gennady V., et al.
(författare)
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The effect of manganese oxidation state on antiferromagnetic order in SrMn1-xSbxO3 (0 < x < 0.5) perovskite solid solutions
- 2019
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 7:7, s. 2085-2095
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Tidskriftsartikel (refereegranskat)abstract
- The mixed-valence manganese (Mn3+/Mn4+) solid solution, SrMn1-xSbxO3, was prepared for the first time. Two ranges of solid solutions were found: (1) SrMn1-xSbxO3 (0.025 x 0.09) with monoclinically distorted 6H-SrMnO3 polytype (sp. gr. C/2c) and (2) SrMn1-xSbxO3 (0.17 x 0.50) with a tetragonal unit cell (sp. gr. I4/mcm). Crystal structure refinement using X-ray and neutron powder diffraction data showed that the structure of the monoclinic solid solution consists of corner-sharing octahedra around sites occupied by manganese and antimony ions and face-sharing octahedra around sites occupied by manganese ions only, while the tetragonal solid solution has a random distribution of B-site cations. The presence of long-range antiferromagnetic order with a Neel temperature of about 148 K for SrMn0.80Sb0.20O3 and about 280 K for SrMn0.925Sb0.075O3 was found from the results of DC and AC susceptibility and neutron diffraction experiments at 5 K and 80 K.
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| 7. |
- Berastegui, Pedro, et al.
(författare)
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Electrochemical reactions of AgFeO2 as negative electrode in Li- and Na-ion batteries
- 2018
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Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 401, s. 386-396
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Tidskriftsartikel (refereegranskat)abstract
- AgFeO2 nanoparticles synthesized via precipitation at room temperature are investigated in Li- and Na-ion cells through electrode coatings with an alginate binder. The electrochemical reactions of AgFeO2 with Li+ and Na+ions, as well as its role as alternative negative electrode in these cell systems are carefully evaluated. Initial Li uptake causes irreversible amorphization of the AgFeO2 structure with concomitant formation of Ag0 nanoparticles. Further Li incorporation results in conversion into Fe0 nanoparticles and Li2O, together with Li-alloying of these Ag0 clusters. Similar mechanisms are also found upon Na uptake, although such processes are hindered by overpotentials, the capacity and reversibility of the reactions with Na+ ions being not comparablewith those of their Li+ counterparts. The behaviour of AgFeO2 at low potentials vs. Li+/Li displays a synergic pseudo-capacitive charge storage overlapping Li-Ag alloying/de-alloying. This feature is exploited in full cells having deeply lithiated AgFeO2 and LiFePO4 as negative and positive electrodes, respectively. These environmentally friendly iron-based full cells exhibit attractive cycle performances with ≈80% capacity retention after 1000 cycles without any electrolyte additive, average round trip efficiency of ≈89% and operational voltage of 3.0 V combined with built-in pseudo-capacitive characteristics that enable high cycling rates up to≈25C.
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| 8. |
- Bruneau, Alexandre, et al.
(författare)
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Synthesis of Benzofurans and Indoles from Terminal Alkynes and Iodoaromatics Catalyzed by Recyclable Palladium Nanoparticles Immobilized on Siliceous Mesocellular Foam
- 2017
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 23:52, s. 12886-12891
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the utilization of a heterogeneous catalyst, consisting of Pd nanoparticles supported on a siliceous mesocellular foam (Pd-0-AmP-MCF), for the synthesis of heterocycles. Reaction of o-iodophenols and protected o-iodoanilines with acetylenes in the presence of a Pd nanocatalyst produced 2-substituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands. Moreover, the structure of the reported Pd nanocatalyst was further elucidated with extended X-ray absorption fine-structure spectroscopy, and it was proven that the catalyst could be recycled multiple times without significant loss of activity.
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| 9. |
- Chamoun, Mylad, et al.
(författare)
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Rechargeability of aqueous sulfate Zn/MnO2 batteries enhanced by accessible Mn2+ ions
- 2018
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Ingår i: Energy Storage Materials. - : Elsevier BV. - 2405-8289 .- 2405-8297. ; 15, s. 351-360
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Tidskriftsartikel (refereegranskat)abstract
- The Zn/MnO2 battery is safe, low cost and comes with a high energy density comparable to Li-ion batteries. However, irreversible spinel phases formed at the MnO2 electrode limits its cyclability. A viable solution to overcome this inactive phase is to use an aqueous ZnSO4-based electrolyte, where pH is mildly acidic leading to a different reaction mechanism. Most importantly, the addition of MnSO4 achieves excellent cyclability. How accessible Mn2+ ions in the electrolyte enhances the reversibility is presented. With added Mn2+, the capacity retention is significantly improved over 100 cycles. Zn2+ insertion plays an important role on the reversibility and a hydrated layered Zn-buserite structure formed during charge is reported. Furthermore, Zn4SO4(OH)(6) center dot 5H(2)O precipitates during discharge but is not involved in the electrochemical reaction. This precipitate both buffers the pH and partly insulates the surface. Described in operando study show how the phase transformations and the failure mechanisms depend on the presence of Mn2+-ions in the electrolyte. These results give insight necessary to improve this battery further to make it a worthy contender to the Li-ion battery in large scale energy storage solutions.
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| 10. |
- Cordova, Armando, 1970-, et al.
(författare)
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A sustainable strategy for production and functionalization of nanocelluloses
- 2019
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Ingår i: Pure and Applied Chemistry. - : Walter de Gruyter GmbH. - 0033-4545 .- 1365-3075. ; 91:5, s. 865-874
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Tidskriftsartikel (refereegranskat)abstract
- A sustainable strategy for the neat production and surface functionalization of nanocellulose from wood pulp is disclosed. It is based on the combination of organocatalysis and click chemistry (organoclick chemistry) and starts with nanocellulose production by organic acid catalyzed hydrolysis and esterification of the pulp under neat conditions followed by homogenization. This nanocellulose fabrication route is scalable, reduces energy consumption and the organic acid can be efficiently recycled. Next, the surface is catalytically engineered by organoclick chemistry, which allows for selective and versatile attachment of different organic molecules (e.g. fluorescent probes, catalyst and pharmaceuticals). It also enables binding of metal ions and nanoparticles. This was exemplified by the fabrication of a heterogeneous nanocellulose palladium nanoparticle catalyst, which is used for Suzuki cross-coupling transformations in water. The disclosed surface functionalization methodology is broad in scope and applicable to different nanocelluloses and cellulose based materials as well.
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| 11. |
- Gustafson, Karl P. J., et al.
(författare)
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Chemoenzymatic Dynamic Kinetic Resolution of Primary Benzylic Amines using Pd-0-CalB CLEA as a Biohybrid Catalyst
- 2019
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 25:39, s. 9174-9179
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the use a biohybrid catalyst consisting of palladium nanoparticles immobilized on cross-linked enzyme aggregates of lipase B of Candida antarctica (CalB CLEA) for the dynamic kinetic resolution (DKR) of benzylic amines. A set of amines were demonstrated to undergo an efficient DKR and the recyclability of the catalysts was studied. Extensive efforts to further elucidate the structure of the catalyst are presented.
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| 12. |
- Gustafson, Karl P. J., et al.
(författare)
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Water oxidation mediated by ruthenium oxide nanoparticles supported on siliceous mesocellular foam
- 2017
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Ingår i: Catalysis Science & Technology. - : Royal Society of Chemistry. - 2044-4753 .- 2044-4761. ; 7:1, s. 293-299
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Tidskriftsartikel (refereegranskat)abstract
- Artificial photosynthesis is an attractive strategy for converting solar energy into fuel. In this context, development of catalysts for oxidation of water to molecular oxygen remains a critical bottleneck. Herein, we describe the preparation of a well-defined nanostructured RuO2 catalyst, which is able to carry out the oxidation of water both chemically and photochemically. The developed heterogeneous RuO2 nanocatalyst was found to be highly active, exceeding the performance of most known heterogeneous water oxidation catalysts when driven by chemical or photogenerated oxidants.
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| 13. |
- Görlin, Mikaela, et al.
(författare)
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Formation of unexpectedly active Ni-Fe oxygen evolution electrocatalysts by physically mixing Ni and Fe oxyhydroxides
- 2019
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 55:6, s. 818-821
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Tidskriftsartikel (refereegranskat)abstract
- We present an unusual, yet facile, strategy towards formation of physically mixed Ni-Fe(OxHy) oxygen evolution electrocatalysts. We use in situ X-ray absorption and UV-vis spectroscopy, and high-resolution imaging to demonstrate that physical contact between two inferior Ni(OH)(2) and Fe(OOH) catalysts self-assemble into atomically intermixed Ni-Fe catalysts with unexpectedly high activity.
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| 14. |
- Hao, Wenming, et al.
(författare)
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Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar
- 2019
-
Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.
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| 15. |
- Ibrahem, Ismail, et al.
(författare)
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Copper Nanoparticles on Controlled Pore Glass and TEMPO for the Aerobic Oxidation of Alcohols
- 2018
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Ingår i: ChemNanoMat. - : Wiley. - 2199-692X. ; 4:1, s. 71-75
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the facile synthesis of a heterogeneous copper nanocatalyst and its combination with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) for the aerobic oxidation of alcohols to their corresponding carbonyl compounds. This low cost copper nanocatalyst was found to exhibit excellent recyclability, making it a highly attractive catalytic system from an economical and environmental point of view. Extensive characterization of the catalyst by a number of techniques revealed that it was comprised of well-dispersed Cu(I/II) nanoparticles with an average size of around 6nm.
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| 16. |
- Kumar, Ankit, et al.
(författare)
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Effect of in situ electric-field-assisted growth on antiphase boundaries in epitaxial Fe3O4 thin films on MgO
- 2018
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 2:5
-
Tidskriftsartikel (refereegranskat)abstract
- Antiphase boundaries (APBs) normally form as a consequence of the initial growth conditions in all spinel ferrite thin films. These boundaries result from the intrinsic nucleation and growth mechanism, and are observed as regions where the periodicity of the crystalline lattice is disrupted. The presence of APBs in epitaxial films of the inverse spinel Fe3O4 alters their electronic and magnetic properties due to strong antiferromagnetic (AF) interactions across these boundaries. We explore the effect of using in-plane in situ electric-field-assisted growth on the formation of APBs in heteroepitaxial Fe3O4(100)/MgO(100) thin films. The electric-field-assisted growth is found to reduce the AF interactions across APBs and, as a consequence, APB-free thin-film-like properties are obtained, which have been probed by electronic, magnetic, and structural characterization. The electric field plays a critical role in controlling the density of APBs during the nucleation process by providing an electrostatic force acting on adatoms and therefore changing their kinetics. This innovative technique can be employed to grow epitaxial spinel thin films with controlled AF interactions across APBs.
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| 17. |
- Lee, Kian Keat, et al.
(författare)
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Tailored activated carbons for supercapacitors derived from hydrothermally carbonized sugars by chemical activation
- 2016
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 6:112, s. 110629-110641
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Tidskriftsartikel (refereegranskat)abstract
- Activated carbons (ACs) are actively researched as electrode materials for supercapacitors and there is a significant interest to produce ACs from sustainable and low cost precursors. In this study, various ACs were prepared from hydrothermally carbonized sugars by KOH activation. Both the hydrothermal carbonization and activation processes were optimized to tailor the properties (e.g. textural properties, chemical composition, N-doping, electrical conductivity) of the ACs. For instance, the Brunauer-Emmett-Teller (BET) surface areas (S-BET) were tuned in the range of 800-3000 m(2) g(-1) with associated variation in the extent of microporosity and pore size distributions (PSDs). The ACs were evaluated electrochemically as materials for supercapacitor electrodes in a symmetrical two-electrode cell using an aqueous electrolyte. The relationship between the electrochemical, textural, electrical, and physicochemical properties were analyzed systematically to understand the key factors determining the electrochemical performance. A high specific capacitance (C-m) of similar to 260 F g(-1) was achieved at a moderately high S-BET of similar to 1300 m(2) g(-1), which was equivalent to a C-m/S-BET of 20 mu F cm(-2), for an optimal AC prepared from hydrothermally carbonized glucose. The very high surface-specific capacitance highlights that the specific surface area is certainly not the sole limiting parameter for effective electrode materials.
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| 18. |
- Li, Man-Bo, et al.
(författare)
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Diastereoselective Cyclobutenol Synthesis : A Heterogeneous Palladium-Catalyzed Oxidative Carbocyclization-Borylation of Enallenols
- 2019
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 25:1, s. 210-215
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Tidskriftsartikel (refereegranskat)abstract
- A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution.
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| 19. |
- Liu, Aijie, et al.
(författare)
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Hollow polymer dots : nature-mimicking architecture for efficient photocatalytic hydrogen evolution reaction
- 2019
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 7:9, s. 4797-4803
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Tidskriftsartikel (refereegranskat)abstract
- Mimicking nature is always beneficial for improving the performance of artificial systems. Artificial photosynthesis for hydrogen production is one of the examples, where we can derive significant inspiration from nature. In this study, polymer dots (Pdots) prepared using photoactive polymer PFODTBT and amphiphilic co-polymer under ultra-sonication exhibited a hollow structure mimicking a photosynthetic bacterial, which was highly beneficial for hydrogen evolution. A systematic study of this structure showed that the polymer shell acts as a biological membrane that maintains a slightly higher pH inside the cavity (pH 0.4) compared to the bulk solution. More importantly, a fast proton diffusion across the porous polymer shell was detected. The photocatalytic activity of hollow nanostructure shows 50 times enhancement of initial hydrogen evolution reaction (HER) rate as compared to solid nanoparticles. Further optimization of the photocatalytic performance was achieved by verifying the decrease in Pdots size from 90 nm to 50 nm, showing a significant increase in the photocatalytic performance of the system. This study reveals nature-mimicking hollow Pdots with porous shells as can be a type of promising photocatalysts in the application of solar energy conversion and storage.
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| 20. |
- Liu, Chenjuan, et al.
(författare)
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3-D binder-free graphene foam as a cathode for high capacity Li-O-2 batteries
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:25, s. 9767-9773
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Tidskriftsartikel (refereegranskat)abstract
- To provide energy densities higher than those of conventional Li-ion batteries, a Li-O-2 battery requires a cathode with high surface area to host large amounts of discharge product Li2O2. Therefore, reversible formation of discharge products needs to be investigated in Li-O-2 cells containing high surface area cathodes. In this study, a binder-free oxygen electrode consisting of a 3-D graphene structure on aluminum foam, with a high defect level (I-D/I-G = 1.38), was directly used as the oxygen electrode in LiO2 batteries, delivering a high capacity of about 9 x 10(4) mA h g(-1) (based on the weight of graphene) at the first full discharge using a current density of 100 mA g(graphene)(-1). This performance is attributed to the 3-D porous structure of graphene foam providing both an abundance of available space for the deposition of discharge products and a high density of reactive sites for Li-O-2 reactions. Furthermore, the formation of discharge products with different morphologies and their decomposition upon charge were observed by SEM. Some nanoscaled LiOH particles embedded in the toroidal Li2O2 were detected by XRD and visualized by TEM. The amount of Li2O2 formed at the end of discharge was revealed by a titration method combined with UV-Vis spectroscopy analysis.
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| 21. |
- Liu, Chenjuan, 1988-, et al.
(författare)
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3-D binder-free graphene foam as cathode for high capacity Li-O2 batteries
- 2016
-
Ingår i: Journal of Materials Chemistry A. - 2050-7488. ; 4:25, s. 9767-9773
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- To provide energy densities higher than those of conventional Li-ion batteries, a Li–O2 battery requires a cathode with high surface area to host large amounts of discharge product Li2O2. Therefore, reversible formation of discharge products needs to be investigated in Li–O2 cells containing high surface area cathodes. In this study, a binder-free oxygen electrode consisting of a 3-D graphene structure on aluminum foam, with a high defect level (ID/IG = 1.38), was directly used as the oxygen electrode in Li– O2 batteries, delivering a high capacity of about 9 *104 mA h g-1 (based on the weight of graphene) at the first full discharge using a current density of 100 mA ggraphene-1 . This performance is attributed to the 3-D porous structure of graphene foam providing both an abundance of available space for the deposition of discharge products and a high density of reactive sites for Li–O2 reactions. Furthermore, the formation of discharge products with different morphologies and their decomposition upon charge were observed by SEM. Some nanoscaled LiOH particles embedded in the toroidal Li2O2 were detected by XRD and visualized by TEM. The amount of Li2O2 formed at the end of discharge was revealed by a titration method combined with UV-Vis spectroscopy analysis.
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| 22. |
- Ma, Yue, et al.
(författare)
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Iron Doping in Spinel NiMn2O4 : Stabilization of the Mesoporous Cubic Phase and Kinetics Activation toward Highly Reversible Li+ Storage
- 2015
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 27:22, s. 7698-7709
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Tidskriftsartikel (refereegranskat)abstract
- Quaternary oxide structures with a three-dimensional macro/mesoporous network are synthesized via a facile nanocasting method followed by a calcination process. Structural engineering integrates multiscale pores by using a hydrophilic membrane with tunable-porosity as the sacrificial template. Through tailoring the metal precursor ratio, the tetragonal sites of spinel oxide are preferentially occupied by iron, resulting in a stabilized mesoporous cubic phase. Crystal field theory together with compositional characterizations from energy-dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), Mossbauer, and electron energy loss spectroscopy (EELS) direct our detailed analysis of the cation distribution in the spinel structures. Galvanostatic tests based on the best performing electrode exhibits a robust cycle life stable for 1200 cycles at a high current density of 1500 mA g(-1). This good Li+ storage performance could be attributed to the mutually beneficial synergy of the optimal level of iron doping which improves the electrical conductivity and structural robustness, as well as the presence of extended, hierarchical macro/mesoporous network. Finally, we demonstrate three feasible surface modification strategies for the oxide anodes toward better reversibility of Li+ storage.
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| 23. |
- Ma, Yue, et al.
(författare)
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Multiscale Interfacial Strategy to Engineer Mixed Metal-Oxide Anodes toward Enhanced Cycling Efficiency
- 2018
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:23, s. 20095-20105
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Tidskriftsartikel (refereegranskat)abstract
- Interconnected macro/mesoporous structures of mixed metal oxide (MMO) are developed on nickel foam as freestanding anodes for Li-ion batteries. The sustainable production is realized via a wet chemical etching process with bio-friendly chemicals. By means of divalent iron doping during an in situ recrystallization process, the as-developed MMO anodes exhibit enhanced levels of cycling efficiency. Furthermore, this atomic-scale modification coherently synergizes with the encapsulation layer across a micrometer scale. During this step, we develop a quasi-gel-state tri-copolymer, i.e., F127-resorcinol-melamine, as the N-doped carbon source to regulate the interfacial chemistry of the MMO electrodes. Electrochemical tests of the modified FexN1-xO@NC-NiF anode in both half-cell and full-cell configurations unravel the favorable suppression of the irreversible capacity loss and satisfactory cyclability at the high rates. This study highlights a proof-of-concept modification strategy across multiple scales to govern the interfacial chemical process of the electrodes toward better reversibility.
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| 24. |
- Ma, Yue, et al.
(författare)
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Recycled Poly(vinyl alcohol) Sponge for Carbon Encapsulation of Size-Tunable Tin Dioxide Nanocrystalline Composites
- 2015
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Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 8:12, s. 2084-2092
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Tidskriftsartikel (refereegranskat)abstract
- The recycling of industrial materials could reduce their environmental impact and waste haulage fees and result in sustainable manufacturing. In this work, commercial poly(vinyl alcohol) (PVA) sponges are recycled into a macroporous carbon matrix to encapsulate size-tunable SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) through a scalable, flash-combustion method. The hydroxyl groups present copiously in the recycled PVA sponges guarantee a uniform chemical coupling with a tin(IV) citrate complex through intermolecular hydrogen bonds. Then, a scalable, ultrafast combustion process (30s) carbonizes the PVA sponge into a 3D carbon matrix. This PVA-sponge-derived carbon could not only buffer the volume fluctuations upon the Li-Sn alloying and dealloying processes but also afford a mixed conductive network, that is, a continuous carbon framework for electrical transport and macropores for facile electrolyte percolation. The best-performing electrode based on this composite delivers a rate performance up to 9.72C (4Ag(-1)) and long-term cyclability (500cycles) for Li+ ion storage. Moreover, cyclic voltammograms demonstrate the coexistence of alloying and dealloying processes and non-diffusion-controlled pseudocapacitive behavior, which collectively contribute to the high-rate Li+ ion storage.
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| 25. |
- Mayence, Arnaud, et al.
(författare)
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Interfacial strain and defects in asymmetric Fe-Mn oxide hybrid nanoparticles
- 2016
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 8:29, s. 14171-14177
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Tidskriftsartikel (refereegranskat)abstract
- Asymmetric Fe-Mn oxide hybrid nanoparticles have been obtained by a seed-mediated thermal decomposition-based synthesis route. The use of benzyl ether as the solvent was found to promote the orientational growth of Mn1-xO onto the iron oxide nanocube seeds yielding mainly dimers and trimers whereas 1-octadecene yields large nanoparticles. HRTEM imaging and HAADF-STEM tomography performed on dimers show that the growth of Mn1-xO occurs preferentially along the edges of iron oxide nanocubes where both oxides share a common crystallographic orientation. Fourier filtering and geometric phase analysis of dimers reveal a lattice mismatch of 5% and a large interfacial strain together with a significant concentration of defects. The saturation magnetization is lower and the coercivity is higher for the Fe-Mn oxide hybrid nanoparticles compared to the iron oxide nanocube seeds.
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| 26. |
- Nagendiran, Anuja, et al.
(författare)
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Mild and Selective Catalytic Hydrogenation of the C=C Bond in a,b-Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles
- 2016
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 22:21, s. 7184-7189
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Tidskriftsartikel (refereegranskat)abstract
- Chemoselective reduction of the C=C bond in a variety of α,β-unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H2: 1) nano-Pd on a metal–organic framework (MOF: Pd0-MIL-101-NH2(Cr)), 2) nano-Pd on a siliceous mesocellular foam (MCF: Pd0-AmP-MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd0-MIL-101-NH2(Cr) and Pd0-AmP-MCF were capable of delivering the desired products in very short reaction times (10–90 min) with low loadings of Pd (0.5–1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.
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| 27. |
- Nagendiran, Anuja, et al.
(författare)
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Nanopalladium-catalyzed conjugate reduction of Michael acceptors - application in flow
- 2016
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Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 18:9, s. 2632-2637
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Tidskriftsartikel (refereegranskat)abstract
- A continuous-flow approach towards the selective nanopalladium-catalyzed hydrogenation of the olefinic bond in various Michael acceptors, which could lead to a greener and more sustainable process, has been developed. The nanopalladium is supported on aminofunctionalized mesocellular foam. Both aromatic and aliphatic substrates, covering a variation of functional groups such as acids, aldehydes, esters, ketones, and nitriles were selectively hydrogenated in high to excellent yields using two different flow-devices (H-Cube (R) and Vapourtec). The catalyst was able to hydrogenate cinnamaldehyde continuously for 24 h (in total hydrogenating 19 g cinnanmaldehyde using 70 mg of catalyst in the H-cube (R)) without showing any significant decrease in activity or selectivity. Furthermore, the metal leaching of the catalyst was found to be very low (ppb amounts) in the two flow devices.
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| 28. |
- Neagu, Alexandra, et al.
(författare)
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Investigation of local structural phase transitions in 95Na(0.5)Bi(0.5)TiO(3)-5BaTiO(3) piezoceramics by means of in-situ transmission electron microscopy
- 2018
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 123:24
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Tidskriftsartikel (refereegranskat)abstract
- The temperature-dependence of superstructure reflections, diffuse scattering intensity, and ferroelectric domain morphology for 95Na(0.5)Bi(0.5)TiO(3)-5BaTiO(3) ceramics was investigated by in-situ transmission electron microscopy. A subtle local structural phase transition was observed around 110 degrees C. This local phase transition is characterized by a transformation in the dominant octahedral-tilt system from antiphase to in-phase tilting and was correlated with the depolarization mechanism common in this type of materials. Simulations of the octahedral-tilt disorder were developed at different temperatures which enabled us to provide a comprehensive structural model that explains the temperature-dependence of superstructure reflections and electron diffuse scattering intensity. This model revealed that plate-like in-phase nanodomains tilted about three orthogonal axes coexist with an antiphase tilted matrix, even at room temperature. With increasing temperature, the concentration of in-phase nanodomains is increased till a critical volume fraction is reached. We propose that these plate-like in-phase nanodomains are an inherent characteristic of NBT-based compounds and that the local phase transition observed around 110 degrees C leads to a disruption in the long-range ferroelectric order and is responsible for the depolarization mechanism.
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| 29. |
- Neagu, Alexandra, et al.
(författare)
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Local disorder in Na0.5Bi0.5TiO3-piezoceramic determined by 3D electron diffuse scattering
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Local structural distortions in Na0.5Bi0.5TiO3-based solid solutions have been proved to play a crucial role in understanding and tuning their enhanced piezoelectric properties near the morphotropic phase boundary. In this work all local structural disorders in a lead-free ternary system, namely 85% Na0.5Bi0.5TiO3-10% Bi0.5K0.5TiO3-5% BaTiO3, were mapped in reciprocal space by 3D electron diffraction. Furthermore, a comprehensive model of the local disorder was developed by analysing the intensity and morphology of the observed weak diffuse scattering. We found that the studied ceramics consists of plate-like in-phase oxygen octahedral nanoscale domains randomly distributed in an antiphase tilted matrix. In addition, A-site chemical short-range order of Na/Bi and polar displacements contribute to different kinds of diffuse scattering. The proposed model explains all the observed diffraction features and offers insight into the ongoing controversy over the nature of local structural distortions in Na0.5Bi0.5TiO3-based solid solutions.
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| 30. |
- Neagu, Alexandra, 1989-
(författare)
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Local structure of perovskite ferroelectric ceramics as revealed by 3D electron diffuse scattering : A walk in between the Bragg peaks
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Local structural disorder in crystalline materials plays a crucial role in understanding their properties. The means to study structural disorder is diffuse scattering (DS). Even though DS was observed since the early days of X-ray diffraction the weak intensity and the sheer number of different kinds of disorder hindered the development of a unique solution strategy. However, the advent of X-ray and neutron synchrotron sources together with recent advances in automated electron diffraction techniques have unraveled a new world in between Bragg peaks where a wealth of information is available.In this thesis electron diffraction is used to explore the different kinds of DS in three-dimensions, for several perovskite ferroelectric ceramics. Based on the information presented in the reconstructed 3D reciprocal space volumes, disordered atomic structures were proposed and verified by the calculated electron diffraction patterns. A complex structural model for the local disorder in 85Na0.5Bi0.5TiO3-10K0.5Bi0.5TiO3-5BaTiO3 piezoceramic was developed by analyzing the morphology and intensity of electron DS in 3D. Next, the influence of potassium-content on the octahedral-tilt disorder for three different piezoceramics was studied by a combination of dark-field imaging and electron diffraction. Further on, the temperature-dependence of electron DS for 95Na0.5Bi0.5TiO3-5BaTiO3 piezoceramic revealed a local structural phase transition that was correlated with the depolarization mechanism. Lastly, strong electron DS was recorded from a Pb-based relaxor and simulations of disordered atomic structures showed that the local structure resembles a dipolar glass state. These demonstrate that electron diffraction is a powerful tool for the study of local structural disorder in crystalline materials, especially for ceramics. The major advantage is that we are able to record single-crystal electron diffraction data from individual grains. Moreover, since we are analyzing a 3D reciprocal volume several orientations can be studied simultaneously and we are not limited to zero-Laue zones. Finally, the models for local structural disorder provided valuable insight into how macroscopic properties are influenced by local structural disorder, in addition to the average structure.
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| 31. |
- Neagu, Alexandra, et al.
(författare)
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The influence of potassium content on octahedral-tilt disorder in Na0.5Bi0.5TiO3-solid solutions near morphotropic phase boundary
- 2018
-
Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 152, s. 49-54
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Tidskriftsartikel (refereegranskat)abstract
- A semi-quantitative comparison of 3D electron diffraction data revealed structural differences at the nanoscale for three (95-x)Na0.5Bi0.5TiO3-xK0.5Bi0.5TiO3-5BaTiO3 solid solutions close to the morphotropic phase boundary, with x = 0, 5, 10. Using a novel rotation electron diffraction technique, diffuse scattering intensity was recorded in 3D as continuous rods along hk0.5 reciprocal-planes. By analyzing the different superstructure reflections and the intensity/morphology of diffuse scattering, a structural model of the local octahedral-tilt disorder for the different ceramics was developed. A good agreement was obtained between the experimental and simulated data with a model comprising of antiphase (a−a−a−) and plate-like in-phase (a0a0c+) nanodomains.
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| 32. |
- Nedumkandathil, Reji, et al.
(författare)
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Hydride Reduction of BaTiO3 ? Oxyhydride Versus O Vacancy Formation
- 2018
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 3:9, s. 11426-11438
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the hydride reduction of tetragonal BaTiO3 using the metal hydrides CaH2, NaH, MgH2, NaBH4, and NaAlH4. The reactions employed molar BaTiO3/H ratios of up to 1.8 and temperatures near 600 °C. The air-stable reduced products were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy, thermogravimetric analysis (TGA), and 1H magic angle spinning (MAS) NMR spectroscopy. PXRD showed the formation of cubic products - indicative of the formation of BaTiO3-xHx - except for NaH. Lattice parameters were in a range between 4.005 Å (for NaBH4-reduced samples) and 4.033 Å (for MgH2-reduced samples). With increasing H/BaTiO3 ratio, CaH2-, NaAlH4-, and MgH2-reduced samples were afforded as two-phase mixtures. TGA in air flow showed significant weight increases of up to 3.5% for reduced BaTiO3, suggesting that metal hydride reduction yielded oxyhydrides BaTiO3-xHx with x values larger than 0.5. 1H MAS NMR spectroscopy, however, revealed rather low concentrations of H and thus a simultaneous presence of O vacancies in reduced BaTiO3. It has to be concluded that hydride reduction of BaTiO3 yields complex disordered materials BaTiO3-xHy?(x-y) with x up to 0.6 and y in a range 0.04-0.25, rather than homogeneous solid solutions BaTiO3-xHx. Resonances of (hydridic) H substituting O in the cubic perovskite structure appear in the ?2 to ?60 ppm spectral region. The large range of negative chemical shifts and breadth of the signals signifies metallic conductivity and structural disorder in BaTiO3-xHy?(x-y). Sintering of BaTiO3-xHy?(x-y) in a gaseous H2 atmosphere resulted in more ordered materials, as indicated by considerably sharper 1H resonances.
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| 33. |
- Palo-Nieto, Carlos, et al.
(författare)
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Integrated Heterogeneous Metal/Enzymatic Multiple Relay Catalysis for Eco-Friendly and Asymmetric Synthesis
- 2016
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6, s. 3932-3940
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Tidskriftsartikel (refereegranskat)abstract
- Organic synthesis is in general performed using stepwise transformations where isolation and purification of key intermediates is often required prior to further reactions. Herein we disclose the concept of integrated heterogeneous metal/enzymatic multiple relay catalysis for eco-friendly and asymmetric synthesis of valuable molecules (e.g., amines and amides) in one-pot using a combination of heterogeneous metal and enzyme catalysts. Here reagents, catalysts, and different conditions can be introduced throughout the one-pot procedure involving multistep catalytic tandem operations. Several novel cocatalytic relay sequences (reductive amination/amidation, aerobic oxidation/reductive amination/amidation, reductive amination/kinetic resolution and reductive amination/dynamic kinetic resolution) were developed. They were next applied to the direct synthesis of various biologically and optically active amines or amides in one-pot from simple aldehydes, ketones, or alcohols, respectively.
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| 34. |
- Polido Legaria, Elizabeth, et al.
(författare)
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Unusual seeding mechanism for enhanced performance in solid-phase magnetic extraction of Rare Earth Elements
- 2017
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Due to the increasing demand of Rare Earth Elements (REE or RE), new and more efficient techniques for their extraction are necessary, suitable for both mining and recycling processes. Current techniques such as solvent extraction or solid adsorbents entail drawbacks such as using big volumes of harmful solvents or limited capacity. Hybrid nanoadsorbents based on SiO2 and highly stable gamma-Fe2O3-SiO2 nanoparticles, proved recently to be very attractive for adsorption of REE, yet not being the absolute key to solve the problem. In the present work, we introduce a highly appealing new approach in which the nanoparticles, rather than behaving as adsorbent materials, perform as inducers of crystallization for the REE in the form of hydroxides, allowing their facile and practically total removal from solution. This induced crystallization is achieved by tuning the pH, offering an uptake efficiency more than 20 times higher than previously reported (up to 900 mg RE3+/g vs. 40 mg RE3+/g). The obtained phases were characterized by SEM-EDS, TEM, STEM and EFTEM and C-13 and Si-29 solid state NMR. Magnetic studies showed that the materials possessed enough magnetic properties to be easily removed by a magnet, opening ways for an efficient and industrially applicable separation technique.
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| 35. |
- Qi, Kezhen, et al.
(författare)
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Enhanced photocatalytic activity of anatase-TiO2 nanoparticles by fullerene modification : A theoretical and experimental study
- 2016
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 387, s. 750-758
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Tidskriftsartikel (refereegranskat)abstract
- A series of fullerene (C-60)-modified anatase TiO2 (a-TiO2) nanocomposites with different weight loadings of C-60 were successfully synthesized by a simple solution phase method. The as-prepared C-60@a-TiO2 nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET), UV-vis diffuse reflectance absorption spectra (DRS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The photocatalytic degradation of methylene blue (MB) by the neat a-TiO2 and C-60@a-TiO2 nanocomposites was investigated under UV-A light irradiation, demonstrating that C-60 effectively enhances the photocatalytic activity of a-TiO2 nanoparticles with an optimal amount of 2.0 wt%. By combining with the density functional theory (DFT) calculations, we investigated the electronic structures of C-60@a-TiO2 hetero-interfaces to reveal the underlying principle of the C-60 loading on the photocatalytic activity. It was found that the incorporation of C-60 on the a-TiO2 surface not only narrowed the band gap, but also introduced an additional doping state between the valance and conduction band. Therefore, the presence of intermediate electronic state will in turn contribute to the efficient charge separation and enhanced light adsorption for the C-60@a-TiO2 nanocomposites, resulting in an improved photocatalytic performance.
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| 36. |
- Qi, Kezhen, et al.
(författare)
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Hierarchical alpha-MnS microspheres : Solvothermal synthesis and growth mechanism
- 2016
-
Ingår i: Materials letters (General ed.). - : Elsevier BV. - 0167-577X .- 1873-4979. ; 166, s. 116-120
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchical-like alpha-MnS microspheres have been successfully synthesized via a simple solvothermal route using L-Cystein as both sulfur source and capping agent. X-ray diffraction (XRD) analysis confirmed that these hierarchical microspheres were made of alpha-phase MnS. Morphological studies performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods showed that the alpha-MnS hierarchical microspheres are obtained from the nanocubes by self-assembly due to the main driving force of the minimization of overall surface energy. It is highly expected this research can provide a useful fundamental understanding of shape-controlled synthesis of the semiconductor material with hierarchical microstructures.
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| 37. |
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| 38. |
- Qiu, Zhen, et al.
(författare)
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Direct observation of active catalyst surface phases and the effect of dynamic self-optimization in NiFe-layered double hydroxides for alkaline water splitting
- 2019
-
Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 12:2, s. 572-581
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Tidskriftsartikel (refereegranskat)abstract
- Earth-abundant transition metal-based compounds are of high interest as catalysts for sustainable hydrogen fuel generation. The realization of effective electrolysis of water, however, is still limited by the requirement of a high sustainable driving potential above thermodynamic requirements. Here, we report dynamically self-optimized (DSO) NiFe layered double hydroxide (LDH) nanosheets with promising bi-functional performance. Compared with pristine NiFe LDH, DSO NiFe LDH exhibits much lower overpotential for the hydrogen evolution reaction (HER), even outperforming platinum. Under 1 M KOH aqueous electrolyte, the bi-functional DSO catalysts show an overpotential of 184 and -59 mV without iR compensation for oxygen evolution reaction (OER) and HER at 10 mA cm(-2). The material system operates at 1.48 V and 1.29 V to reach 10 and 1 mA cm(-2) in two-electrode measurements, corresponding to 83% and 95% electricity-to-fuel conversion efficiency with respect to the lower heating value of hydrogen. The material is seen to dynamically reform the active phase of the surface layer during HER and OER, where the pristine and activated catalysts are analyzed with ex situ XPS, SAED and EELS as well as with in situ Raman spectro-electrochemistry. The results show transformation into different active interfacial species during OER and HER, revealing a synergistic interplay between iron and nickel in facilitating water electrolysis.
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| 39. |
- Raudonyte-Svirbutaviciene, Eva, et al.
(författare)
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Two-step photochemical inorganic approach to the synthesis of Ag-CeO2 nanoheterostructures and their photocatalytic activity on tributyltin degradation
- 2018
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Ingår i: Journal of Photochemistry and Photobiology A. - : Elsevier BV. - 1010-6030 .- 1873-2666. ; 351, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report a simple, sustainable and low-cost approach to design Ag-CeO2 nanoheterostructures in pure aqueous and ethanol containing aqueous solutions via photochemical UV-light driven process with no capping agents nor stabilizers required. To this end, photochemically synthesized CeO2 nanoparticles were applied as photoactive compounds in order to generate formation of metallic silver nanoparticles. Irradiation of deaerated CeO2 suspensions in the presence of Ag+ resulted in the rise of a strong surface plasmon resonance band with a maximum at 393-422 nm in the absorption spectra of the solutions, indicating formation of small metallic silver particles. Faster formation of Ag nanoparticles with the lower amount of silver precursor being required was observed when ethanol was introduced to the reaction solution before the irradiation. This implies that oxidative reactions can be strongly suppressed in deaerated ethanol containing solutions with respect to the pure aqueous media. Not only was the overall efficiency of the process remarkably increased by the use of alcohol, but also smaller and more uniform silver nanoparticles with a size comparable to that of ceria nanoparticles (around 15 nm) were formed when compared to those synthesized without radical scavengers as revealed by TEM analysis. The proposed photochemical approach enables the production of silver-semiconductor system without employing organic stabilizers, thus resulting in formation of nanoparticles with clean, highly reactive metal surface. The as-synthesized silver-ceria nanoheterostructures demonstrated enhanced visible light driven photocatalytic activity on tributyltin (TBT) degradation if compared to pure ceria nanoparticles.
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| 40. |
- Rehnlund, David, et al.
(författare)
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Electrochemical fabrication and characterization of Cu/Cu2O multi-layered micro and nanorods in Li-ion batteries
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:32, s. 13591-13604
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Tidskriftsartikel (refereegranskat)abstract
- Electrodes composed of freestanding nano- and microrods composed of stacked layers of copper and cuprous oxide have been fabricated using a straightforward one-step template-assisted pulsed galvanostatic electrodeposition approach. The approach provided precise control of the thickness of each individual layer of the high-aspect-ratio rods as was verified by SEM, EDS, XRD, TEM and EELS measurements. Rods with diameters of 80, 200 and 1000 nm were deposited and the influence of the template pore size on the structure and electrochemical performance of the conversion reaction based electrodes in lithium-ion batteries was investigated. The multi-layered Cu2O/Cu nano-and microrod electrodes exhibited a potential window of more than 2 V, which was ascribed to the presence of a distribution of Cu2O (and Cu, respectively) nanoparticles with different sizes and redox potentials. As approximately the same areal capacity was obtained independent of the diameter of the multi-layered rods the results demonstrate the presence of an electroactive Cu2O layer with a thickness defined by the time domain of the measurements. It is also demonstrated that while the areal capacity of the electrodes decreased dramatically when the scan rate was increased from 0.1 to 2 mV s(-1), the capacity remained practically constant when the scan rate was further increased to 100 mV s(-1). This behaviour can be explained by assuming that the capacity is limited by the lithium ion diffusion rate though the Cu2O layer generated during the oxidation step. The electrochemical performance of present type of 3-D multi-layered rods provides new insights into the lithiation and delithiation reactions taking place for conversion reaction materials such as Cu2O.
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| 41. |
- Rehnlund, David, et al.
(författare)
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Electrochemical fabrication of 3D Cu/Cu2O multilayered nanostructures
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The possibility of engineering multilayered nanostructures and coatings with a wide variety of compositions has in the last decades attracted a great deal of scientific interest. In fact, multilayered structures with tailored properties have been investigated for solar conversion [1], the semiconductor industry [2] and tribological systems [3].Electrochemical engineering has emerged as a particularly promising technique for fabrication of nanostructured electrodes with excellent control on morphology [4]. The technique shows great promise in the copper system as Cu/Cu2O multilayers have been produced by allowing spontaneous potential oscillations to dictate the deposition [5, 6].Although this natural phenomenon provides a simple route to obtain mixedcomposition, improved control is required to obtain fine detailed multilayers. The presented study has been focused on preventing spontaneous potential oscillations to provide controlled deposition of Cu/Cu2O multilayers. In addition copper based multilayers have hereby been transported into the world of 3D electrodes via a one-step electrodeposition fabrication.Figure 1: Multilayered Cu/Cu2O nanopillars fabricated through electrodeposition.References1. W. Wei, et al.. Advanced Materials, 2010. 22: p. 4770-4774.2. G. Binasch, et al.. Physical Review B, 1989. 39: p. 4828-4830.3. P. E. Hovsepian, et al.. Surface and Coatings Technology, 1999. 116-119: p.727-734.4. K. Edström, et al.. The Electrochemical Society Interface, 2011. 20: p. 41-46.5. J. Eskhult, et al.. Journal of Electroanalytical Chemistry, 2006. 594: p. 35-49.6. S. Leopold, et al.. Electrochimica Acta, 2002. 47
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| 42. |
- Renman, Viktor, et al.
(författare)
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Investigation of the Structural and Electrochemical Properties of Mn2Sb3O6CI upon Reaction with Li Ions
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:11, s. 5949-5958
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Tidskriftsartikel (refereegranskat)abstract
- The structural and electrochemical properties of a quaternary layered compound with elemental composition Mn2Sb3O6Cl have been investigated upon reaction with lithium in Li half cells. Operando XRD was used to investigate the potential impact of this particular layered structure on the lithiation process. Although the results suggest that the material is primarily reacted through a conventional conversion mechanism, they also provide some hints that the space between the slabs may act as preferential entry points for lithium ions but not for the larger sodium ions. Cyclic voltammetry, galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed to unravel the details of the reaction mechanism with the lithium ions. It is found that two pairs of reactions are mainly responsible for the reversible electrochemical cycling of this compound, namely, the alloying of Li-Sb and the conversion of MnxOy to metallic Mn with concomitant formation of Li2O upon lithium uptake. A moderate cycling stability is achieved with a gravimetric capacity of 467 mAh g(-1) after 100 cycles between 0.05 and 2.2 V vs Li+/Li despite the large particle sizes of the active material and its nonoptimal inclusion into composite coatings. The electrochemical activity of the title compound was also tested in Na half cells between 0.05 and 2 V vs Ne/Na. It was found that a prolonged period of electrochemical milling is required to fully gain access to the active material, after which the cell delivers a capacity of 350 mAh CI. These factors are demonstrated to clearly limit the ultimate performances for these electrodes.
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| 43. |
- Renman, Viktor, et al.
(författare)
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Manganese pyrosilicates as novel positive electrode materials for Na-ion batteries
- 2018
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Ingår i: Sustainable Energy & Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 2:5, s. 941-945
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Tidskriftsartikel (refereegranskat)abstract
- A carbon-coated pyrosilicate, Na2Mn2Si2O7/C, was synthesized and characterized for use as a new positive-electrode material for sodium ion batteries. The material consists of 20-80 nm primary particles embedded in a approximate to 10 nm-thick conductive carbon matrix. Reversible insertion of Na+ ions is clearly demonstrated with approximate to 25% of its theoretical capacity (165 mA h g(-1)) being accessible at room temperature at a low cycling rate. The material yields an average potential of 3.3 V vs. Na+/Na on charge and 2.2 V on discharge. DFT calculations predict an equilibrium potential for Na2Mn2Si2O7 in the range of 2.8-3.0 V vs. Na+/Na, with a possibility of a complete flip in the connectivity of neighboring Mn-polyhedra - from edge-sharing to disconnected and vice versa. This significant rearrangement in Mn coordination (approximate to 2 angstrom) and large volume contraction (>10%) could explain our inability to fully desodiate the material, and illustrates well the need for a new electrode design strategy beyond the conventional down-sizing/coating procedure.
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| 44. |
- Schitco, Cristina, et al.
(författare)
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Silicon oxycarbonitrides synthesized by ammonia-assisted thermolysis route from polymers : A total X-ray scattering, solid-state NMR, and TEM structural study
- 2016
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:4, s. 979-989
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Tidskriftsartikel (refereegranskat)abstract
- Solid-state nuclear magnetic resonance (NMR) spectroscopy, total X-ray scattering with a pair distribution function (PDF) analysis, and transmission electron microscopy (TEM) were employed to explore the structures of microporous and non-porous ceramics synthesized by an NH3-assisted thermolysis from polymers. Polysiloxane (SPR-212a, Starfire® Systems) and polysilazane (HTT-1800, KiON Speciality Polymers) polymers form microporous silicon oxycarbonitride ceramics with accessible and tailored micropores. 29Si magic-angle-spinning NMR showed that the introduction of nitrogen leads to structures incorporating considerable amounts of SiN4 and SiO2N2 building blocks. The samples derived from a polycarbosilane (SMP-10, Starfire® Systems) remained non-porous: for such a C-rich and N-bearing phase, the NMR, TEM, and PDF results suggested a Si network exhibiting domains dominated by either SiN or SiC bonds. 13C NMR revealed primarily “carbidic” CSi4 environments in the C-rich phases, as well as the formation of an amorphous sp2-hybridized carbon phase; both are believed to be detrimental for the micropore formation.
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| 45. |
- Shi, Liyang, et al.
(författare)
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Biocompatible Injectable Magnetic Hydrogel Formed by Dynamic Coordination Network
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:49, s. 46233-46240
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic hydrogel that can respond to a magnetic stimulus is a promising biomaterial for tissue regeneration and cancer treatment. In this study, a novel magnetic hydrogel is formed by simply mixing bisphosphonate (BP)-modified hyaluronic acid (i.e., HA-BP) polymeric solution and iron oxide (Fe3O4) nanoparticle dispersion, in which the hydrogel networks are cross linked by BP groups and iron atoms on the surface of particle. The iron BP coordination chemistry affords a dynamic network, characterized by self-healing, shear-thinning, and smoothly injectable properties. Moreover, the HA-BP-Fe3O4 magnetic hydrogel demonstrates heat-generation characterization under an alternating magnetic field. The animal experiments confirm the biocompatibilities of HA BP center dot Fe3O4 hydrogel, which presents the hydrogels potential for tissue regeneration and anticancer treatment applications.
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| 46. |
- Sun, Rui, et al.
(författare)
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Amorphous Calcium Carbonate Constructed from Nanoparticle Aggregates with Unprecedented Surface Area and Mesoporosity
- 2018
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 10:25, s. 21556-21564
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous calcium carbonate (ACC), with the highest reported specific surface area of all current forms of calcium carbonate (over 350 m(2) g(-1)), was synthesized using a surfactant-free, one-pot method. Electron microscopy, helium pycnometry, and nitrogen sorption analysis revealed that this highly mesoporous ACC, with a pore volume of similar to 0.86 cm(3) g(-1) and a pore-size distribution centered at 8-9 nm, is constructed from aggregated ACC nanoparticles with an estimated average diameter of 7.3 nm. The porous ACC remained amorphous and retained its high porosity for over 3 weeks under semi-air-tight storage conditions. Powder X-ray diffraction, large-angle X-ray scattering, infrared spectroscopy, and electron diffraction exposed that the porous ACC did not resemble any of the known CaCO3 structures. The atomic order of porous ACC diminished at interatomic distances over 8 angstrom. Porous ACC was evaluated as a potential drug carrier of poorly soluble substances in vitro. Itraconazole and celecoxib remained stable in their amorphous forms within the pores of the material. Drug release rates were significantly enhanced for both drugs (up to 65 times the dissolution rates for the crystalline forms), and supersaturation release of celecoxib was also demonstrated. Citric acid was used to enhance the stability of the ACC nanoparticles within the aggregates, which increased the surface area of the material to over 600 m(2) g(-1). This porous ACC has potential for use in various applications where surface area is important, including adsorption, catalysis, medication, and bone regeneration.
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| 47. |
- Sun, Rui, et al.
(författare)
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Hierarchical Porous Carbon Synthesized from Novel Porous Amorphous Calcium or Magnesium Citrate with Enhanced SF6 Uptake and SF6/N-2 Selectivity
- 2019
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Ingår i: Acs Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 2:2, s. 778-789
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Tidskriftsartikel (refereegranskat)abstract
- The emission of greenhouse gases such as CO2 and SF6 is believed to contribute significantly toward global warming. One way to reduce their release is by adsorption at point sources using a suitable adsorbent. In this work we present the synthesis of two hierarchical porous carbon materials (referred to as PC-CaCit and PC-MgCit) with a high uptake of SF 6 (5.23 mmol/g, 0 degrees C, 100 kPa) and a reasonable uptake of CO2 (>3 mmol/g). PC-CaCit and PC-MgCit were obtained by pyrolysis of the most porous calcium citrate and magnesium citrate ever reported, which were synthesized by us. The Langmuir specific surface area of PC-CaCit and PC-MgCit was over 2000 m(2)/g (BET surface area also close to 2000 m(2)/g). We characterized PC-CaCit and PC-MgCit using a range of advanced characterization techniques including N-2 adsorption, high-resolution electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. PC-CaCit and PC-MgCit also showed a SF6-over-N-2 selectivity of similar to 33 at 0 degrees C (100 kPa), good cyclic performance, and moderately low heat of adsorption. The porous carbons synthesized in this work are good candidate adsorbents for greenhouse gases.
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| 48. |
- Thersleff, Thomas, et al.
(författare)
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Single-pass STEM-EMCD on a zone axis using a patterned aperture : progress in experimental and data treatment methods
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Measuring magnetic moments in ferromagnetic materials at atomic resolution is theoretically possible using the electron magnetic circular dichroism (EMCD) technique in a (scanning) transmission electron microscope ((S)TEM). However, experimental and data processing hurdles currently hamper the realization of this goal. Experimentally, the sample must be tilted to a zone-axis orientation, yielding a complex distribution of magnetic scattering intensity, and the same sample region must be scanned multiple times with sub-atomic spatial registration necessary at each pass. Furthermore, the weak nature of the EMCD signal requires advanced data processing techniques to reliably detect and quantify the result. In this manuscript, we detail our experimental and data processing progress towards achieving single-pass zone-axis EMCD using a patterned aperture. First, we provide a comprehensive data acquisition and analysis strategy for this and other EMCD experiments that should scale down to atomic resolution experiments. Second, we demonstrate that, at low spatial resolution, promising EMCD candidate signals can be extracted, and that these are sensitive to both crystallographic orientation and momentum transfer.
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| 49. |
- Tran, Dung Trung, et al.
(författare)
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SUePDF : a program to obtain quantitative pair distribution functions from electron diffraction data
- 2017
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Ingår i: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 50, s. 304-312
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Tidskriftsartikel (refereegranskat)abstract
- SUePDF is a graphical user interface program written in MATLAB to achieve quantitative pair distribution functions (PDFs) from electron diffraction data. The program facilitates structural studies of amorphous materials and small nanoparticles using electron diffraction data from transmission electron microscopes. It is based on the physics of electron scattering as well as the total scattering methodology. A method of background modeling is introduced to treat the intensity tail of the direct beam, inelastic scattering and incoherent multiple scattering. Kinematical electron scattering intensity is scaled using the electron scattering factors. The PDFs obtained after Fourier transforms are normalized with respect to number density, nanoparticle form factor and the non-negativity of probability density. SUePDF is distributed as free software for academic users.
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| 50. |
- Trushkina, Yulia, et al.
(författare)
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Fabrication of Maghemite Nanoparticles with High Surface Area
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:7
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Tidskriftsartikel (refereegranskat)abstract
- Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 x 10(3) m(2)/mol, with pore volumes in the order of 70 cm(3)/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180-250 degrees C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.
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