| 1. |
- Asfaw, Habtom D., et al.
(författare)
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Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sot-gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4 nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm(-2) at 0.1 mA cm(-2) (lowest rate) and 1.1 mA h cm(-2) at 6 mA cm(-2) (highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
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| 2. |
- Asfaw, Habtom Desta, 1986-, et al.
(författare)
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Nanosized LiFePO4-decorated emulsion-templated carbon foam for 3D micro batteries : a study of structure and electrochemical performance
- 2014
-
Ingår i: Nanoscale. - Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 6:15, s. 8804-8813
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, we report a novel 3D composite cathode fabricated from LiFePO4 nanoparticles deposited conformally on emulsion-templated carbon foam by a sol–gel method. The carbon foam is synthesized via a facile and scalable method which involves the carbonization of a high internal phase emulsion (polyHIPE) polymer template. Various techniques (XRD, SEM, TEM and electrochemical methods) are used to fully characterize the porous electrode and confirm the distribution and morphology of the cathode active material. The major benefits of the carbon foam used in our work are closely connected with its high surface area and the plenty of space suitable for sequential coating with battery components. After coating with a cathode material (LiFePO4nanoparticles), the 3D electrode presents a hierarchically structured electrode in which a porous layer of the cathode material is deposited on the rigid and bicontinuous carbon foam. The composite electrodes exhibit impressive cyclability and rate performance at different current densities affirming their importance as viable power sources in miniature devices. Footprint area capacities of 1.72 mA h cm−2 at 0.1 mA cm−2 (lowest rate) and 1.1 mA h cm−2 at 6 mA cm−2(highest rate) are obtained when the cells are cycled in the range 2.8 to 4.0 V vs. lithium.
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| 3. |
- Barzegar, Hamid Reza, et al.
(författare)
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Water assisted growth of C60 rods and tubes by liquid-liquid interfacial precipitation method
- 2012
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Ingår i: Molecules. - : MDPI. - 1431-5157 .- 1420-3049. ; 17:6, s. 6840-6853
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Tidskriftsartikel (refereegranskat)abstract
- C60 nanorods with hexagonal cross sections are grown using a static liquid-liquid interfacial precipitation method in a system of C60/m-dichlorobenzene solution and ethanol. Adding water to the ethanol phase leads instead to C60 tubes where both length and diameter of the C60 tubes can be controlled by the water content in the ethanol. Based on our observations we find that the diameter of the rods/tubes strongly depends on the nucleation step. We propose a liquid-liquid interface growth model of C60 rods and tubes based on the diffusion rate of the good C60 containing solvent into the poor solvent as well as on the size of the crystal seeds formed at the interface between the two solvents. The grown rods and tubes exhibit a hexagonal solvate crystal structure with m-dichlorobenzene solvent molecules incorporated into the crystal structure, independent of the water content. An annealing step at 200 °C at a pressure <1 kPa transforms the grown structures into a solvent-free face centered cubic structure. Both the hexagonal and the face centered cubic structures are very stable and neither morphology nor structure shows any signs of degradation after three months of storage.
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| 4. |
- Bhatt, Aarti Sripathi, et al.
(författare)
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Chitosan/NiO nanocomposites : a potential new dielectric material
- 2011
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 21:35, s. 13490-13497
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Tidskriftsartikel (refereegranskat)abstract
- The study of electrochemical behavior of organic-inorganic nanocomposite materials remains a major challenge for application in energy storage devices. Here, new composite materials of chitosan and NiO nanoparticles have been fabricated. The NiO nanoparticles are well characterized by infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The electrical properties of the films are studied by impedance spectroscopy at different temperatures; and thereby permittivity, electric modulus and conductivity data are obtained. By studying the variations in permittivity and electric modulus spectra with respect to applied frequency signal and temperature, the ionic conductivity of the material is investigated. The Correlated Barrier Hopping model is employed to understand the conduction mechanism. An admirable conductivity of 1.4 x 10(-2) S cm(-1) is obtained for a nanocomposite with 4 wt% NiO content. The activation energies of the composite films decrease with increase in NiO content, from 16.5 to 4.8 kJ mol(-1).
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| 5. |
- Deiana, Luca, et al.
(författare)
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Combined Heterogeneous Metal/Chiral Amine : Multiple Relay Catalysis for Versatile Eco-Friendly Synthesis
- 2014
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 53:13, s. 3447-3451
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Tidskriftsartikel (refereegranskat)abstract
- Herein is described a versatile and broad synergistic strategy for expansion of chemical space and the synthesis of valuable molecules (e.g. carbocycles and heterocycles), with up to three quaternary stereocenters, in a highly enantioselective fashion from simple alcohols (31examples, 95:5 to >99.5:0.5 e.r.) using integrated heterogeneous metal/chiral amine multiple relay catalysis and air/O-2 as the terminal oxidant. A novel highly 1,4-selective heterogeneous metal/amine co-catalyzed hydrogenation of enals was also added to the relay catalysis sequences.
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| 6. |
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| 7. |
- Gebauer, Denis, et al.
(författare)
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Proto-Calcite and Proto-Vaterite in Amorphous Calcium Carbonates
- 2010
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 49:47, s. 8889-8891
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Hallberg, Rolf, et al.
(författare)
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Multiwall Carbon Nanotubes and Nanofibers in Gallionella
- 2014
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 31:9, s. 764-768
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Tidskriftsartikel (refereegranskat)abstract
- This is a report of microbial formation of multiwall carbon nanotubes (MWCNT) and nanofibers at normal pressure and temperature. Our results demonstrate a single cell organism's ability to form complicated material of high industrial interest. The microorganism, Gallionella, is classified as autotrophic and dysoxic. It uses CO2 for its carbon source and grows in environments with low concentrations of free oxygen. The organisms were taken from a deep bedrock tunnel where water leaking from cracks in the rock formed a precipitate of iron as a bacterial slime on the rock wall. Detailed investigations of the samples by transmission electron microscopy (TEM) revealed several types of MWCNT. The stalk single MWCNT was observed with a diameter of about 10nm and with an inner diameter of 1.35nm. The wall of the nanotube is built by graphite layers. The 10 to 20 sheets are used to form the tubes. The measured spacing between the lines is 0.34nm, which is an average value of interlayer spacing, close to the graphitic distance (0.335nm). HRTEM images reveal a two-dimensional lattice with a spacing of 0.24nm, indicating the presence of graphene.
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| 9. |
- Hu, Guangzhi, et al.
(författare)
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Palladium nanocrystals supported on helical carbon nanofibers for highly efficient electro-oxidation of formic acid, methanol and ethanol in alkaline electrolytes
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 209, s. 236-242
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Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis of palladium nanocrystals self-assembled on helical carbon nanofibers functionalized with benzyl mercaptan (Pd-S-HCNFs) and their electrocatalytic activity toward the oxidation of formic acid, methanol and ethanol. Helical carbon nanofibers (HCNFs) were first functionalized with benzyl mercaptan based on the pi-pi interactions between phenyl rings and the graphitic surface of HCNFs. Palladium nano crystals (PdNC) were fixed on the surface of functionalized HCNF by Pd-S bonds in a simple self-assembly method. The as-prepared materials were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and fuel cell tests. CV characterization of the as-prepared materials shows a very high electrocatalytic activity for oxidation of formic acid, ethanol and methanol in strong alkaline electrolyte. In comparison to commercial catalyst Vulcan XC-72 decorated with Pd nanoparticles, the proposed Pd-S-HCNFs nano composite material shows oxidation currents for formic acid, ethanol and methanol at the Pd-S-HCNF-modified electrode that are higher than that at the Pd/XC-72 modified electrode with a factor of 2.0, 1.5, and 2.3, respectively. In a formic acid fuel cell the Pd-S-HCNF modified electrode yields equal power density as commercial Pd/XC-72 catalyst. Our results show that Pd-decorated helical carbon nanofibers with diameters around 40-60 nm have very high potential as active material in fuel cells, electrocatalysts and sensors.
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| 10. |
- Hu, Guangzhi, et al.
(författare)
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Phase-transfer synthesis of amorphous palladium nanoparticle-functionalized 3D helical carbon nanofibers and its highly catalytic performance towards hydrazine oxidation
- 2012
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 543, s. 96-100
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous palladium nanoparticles functionalized helical carbon nanofibers (ApPd-HCNFs) were synthesized using a phase-transfer method. Palladium nanoparticles (Pd-NP) were first prepared using n-dodecyl sulfide as reducing agent and stabilizing ligands in ethanol. The Pd-NPs were then modified with benzyl mercaptan and transferred into a toluene solution with HCNFs which were decorated with amorphous palladium. The materials were characterized with high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and cyclic voltammetry showing that amorphous palladium nanoparticles were uniformly anchored at the HCNFs surface and that the ApPd-HCNFs exhibit high electrocatalytic activity towards hydrazine oxidation.
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| 11. |
- Jia, Xueen, et al.
(författare)
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Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection
- 2013
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:22, s. 12017-12022
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Tidskriftsartikel (refereegranskat)abstract
- We report on a novel sensing platform for H2O2 and glucose based on immobilization of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostnictures and glucose oxidase (GOx) with Nafion on a glassy carbon electrode (GCE). HCNFs were synthesized by a chemical vapor deposition process on a C-60-supported Pd catalyst. Pd-HCNF nanocomposites were prepared by a one-step reduction free method in dimethylformamide (DMF). The prepared materials were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits excellent electrocatalytic sensitivity toward H2O2 (315 mA M-1 cm(-2)) as probed by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified electrodes significantly reduce the overpotential and enhance the electron transfer rate. A linear range from 5.0 mu M to 2.1 mM with a detection limit of 3.0 mu M (based on the S/N = 3) and good reproducibility were obtained. Furthermore, a sensing platform for glucose was prepared by immobilizing the Pd-HCNFs and glucose oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting biosensor exhibits a good response to glucose with a wide linear range (0.06-6.0 mM) with a detection limit of 0.03 mM and a sensitivity of 13 mA M-1 cm(-2). We show that small size and homogeneous distribution of the Pd nanoparticles in combination with good conductivity and large surface area of the HCNFs lead to a H2O2 and glucose sensing platform that performs in the top range of the herein reported sensor platforms.
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| 12. |
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| 13. |
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| 14. |
- Malmgren, Joel, 1985-, et al.
(författare)
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C-2 Selective Arylation of Indoles with Heterogeneous Nanopalladium and Diaryliodonium Salts
- 2014
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley. - 0947-6539 .- 1521-3765. ; 20:42, s. 13531-13535
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Tidskriftsartikel (refereegranskat)abstract
- A simple and efficient method to prepare synthetically useful 2-arylindoles is presented, using a heterogeneous Pd catalyst and diaryliodonium salts in water under mild conditions. A remarkably low leaching of metal catalyst was observed under the applied conditions. The developed protocol is highly C-2 selective and tolerates structural variations both in the indole and in the diaryliodonium salt. Arylations of both NH indoles and N-protected indoles with ortho-substituted, electron-rich, electron-deficient, or halogenated diaryliodonium salts were achieved to give the desired products in high to excellent isolated yields within 6 to 15 h at room temperature or 40 °C.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Nitze, Florian, et al.
(författare)
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Synthesis and characterization of palladium carbon nanostructure composites
- 2011
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a synthesis approach to produce carbon nanostructures decorated with Pd nanoparticles. Helical carbon nanofibers were synthesized by CVD on Pd supported C 60 catalyst. Their structure has a high and unique surface area. They are an ideal candidate to be decorated with metallic nanoparticles. Nanostructures were functionalized by H 2O2, HNO3 or benzyl mercaptan. The attached functional groups improved the hydrophilicity of the surface and created attachment sites for Pd. Carbon nanotubes and helical carbon nanofibers were successfully decorated with Pd nanoparticles. Transmission electron micrographs clearly show the successful decoration of the carbon support. The influence of the support was investigated. The material was also characterized by a variety of methods such as selected area electron diffraction and thermo gravimetric analysis. The composites show highcatalytic activity towards formic acid, methanol and ethanol oxidation investigated by cyclic voltammetry.
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| 19. |
- Nitze, Florian, et al.
(författare)
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Synthesis of palladium nanoparticles decorated helical carbon nanofiber as highly active anodic catalyst for direct formic acid fuel cells
- 2012
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Ingår i: Electrochimica Acta. - Oxford : Elsevier BV. - 0013-4686 .- 1873-3859. ; 63, s. 323-328
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Tidskriftsartikel (refereegranskat)abstract
- We present a single metal approach to produce highly active catalyst materials based on Pd-decorated helical carbon nanofibers. Helical carbon fibers are synthesized by a chemical vapor deposition process on a C-60 supported Pd catalyst and the obtained fibers are functionalized by H2O2 followed by a decoration with Pd nanoparticles. Although transmission electron microscopy images show that the decoration is relatively inhomogeneous the electrocatalytic activity for formic acid oxidation is very high. Cyclic voltammetry measurements (CV) show that the generated current peak value for Pd-decorated helical carbon nanofibers is 300 mA/mg(Pd) for a scan rate of 10 mV/s. This is significantly higher than the corresponding value of a reference sample of multiwalled carbon nanotubes decorated with Pd nanoparticles by the same process. Fuel cell tests for our Pd-decorated helical carbon nanofibers also displayed a high power density, although not as superior to Pd-decorated multiwalled nanotubes as measured by CV. Our results show that helical carbon nanofibers have several good properties, such as a rigid anchoring of catalyst nanoparticles and a suitable structure for creating functionalization defects which make them an interesting candidate for electrochemical applications.
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| 20. |
- Oltean, Gabriel, et al.
(författare)
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On the origin of the capacity fading for aluminium negative electrodes in Li-ion batteries
- 2014
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 269, s. 266-273
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Tidskriftsartikel (refereegranskat)abstract
- The origin of the capacity loss for aluminium negative electrodes in Li-ion batteries has been studied for electrodeposited aluminium nanorod electrodes coated with Al2O3 layers of different thicknesses (i.e. a native oxide layer, 30 and 60 nm) mainly employing pouch cell voltammetric cycling versus metallic lithium. Whereas the capacity decreased continuously during cycling between 0.1 and 3 V vs. Li+/Li, good cycling stability was obtained when the cycling was carried out between 0.1 and 1 V vs. Li+/Li. Since no significant dependence of the cycling stability on the thickness of the alumina layer was found in any of the experiments, the observed loss of capacity is unlikely to have been caused by volume expansion effects. The latter is further supported by the finding that the capacity (obtained when cycling between 0.1 and 3 V vs. Li+/Li) decreased linearly with the inverse of the square root of the cycling time, indicating that the capacity loss was due to the loss of lithium as a result of lithium diffusion into the bulk of the aluminium electrodes. The latter is explained based on a lithium-aluminium alloying and dealloying model which complements previously published models.
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| 21. |
- Rengaraj, Selvaraj, et al.
(författare)
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Cauliflower-like CdS Microspheres Composed of Nanocrystals and Their Physicochemical Properties
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:1, s. 352-358
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Tidskriftsartikel (refereegranskat)abstract
- Cauliflower-like cadmium sulfide (CdS) microspheres composed of nanocrystals have been successfully synthesized by a hydrothermal method using poly(ethylene glycol) (PEG) as the template coordination agent and characterized by a variety of methods. Our experiments confirmed that the size of the CdS microspheres could be easily modified by controlling the chain length of PEG. Powder X-ray diffraction and Raman spectroscopy measurements revealed the cubic structure of the CdS microspheres; morphological studies performed by HR-SEM and HR-TEM methods showed the cauliflower-like structure of the synthesized CdS microspheres. Each microsphere was identified to be created by the self-assembly of CdS nanocrystals and is attributed to the oriented aggregation of the CdS nanocrystals around a polymer-Cd(2+) complex spherical framework structure. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) analysis confirmed the stoichiometries of the CdS microspheres. Diffuse reflectance spectrum (DRS) measurements showed that increasing the PEG chain length increased the band gap value of the CdS microspheres slightly, from 1.99 to 2.06 eV. The cauliflower-like CdS microspheres could be applied to photocatalytic degradation studies.
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| 22. |
- Rengaraj, Selvaraj, et al.
(författare)
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Self-Assembled Mesoporous Hierarchical-like In(2)S(3) Hollow Microspheres Composed of Nanofibers and Nanosheets and Their Photocatalytic Activity
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:9, s. 5534-5541
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Tidskriftsartikel (refereegranskat)abstract
- Novel template-free hierarchical-like In(2)S(3) hollow microspheres were synthesized using thiosemicarbazide (NH(2)NHCSNH(2)) as both a sulfur source and a capping ligand in a ethanol/water system. In this study, we demonstrate that several process parameters, such as the reaction time and precursor ratio, strongly influence the morphology of the final product. The In(NO(3))(3)/thiosemicarbazide ratios were found to effectively play crucial roles in the morphologies of the hierarchical-like In(2)S(3) hollow microsphere nanostructure. With the ratios increasing from two to four, the In(2)S(3) crystals exhibited almost spherical morphologies. The synthesized products have been characterized by a variety of methods, including X-ray powder diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible diffused reflectance spectroscopy (UV-vis DRS). XRD analysis confirmed the tetragonal structure of the In(2)S(3) hollow microspheres. The products show complex hierarchical structures assembled from nanoscale building blocks. The morphology evolution can be realized on both outside (surface) and inside (hollow cavity) the microsphere. The surface area analysis showed that the porous In(2)S(3) possesses a specific surface area of 108 m(2)/g and uniform distribution of pore sizes corresponding to the size of pores resulting from the self-assembled structures with flakes. The optical properties of In(2)S(3) were also investigated by UV-vis DRS, which indicated that our In(2)S(3) microsphere samples possess a band gap of similar to 1.96 eV. Furthermore, the photocatalytic activity studies revealed that the synthesized In(2)S(3) hollow microspheres exhibit an excellent photocatalytic performance in rapidly degrading aqueous methylene blue dye solution under visible light irradiation. These results suggest that In(2)S(3) hollow microspheres will be an interesting candidate for photocatalytic detoxification studies under visible light radiation.
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| 23. |
- Selvaraj, Rengaraj, et al.
(författare)
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A simple hydrothermal route for the preparation of HgS nanoparticles and their photocatalytic activities
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:30, s. 15371-15376
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Tidskriftsartikel (refereegranskat)abstract
- HgS nanoparticles have been successfully prepared by a hydrothermal method using polyethylene glycol (PEG) as stabilizing agent and characterized by a variety of methods. Our experiments confirmed that the size of the HgS nanocrystals could be easily modified by tuning the chain length of PEG. X-ray powder diffraction (XRD) results for the nanoparticles revealed the hexagonal structure of the HgS, i. e. a-phase known as cinnabar. Morphological studies performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that the synthesized nanocrystals were nanoparticles. Furthermore, a rational mechanism of the formation and evolution of the products was proposed. The optical properties of HgS were investigated by diffuse reflectance spectroscopy (DRS), which indicated that the band gap of the nanoparticles is slightly decreased from 2.05 to 2.00 eV as the average particle size decreases from 55 to 35 nm. Furthermore, the photocatalytic activity studies of the particles demonstrated their excellent photocatalytic performance in rapidly degrading aqueous methylene blue dye solution under visible light irradiation. These results suggest that HgS nanoparticles will be an interesting candidate of photocatalyst working in visible light range.
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| 24. |
- Shakeri, Mozaffar, et al.
(författare)
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Small Pd Nanoparticles Supported in Large Pores of Mesocellular Foam : An Excellent Catalyst for Racemization of Amines
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:47, s. 13269-13273
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Tidskriftsartikel (refereegranskat)abstract
- Highly dispersed palladium nanoparticles (1–2 nm) supported in large-pore mesocellular foam (MCF; 29 nm) were synthesized. The Pd-nanocatalyst/MCF system was characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The performance of the Pd nanocatalyst obtained was examined for amine racemization. The Pd nanocatalyst showed higher activity and selectivity toward racemization of (S)-1-phenylethyl amine than any other amine racemization catalyst reported so far and it could be reused several times. Our data from TEM and XRD suggest a restructuring of the Pd nanocatalyst from amorphous to crystalline and an increase in Pd nanocatalyst size during the racemization reaction. This led to an unexpected increase of activity after the first use. The Pd nanocatalyst obtained can be integrated with other resolving processes of racemic organic compounds to increase the yield of chiral organic products.
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| 25. |
- Sharifi, Tiva, et al.
(författare)
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Formation of nitrogen-doped graphene nanoscrolls by adsorption of magnetic gamma-Fe2O3 nanoparticles
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4, s. 2319-
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Tidskriftsartikel (refereegranskat)abstract
- Graphene nanoscrolls are Archimedean-type spirals formed by rolling single-layer graphene sheets. Their unique structure makes them conceptually interesting and understanding their formation gives important information on the manipulation and characteristics of various carbon nanostructures. Here we report a 100% efficient process to transform nitrogen-doped reduced graphene oxide sheets into homogeneous nanoscrolls by decoration with magnetic gamma-Fe2O3 nanoparticles. Through a large number of control experiments, magnetic characterization of the decorated nanoparticles, and ab initio calculations, we conclude that the rolling is initiated by the strong adsorption of maghemite nanoparticles at nitrogen defects in the graphene lattice and their mutual magnetic interaction. The nanoscroll formation is fully reversible and upon removal of the maghemite nanoparticles, the nanoscrolls return to open sheets. Besides supplying information on the rolling mechanism of graphene nanoscrolls, our results also provide important information on the stabilization of iron oxide nanoparticles.
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| 26. |
- Sharifi, Tiva, et al.
(författare)
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Nitrogen doped multi walled carbon nanotubes produced by CVD-correlating XPS and Raman spectroscopy for the study of nitrogen inclusion
- 2012
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 50:10, s. 3535-3541
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Tidskriftsartikel (refereegranskat)abstract
- High purity aligned nitrogen doped multi walled carbon nanotubes were synthesized by the catalytic chemical vapor deposition method using pyridine and Fe/Co (2:1 volume ratio) as the single C/N precursor and catalyst material. The average diameter of the synthesized tubes ranges between 29 nm and 57 nm and the nitrogen content of the tubes reaches a maximum of 9.2 (at.)% nitrogen. The effect of nitrogen doping on the Raman scattering of doped tubes and its correlation with X-ray photoelectron spectra (XPS) was investigated. The analysis is based on the investigation of the I-D/I-G (integrated area ratio), other nitrogen characteristic Raman modes and the type of nitrogen inclusion interpreted from the N 1s electron bonding energies in XPS. At doping levels higher than 5% the nitrogen inclusion takes place through another mechanism than at low nitrogen doping levels. Most significant is that pyridinic defects are relatively readily incorporated at low nitrogen doping levels while at nitrogen content higher than 5% the major incorporation mechanism is dominated by pyridinic and pyrrolic defects on an equal basis. Our study gives further insight into nitrogen doping effects and the relation between type of nitrogen inclusion and nitrogen doping levels.
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| 27. |
- Sobkowiak, Adam, et al.
(författare)
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Understanding and Controlling the Surface Chemistry of LiFeSO4F for an Enhanced Cathode Functionality
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:15, s. 3020-3029
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Tidskriftsartikel (refereegranskat)abstract
- The tavorite polymorph of LiFeSO4F has recently attracted a lot of interest as a cathode material for lithium ion batteries stimulated by its competitive specific capacity, high potential for the Fe2+/Fe3+ redox couple, and low-temperature synthesis. However, the synthesis routes explored to date have resulted in notably varied electrochemical performance. This inconsistency is difficult to understand given the excellent purity, crystallinity, and similar morphologies achieved via all known methods. In this work, we examine the role of the interfacial chemistry on the electrochemical functionality of LiFeSO4F. We demonstrate that particularly poor electrochemical performance may be obtained for pristine materials synthesized in tetraethylene glycol (TEG), which represents one of the most economically viable production methods. By careful surface characterization, we show that this restricted performance can be largely attributed to residual traces of TEG remaining on the surface of pristine materials, inhibiting the electrochemical reactions. Moreover, we show that optimized cycling performance of LiFeSO4F can be achieved by removing the unwanted residues and applying a conducting polymer coating, which increases the electronic contact area between the electrode components and creates a highly percolating network for efficient electron transport throughout the composite material. This coating is produced using a simple and scalable method designed to intrinsically favor the functionality of the final product.
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| 28. |
- Stingaciu, Marian, et al.
(författare)
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The magnetodielectric effect in BaTiO3-SrFe12O19 nanocomposites
- 2014
-
Ingår i: Journal of Materials Chemistry C: Materials for Optical and Electronic Devices. - : Royal Society of Chemistry (RSC). - 2050-7526. ; 2:2, s. 325-330
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Tidskriftsartikel (refereegranskat)abstract
- A nanoscale composite consisting of 30 vol% magnetic strontium hexaferrite SrFe12O19 embedded in a high dielectric permittivity matrix of BaTiO3 has been produced by the spark plasma sintering method. The morphology and phase composition were characterized by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) techniques. TEM micrographs indicate that no considerable grain growth occurs and different strained regions were formed by the sintering process. XRD investigations show no evidence of a chemical reaction between the constituents. The dielectric properties of such a nanocomposite were investigated versus temperature (50-300 K), frequency (100 Hz to 100 kHz) and magnetic field (0-5.6 Tesla). A magnetodielectric (MD) effect was detected in the whole studied temperature range. Above 150 K the occurrence of sharp magnetodielectric resonances around 1 kHz leads to a considerable enhancement of the effect. At temperatures below 150 K a positive MD effect was detected which is independent of the frequency.
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| 29. |
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| 30. |
- Tai, Cheuk-Wai
(författare)
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Ferroelectric domain morphology, electrical and electromechanical properties of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics
- 2011
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Ingår i: Ferroelectric and Multiferroic Materials. - : Springer Science and Business Media LLC.
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Konferensbidrag (refereegranskat)abstract
- Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics were fabricated by mixed-oxide route. The compositions along morphotropic phase boundary were investigated. Dielectric properties and piezoelectric coefficient were measured. The maximum relative permittivity is 33600 found in the (PIN-PT)x(PMN-PT)1-x ceramics with x = 0.1 at 167 °C. When increasing the amount of Pb(In1/2Nb1/2)O3, the piezoelectric coefficient of the ceramics decreases but the phase transition temperature increases. The selected-area electron diffraction patterns show the pseudo-cubic perovskite symmetry. Diffuse scattering is found in the diffraction pattern taken at higher order zone axis. Transmission electron microscopy study shows that the morphology of ferroelectric/ferroelastic domains is neither tetragonal nor rhombohedral configuration
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| 31. |
- Tai, Cheuk-Wai, et al.
(författare)
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Microwave assisted systhesis and magnetics studies of cobalt oxide nanoparticles
- 2010
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 125, s. 347-350
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Tidskriftsartikel (refereegranskat)abstract
- An efficient microwave-assisted route has been used to synthesize nanoparticles of cobalt oxide. The particles were well characterized by transmission electron microscopy (TEM) which showed that the average diameter of the particles is around 6 nm. X-ray diffraction (XRD) studies further confirmed the formation of the spinel Co3O4. Purity of the products was detected by Fourier transform infrared spectroscopy (FTIR) combined with thermal gravimetric analysis (TG/DTG). The magnetic measurements revealed a small hysteresis loop at room temperature indicating a weak ferromagnetic nature of the synthesized Co3O4 nanoparticles. The magnetic moment of the particles was measured to be 4.27 μeff.
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| 32. |
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| 33. |
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| 34. |
- Tai, Cheuk-Wai
(författare)
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Synthesis and characterization of carbon nanotubes decorated with gold nanoparticles
- 2010
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Ingår i: Acta Physica Polonica. A. - 0587-4246 .- 1898-794X. ; 118:3, s. 483-486
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Tidskriftsartikel (refereegranskat)abstract
- In presented work we report results of simple and viable method for producing Au/CNT composites. Chemicalcomposition and crystallographic structure of the Au/CNT composites was confirmed by X-ray diffractionmeasurements, while transmission and scanning electron microscopy were used to characterize the morphology ofnanocrystals as well as the distribution of nanocrystals in the composite. The obtained particles with relativelysmall diameter (less than 9 nm) were found to be spatially well dispersed on the carbon nanotubes. The densityof attached Au–nanoparticles is not sufficient, and cannot be improved by simple increasing gold loading.
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| 35. |
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| 36. |
- Talyzin, Alexandr, 1969-, et al.
(författare)
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Coronene Fusion by Heat Treatment : Road to Nanographenes
- 2011
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Ingår i: The Journal of Physical Chemistry C. - Washington : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:27, s. 13207-13214
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Tidskriftsartikel (refereegranskat)abstract
- The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500-700 degrees C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550 degrees C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550-600 degrees C by oligomerization into larger molecules. Above 600 degrees C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.
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| 37. |
- Tinnis, Fredrik, 1976-, et al.
(författare)
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Efficient Palladium-Catalyzed Aminocarbonylation of Aryl Iodides Using Palladium Nanoparticles Dispersed on Siliceous Mesocellular Foam
- 2014
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH Verlag GmbH & Co. KGaA. - 0947-6539 .- 1521-3765. ; 20:20, s. 5885-5889
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Tidskriftsartikel (refereegranskat)abstract
- A highly dispersed nanopalladium catalyst supported on mesocellular foam (MCF), was successfully used in the heterogeneous catalysis of aminocarbonylation reactions. During the preliminary evaluation of this catalyst it was discovered that the supported palladium nanoparticles exhibited a “release and catch” effect, meaning that a minor amount of the heterogeneous palladium became soluble and catalyzed the reaction, after which it re-deposited onto the support.
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| 38. |
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| 39. |
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| 40. |
- Verho, Oscar, et al.
(författare)
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Mild and Selective Hydrogenation of Nitro Compounds using Palladium Nanoparticles Supported on Amino-Functionalized Mesocellular Foam
- 2014
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Ingår i: ChemCatChem. - Weinheim : Wiley. - 1867-3880 .- 1867-3899. ; 6:11, s. 3153-3159
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Tidskriftsartikel (refereegranskat)abstract
- We present the utilization of a heterogeneous catalyst comprised of Pd nanoparticles supported on aminopropyl-functionalized siliceous mesocellular foam (Pd-0-AmP-MCF) for the selective hydrogenation of aromatic, aliphatic, and heterocyclic nitro compounds to the corresponding amines. In general, the catalytic protocol exclusively affords the desired amine products in excellent yields within short reaction times with the reactions performed at room temperature under ambient pressure of H-2. Moreover, the reported Pd nanocatalyst displayed excellent structural integrity for this transformation as it could be recycled multiple times without any observable loss of activity or leaching of metal. In addition, the Pd nanocatalyst could be easily integrated into a continuous-flow device and used for the hydrogenation of 4-nitroanisole on a 2.5 g scale, where the product p-anisidine was obtained in 95% yield within 2 h with a Pd content of less than 1 ppm.
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| 41. |
- Verho, Oscar, et al.
(författare)
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Nanopalladium on Amino-Functionalized Mesocellular Foam : An Efficient Catalyst for Suzuki Reactions and Transfer Hydrogenations
- 2013
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Ingår i: ChemCatChem. - : Wiley. - 1867-3880 .- 1867-3899. ; 5:2, s. 612-618
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Tidskriftsartikel (refereegranskat)abstract
- The applications of a heterogeneous Pd0-AmP-MCF nanoparticle catalyst in Suzuki cross-coupling reactions and transfer hydrogenations of alkenes are described. The catalyst was highly efficient for both transformations, resulting in 1)coupling of a wide range of aryl halides with various boronic acids in high yields and 2)chemoselective reduction of a variety of alkenes with the use of 1-methyl-1,4-cyclohexadiene as hydrogen donor. Moreover, the catalyst can be recycled several times without any significant decrease in activity or leaching of metal into solution, making the protocol economical and environmentally friendly. In the case of the Suzuki cross-coupling, a 15-fold increase in reaction rate was observed if the reaction was performed under microwave irradiation compared to conventional heating in an oil bath.
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| 42. |
- Verho, Oscar, et al.
(författare)
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Nanopalladium on Amino-Functionalized Mesocellular Foam as an Efficient and Recyclable Catalyst for the Selective Transfer Hydrogenation of Nitroarenes to Anilines
- 2014
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Ingår i: ChemCatChem. - : Wiley-VCH Verlagsgesellschaft. - 1867-3880 .- 1867-3899. ; 6:1, s. 205-211
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the use of nanopalladium on amino-functionalized siliceous mesocellular foam as an efficient heterogeneous catalyst for the transfer hydrogenation of nitroarenes to anilines. In all cases, the protocol proved to be highly selective and favored the formation of the desired aniline as the single product in high yields with short reaction times if naturally occurring and renewable -terpinene was employed as the hydrogen donor. Furthermore, the catalyst displayed excellent recyclability over five cycles and negligible leaching of metal into solution, which makes it an eco-friendly and economic catalyst to perform this transformation. The scalability of the protocol was demonstrated with the reduction of 4-nitroanisole on a 2g scale, in which p-anisidine was isolated in 98% yield.
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| 43. |
- Wei, Wei, et al.
(författare)
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High energy and power density TiO2 nanotube electrodes for 3D Li-ion microbatteries
- 2013
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 1:28, s. 8160-8169
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Tidskriftsartikel (refereegranskat)abstract
- Highly ordered anodic TiO2 nanotube arrays with a tube length of 9 mm are shown to provide areal capacities of 0.24 mA h cm(-2) (i.e. 96 mA h g(-1)) at a charge/discharge current density of 2.5 mA cm(-2) (corresponding to a rate of 5 C) and 0.46 mA h cm(-2) (i.e. 184 mA h g(-1)) at 0.05 mA cm(-2), when used as 3D free-standing anodes in Li-ion microbatteries. The present nanotube electrodes, which could be cycled for 500 cycles with only 6% loss of capacity, exhibited significantly higher energy and power densities, as well as an excellent cycling stability compared to previously reported TiO2-based Li-ion microbattery electrodes. The influence of parameters such as ordering, geometry and crystallinity of the nanotubes on the microbattery performance was investigated. A two-step anodization process followed by annealing of the nanotubes was found to yield the best microbattery performance. It is also demonstrated that the rate capability of the electrode depends mainly on the rate of the structural rearrangements associated with the lithiation/delithiation reaction and that the areal capacity at various charge/discharge rates can be increased by increasing the tube wall thickness or the length of the nanotubes, up to 0.6 mA h cm(-2) for 100 cycles.
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| 44. |
- Wei, Wei, et al.
(författare)
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High energy and power density TiO2 nanotube electrodes for 3D Li-ion microbatteries
- 2013
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Ingår i: Journal of Materials Chemistry A. - 2050-7488. ; 1:28, s. 8160-8169
-
Tidskriftsartikel (refereegranskat)abstract
- Highly ordered anodic TiO2 nanotube arrays with a tube length of 9 [small mu ]m are shown to provide areal capacities of 0.24 mA h cm-2 (i.e. 96 mA h g-1) at a charge/discharge current density of 2.5 mA cm-2 (corresponding to a rate of 5 C) and 0.46 mA h cm-2 (i.e. 184 mA h g-1) at 0.05 mA cm-2, when used as 3D free-standing anodes in Li-ion microbatteries. The present nanotube electrodes, which could be cycled for 500 cycles with only 6% loss of capacity, exhibited significantly higher energy and power densities, as well as an excellent cycling stability compared to previously reported TiO2-based Li-ion microbattery electrodes. The influence of parameters such as ordering, geometry and crystallinity of the nanotubes on the microbattery performance was investigated. A two-step anodization process followed by annealing of the nanotubes was found to yield the best microbattery performance. It is also demonstrated that the rate capability of the electrode depends mainly on the rate of the structural rearrangements associated with the lithiation/delithiation reaction and that the areal capacity at various charge/discharge rates can be increased by increasing the tube wall thickness or the length of the nanotubes, up to 0.6 mA h cm-2 for 100 cycles.
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| 45. |
- Wetterskog, Erik, 1983-, et al.
(författare)
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Anomalous Magnetic Properties of Nanoparticles Arising from Defect Structures : Topotaxial Oxidation of Fe1-xO|Fe3-δO4 Core|Shell Nanocubes to Single-Phase Particles
- 2013
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 7:8, s. 7132-7144
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Tidskriftsartikel (refereegranskat)abstract
- Here we demonstrate that the anomalous magnetic properties of iron oxide nanoparticles are correlated with defects in their interior. We studied the evolution of microstructure and magnetic properties of biphasic core|shell Fe1–xO|Fe3−δO4 nanoparticles synthesized by thermal decomposition during their topotaxial oxidation to single-phase nanoparticles. Geometric phase analysis of high-resolution electron microscopy images reveals a large interfacial strain at the core|shell interface and the development of antiphase boundaries. Dark-field transmission electron microscopy and powder X-ray diffraction concur that, as the oxidation proceeds, the interfacial strain is released as the Fe1–xO core is removed but that the antiphase boundaries remain. The antiphase boundaries result in anomalous magnetic behavior, that is, a reduced saturation magnetization and exchange bias effects in single-phase nanoparticles. Our results indicate that internal defects play an important role in dictating the magnetic properties of iron oxide nanoparticles.
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| 46. |
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| 47. |
- Wikberg, J Magnus, et al.
(författare)
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Magnetocrystalline anisotropy and uniaxiality of MnAs/GaAs(100) films
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:2, s. 024417-
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Tidskriftsartikel (refereegranskat)abstract
- We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature (Tc), and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants, the enhancement of the magnetic moment at saturation is significant. Results of x-ray magnetic circular dichroism show a behavior of the spin and orbital moment that is consistent with a structural transition at Tc. In particular, we find that the ratio of the orbital to the spin moment shows a marked increase in the coexistence region of the ferromagnetic α- and paramagnetic β-phases a result that is well in accord with the observed increase in the c/a ratio in the same temperature region. The ab initio density functional calculations reveal that the magnetic properties are more sensitive towards change in the ab-plane compared to change in the c-axis which is explained by the analysis of band structures. The effects of electron correlation in MnAs using ab initio dynamical mean field theory are also presented.
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| 48. |
- Zhang, Yunfan, et al.
(författare)
-
Coprecipitates Synthesis of CaIn2O4 and Its Photocatalytic Degradation of Methylene Blue by Visible Light Irradiation
- 2014
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 53:29, s. 11720-11726
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Tidskriftsartikel (refereegranskat)abstract
- Visible light-activated photocatalyst calcium indate (CaIn2O4) has been successfully prepared by a new approach with lower temperature calcinations. The sub-micrometer-sized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. High-purity CaIn2O4 particles were synthesized by controlling the sintering temperature and their photocatalytic performance were evaluated. Under visible light irradiation, 10 ppm of methylene blue solution was effectively degraded in 3.0 h. The excellent photocatalytic activity of CaIn2O4 is attributed to the high purity, small particle size, and large surface area because of lower sintering temperature by thermal decomposition of metal oxalate precursor.
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| 49. |
- Zhang, Yunfan, et al.
(författare)
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The influence of operating parameters on heterogeneous photocatalytic mineralization of phenol over BiPO4
- 2014
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 245, s. 117-123
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Tidskriftsartikel (refereegranskat)abstract
- The photocatalytic mineralization of phenol was investigated in the presence of BiPO4 prepared by hydrothermal method. The crystal structure and morphology of synthesized sample was inspected with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The photocatalytic activity of BiPO4 was evaluated by the degradation of phenol in a batch reactor under UV-C irradiation. In order to investigate the influence of catalyst dosage, pH value, initial concentration and additives on mineralization behavior, these key operating parameters were systematically changed during the photocatalytic process. The findings confirmed that the phenol was degraded by BiPO4 under UV-C irradiation, and the TOC (Total Organic Carbon) analysis proved that the mineralization was efficient under the optimized conditions. It is also found that the intermediate process between photocatalytic degradation and mineralization is negligibly short.
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