| 1. |
- Chi, X, et al.
(författare)
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Structure and transport properties of the charge-transfer salt coronene - TCNQ
- 2004
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 16:26, s. 5751-5755
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Tidskriftsartikel (refereegranskat)abstract
- Coronene is a highly symmetric organic molecule whose molecular structure resembles a fragment of graphite. We have crystallized a charge-transfer complex based on coronene and TCNQ, and present crystal structure and transport properties. The complex adopts alternate stacking between coronene and TCNQ and the charge-transfer was estimated to be of the order of 0.3 by the structure and IR analysis of TCNQ. This degree of charge-transfer is larger than those of other hydrocarbon based charge-transfer complexes reported. We find semiconductor behavior with an optical gap of 1.55 eV and a transport gap of 0.49 eV. The Child's law mobility is estimated to be 0.3 cm(2)/Vs-this alone, with the small tran-sport gap suggests this compound might be attractive for device applications.
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| 2. |
- Crowley, T.A., et al.
(författare)
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Synthesis of metal and metal oxide nanowires and nanotube arrays within a mesoporous silica template
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:18, s. 3518-3522
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Tidskriftsartikel (refereegranskat)abstract
- Metallic nanowires of cobalt, copper, and iron oxide magnetite (Fe3O4) have been synthesized within the pores of mesoporous silica using a supercritical fluid inclusion technique. The mesoporous matrix provides a means of producing a high density of stable, hexagonally ordered arrays of highly crystalline nanowires. The formation of the metal and metal oxide nanowires within the silica mesopores was confirmed by transmission electron microscopy (TEM), N2 adsorption experiments, and powder X-ray diffraction (PXRD). The mechanism of nanowire formation within the mesopores appears to occur through the initial binding and coating of the pore walls with the metal atoms to form tubelike structures within the mesoporous template. The thickness of these tubes subsequently increases with further metal deposition until nanowires are formed. Additionally, the crystal structure of the cobalt nanowires formed within the mesoporous template can be readily changed by manipulating the density of the supercritical fluid phase.
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| 3. |
- Jannasch, Patric
(författare)
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Ionic conductivity in physical networks of polyethylene-polyether-polyethylene triblock copolymers
- 2002
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 14:6, s. 2718-2724
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Tidskriftsartikel (refereegranskat)abstract
- A self-assembling ABA triblock copolymer complexed with lithium bis(trifluorometliylsulfonyl)imide (LiTFSI) salt showed ion conductivities (sigma) approaching 10(-5) S/cm at 20 degreesC. The block copolymer had endblocks of polyethylene (PE) and midblocks of poly(ethylene oxide-co-propylene oxide) (PEOPO) and formed physical networks with PEOPO chains interconnected by crystalline PE domains. Thermal analysis showed a PEOPO glass transition at -68 degreesC and a PE melting point at 100 degreesC. When the melting region of the PE phase was reached, sigma of the electrolytes was found to increase sharply to attain the same level as the corresponding electrolyte based on the neat PEOPO precursor block. Furthermore, the level of sigma of the block copolymer electrolytes was found to be strongly dependent on the thermal history of the samples, and they showed a hysteresis behavior where sigma increased by a factor of approximate to3 after annealing above 110 degreesC. This may be explained by a reduction of the chain constraints of the PEOPO blocks in the physical network after annealing. The electrolytes behaved essentially like thermoplastics and were soft, tacky, self-supporting materials at room temperature.
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| 4. |
- Kim, D. K., et al.
(författare)
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Protective coating of superparamagnetic iron oxide nanoparticles
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:8, s. 1617-1627
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles are becoming increasingly important for several biomedical applications. For example, superparamagnetic magnetite nanoparticles with suitable biocompatible coatings are useful in magnetic resonance imaging, tissue engineering, and drug delivery, etc. In this study we report the synthesis of magnetite nanoparticles and the further coating of these particles by several types of protective layers. Thermodynamic modeling of the chemical system has been adopted as a rational approach to establish routes to better synthesis conditions for pure phase magnetite. Quantitative analysis of different reaction equilibria involved in the precipitation of magnetite from aqueous solutions has been used to determine optimum synthesis conditions. Superparamagnetic magnetite nanoparticles (SPION) with diameters of 6 and 12 nm have been prepared by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+ under inert atmosphere. Pure magnetite phase SPION could be observed from X-ray diffraction. Magnetic colloid suspensions containing particles with three different types of coatings (sodium oleate (NaOl), starch, and methoxypoly(ethylene glycol) (MPEG)) have been prepared by using different stabilization methods. SPION coatings were studied by determining the change of the surface charge by electrokinetic sonic amplitude (ESA) measurements, as a function of varying NaOl in the solution, where the amount of NaOl needed to form a stable suspension was determined. For stable suspension, the optimum concentration of sodium oleate (NaOl) chemisorbed at 2.5 g of SPION surface is 5.2 x 10(-7) M NaOl which shows maximum ESA value of 0.034 mPa(.)M/V. SPION coating by starch results in the formation of agglomerate. The agglomeration size of starch-coated SPION can be decreased by introducing H2O2 as an oxidizing agent; the resulting particle size is 42 nm as determined by dynamic light scattering (DLS). For the modification of SPION surfaces with MPEG, the surface was first silanized by 3-aminopropyltrimethoxy silane (APTMS) as a coupling agent with a thickness of two or three molecular layers. AFM image shows that each cluster includes several magnetite single particles with the cluster size around 120 nm. SPION, both coated and uncoated, have been characterized by several techniques. AFM was used to image the MPEG-coated SPION. FTIR study indicated that the different coating agents cover the SPION surface. Magnetic characterization was carried out using SQUID and Mossbauer spectroscopy.
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| 5. |
- Kim, D. K., et al.
(författare)
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Starch-coated superparamagnetic nanoparticles as MR contrast agents
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:23, s. 4343-4351
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Tidskriftsartikel (refereegranskat)abstract
- Superparamagnetic iron oxide nanoparticles (SPION) with suitable bio-compatible coatings have been used in biomedicine, particularly in magnetic resonance imaging (MRI), tissue engineering, and drug delivery applications. In this study, we describe the synthesis of SPION and its use for experimental in-vivo applications in MRI. SPION with a mean size of 6 nm have been prepared under inert atmosphere, in a polymeric starch matrix, by controlled chemical coprecipitation of magnetite phase from aqueous solutions containing suitable salts of Fe2+ and Fe3+. X-ray powder diffraction was used to confirm a pure magnetite phase for the SPION. The influence of oxidizing agents on the cleavage of the starch chains was investigated by changing the concentration of H2O2. An aqueous solution of H2O2/NaOH cleaves the glycosidic bonds and reduces the polymer chains to a critical average molecular weight. From the dynamic light scattering (DLS) size distribution, the bulk agglomeration size was decreased by approximately 50% of the bulk size when treated by H2O2. Freshly synthesized starch-coated SPION in buffered artificial cerebro-spinal fluid were injected into the brain parenchyma of anaesthetized rats for in-vivo monitoring. Analysis of T-2*-weighted images and T-2*-maps revealed formation of a. concentration gradient for the SPION at the injection site, indicating SPION dispersion in the living brain parenchyma from the center of the injection site toward the periphery. The starch-coated SPION show a biocompatibility and possibility of being transported in the extracellular space as well as being internalized in nerve cells.
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| 6. |
- Lettau, K, et al.
(författare)
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An esterolytic imprinted polymer prepared via a silica-supported transition state analogue
- 2004
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 16:14, s. 2745-2749
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Tidskriftsartikel (refereegranskat)abstract
- In this work we describe a new preparation method for an esterolytic imprinted polymer with catalytic sites on the surface. A template was prepared by immobilizing a transition state analogue (phosphoramidic acid derivative) of an esterolytic reaction within porous silica particles. Polymerization within the pores was carried out using 4-vinylimidazole as a functional monomer and divinylbenzene as a cross-linker. The polymer was released by dissolution of the silica support with hydrofluoric acid and catalytic properties were studied by incubation with three different 4-nitrophenylesters and spectrophotometric determination of the released 4-nitrophenol. For 4-nitrophenyl acetate an activity of 211 nmol min(-1) mg(-1) and a K-m value of 2.2 mmol L-1 was obtained.
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| 7. |
- Mikhaylova, Maria, et al.
(författare)
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BSA immobilization on amine-functionalized superparamagnetic iron oxide nanoparticles
- 2004
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 16:12, s. 2344-2354
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Tidskriftsartikel (refereegranskat)abstract
- Immobilization of bovine serum albumin (BSA) on surface-modified superparamagnetic iron oxide nanoparticles (SPION) has been performed by two different double-step immobilization approaches. The first approach consists of preparation of SPION by controlled chemical coprecipitation in the presence of BSA solution, whereas the second approach includes preliminary surface modification of SPION with an amine group using a coupling agent of 3-aminepropyltrimethoxysilane (APTMS). Both procedures are followed by 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride (EDC) activation with sequential immobilization of the layer of BSA. Additionally, an attempt to modify the surface of SPION with amine and carboxylic groups is undertaken by using L-aspartic acid (LAA). TEM shows that the particle size varies in the range 10-15 nm and does not change significantly after the coating process. The presence of BSA and amine groups on the surface of SPION is confirmed by FT-IR. Magnetic properties are investigated by VSM and results indicate that the superparamagnetic properties are retained for BSA-coated SPION while reducing the value of saturation magnetization (M-s). The binding capacity is estimated from thermo-gravimetric and chemical analyse;. APTMS-coated SPION show higher BSA binding capacity compared to that of coprecipitated SPION in the presence of BSA. In vitro tests have been performed after the functionalization of SPION with LAA and BSA. Human dermal fibroblasts are incubated with the surface-modified SPION for 6 and 24 h to observe cell behavior, morphology, cytoskeletal organization, and interactions between cell and SPION. BSA-coated SPION incubated with cells demonstrated a cell response similar to that of control cells, with no adverse cell damage and no endocytosis, whereas LAA-coated SPION show partial endocytosis without cytoskeletal disorganization.
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| 8. |
- Naydenov, Valeri, et al.
(författare)
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Palladium-containing zeolite beta macrostructures prepared by resin macrotemplating
- 2002
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 14:12, s. 4881-4885
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Tidskriftsartikel (refereegranskat)abstract
- A multistep procedure for the preparation of palladium-containing zeolite beta spheres using anion-exchange resin beads as shape-directing macrotemplates is presented. In a first step, resin beads are hydrothermally treated with zeolite beta synthesis solutions, and as a result resin-zeolite beta composite particles are obtained. In a second step, anionic palladium precursor species are introduced into the composite using the residual ion-exchange capacity of the resin. Finally, the ion exchanger is removed by calcination, leaving self-bonded palladium-containing zeolite beta spheres. The spheres obtained by the procedure were characterized by AAS, XRD, SEM, EDS, UV-vis DRS spectroscopy, nitrogen adsorption measurements, and chemisorption. Materials with controlled macroshape, porosity, and palladium content were prepared by the method.
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| 9. |
- Nissinen, T. A., et al.
(författare)
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MnCo2O4 preparation by microwave-assisted route synthesis (MARS) and the effect of carbon admixture
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 15:26, s. 4974-4979
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst spinel MnCo2O4 with particle size <30 nm was prepared by a novel microwave-assisted route. To determine the optimal amount of carbon needed as a microwave susceptor, varying amounts of amorphous carbon powder (7-26 wt %) were mixed with the aqueous solutions of Mn- and Co-nitrates. After heat treatment at 200degreesC in a conventional oven, the mixtures were heat-treated in a microwave oven (2.45 GHz) at a power of 350 W. The effect of the carbon amount on the formation and properties of the catalysts was studied. In this production method, 13 wt % of carbon was found to be the minimum needed for spinel MnCo2O4 formation. Most of the carbon was oxidized during the microwave treatment. When the carbon content in the nitrate-carbon mixture was increased beyond 13 wt %, the carbon content and the specific surface area of the final catalyst started to decrease. However, the carbon amount of 18 wt % in the initial nitrate-carbon mixture was found to be the most preferable when considering the catalytic activity of the spinel toward oxygen reduction reaction in alkaline electrolyte.
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| 10. |
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| 11. |
- Nyström, Andreas, et al.
(författare)
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Porphyrin-Cored 2,2-Bis(methylol)propionic Acid Dendrimers
- 2004
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 16:14, s. 2794-2804
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of dendron-coated porphyrins up to the fifth generation are described. Both free base and zinc-cored tetraphenylporphyrin (TPPH2 and TPPZn) were used, from which the dendrons were divergently grown using the anhydride of acetonide-protected bis-MPA (acetonide-2,2-bis(methoxy)propanoic anhydride). It is shown that a spacer must be attached to the porphyrin to increase the hydrolytic stability and allow synthesis of higher generations. Direct coupling of dendrons to the porphyrins was also investigated but failed to give full substitution of the porphyrin core. The absorption and fluorescence emission data for the TPPZn dendrimers indicate that the porphyrin configuration may change at higher generations. The hydrodynamic volume of the dendrimers is calculated from the polarization anisotropy decay data. It is shown that these bis-MPA dendrimers are significantly smaller than the same generation Frechet-type benzyl ether TPP dendrimer.
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| 12. |
- Paronen, M, et al.
(författare)
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Preparation of proton-conducting membranes by direct sulfonation. 1. Effect of radicals and radical decay on the sulfonation of poly(vinyl fluoride) films
- 2003
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 15:23, s. 4447-4455
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Tidskriftsartikel (refereegranskat)abstract
- The effect of irradiation treatment on the structure and sulfonation reactivity of polyvinyl fluoride (PVF) films was studied mainly with EPR and IR spectroscopy. The main radical species produced by electron irradiation are aliphatic radicals, whereas proton irradiation creates a significant amount of polyenyl radicals. The half-life time of the aliphatic radicals was about 6 h. FTIR study shows that sulfonation reaction of PVF is a single-stage process and thus the formed sulfonic acid structures do not react further and produce new structures. In addition, it is independent of the irradiation treatment. Despite the careful synthesis and removal of O 2 from the sulfonation solution, the most important side reaction produced by the sulfonation is the formation of C=O functionalities. Irradiation treatment increases the C=O content. Both the sulfonation time and sulfonation reagent concentration demonstrate similar linear correlation with the extent of oxidation. Therefore, the oxidation cannot be decreased by means of optimizing these variables. The only important factor allowing adjustment of the structure of the final membranes is the type of irradiation and radical decay in the case of proton irradiation. Irradiation with either electrons or protons did not increase the ion exchange capacity as measured with a titrimetric method. IR study of the samples showed, however, indication of the formation of derivates of sulfonic acid in the proton-irradiated samples containing radicals.
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| 13. |
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| 14. |
- Qinghua, Li, et al.
(författare)
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An investigation of the nucleation/crystallization kinetics of nanosized colloidal faujasite zeolites
- 2002
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 14:3, s. 1319-1324
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Tidskriftsartikel (refereegranskat)abstract
- two-stage varying-temperature technique was utilized to study the nucleation/crystallization kinetics of nanosized faujasite zeolites from clear solutions. At 100 C, the nucleation period of zeolite Y was determined to be about 6.5 days, which extended over almost the whole period of crystal growth. The crystallization kinetics of colloidal zeolite Y differed from those for another clear solution, colloidal zeolite system, namely, TPA-silicalite-1, where the nucleation and crystal growth were found to occur as separate processes. Despite the occurrence of simultaneous nucleation and crystal growth, the colloidal zeolite Y product had a crystal size distribution similar to that for TPA-silicalite-1. In addition, the influence of the growth-limiting nutrient (Na+) on the crystallization of zeolite Y was investigated. The sodium concentration in the synthesis solution could be controlled below a critical level to avoid the nucleation of zeolite A.
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| 15. |
- Skårman, Björn, et al.
(författare)
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Morphology and structure of CuOx/CeO2 nanocomposite catalysts produced by inert gas condensation: An HREM, EFTEM, XPS, and high-energy diffraction study
- 2002
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 14:9, s. 3686-3699
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Tidskriftsartikel (refereegranskat)abstract
- Inert gas condensation (IGC) has been employed to produce nanoparticles of the low-temperature combustion catalyst CuOx/CeO2. For the first time we have used a multiple heating crucible setup to tailor various morphologies over the whole compositional range (2-98% Cu). The factors that control the growth, structure, and morphology of the nanocomposite have been studied. A powerful combination of complementary characterization methods has been used to elucidate the catalytic synergistics of this material. Investigations by high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) are supported by X-ray photoelectron spectroscopy (XPS) and high-energy diffraction (HED) measurements. The nonstoichiometric CuOx/CeO2 composite displays an amorphous character consisting of aggregated CeO2 (ceria) nanocrystallites over which amorphous copper clusters (or a thin film of a solid solution) are finely dispersed. In the range 6similar to20% Cu, copper is predominantly located at the surface, which can give the material optimum catalytic properties. Development of crust structures, for example, core-shells, are formed in the 30similar to70% Cu concentration range and is attributable to a sequential oxidation of Ce followed by Cu and an ideal proportion of lattice expansion for the oxides. We suggest a model that illustrates the formation of the crust structure and may explain the observed extreme dispersion of copper on ceria. The helium gas pressure during the thermalization controls the crystal size and the degree of crystallite aggregation. Rounded particle shapes consisting of epitaxially interfaced nanocrystallites exhibit an X-ray amorphous character, while block-shaped crystals displaying sharp edges and distinct flat surfaces give rise to a higher X-ray crystallinity. Bulk CuO crystals were detected by high-energy diffraction above a 30% Cu content. However, the extreme copper dispersion is preserved even for higher copper contents, showing no limit of surface saturation.
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| 16. |
- Vayssieres, Lionel, et al.
(författare)
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Three-dimensional array of highly oriented crystalline ZnO microtubes
- 2001
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 13:12, s. 4395-4398
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Tidskriftsartikel (refereegranskat)abstract
- The ability to generate homogeneous particulate thin films of highly orientedand highly porous microparticles of a post transition metal oxide onto polycrystalline and single-crystalline substrates, at low cost, by a template-free, aqueous low-temperature coating process is demonstrated by the fabrication of a large three-dimensional array ofperpendicularly oriented hexagonal microtubes of crystalline zincite ZnO from an aqueous solution of zinc nitrate and methenamine.
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| 17. |
- Wang, ZC, et al.
(författare)
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High Li+-ion storage capacity and double-electrochromic behavior of sol-gel-derived iron oxide thin films with sulfate residues
- 2001
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 13:6, s. 1976-1983
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Tidskriftsartikel (refereegranskat)abstract
- FeSO4. 7H(2)O was precipitated with ammonia solution in the presence of H2O2 as an oxidant. The precipitate was washed slightly with deionized water and then peptized with acetic acid (ca. 60 mol %) to attain a homogeneous sol. Iron oxide films were fabricated by spin-coating the sol onto ITO-coated glass substrates and annealing at 350 degreesC or above. Structural and compositional analyses were done by TG-DTA, FTIR, XRD, TEM, and XPS. The results showed that sulfate residues were adsorbed on the surface of the Fe2O8 nanoparticles constituting the films by monodentate coordination with Fe(III) surface sites when heat treatment was carried out at less than or equal to 450 degreesC, while a conversion to bidentate occurred at 500 degreesC, As shown by the cyclic voltammograms results, the films annealed at 350 degreesC exhibited Li+-ion storage capacity as high as ca. 0.50 mC(.)cm(-2) per nanometer of the film thickness and showed double-electrochromic behavior depending on the extent of intercalation during the electrochemical lithium insertion/extraction processes. It is proposed that the adsorbed sulfate residues lead to the enhanced electroactivity of the iron oxide films by retarding crystallization and dehydration of the films. The high charge capacity and nearly optical passiveness of the iron oxide films suggest their promising applications as counter-electrodes in electrochromic devices.
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| 18. |
- Yan, Mingdi, et al.
(författare)
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Covalent immobilization of ultrathin polymer films by thermal activation of perfluorophenyl azide
- 2004
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 16:9, s. 1627-1632
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Tidskriftsartikel (refereegranskat)abstract
- The attachment of thin films on solid materials is an effective way to tailor the chemical and physical properties of the surface layer. In this article, we report an alternative approach to the covalent immobilization of ultrathin polymer films. The immobilization chemistry is based on the C-H/N-H insertion reaction of perfluorophenyl nitrenes that were generated by the thermal activation of perfluorophenyl azides (PFPAs). In the process, a silicon wafer was treated with PFPA-silane 1 to give a monolayer of azido groups on the surface. A polymer was then spin coated on the functionalized wafer and the sample was heated. Thermolysis produced perfluorophenyl nitrenes which underwent insertion reactions with the neighboring polymer chains. Removal of the excess polymer by solvent extraction resulted in nanometer-thick polymer thin films covalently attached to the wafer surface. Using polystyrene and poly(2-ethyl-2-oxazoline) as examples, covalently immobilized thin films with thicknesses ranging from a few to over a hundred A were obtained. The thickness of the film could be controlled by the type and the molecular weight of the polymer. Patterned polymer films were also fabricated using this method.
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| 19. |
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| 20. |
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