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Nanosized alumina (Al2O3) powders had been successfully fabricated by a simple polymer solution route employing polyvinyl alcohol (PVA) as an organic carrier. The fabricated alumina powders had an average particle size of 6.1 nm with a high specific surface area of 99.5 m2/g. As well, the alumina powders were fully crystallized to alpha phase at a relatively low temperature of 1000 degrees C. The PVA polymer contributed to a soft and porous microstructure of the calcined alumina powders, and ball-milling process with the porous powders was effective in making nanosized alumina powders. In addition, the content and degree of polymerization of the PVA affected the development of crystallization and powder properties. In this study, the simple polymer technique and milling process for the fabrication of nanosized alumina powders are introduced, and the effects of PVA on the property of the synthesized alumina powders are observed. For the study, the characterizations of the synthesized powders are conducted by using XRD, TEM, particle size analyzer, and nitrogen gas adsorption.
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PMID:Fabrication of nanosized alumina powders by a simple polymer solution route. 1725 26

Morphologies of surface micelles of the diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) at different concentrations were investigated using TEM. Highly-ordered spherical micelles were observed. The morphology was found to depend strongly on the solution concentration. A transformation from spherical to cylindrical micelles and the formation of multilayers of micelles were observed when the concentration was increased. The evolution of the morphology of the diblock copolymer film cast on Si substrates in the presence of different solvents was also investigated using AFM. We find that there is a discrepancy in the structure obtained using TEM and AFM because of the presence of a selective solvent in the TEM sample. The transformation from cylindrical to spherical micelles was observed for the film prepared under a nitrogen atmosphere. Hexagonally ordered holes were observed in the film prepared in air. The presence of moisture in the air may play an important role in the formation of this structure.
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PMID:Morphology evolution in a diblock copolymer film. 1725 50

Mesoporous titania nanorod/titanate nanotube composites were prepared using TiF4 and H(3)BO(3) as the precursors. The prepared samples were characterized with TEM, SEM, XRD, HRTEM, and nitrogen adsorption-desorption isotherms. The photocatalytic activities were evaluated by photocatalytic oxidation of acetone in a gas phase and photocatalytic discolorization of methyl orange aqueous solution in an aqueous phase, respectively. The results indicated that the photocatalytic activity of the mesoporous titania nanorod/titanate nanotube composites exceeded that of P25 by a factor of about 2.5 times for the photocatalytic oxidation of acetone. This could be attributed to the fact that the former had a larger specific surface area and a higher pore volume. Moreover, the mesoporous titania nanorod/titanate nanotube composites, which could be readily separated after photocatalytic reaction in an aqueous phase, exhibited highly photocatalytic activity for the degradation of methyl orange aqueous solution.
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PMID:Synthesis, characterization and photocatalytic activity of mesoporous titania nanorod/titanate nanotube composites. 1729 35

Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation.
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PMID:Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor. 1730 71

A series of WO3/SBA-15 materials with different Si/W ratios have been prepared by impregnating the host material SBA-15 with aqueous ammonium paratungstate solutions. After temperature-programmed carburization (TPC) in flowing CH4/H2 (20/80 v/v mixture), the materials are converted to the corresponding W2C/SBA-15 species. Both the oxide and carbide materials are characterized using X-ray diffraction, nitrogen adsorption-desorption, 29Si NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and TEM measurements. The XRD results show that after impregnation with different amounts of tungsten and subsequent carburization, the materials retain the mesopore structure of SBA-15. The nitrogen adsorption-desorption results indicate that a thin layer of W2C covers the internal walls of SBA-15. Quantitative 29Si single-pulse excitation MAS experiments and FTIR spectroscopy show that the incorporation of W2C in the channels of SBA-15 is correlated with the formation of Si-O-W bonds. Some Si-O-W bonds are transformed into Si-O-H bonds after carburization. The TEM results show that the thickness of the W2C thin layer is 1.7-1.9 nm in W2C/SBA-15. A model involving a discrete W2C thin layer in the channels of SBA-15 is proposed on the basis of the NMR data. The calculated thickness of the discrete W2C thin layer is consistent with value given by HRTEM.
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PMID:Preparation and characterization of tungsten carbide confined in the channels of SBA-15 mesoporous silica. 1738 15

A study of the synergistic tuning of nitrogen-doped carbon nanotubes (NCNTs) as support- and size-monodisperse platinum nanoparticles templated from G4-NH2 dendrimers (Pt-DEN's) as catalysts targeted toward oxygen reduction is reported. UV-vis spectroscopy, adsorption isotherms, TGA, TEM, and voltammetry were used to characterize the loading and activity of Pt-DENs immobilized on CNT and NCNT supports. The facile uptake of Pt-DENs was found to be influenced by the number of edge plane sites on the NCNT support with higher adsorption rates observed for NCNTs with increased nitrogen content. Pt-DEN/NCNT composites exhibit high activity with a mass-transport-limited current density and mass activity of 2.3 mA cm(-2) and 0.05 mA g(-1), respectively, for the oxygen reduction reaction (ORR).
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PMID:Synergistic assembly of dendrimer-templated platinum catalysts on nitrogen-doped carbon nanotube electrodes for oxygen reduction. 1742 74

A high-temperature reductive sulfuration method is demonstrated to synthesize highly ordered mesoporous metal sulfide crystallites by using mesoporous silica as hard templates. H2S gas is utilized as a sulfuration agent to in situ convert phosphotungstic acid H3PW12O40.6H2O to hexagonal WS2 crystallites in the silica nanochannels at 600 degrees C. Upon etching silica, mesoporous, layered WS2 nanocrystal arrays are produced with a yield as high as 96 wt %. XRD, nitrogen sorption, SEM, and TEM results reveal that the WS2 products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure (space group, p6mm) and rodlike morphology, analogous to the mother template. The S-W-S trilayers of the WS2 nanocrystals are partially oriented, parallel to the mesochannels of the SBA-15 template. This orientation is related with the reduction of the high-energy layer edges in layered metal dichalcogenides and the confinement in anisotropic nanochannels. The mesostructure can be 3-D cubic bicontinuous if KIT-6 (Iad) is used as a hard template. Mesoporous WS2 replicas have large surface areas (105-120 m2/g), pore volumes ( approximately 0.20 cm3/g), and narrow pore size distributions ( approximately 4.8 nm). By one-step nanocasting with the H3PMo12O40.6H2O (PMA) precursor into the mesochannels of SBA-15 or KIT-6 hard template, highly ordered mesoporous MoS2 layered crystallites with the 2-D hexagonal (p6mm) and 3-D bicontinuous cubic (Iad) structures can also be prepared via this high-temperature reductive sulfuration route. When the loading amount of PMA precursor is low, multiwalled MoS2 nanotubes with 5-7 nm in diameter can be obtained. The high-temperature reductive sulfuration method is a general strategy and can be extended to synthesize mesoporous CdS crystals and other metal sulfides.
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PMID:Synthesis of highly ordered mesoporous crystalline WS(2) and MoS(2) via a high-temperature reductive sulfuration route. 1762 61

Zinc oxide nanoparticle was obtained by zinc hydrate deposited on the silica nanoparticle surface and zinc hydrate was dispersed in starch gel. The structure of zinc oxide particle was characterized by nitrogen adsorption-desorption and XRD, the morphology was observed by TEM. The result showed that the zinc oxide nanoparticle deposited on the silica nanoparticle surface was well-dispersed and less than 50nm, displayed higher photocatalytic activity for methylene blue degradation. However, the zinc oxide nanoparticle in a size of 60nm was derived from starch gel and showed poorer photocatalytic activity. It provided a simple and effective route to prepare zinc oxide nanoparticle with higher photocatalytic activity through depositing zinc oxide on the silica particle surface, moreover, the catalyst is easier to recover due to its higher density.
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PMID:Photocatalytic degradation for methylene blue using zinc oxide prepared by codeposition and sol-gel methods. 1768 8

The stability and oxidation of copper nanoparticles stabilized with various ligands have been studied. Lauric acid-capped copper nanoparticles were prepared by a modified Brust-Schiffrin method. Then, ligand exchange with an excess of different capping agents was performed. Oxidation and stability were studied by UV-vis, XRD, and TEM. Alkanethiols and oleic acid were found to improve air stability. The oxidation resistance of thiol-capped copper nanoparticles was found to increase with the chain length of the thiol. However, excess thiol caused etching of the particles under nitrogen. With oleic acid no etching was observed under nitrogen. After oxidation, no traces of the ligand-exchanged particles were found, suggesting their dissolution due to excess ligand. Oleic acid protected the particles against oxidation better than the tested thiols at large excess (ligand-copper ratio 20:1).
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PMID:Influence of ligand structure on the stability and oxidation of copper nanoparticles. 1796 85

Nanocrystalline Lu2O3:Eu3+ was prepared by co-precipitation method using ammonium hydrogen carbonate and ammonium oxalic acid as precipitants, respectively. The crystal structure and morphology were analyzed by means of XRD and TEM. The resultant powders were sintered into transparent ceramics in vacuum and then in nitrogen without any additive. The surface morphology of the unpolished sintered specimens was characterized using SEM. The effect of different precipitants on microstructure of the nanopowders and transparency of the ceramics are compared. The excitation and emission spectra of Lu2O3:Eu3+ powders and ceramics were measured at room temperature by using synchrotron radiation as the light source. The fluorescence decay times of all specimens were analyzed. Luminescence of the ceramics decays faster than the corresponding nanopowders.
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PMID:Effects of precipitant on microstructure and luminescent properties of Lu2O3:Eu3+ nanopowders and ceramics. 1798 Oct 80


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