Functionalization of electrospun TiO2 nanofibers with Pt nanoparticles and nanowires for catalytic applications

This paper reports a simple procedure for derivatizing the surface of anatase TiO2 nanofibers with Pt nanoparticles and then Pt nanowires. The nanofibers were prepared in the form of a nonwoven mat by electrospinning with a solution containing both poly(vinyl pyrrolidone) and titanium tetraisopropoxide, followed by calcination in air at 510 degrees C. The fiber mat was then immersed in a polyol reduction bath to coat the surface of anatase fibers with Pt nanoparticles of 2-5 nm in size with controllable density of coverage. Furthermore, the coated fibers could serve as a three-dimensional scaffold upon which Pt nanowires of roughly 7 nm in diameter could be grown at a high density and with a length up to 125 nm. The fiber membranes functionalized with Pt nanoparticles and nanowires are interesting for a number of catalytic applications. It was found to show excellent catalytic activity for the hydrogenation of azo bonds in methyl red, which could be operated in a continuous mode by passing the dye solution through the membrane at a flow rate of 0.5 mL/s.     

Facile synthesis of bimetallic nanoplates consisting of Pd cores and Pt shells through seeded epitaxial growth

Pd-Pt core-shell nanoplates with hexagonal and triangular shapes were synthesized through the heterogeneous, epitaxial growth of Pt on Pd nanoplates. The Pd nanoplates were synthesized by reducing Na2PdCl4 precursor with PVP as a reducing agent, which then served as seeds for the nucleation of Pt atoms formed by reducing H2PtCl6 with citric acid. Characterization of the as-prepared Pd-Pt nanoplates by scanning transmission electron microscopy and high-resolution transmission electron microscopy reveals that a thin, uniform Pt shell was formed around the Pd nanoplate, demonstrating the layer-by-layer epitaxial growth of Pt on Pd surface in this approach. The close lattice match between Pd and Pt (lattice mismatch of only 0.77%) and the slow reduction rate associated with the mild reducing power of citric acid play key roles in achieving the epitaxial growth of Pt shells on Pd nanoplates.     

Rheology of the gel formed in the California Mastitis Test

The California Mastitis Test has previously been adapted for use in an inline, cow-side sensor and relies on the fact that the viscosity of the gel formed during the test is proportional to the somatic cell concentration. In this paper, the use of capillary and rotational viscometry was compared in light of the expected rheology of the gel formed during the test. It was found that the gel is non-Newtonian, but the initial phase of viscosity increase was not due to shear dependence, but rather due to the gelation reaction. The maximum apparent viscosity of the gel was shear dependent while the time it took to reach the maximum was not truly shear dependent, but was rather dependent on the degree of mixing during gelation. This was confirmed by introducing a delay time prior to viscosity measurement, in both capillary and rotational viscometry. It was found that by mixing the reagent and infected milk, then delaying viscosity measurement for 30 s, shortened the time it took to reach maximum viscosity by more than 60 s. The maximum apparent viscosity, however, was unaffected. It was found that capillary viscometry worked well to correlate relative viscosity with somatic cell count, but that it was sensitive to the reagent concentration. It can therefore be deduced that the rheology of the gel is complicated not only by it being non-Newtonian, but also by the strong dependence on test conditions. These make designing a successful sensor much more challenging.     

Bundled tungsten oxide nanowires under thermal processing

Ultra-thin W(18)O(49) nanowires were initially obtained by a simple solvothermal method using tungsten chloride and cyclohexanol as precursors. Thermal processing of the resulting bundled nanowires has been carried out in air in a tube furnace. The morphology and phase transformation behavior of the as-synthesized nanowires as a function of annealing temperature have been characterized by x-ray diffraction and electron microscopy. The nanostructured bundles underwent a series of morphological evolution with increased annealing temperature, becoming straighter, larger in diameter, and smaller in aspect ratio, eventually becoming irregular particles with size up to 5?μm. At 500?°C, the monoclinic W(18)O(49) was completely transformed to monoclinic WO(3) phase, which remains stable at high processing temperature. After thermal processing at 400?°C and 450?°C, the specific surface areas of the resulting nanowires dropped to 110?m(2)?g(-1) and 66?m(2)?g(-1) respectively, compared with that of 151?m(2)?g(-1) for the as-prepared sample. This study may shed light on the understanding of the geometrical and structural evolution occurring in nanowires whose working environment may involve severe temperature variations.     

Removal of ammonia from gas streams with dielectric barrier discharge plasmas

We reported on the experimental study of gas-phase removal of ammonia (NH3) via dielectric barrier discharge (DBD) at atmospheric pressure, in which we mainly concentrated on three aspects--influence of initial NH3 concentration, peak voltage, and gas residence time on NH3 removal efficiency. Effectiveness, e.g. the removal efficiency, specific energy density, absolute removal amount and energy yield, of the self-made DBD reactor had also been studied. Basic analysis on DBD physical parameters and its performance was made in comparison with previous investigation. Moreover, products were detected via ion exchange chromatography (IEC). Experimental results demonstrated the application potential of DBD as an alternative technology for odor-causing gases elimination from gas streams.     

Nanomaterials at work in biomedical research

With some nanomaterial-based medicines having entered the marketplace, and more on the verge of doing so, nanomedicine is expected to become an exciting playground for chemists and material scientists.     

Synthesis and characterization of surface-functionalized conducting polyaniline-chitosan nanocomposite

We describe in this paper an easy route to the synthesis of a novel surface-functionalized conducting polyaniline-chitosan nanocomposite. A stable colloidal dispersion was prepared when aniline was polymerized in the presence of chitosan as the steric stabilizer. TEM study shows that these surface-functionalized polyaniline-chitosan nanoparticles have rice-grain morphologies. The effect of reaction parameters on the mean size of the polyaniline-chitosan nanoparticles was studied. The steric electrostatic interaction between segments of these two polymers explains the excellent storage stability of the polyaniline-chitosan dispersion. Reaction parameters were optimized in order to get stable polyaniline-chitosan dispersion. The chemical structures of polyaniline-chitosan nanocomposite were characterized. FT-IR spectra of the polyaniline-chitosan nanocomposite show that there exist a certain interaction between polyaniline and chitosan. X-ray photoelectron spectroscopy spectra show that chitosan is largely present at the surface of polyaniline-chitosan nanoparticles. The electrical conductivity of the polyaniline-chitosan nanocomposite increases with increasing the amount of polyaniline to a high value of 0.25 S/cm.     

Monodispersed spherical colloids of Se@CdSe: synthesis and use as building blocks in fabricating photonic crystals

Monodispersed spherical core-shell colloids of Se@Ag(2)Se have been exploited as a chemical template to synthesize Se@CdSe core-shell particles using a cation-exchange reaction. A small amount of tributylphosphine could facilitate the replacement of Ag(+) by Cd(2+) in methanol at 50 degrees C to complete the conversion within 150 min. The orthorhombic structure of beta-Ag(2)Se changed to a well-defined wurtzite lattice for CdSe. The CdSe shells could be converted back to beta-Ag(2)Se by reacting with AgNO(3) in methanol at room temperature. Because of the uniformity in size and high refractive index associated with the Se@CdSe core-shell colloids, they could serve as a new class of building blocks to fabricate photonic crystals with wide and strong stop bands.