Exploring quantum Griffiths phase in Ni1-x V x nanoalloys.

Metallic Ni1-x V x alloys exhibit a ferromagnetic to paramagnetic disordered quantum phase transition in bulk. Such a phase transition is accompanied by a quantum Griffiths phase (QGP), featuring fractional power-law temperature dependences of physical variables, like magnetic susceptibility and specific heat, at low temperatures. As nanoparticles (NP's) usually exhibit properties significantly different from their bulk counterparts, it is intriguing to explore the occurrence of quantum Griffiths phase in Ni1-x V x nanoalloys. NP's of Ni1-x V x (0 ≤ x ≤ 0.17) alloys are prepared by a chemical reflux method. The structure and composition of the nanoalloys are determined by X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy techniques. Metallicity of the samples has been ensured by electrical resistivity measurements. DC magnetization results suggest that ferromagnetism persists in the NP's until x = 0.17. Low-temperature upturns in magnetic susceptibility and heat capacity hint at critical fluctuations evolving with V-doping. The fluctuations might stem from isolated Ni-clusters within the ferromagnetic NP, indicating a QGP region ranging from x = 0.085 to x ≫ 0.17.

Trapping of microwave radiation in hollow polypyrrole microsphere through enhanced internal reflection: a novel approach.

In present work, spherical core (polystyrene, PS)/shell (polypyrrole, PPy) has been synthesized via in situ chemical oxidative copolymerization of pyrrole (Py) on the surface of sulfonated PS microsphere followed by the formation of hollow polypyrrole (HPPy) shell by dissolving PS inner core in THF. Thereafter, we first time established that such fabricated novel art of morphology acts as a conducting trap in absorbing electromagnetic (EM) wave by internal reflection. Further studies have been extended on the formation of its silver nanocomposites HPPy/Ag to strengthen our contention on this novel approach. Our investigations showed that electromagnetic interference (EMI) shielding efficiency (SE) of HPPy (34.5-6 dB) is significantly higher compared to PPy (20-5 dB) in the frequency range of 0.5-8 GHz due to the trapping of EM wave by internal reflection. We also observed that EMI shielding is further enhanced to 59-23 in 10 wt% Ag loaded HPPy/Ag-10. This is attributed to the simultaneous contribution of internal reflection as well as reflection from outer surface. Such high EMI shielding capacity using conducting polymers are rarely reported.

Synthesis, characterization and photocatalytic activity of magnetically separable hexagonal Ni/ZnO nanostructure.

The hexagonal zinc oxide coated nickel (Ni/ZnO) nanostructure photocatalyst has successfully been prepared by the reduction of nickel chloride hexahydrate using hydrazine hydrate through the solvothermal process at 140 °C followed by surface modification of the product by the reflux method at 110 °C for 1 h. The X-ray diffraction (XRD) pattern showed that the 'as prepared' sample consists of face centered cubic Ni and hexagonal wurtzite ZnO without any traces of impurity. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images confirmed the formation of nickel nanoparticles under solvothermal conditions. These nickel nanoparticles, when subjected to reflux, formed the hexagonal zinc oxide coated nickel nanostructure. Fourier transform infrared (FTIR) spectra, photoluminescence (PL) and Raman studies also confirmed the presence of zinc oxide in the hybrid nanostructure. The growth mechanism for the development of the hexagonal zinc oxide coated nickel (Ni/ZnO) nanostructure has also been proposed. The appearance of the hysteresis loop, in the as-prepared Ni/ZnO hybrid nanostructure, demonstrated its ferromagnetic character at room temperature. The hexagonal Ni/ZnO nanostructure also acts as an efficient photocatalyst in the degradation of methylene blue under ultraviolet light irradiation. It is observed that the catalytic efficiency of the hybrid nanocatalyst is better compared to pure zinc oxide. Most importantly, the Ni/ZnO catalyst could also be easily separated, simply by applying an external magnetic field, and reused.

Fabrication of gold nanoparticle assembled polyurethane microsphere template in trypsin immobilization.

The separation, reusability and high catalytic activity of bioconjugate remain challenging task in proteins bound gold nanoparticles. A facile synthetic route for the fabrication of gold nanoparticle assembled polyurethane microsphere template and immobilization of trypsin on gold/polyurethane surface to form trypsin-nanogold-polyurethane bioconjugate was developed. The bioconjugate was characterized by X-ray diffraction, Field emission scanning electron microscopy, Transmission electron microscopy, UV-visible, Fourier transform infrared, Fluorescence and Circular dichroism spectroscopy. The catalytic studies confirmed retention of approximately 40% of its original activity even after eight consecutive reaction cycles. The bioconjugate is also very effective for its separation from the reaction medium and exhibited significant enhanced stability over a wide range of pH and temperature compared to free trypsin. These findings clearly demonstrate that trypsin immobilized gold nanoparticle assembled polyurethane microsphere acts as an excellent recyclable biocatalyst with enzyme-specific biocompatibility.

A new hydrothermal route for synthesis of molybdenum disulphide nanorods and related nanostructures.

A simple approach to prepare nanorods of Molybdenum Disulphide (MoS2) using hydrothermal method by reacting aqueous solutions of (NH4)6Mo7O24.4H20, C2H4NS and Na2S2O4 at 190 degrees C for 24 h is described. The hydrothermal product has been subsequently subjected to the thermal treatment in nitrogen atmosphere at 675 degrees C for 6 h and characterized. X-ray diffraction (XRD) of the hydrothermal product indicated the formation of MoS2 relatively with much lower crystallinity compared to when it thermally treated. Energy dispersive analysis (EDX) was done to know the chemical composition of the product. TEM showed onset growth of MoS2 nanorods within the hydrothermal products itself and in thermally treated products it was prominent with the diameter of the nanorods ranging between 10-20 nm. Photoluminescence spectra MoS2 nanorods shows an intense absorbance at around 429 nm. TGA of the MoS2 nanorods in air and nitrogen atmosphere has also been studied. The extent of formation of MoS2 from the precursors obtained at 190 degrees C for duration of 12, 18, and 24 h and annealed at 675 degrees C for 6 h under nitrogen atmosphere is also demonstrated based on XRD data.

A simple hydrothermal method for the growth of Bi2Se3 nanorods.

Bi2Se3 nanorods have been synthesized through a simple hydrothermal reduction approach. The nanorods formed were ≈10 nm in diameter and 100-200 nm in length. XRD characterization suggested that the product consisted of the hexagonal phase of pure Bi2Se3. EDX and XPS studies further confirmed the composition and purity of the product. A possible mechanism for the reaction is proposed, where Bi2Se3 microsheets are presumed to be the intermediate for the formation of the nanorods. The effect of solvent on the morphology of the final product is discussed, where, in the presence of aprotic solvent DMF, nanoparticle formation is observed. A bandgap of 2.25 eV is observed from the UV-visible absorption spectra.

Low temperature micelle-template assisted growth of Bi(2)S(3) nanotubes.

The growth of Bi(2)S(3) nanotubes through a simple soft chemical route using the surfactant Triton-X 100 as the template at the relatively very low temperature of 115 degrees C/12 h has been reported for the first time. These nanotubes are nearly uniform in dimensions, with diameter around 120 nm and length up to 8 microm, their nature being single crystalline. The reaction conditions are optimized. Development of nanotubes and nanoparticles from the same precursor is discussed. The optical properties of the nanotubes are studied by means of UV-visible and photoluminescence spectra. The band gap calculated from the absorption spectra is found to be 1.76 eV, indicating a considerable blue shift relative to the bulk.