سال:1391 | دوره: | شماره: |تعداد مقالات:5

One of the most convenient techniques for optical material fabrication is the sol-gel processing. It can be performed at low temperature that enables one to entrap even relatively unstable organic substances into silica matrix at the nanometer scale, thus developing homogeneous hybrid organic-inorganic nanocomposite materials of various functionalities. Here, novel hybrid organic-inorganic nanocomposites with good optical transparency and high third-order nonlinearity were prepared biomimetically through the mineralization of dendritic macromolecules (hyperbranched polyglycidols) using a compatible ethylene glycol-containing silica precursor. The synthesis was performed at neutral pH media in aqueous solutions without addition of organic solvents at ambient conditions owing to the catalysis of processing. Polyglycidols provided also the formation of gold nanoparticles localized in their core. They served as reducing and stabilizing agents. It is shown that trace amounts of nanoparticles could regulate nonlinear properties of a nanocomposite. High nonlinearity manifests itself in a supercontinuum generation at remarkably short lengthsca.1 mm. The phenomenon consists of filamentous intense white lighting due to the spectral broadening of initial ultrashort (femtosecond) laser pulses propagating through the material. The developed hybrid nanocomposites possessing large nonlinearity, high-speed optical response, stability under intense lighting, lowcost, and easy preparation are promising for a diverse range of applications as active components for all-optical signal processing from chemical sensing to biological cell imaging and lighting control in telecommunication.

Copper oxide nanoparticles were prepared and subsequently deposited onto surface of the cotton fibers by ultrasonic irradiation. The structure and morphology of the coated and un-coated cottons were examined by X-ray diffraction and scanning electron microscopy/energy dispersive X-ray analysis. These methods revealed that of CuO nanoparticles are crystalline and corresponds to monoclinic phase, and that these nanoparticles are physically adsorbed onto the cotton fiber surface. They have an average crystallite size of 10 nm, the physical and chemical properties of the treated cotton fibers are markedly different from those of the untreated cotton fibers. The CuOcotton fiber nanocomposites were tested against Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive) cultures and showed a significant antimicrobial activity, whereas its analogous CuS-coated cotton material formed by the reaction CuO-coated cotton fibers with H2S showed no activity.

Graphene wrapped BiVO4 (GW-BiVO4) photocatalyst is successfully synthesized via facile sol-gel method and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy techniques. The morphology of GW-BiVO4 looks like a human embryo embedded inside the amniotic sac. The photocatalytic performance of GW-BiVO4 for the decolorization of methylene blue is investigated. GW-BiVO4 system reveals enhanced photocatalytic activity for degradation of methylene blue in water under visible light irradiation as compare to pure BiVO4 catalyst and BiVO4 decorated on graphene sheet (GDBiVO4). The experimental result shows that the wrapping of the graphene sheets in this composite catalyst enhances the photocatalytic performance under visible light. This enhance activity is mainly attributed to the effective quenching of the photogenerated electron-hole pairs which confirmed by photoluminescence spectra. Trapping experiments of radicals and holes were performed to detect the reactive species generated in the photocatalytic system, experimental results found that the direct hole oxidation reaction is obviously dominant during the photocatalytic reactions on the GW-BiVO4 system.

A novel, simple, less time consuming and cost-effective sol–gel method has been developed to synthesize nano titania-silica with polyvinyl alcohol (PVA) composite relatively at low temperature in acidic pH. Titania sol is prepared by hydrolysis of titanium tetrachloride and was mixed with silicic acid and tetrahydrofuran mixture. The reaction was carried out under vigorous stirring for 6 h and dried at room temperature with the addition of PVA solution. The resulting powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared (FT-IR), UV-visible spectroscopy and thermal techniques. The grain size of the particles was calculated by X-ray diffraction, surface morphology and chemical composition were determined from scanning electron microscopy-energy dispersive spectroscopy, metal oxide stretching was confirmed from FT-IR spectroscopy, bandgap was calculated using UV-visible spectroscopy, and thermal stability of the prepared composite was determined by thermogravimetric/differential thermal analysis. Since TiO2 got agglomerated on the surface of SiO2, effective absorptive sites increase which in turn increase the photocatalytic efficiency of the resulting composite.

Nanocrystalline CuAlO2 was synthesized by mechanical alloying of Cu2O and a-Al2O3 powders in the molar ratio of 1: 1 for 20 h in toluene medium with tungsten carbide balls and vials using planetary ball mill. The ball milling was carried out at 300 rpm with a ball to powder weight ratio of 10: 1 and then annealed at 1373 K in a platinum crucible for 20 h to get CuAlO2 phase with average crystallite size 45 nm. Complex impedance spectroscopic measurement in the frequency region 1 Hz to 10 MHz between the temperatures 333 to 473 K was carried out for nanocrystalline CuAlO2 sample. The obtained complex impedance data was analyzed for AC conductivities, DC and AC conductivities correlations and crossover frequencies (fco). The BNN (Barton, Nakajima and Namikawa) relation was applied to understand the correlation between DC and AC conductivities. The observed experimental results were discussed in the paper.