Nanohybrid layered double hydroxide materials as efficient catalysts for methanol electrooxidation.

In this work, efficient methanol oxidation fuel cell catalysts with excellent stability in alkaline media have been synthesized by including transition metals to the layered double hydroxide (LDH) nanohybrids. The nanohybrids CoCr-LDH, NiCoCr-LDH and NiCr-LDH were prepared by co-precipitation and their physicochemical characteristics were investigated using TEM, XRD, IR and BET analyses. The nanohybrid CoCr-LDH is found to have the highest surface area of 179.87 m2 g-1. The electrocatalytic activity measurements showed that the current density was increased by increasing the methanol concentration (from 0.1 to 3 M) as a result of its increased oxidation at the surface. The nanohybrid NiCr-LDH, showing the highest pore size (55.5 Å) showed the highest performance for methanol oxidation, with a current density of 7.02 mA cm-2 at 60 mV s-1 using 3 M methanol. In addition, the corresponding onset potential was 0.35 V (at 60 mV s-1 using 3 M methanol) which is the lowest value among all other used LDH nanohybrids. Overall, we observed the following reactivity order: NiCr-LDH > NiCoCr-LDH > CoCr-LDH, as derived from the impedance spectroscopy analysis.

Structural, morphological and optical properties of ZnSe quantum dot thin films.

ZnSe powder was prepared via hydrothermal technique using zinc acetate and sodium selenite as source materials. The prepared ZnSe powder was used for preparing film with different thickness values (95, 135 and 230 nm) via thermal evaporation technique. X-ray diffraction showed that the prepared powder has cubic zinc-blende structure with a space group, F43m. The high resolution transmittance electron microscope results show that the films are composed of spherical-shaped nanoparticles with a diameter in the range of 2-8 nm. The optical properties of ZnSe films with differing thicknesses are investigated by means of spectrophotometric measurements of the photoluminescence, transmittance and reflectance. The absorption coefficient of the films is calculated and the optical band gap is estimated. The refractive index of the films is determined and its normal dispersion behavior is analyzed on the basis of a single oscillator model, in which oscillator energy, dispersion energy and dielectric constant at high frequency are evaluated. Drude model is also applied to determine the lattice dielectric constant and the ratio of the carriers' concentration to their effective mass.

Optical properties and device characteristics of 2-(antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile thin films for photodiode applications.

2-(Antipyrin-4-ylhydrazono)-2-(4-nitrophenyl)acetonitrile (AHNA) films were deposited via thermal evaporation technique. The optical properties of AHNA films and electrical characteristics of Au/AHNA/n-Si/Au heterojunction diode have been reported. The optical properties of AHNA films were investigated using the spectrophotometric measurements of optical transmittance and reflectance over spectral range 190-2500 nm. The films have indirect allowed optical band gap of 3.6 eV. The refractive index of the films was calculated and the dispersion parameters of the films were determined on the light of the single oscillator model. The electrical properties of Au/AHNA/n-Si/Au heterojunction diode were studied in terms of current-voltage characteristics. The device showed rectification behaviour with a rectification ratio of 100 at ±1 V. The conduction mechanisms and diode parameters such as ideality factor, barrier height and series resistance of the device were determined. The device under illumination showed photovoltaic properties. The short circuit current and open circuit voltage were found to be function of illumination intensity. The device satisfies the conditions to be used as photodiode.