Advanced Materials Letters

A new preparation method of lamellar core-shell ZnO-(Si)-ZnO nanostructures with high specific surface area and high photocatalytic efficiency is presented in this article. This novel method is based on the application of controlled vacuum sublimation of the frozen liquid dispersion of silicon nanoparticles which were prepared by using the "top-down" process in cavitation Water Jet Mill disintegrator. The particle size of thus disintegrated silicon nanoparticles was measured by dynamic light scattering (DLS). Final product ZnO-(Si)-ZnO was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and amount of ZnO and Si was measured by energy dispersive x-ray spectroscopy (EDAX). Specific surface area was obtained from Brunauer-Emmett-Teller analysis (BET). The photocatalytic activity of ZnO-(Si)-ZnO nanostructure was verified by the decomposition of methylene blue (MB) solution. The Final nanomaterial shows a relatively high specific surface area of 134 m2/g and significantly higher photocatalytic activity compared to standard TiO2 (Degussa P25). Such procedure based on the controlled vacuum sublimation of frozen liquid of suitable metal salts could be a promising method for obtaining photocatalytic nanomaterials with higher specific surface area.

In continuation to our previous work, the superparamagnetic Fe3O4@Au core-shell type nanoparticles (NPs) were further characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), electrical conductivity, impedance and cyclic voltammetry measurements. From the analysis of DSC and TGA results with our Fe3O4@Au NPs of about 6.25 ± 0.6 nm size, we observed a clear endothermic peak at 310°C due to the decomposition of the oleic acid/oleylamine surface ligands and the particles found to contain more than 80% of the metallic content from the mixed compositions of gold and iron oxide were observed. Because of the conduction through the Fe3O4@Au grain, the impedance profile of the pellet exhibited a well-resolved semi-circle and an inclined spike in a far low-frequency region. The electrical conductivity of the Fe3O4@Au material found to be increased with an increase of temperature. The standard Gibbs free energy (ΔG) of the reaction provided a criterion for spontaneous changes in the equilibrium of the material. From the analysis of the results of ΔG, it appears that at 25°C temperature, ΔS found to be negative. The calculated enthalpy, ΔH = -0.635 kJ/mol, at the corresponding entropy of ΔS = -0.132 kJ/mol. Finally, the activation energy in temperature range of 25-200°C for the Fe3O4@Au core-shell material was calculated using Line fitting and the surface characterization by using cyclic voltammetry. The electrochemical redox property of the Fe3O4@Au shows quasi-reversible wave corresponding to Au 3+ /Au 2+ .In addition, the electrochemical parameters for Fe3O4@Au NPs of E c p < /sub>, E a p < /sub>, E o 1/2 and were also obtained. Since the Fe3O4@Au material has low activation energy at low temperature range which makes it a good candidate as an ion conductor and even has the potential uses in many solid state devices and also in the future prospects of electrochemistry applications.

Nanocrystalline NixCo1-xFe2O4 were synthesized and studied for their structural and magnetic properties. The effect of doping ion concentration on lattice parameter, crystallite size and the lattice strain pertaining to the ionic radii has been investigated. Electron microscopy supports the parameters and gives morphological view of the system. The magnetic measurement reveals the information on the effect of stoichiometry variation in existing superparamagnetism. Further, the spin dynamics and their role on dipolar interactions, extent of superexchange and spin-spin relaxation among nanoparticles have been investigated. Also, an attempt has been made to understand the UV irradiation effect on photosensitive Co 2+ ion on Ni ferrite by in-situ electron spin resonance measurements.