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Abstract

ZnO nano-powders were used for the one-pot synthesis of pyrano[2,3- d]pyrimidines via the solvent-free multi-component reaction of aromatic aldehydes, 1,3-dimethylbarbituric acid and malononitrile, in good to excellent yields of products.

Abstract

Structural and optical properties of CdxZn1−x O (x = 0.0, 0.025, 0.050, 0.075, 0.1) nanopowder, synthesized by co-precipitation method have been investigated. The effect of annealing on the structural and morphological properties was studied using X-ray diffraction. The samples with x = 0.0 up to 0.075 exhibit wurtzite hexagonal phase, whereas, the sample with x = 0.1 shows two phases: wurtzite hexagonal ZnO and cubic CdO phase. This behavior is explained on the basis of solubility of CdO in ZnO. Energy Dispersive X-ray analysis (EDX) results revealed the existence of Cd, Zn, and O elements in the nanopowder. Transmission Electron Microscopy (TEM) images confirm that the particle size of the prepared samples is in nano range. The optical band gap values obtained from the absorption spectra show that absorption depends on Cd composition. By doping of ZnO with CdO, a red shift in the absorption edge was observed.

Abstract

Photocatalytic activity of TiO2 and ZnO nanopowders is studied depending on the morphology, grain sizes and method of synthesizing. Photocatalysis of the prepared powders was evaluated by degradation of the methylene blue aqueous solution. Absorbance spectra (190-100 nm) were measured during exposure of the solution to UV light. The relationships between the photocatalytic activity and the particle size, crystal polymorph phases and grain morphology were analyzed. The photocatalytic activity of prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile phase ratio. Comparison is given for the photocatalytic activity of ZnO nanopowders prepared by sol-gel and solar physical vapour deposition (SPVD) methods

Abstract

The (V,Al) co-doped ZnO nano-structured powders (Zn0.9-xV0.1AlxO, where x = 0.02, 0.03 and 0.04) were synthesized via the sol-gel technique and their structural and optical properties were investigated. The effect of Al concentration on the structural and optical properties of the Zn0.9-xV0.1AlxO nanopowders was studied using various techniques. The XRD patterns indicate that the samples have a polycrystalline wurtzite structure. The crystallite size increases with increasing the Al content and lies in the range of 23 to 30 nm. The lattice strain, estimated by the Stokes-Wilson equation, decreases when Al content increases. SEM and TEM micrographs show that Zn0.9-xV0.1AlxO powders are the agglomeration of nanoparticles having spherical and hexagonal shapes with dimensions ranging from 20 to 30 nm. FT-IR spectra show a distinct absorption peak at about 500 cm-1 for ZnO stretching modes and other peaks related to OH and H2O bands. Raman spectra confirm the wurtzite structure of the Zn0.9-xV0.1AlxO nanoparticles. The direct band gaps of the synthesized Zn0.9-xV0.1AlxO nanopowders, estimated from the Brus equation and the crystallite sizes deduced from XRD, are around 3.308 eV. The decomposition process of the dried gel system was investigated by thermal gravimetric analysis (TGA).

Abstract

Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the trans-crystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = Idef/Iexc in comparison with the undoped ceramics. Results characterise ZnO:In cera-mics with improved GBs properties as a prospective material for scintillators.

concentration (0.1 wt.%) in non-magnetic matrix of PEN-b-PTMO polymer. For this aim DC magnetometry and ferromagnetic resonance (FMR) spectroscopy at microwave frequency have been employed. Moreover, the influence of the 0.7(Fe 2 O 3 )/0.3(ZnO) nanocomposite on thermal properties of PEN-b-PTMO polymer have been studied by thermogravimetric analysis (TGA). 2 Experimental The 0.7(Fe 2 O 3 )/0.3(ZnO) nanopowder was synthesized by traditional wet chemistry method followed by calcination. A mixture of iron and zinc hydroxides was obtained by adding ammonia solution to the solution

TiO2. Sol. Energy Mater. C, 77(1), 65-82. DOI: 10.1016/S0927-0248(02)00255-6. 11. Huihu, W., Changsheng, X., Wei, Z., Shuizhou, C., Zhihong, Y. & Yanghai, G. (2004). Comparison of dye degradation efficiency using ZnO powders with various size scales. J. Hazard. Mater. B, 141(3), 645-652. DOI: 10.1016/j.jhazmat.2006.07.021. 12. Daneshvar, N., Rasoulifard, M.H., Khataee, A.R. & Hosseinzadeh, F. (2007). Removal of C.I. Acid Orange 7 from aqueous solution by UV irradiation in the presence of ZnO nanopowder. J. Hazard. Mater., 143(1-2), 95-101. DOI: 10.1016/j

temperature. The importance of this semiconductor lies in its potential applications in gas detection [ 1 ], varistors [ 2 ] and luminescent devices [ 3 ]. A considerable number of methods have been developed to improve the properties of ZnO nanopowders. Among these processes, the sol-gel process synthesis in a supercritical fluid medium is the most advantageous. It is simple, less expensive and allows the production of highly pure and ultrafine nanoparticles with a high degree of transparency [ 5 – 7 ]. Doping ZnO particles is generally carried out with transition metals