Flower-shaped undoped and Ag-doped ZnO nanocrystals have been synthesized by a hydrothermal method. The nanocrystals have been investigated by x-ray powder diffraction and all the particles are found to show the wurtzite structure. Scanning electron microscopy and high resolution transmission electron microscopy reveal the flower-shaped structures of the samples consist of many pricklelike nanopetals. The x-ray photoelectron spectroscopy results provide evidence that Ag ions are mainly in the monovalent state and incorporated into the ZnO lattice at Zn2+ sites. It was found from the UV–visible spectra that the bandgap of ZnO decreases due to Ag doping. Excellent enhancement of luminescence properties in the green band is observed in Ag-doped ZnO nanocrystals. The origin of this enhancement was discussed. It was demonstrated that oxygen vacancies and a spin-split impurity band are the key factors for deep level emissions. We believe that the present approach is a very simple but effective one for synthesis of novel ZnO complex micro/nanostructures, and these flowerlike Ag-doped ZnO nanocrystals may have good prospects in scientific and industrial applications.
Natural fiber-reinforced polymer matrix composites have been increasingly used in automotive and other fields because of their good mechanical properties, low density, excellent damping properties and biodegradability. The objective of this work is to develop and characterize a high-performance lightweight kenaf fiber composite that is processed using unconventional processing methods, wet laid process followed with compression molding process. Kenaf fiber mats produced by wet laid process are stacked with high-density polyethylene films and compression molded into plates from which testing samples are prepared. The effects of fiber length, fiber content, and area density on the tensile properties are investigated. The composite samples with the best tensile properties are also evaluated in its flexural, compression, impact, and fire resistance performance. The processing-structure-property relations of the developed kenaf fiber high-density polyethylene composite are systematically studied, which can be broadly applied to other natural fiber composites.
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