Catalysts have been widely used in industries and can be optimized by tuning the composition and chemical ordering of the elements involved in the nano-alloy. Among bi-metallic alloys, the Au-Cu system is of particular interest because it exhibits ordered phases at low temperatures. Nevertheless, the temperature at which these ordered structures are formed is totally unknown at the nanoscale. Consequently, to speed up the development of these catalysts, this paper theoretically predicts the structural phase transitions between ordered and disordered phases for the Au-Cu system by using nano-thermodynamics. Following the predictions, the suggested annealing temperatures have been carefully chosen and consequently, Au-Cu ordered nanocubes have been successfully synthesized through a solventless protocol. The results are fully supported by electron microscopy observations.
We report the synthesis of MWNTs/ZnO hybrid nanostructures. A simple, affordable, chemical procedure to functionalize MWNT with ZnO nanoparticles was performed. A significant portion of the surface of MWNTs is covered with ZnO nanoparticles, such particles form highly porous spherical nodules of 50-150 nm in diameter, sizes that are in values one order of magnitude larger than similar ZnO nanonodules reported in the literature. Hence, in the self-assembled nanocomposite the ZnO exhibits a large surface to volume ratio, which is a very advantageous property for potential catalytic applications. The resultant MWNTs/ZnO nanocomposites were characterized by X-ray diffraction, scanning and high-resolution transmission electron microscopy, and UV-Vis and Raman spectroscopies. The temperature coefficient of resistance (TCR) of the nanocomposites was measured and reported. The average TCR value goes from -5.6%/K, and up to -18%/K, on temperature change intervals from 10 K to 1 K, respectively. Based on TCR results, the nanocomposite MWNTs/ZnO prepared in this work is a promising material with potential application as a bolometric sensor.
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