Abstract A facile mechanochemical -based method for synthesis of copper oxide (CuO) nanoparticles is here by introduced . For this purpose, copper hydroxide powder was synthesized through a facile solution method (CuSO4+ 2Na(OH)→ Cu(OH)2+ Na2SO4) after which milling of as -prepared Cu(OH)2 precursor and NaCl resulted in the mechanochemical dehydration of Cu(OH)2 and dispersion of CuO nanoparticles into the salt matrix (Cu(OH)2+2NaCl=CuCl2+2NaOH and then CuCl2+2NaOH=CuO+2NaCl+H2O). Subsequently, washing the milled powders led to the removal of salt matrix and separation of CuO particles. The main advantages of the introduced method are synthesis of CuO nanoparticles with narrow size distribution without subsequent annealing during the process. The results of X-ray diffraction (XRD) indicated that the dehydration of Cu(OH)2 into CuO was completed after three hours of milling . Structural analysis using scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and particle size analyzer (PSA) showed that CuO particles had moderately equiaxed shape with sizes ranging from 10 -27 nm. Also, the results of UV –visible absorption spectroscopy indicated that CuO nanoparticles had a band gap of 2.5 eV

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