In this work, graphene oxide was synthesized by a modified Hummer method. In the first stage of preparation process, light brown color of the precursor was appeared, which means that there are some impurity phase in the outcome product. By changing some parameters such as time of mixing, modification the procedure of mixing materials, increasing the temperature and addition of deionized water and hydrogen peroxide separately, the color of sample turned to mustard yellow. Therefore, it means that graphene oxide without any impurity was gained. Then CoFe2O4−RGO nanocomposite were prepared by ball-milling at frequency about 25

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