Green-synthesis And Property Studies Of Cobalt And Cobalt Oxides Nanomaterials In Opened System

Metallic Co and its oxide Co3O4 are important magnetic materials, which have broad application prospects. The development on their simple and mild preparation and morphology-controlled strategy are important topics, which are worthy of study for theoretical research and application. In this paper, metal Co and its oxide nanomaterials were prepared via a green synthesis method in an open system and these nanomaterials possess a series of characteristic parameters and would have many potential applications. We also did in-depth mechanism study of each reaction system. The main research results and innovations of the thesis are given in the following parts.First, Co microspheres of 2-5?m have been synthesized in aqueous-phase at room temperature with hydrazine hydrate as green reductive agent together with small molecule polyol (glycerin or glycol). The mechanism for the formation of microspheres was discussed. Through other synthesis route, uniformed Co microspheres of 600nm assembled by nanoplatelets were also synthesized by employing NaH2PO2 as reducing agent in a low-temperature aqueous system. We proposed the possible reaction process.Secondly, branched Co powders have been synthesized in aqueous at room temperature. We studied the effects of surfactant on the morphology and structure of samples and found that chain length of PEG as surfactant drastically influenced the morphologies of the produced cobalt crystals. Based on the investigation of reaction mechanism, we believe that the reasons for these variations may be caused by the interaction between magnetic properties of Co and direction of PEG. Appropriate citric acid was the key factor to complete the reduction of Co in which hydrazine hydrate was employed as reductive agent to prepare metal Co. In the course of the study, we innovatively found that participation of a small amount of Cu in the reaction system can not only substitute for citric acid to make reaction perform completely but also speed up the reaction. We have synthesized hexagonal Co nanoplates of 100nm in aqueous with help of Cu ions. The possible mechanism on Cu as catalyst was studied preliminarily.Finally, the preparation of Co3O4 powders in aqueous-phase and property evolution has been studied. Co3O4 nanocubes have been synthesized by aqueous precipitation method at low temperature, which can be stable suspension in aqueous or ethanol medium for several months. The as-prepared Co3O4 nanocubes extend improved electrocatalytic activities and decreased oxygen evolution potential in electrochemical reactions. Meanwhile, Co3O4 samples with different morphologies have been synthesized with different types of precipitator under a similar mild condition.In conclusion,different size of Co and Co3O4 nanomaterials with several dimensions are obtained by aqueous synthesis method. Our work gives an improved progress on the mild solution synthesis of Co nanomaterials.The synthesized methods used here are simple and the obtained Co and Co3O4 nanomaterials can be potential applied in magnetic devices, electrochemistry and catalysis.