Preparation And Properties Of Carbon-Coated Magnetic Nanocomposite Particles

Graphene possesses numbers of outstanding properties, such as high light transmittance, high thermal and electron conductivity, excellent mechanical strength, as well as highlight chemical and physical stability. aking advantages of these excellent properties, there exists a trend to prepare composites with other organic or inorganic nano-materials. These composites will possess much better properties in that not only own the excellent properties of graphene, but also introduce the synergistic effect.The graphene and metal nanoparticles composites is not only to remain graphene outstanding properties but also to protect nanoparticles from oxidation, and will improve the anti-oxygenic ability and stability in acid or base atmosphere for metal nanoparticles, as well as decrease the aggregation among nanoparticles, which expand largely the application domain. The traditional methods to prepare the graphene and metal nanoparticles composites include that arc discharge method, ion beam method, thermal decomposition method and chemical vapor deposition and so on. However, there exists disadvantages generally in these methods, such as high preparation cost, rigorous preparation condition, complex process and uncontrollable process parameters and so on. We employed the liquid polyacrylonitrile(LPAN) which prepared as carbon sources and CoO as metal precursor, and mixed different ratio of LPAN and CoO by ball milling method, and after oxidation at air, adopted thermal reduction method furthermore to obtain carbon coated cobalt magnetic nanoparticles composite(C-CoNPs). The method we used take advantage of mild process condition, controllable process parameter, lower preparation cost and high productivity, as well as accomplish the largely production and conquer the traditional preparation method disadvantages. At the same time, we employed XRD, SEM, Raman and other characterization methods to study the influences which the Co content, sintering temperature and reaction time made on the morphology and structures of Co nanoparticles, as well as studied magnetism of the prepared carbon coated cobalt magnetic nanoparticles. The obtained results have demonstrated as follow:1. Co content effect on the structure and performance of C-CoNPs composite have been studied. The results revealed that, at the same sintering temperature, the content of Co is wt%=20%、40%、50%、60%、80% respectively, the magnetic nanoparticles grain size and saturation magnetization increased with increasing the content of Co, however, the composites coercivity decreased with increasing the content of Co. When the sintering temperature was up to 1500oC which is over the Co melting point, because part of Co had melt outside resulting in the the magnetic nanoparticles grain size decreased with the content of Co increasing.2. The sintering temperature effect on the structure and performance of C-CoNPs composites at the same content of Co have been studied. The obtained results revealed that, when the sintering temperature was increased to 1500oC, the composites grain size would grow with increasing the temperature. The characterization results by Raman demonstrated that the obtained ID/IG for C-CoNPs decreased gradually from 1.02 at 900oC to 0.27 at 1500oC, and the results the carbon shell graphitization of Co@C had enhanced gradually increased with increasing the sintering temperature. The research on magnetism showed that the composites saturation magnetization increased and coercivity decreased gradually with increasing the sintering temperature.3. The sintering time effect on the structure and performance of C-CoNPs composites have been studied. The obtained results revealed that, when the sintering temperature was at 1300oC, sintering time made less influences on the crystalline degree and grain size of C-CoNPs composites. With increasing the sintering time, the carbon shell outside of C-CoNPs composites had been graphitization gradually. Among these resultants, when the sintering time was 4 hours, the composites had the best magnetism, and the saturation magnetism was up to 143.89emu/g with 80% Co content. These results demonstrated the obtained C-CoNPs composites did not make an effect on the magnetism of Co and showed good magnetism performance.4. The electrochemical of C-CoNPs composites, which the content of Co was 20% and the sintering temperature and time were 1300oC and 4 hours have been studied respectively, as anodes for Li-ion battery. The obtained results showed that the C-CoNPs possessed good electrochemical performance as anodes for Li-ion battery. At the current density was 200 mA g-1, the remained capacity was still 147mAh/g after 100 cycles and the capacity kept same after 20 cycles. The results demonstrated that the obtained C-CoNPs had wide promising as anodes for Li-ion battery.