| Over the past few years, monodispersed hollow porous spheres composed of nanoscale particles have attracted intensive interest. The permeable shell microstructures with less agglomeration and high surface area lead them to be widely used in many fields such as photocatalyst, drug delivery, lithium ion batteries, gas sensors, magnetic and optical materials, etc. As an important ferromagnetic material, Co has been widely studied for electromagnetic (EM) wave absorption applications due to its high saturation magnetization (Ms) and large anisotropy field, which provide the possibility that Co has EM wave absorption at high frequency. Hollow porous Co spheres will probably provide more efficient EM wave absorption due to their good dispersion degree, hollow porous structure, low density, and large surface area. By now, few contributions have been presented exploring hollow porous Co spheres as EM absorption materials. Therefore, it is still a challenge to find new efficient route to synthesize hollow Co structures with high purity.In the meantime, Co3O4is one of the most significant semiconductor functional materials among diverse transitional metal oxides. It has stable chemical properties and specific magnetic performance, which makes it is has a wide range of applications, e.g. super capacitor, catalyst, gas sensor, lithium ion batteries and many other fields. The theoretical lithium ion capacity of Co3O4is relatively high (approximately890mAh g-1). Hence it received extensive attention of researchers to explore a simple synthetic method to prepare the high-capacity CO3O4as cathode materials of lithium ion battery recently.In this study, we demonstrate facile template-free methods to synthesize hollow porous cobalt spheres, porous flower-like Co3O4and ball-like Co3O4. The magnetic and EM wave absorption properties of hollow porous Co structures, the electrochemical performance of two kinds of Co3O4as cathode materials of lithium ion battery were investigated, which is specifically provided as follows:(1) We report a template-free approach to prepare hollow porous cobalt spheres by combining a facile solvent-thermal route with a chemical reduction process. After a series of control experiments, the ideal cobalt microspheres with diameter of approximately2-4μm have a shell thickness of～150nm. The hollow Co microsphere is built from particle-like ligaments with diameter of ca.80-150nm and there are a lot of pores with size of several tens nm on the shell. The hollow porous cobalt spheres exhibited Ms of163.0emu g-1and large coercivity (Hcj) of307.9Oe. The epoxy resin composites with30wt%and60wt%hollow porous cobalt sample showed efficient EM wave absorption characteristics (RL<-20dB) in ranges of11.3-18.0GHz and4.0-12GHz over absorber thicknesses of1.4-2.0mm and1.4-4.0mm, respectively. Our study demonstrates the potential application of hollow porous ferromagnetic materials as more efficient electromagnetic wave absorber.(2) We got the porous flower-like Co3O4and ball-like Co3O4by using a facile solvent-thermal route and a chemical calcining process with a series of control experiments. The results gained by FESEM, HRTEM and sorption analyzer show that the size of Co3O4flower is approximately4-5μm, and the petaloid two-dimensional sheets of the flower are built from nanoparticles. There are a large amount of pores on the sheets. Meanwhile, the diameter of the Co3O4spheres is about1-4μm. However, the Co3O4spheres are composed of a series of nanorods, among which there are a certain amount of pores. The morphologies and performance are mainly controlled by the calcination temperature. The flower-like Co3O4got by calcination of500℃achieves a reversible capacity of ～1200mAh g-1after110cycles at a current density of100mAh g－1. The ball-like Co3O4 got by got by calcination of500℃has a stable reversible capacity of～700mAh g-1after40cycles. We believe that by using doping method or composition materials, the electrochemical performance of Co3O4will be much better in the future. |
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