Preparation Of Co/C Composites Based On MOFs-like Material ZIF-67 And Their Microwave Absorption Prformance

With the development of science and technology,the electromagnetic interference problem has become increasingly serious.As a universal strategy in dealing with electromagnetic pollution,electromagnetic interference,and military stealth,microwave absorption has received considerable attention in the past decade.The magnetic metal/carbon composite material has both dielectric and magnetic loss mechanisms,and has a low material density to meet people's requirements for new types of microwave absorbing materials.And the direct pyrolysis of metal-organic frameworks(MOFs)has become a highly attractive preparation technology for the preparation of magnetic metal/carbon composites.However,the synthesis method of magnetic metal/carbon composites suffer from poor controllability of morphology and composition content.Therefore,ZIF-67 was chose to prepare Co/C composites based on the MOFs derivative method.The key point is the controllable preparation of the material's morphology and components,and their microwave absorption performance were studied.A Co/C composite(Co/C-HS)with a hollow structure was designed and synthesized.It was found that the higher pyrolysis temperature was beneficial to the improvement of crystallinity,metal particle size,carbon graphitization,and magnetic properties of the material.The experimental results show that the microwave absorption properties of Co/C composites are relatively good when the preparation temperature is 600 oC.Compared with the Co/C composite obtained by pyrolyzing ZIF-67,Co/C-HS has a larger complex permittivity,stronger electromagnetic wave loss,and better impedance matching,which were due to the existence of hollow structures.The maximum reflection loss value reaches up to-66.5 d B at 17.6 GHz with the absorber thickness of 1.53 mm and its response bandwidth(over-10.0 d B,90% absorption)can cover the frequency range of 3.7-18.0 GHz by manipulating the absorber thickness from 1.0 to 5.0 mm.The core-shell Co/C composites with different component contents were further synthesized.In the scope of this paper,as the carbon content in the material increases,the complex permittivity and the dielectric loss capability of the material increases.However,the excessively high dielectric loss ability can not bring better impedance matching to the material.It couldn't improve the electromagnetic wave absorption performance of the material.Therefore,the microwave absorption performance of Co/C-3 is the best,the maximum reflection loss value reaches up to-68.4 d B at 17.8 GHz with the absorber thickness of 1.4 mm and its response bandwidth can cover the frequency range of 3.4-18.0 GHz by manipulating the absorber thickness from 1.0 to 5.0 mm.The research results can provide new ideas for the synthesis of new wave absorbing materials.