Fabrication And Electromagnetic Wave Absorption Properties Of Carbon-based Composites Derived From MOFs

With the rapid development of electronics and information industry,the problems of electromagnetic pollution are becoming increasingly serious.Therefore,there is an urgent demand for the basic research on composion,structural design and application of new high-efficiency electromagnetic wave absorption materials.Due to the well-aligned nanopores and open channel structures,metal-organic frameworks?MOFs?have been demonstrated to achieve porous carbon composites in which metal or metal oxide nanoparticles are evenly embedded.Carbon nanotubes?CNT?and reduced graphene oxide?r GO?are well electromagnetic wave absorbers owing to their unique structure,light weight and excellent dielectric properties.Therefore,the assembly of conductive networks by combining CNT or r GO with MOFs-derived carbon materials is beneficial to overcome the disadvantages of narrow absorption bandwidth and low absorption intensity of microwave absorbers,which shows theoretical significance and practical value in effectively controlling electromagnetic pollution.The main research contents and results of this thesis are shown as follows:?1?Low-dimensional carbon-supported Co Fe alloy@C nanocomposites with excellent electromagnetic wave absorption performances were fabricated.Magnetic quantum dot-like Co Fe alloy@C nanocomposites derived from Zn Co-MOFs using two-dimensional?2D?r GO or one-dimensional?1D?CNT as carriers for electromagnetic wave absorption were successfully synthesized by in-situ growth and pyrolysis.The conductive networks constructed by r GO or CNT enhanced the impedance matching and electromagnetic attenuation of composites,endowing Co Fe@C with distinguished electromagnetic wave absorption performance.The r GO-supported Co Fe@C composites annealed at 900oC?r GO-Co Fe@C-900?revealed a minimum reflection loss of?36.08 d B at the sample thickness of 3.0 mm and an effective absorption bandwidth?refection loss<?10 d B?of 5.17 GHz at 3.5 mm.Moreover,the CNT-supported Co Fe@C nanocomposites pyrolyzed at 900oC?CNT-Co Fe@C-900?exhibited optimum electromagnetic wave absorption performances due to the continuous three-dimensional?3D?conductive networks,the minimum reflection loss of?40.00 d B with the thickness of 3.0 mm,and effective absorption bandwidth reached 5.62 GHz with a thickness of 2.0 mm.In particular,the specific reflection loss values of low-dimensional carbon-supported Co Fe alloy@C nanocomposite significantly preceded that of the reported similar dielectric-magnetic hybrids.?2?Three-dimensional carbon nanotube arrays?3D CNT As?supported Co nanocomposites with excellent microwave aborption properties was also fabricated.The CNT As were fisrtly prepared by chemical vapor deposition?CVD?method,followed by ZIF-67 in-situ grown on CNT As and thermal pyrolysis at different temperatures to obtain the"sugar-coated haws on a stick"string-like CNT As@Co composites.The results indicated that the annealing of CNT As@ZIF-67 significantly enhanced the electromagnetic wave absorption performances due to the improvement of impedance matching degrees of CNT As.CNT As@Co-500 obtaied by pyrolysis of CNT As@ZIF-67 at 500oC exhibited optimal electromagnetic wave absorption properties.The minimum reflection loss was?36.86 d B with the thickness of 5.5 mm,while the reflection loss reached?33.94 d B at 2.5 mm,and the effective absorption bandwidth arrived to 5.78 GHz.In addition,CNT As@Co nanocomposites exhibited excellent thermal conductivity of 9.25 W m^?1K^?1,which was superior to that of most similar CNT-based thermal interface composites.The outstanding characters of CNT As@Co nanocomposites were due to the special 3D string-like nanostructures and their synergic effects.The assembly of MOFs-derived composites supported by low-dimensional or three-dimensional carbon materials can achieve high-efficiency electromagnetic waves absorption.And the effects of different microstructures on microwave absorption properties were systematically investigated,providing new ideas for the rational design and synthesis of new electromagnetic wave absorbers.