Study On Synthesis And Properties Of Hierarchical Structure Of ZnO/Carbon Fibers Nanocomposites

Along with the development of scientific technology, microwave absorptionmaterials are in high demand for radar absorbent and many expandedelectromagnetic interference （EMI） shielding applications with both military andcommercial purposes. Traditional microwave absorbing materials are magnetic ormetal particles. However, because of difficult formulation and high specificgravity, they are restricted in practical application. Therefore, it is essential toresearch electromagnetic absorbing materials that are relatively lightweight,structurally flexible and show strong absorbing ability in a wide-frequency range.Composite materials, with Hierarchical nanostructures, consisting of the sameor different materials, show excellent EMI shielding effectiveness over a broadrange of frequency As indicated by thousands of papers, carbon materials exhibitfascinating dielectric and microwave absorbing capabilities owing to theirparticular electrical and mechanical properties. Therefore, it may be promisingand meaningful to use them for microwave absorbing, such as carbon black,carbon nanocoils, carbon fibers and carbon nanotubes. Carbon fibers areparticularly attractive as templates for forming, connecting and addressing othertypes of nanostructures since they are electrically conductive, mechanically robust,and their surface can be modified chemically. Many types of metal, oxide,polymer and semiconducter nanopaticles have been placed on the outer surface ofcarbon nanotubes or carbon fibers, such as Fe/CFs, Fe₃O₄/CFs, CoFe₂O₃/CNTsand the composites have shown better electromagnetic match and exhibited strongabsorption effect. The excellent absorbing ability and broad bandwidth is believed to result from efficient complementation between the relative permeability andpermittivity. In order to obtain excellent materials with fairly large absorptioneffectiveness and wide frequency range, various combinations of materials havebeen preformed. However, only a few works have been done for combiningdifferent dielectric materials. Among previous reports, ZnO have beeninvestigated for applications including microwave absorbing materials,light-emitting device and vibrational energy harvesters due to their highsurface/volume radio, wide bandgap （≈3.37eV） and unique chemical properties.Also, the large scale synthesis of ZnO is easily realized and the cost of preparationprocess is very low. Based on the advantages discussed above, we designed ZnOnanorods grown on short carbon fibers to achieve larger dielectric loss and meetthe wideband absorptive need.Carbon fibers （CFs） have been successfully coated with ZnO nanorods via asingle solution method at a mild temperature of90℃. The phase structure,chemical compositions and morphologies of the composites were characterized byX-ray diffraction （XRD）, energy dispersive X-ray spectroscopy （EDS） and fieldemission scanning electron microscope （FESEM）. The result shows that ZnOnanorods which have a central symmetric wurtzite crystal structure growuniformly on the acid-treated CFs. The as-synthesized composites were uniformlypasted on metal plate as the microwave absorption test plate. The microwaveabsorption effectiveness was measured over the frequency range of2-18GHz bythe radar-absorbing materials （RAM） reflectivity far field radar cross-section（RCS） method. The maximum absorption effectiveness of claviform ZnO/CFscomposites reach to-16dB at6.4GHz as the absorber thickness is1.2mm.Compared with pure ZnO nanorods or carbon fibers, the ZnO/CFs compositesexhibited essentially enhanced absorption effectiveness.We report using Fe（NO3）3·9H2O as raw material and Fe-doped claviformZnO/CFs is prepared by a single solution method. The structure and morphologywere investigated by X-ray diffraction and energy dispersive X-ray spectroscopy.The measurements provide powerful evidences for the successful doping Fe ions into claviform ZnO/CFs composites. Photodegradation of dyes in an aqueoussolution is investigated using Fe-doped ZnO/CFs composite as a photo-catalyst.The results show that Fe-doped ZnO/CFs composite has outstanding degradationproperties than pure ZnO/CFs composite.