Co/CoO/Lotus Seedpod Nanoporous Carbon Composites Reduced from Co₃O₄ for High-Performance Microwave Absorbers

Abstract

To obtain microwave-absorbing materials with high absorptivity, broad bandwidth, and lightweight properties, Co 3 O 4 / lotus seedpod carbon (Co 3 O 4 /LSC) composites were reduced under a hydrogen pressure of 3 MPa. As the reduction temperature increases, the phases of the Co 3 O 4 /LSC composites change from Co 3 O 4 to CoO/Co. At 200 °C (named as the 3200 nanocomposite), partial Co 3 O 4 changes to CoO, the Co 3 O 4 completely transfers into CoO with a little Co detectable at 300 °C (3300 nanocomposite), and the concentration of Co increases more than that of the 3300 nanocomposite once temperature is raised to 400 °C (3400 nanocomposite). Moreover, the morphology of the Co 3 O 4 /LSC composites changes from irregular particles to a sintering state in the reduction process. When 3200, 3300, and 3400 nanocomposites are compared, the 3400 nanocomposite exhibits the highest permittivity and best microwave absorption performance: the 3400 nanocomposite exhibits a strong reflection loss of −60.63 dB (2.0 mm, 18.0 GHz) and an absorption bandwidth of 14.10 GHz (4.7 mm, 3.9−18.0 GHz). The hydrogenated LSC/Co 3 O 4 nanocomposite has a strong absorption capacity and wide effective bandwidth, is lightweight, and can be used as a high-performance biomass-based microwave-absorbing material.

Flexible, Stretchable, and Lightweight Hierarchical Carbon-Nanotube-Decorated Carbon Fiber Structures for Microwave Absorption

“…For this purpose, several high-performing EMA’s have been created in which carbon-based polymer composites are regarded as advantageous and promising candidates for highly efficient EMA with excellent thermal management capacities, lightweight, cost-effective, enhanced electric and heat conductivity, high dielectric loss, high mechanical stability, and excellent corrosion resistance. − However, the ability of the carbon nanofillers to agglomerate in the form of bundles results from the presence of powerful intermolecular van der Waals interaction, deteriorates the capabilities of carbon nanofillers for EM absorption, and restricts their applicability in industrial applications. , For this purpose, various techniques have recently been used to construct carbon-decorated hybrid morphologies consisting of magnetic or dielectric particles. − For example, Bao et al synthesized the bifunctional hollow Fe@C microsphere and fabricated the nanocomposite microwave absorber by mixing Fe@C (60 wt %) in paraffin, displaying a wide EAB of 7.52 GHz (10.48–18 GHz) at a 1.75 mm thickness . Gou et al made a 2.5 mm thickness nanocomposite consisting of polydimethylsiloxane (PDMS)/CeFe 2 O 4 /graphene oxide (GO) (60 wt %) in paraffin (40 wt %) and achieved the minimum R L value of −52 dB with an EAB of 2.1 GHz (Ku band) .…”

The Improved Microwave Absorption Performance of the 3D Porous (Ni@NO-C)n/NO-C Composite Absorber

“…Ding et al [20] synthesized Co-nanoparticle-loaded carbon nanosheets via a simple swelling and carbonization treatment of cellulose fibrils, and confirmed that the anisotropy derived from the lamellar structure of two-dimensional carbon materials was responsible for the magnetic resonance. Qi et al [21] prepared a composite of Co/CoO/LSC (lotus seedpod carbon) with the carbonization of lotus seedpods and hydrogen reduction of Co 3 O 4 , in which the 3D porous biomass-derived carbon was proven to be conducive to microwave absorption for the improvement of impedance match and multiple scattering. All of the above works are based on the composites of 0D magnetic metals (or their alloys and oxides) and 0-3D carbon materials.…”

The Improved Microwave Absorption Performance of the 3D Porous (Ni@NO-C)n/No-C Composite Absorber

“…Ding et al [20] synthesized Co nanoparticles loaded carbon nanosheets via a simple swelling and carbonization treatment of cellulose fibril and confirmed that the anisotropy derived from the lamellar structure of two-dimensional carbon materials was responsible for magnetic resonance. Qi et al [21] prepared the composite of Co/CoO/LSC (lotus seedpod carbon) by carbonization of lotus seedpods and hydrogen reduction of Co3O4, in which the 3D porous biomass-derived carbon was proved to be conducive to microwave absorption for the improvement of impedance match and multiple scattering. All of the above works are based on the composites of 0D magnetic metals (or their alloys and oxides) and 0-3D carbon materials.…”