Abstract:

Objective The national policy of "carbon peaking and carbon neutral" aims to implement the concept of green and low carbon cycle development. This research aims to improve the social development efficiency through technological progress and governance optimization. This project proposes a green solution derived from porous biomass sources.
Method The highly porous loofah sponge as precursor, Co²⁺ as metal source and 2-methylimidazole as ligand were used to obtain loofah sponge/cobalt 2-methylimidazole(ZIF-67)composites by coordination self-assembly, and the composites were calcined at high temperature to obtain carbon fiber-based cobalt/carbon (LS-Co/C)composites. The structure and properties of the LS-Co/C composites was test and analyzed by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, vibrating sample magnetometer.
Results ZIF-67 was loaded on the surface of the loofah sponge(Fig. 2), and the higher calcination temperature improved the conversion of Co²⁺ into better crystalline Co particles(Fig. 3). The thermal decomposition stability of the carbon component became progressively higher with increased calcination temperature(Fig. 4), and the graphitization of the carbon fraction in the sample was increased with increasing calcination temperature(Fig. 5). The magnetic properties test result showing that the increase in calcination temperature favors the enhancement of the saturation magnetization intensity and the degree of Co crystallization forming. The increase in calcination temperature increased the values of the real and imaginary parts of the dielectric constant of the sample, and too low Co content leads to a smaller variation of the magnetic permeability(Fig. 7). It was concluded that the dielectric loss capability in LS-Co/C composites mainly depended on the conductivity loss, dipole orientation polarization loss and interfacial polarization loss(Fig. 8). The main factor affecting the wave absorption performance of LS-Co/C composites depended on the dielectric loss capability of the samples(Fig. 9), and its absorbing property is excellent when carbonized at 800 ℃(Fig. 10).
Conclusion Using biomass source loofah sponge as the precursor and Co²⁺ as the metal source, a raw material was obtained by coordination assembly and then calcined at high temperature to obtain the carbon fiber-based cobalt/carbon composite. The electromagnetic wave absorbing performance test yielded that the maximum reflection loss of LS-Co/C(carbonized at 800 ℃) reached -21.5 dB at a thickness of 1.5 mm and a frequency of 14.8 GHz, the effective absorption bandwidth was 5.2 GHz (12.8-18.0 GHz), and the excellent absorbing performance of the composite material originated from the enhanced electromagnetic wave loss formed by the special three-dimensional porous network loss structure and multiple interface polarization capability. This experiment provides a new synthetic method for the development of green, lightweight and efficient porous magnetic carbon-based absorbing materials.

Key words: carbon fiber, cobalt/carbon composite, biomass, microwave absorption material, porous material, loofah sponge, metal-organic frameworks composite