Efficient microwave absorption achieved through in situ construction of core-shell Co Fe_(2)O_(4)@mesoporous carbon hollow spheres

Cobalt ferrite(CoFe_(2)O_(4)),with good chemical stability and magnetic loss,can be used to prepare composites with a unique structure and high absorption.In this study,CoFe_(2)O_(4)@mesoporous carbon hollow spheres(MCHS)with a core-shell structure were prepared by introducing CoFe_(2)O_(4)magnetic particles into hollow mesoporous carbon through a simple in situ method.Then,the microwave absorption performance of the CoFe_(2)O_(4)@MCHS composites was investigated.Magnetic and dielectric losses can be effectively coordinated by constructing the porous structure and adjusting the ratio of MCHS and CoFe_(2)O_(4).Results show that the impedance matching and absorption properties of the Co Fe_(2)O_(4)@MCHS composites can be altered by tweaking the mass ratio of MCHS and CoFe_(2)O_(4).The minimum reflection loss of the Co Fe_(2)O_(4)@MCHS composites reaches-29.7 dB at 5.8 GHz.In addition,the effective absorption bandwidth is 3.7 GHz,with the thickness being 2.5 mm.The boosted microwave absorption can be ascribed to the porous core-shell structure and introduction of magnetic particles.The coordination between the microporous morphology and the core-shell structure is conducive to improving the attenuation coefficient and achieving good impedance matching.The porous core-shell structure provides large solid-void and CoFe_(2)O_(4)-C interfaces to induce interfacial polarization and extend the electromagnetic waves’multiple scattering and reflection.Furthermore,natural resonance,exchange resonance,and eddy current loss work together for the magnetic loss.This method provides a practical solution to prepare core-shell structure microwave absorbents.

Carbon nanotube: Controlled synthesis determines its future

Carbon nanotubes(CNTs) have received broad attention in the past decades due to their excellent physical and chemical properties and thus been regarded as a powerful candidate for future star-materials. Although various CNT products and their related applications have been demonstrated recently, their performance can hardly meet the researchers’ expectations compared with their theoretical properties. The current predicament is caused by the immature synthesis method, including the basic science and the producing technology. As the synthesis with controlled structures determines its future, this review summarizes the progress on the basic research and industrialization of CNTs in the past decades, including the fine structure control, aggregation status design and scale-up production, and further points out the way for the future development of CNTs combining with specific applications.