Porous CNTs/Co Composite Derived from Zeolitic Imidazolate Framework: A Lightweight, Ultrathin, and Highly Efficient Electromagnetic Wave Absorber

Abstract

Porous carbon nanotubes/cobalt nanoparticles (CNTs/Co) composite with dodecahedron morphology was synthesized by in situ pyrolysis of the Co-based zeolitic imidazolate framework in a reducing atmosphere. The morphology and microstructure of the composite can be well tuned by controlling the pyrolysis conditions. At lower pyrolysis temperature, the CNTs/Co composite is composed of well-dispersed Co nanoparticles and short CNT clusters with low graphitic degree. The increase of pyrolysis temperature/time promotes the growth and graphitization of CNTs and leads to the aggregation of Co nanoparticles. The optimized CNTs/Co composite exhibits strong dielectric and magnetic losses as well as a good impedance matching property. Interestingly, the CNTs/Co composite displays extremely strong electromagnetic wave absorption with a maximum reflection loss of −60.4 dB. More importantly, the matching thickness of the absorber is as thin as 1.81 mm, and the filler loading of composite in the matrix is only 20 wt %. The highly efficient absorption is closely related to the well-designed structure and the synergistic effect between CNTs and Co nanoparticles. The excellent absorbing performance together with lightweight and ultrathin thickness endows the CNTs/Co composite with the potential for application in the electromagnetic wave absorbing field.

Chemical Immobilization Effect on Lithium Polysulfides for Lithium–Sulfur Batteries

“…Co is a promising electrocatalyst to accelerate the process for high‐order polysulfides to Li 2 S efficiently during the discharging process. Moreover, the N‐doping (especially pyridinic‐N) on the GC surface provides one pair of lone electrons for Li 2 S n species trapping through the strong chemical binding of Li in Li 2 S n with N atoms . It is demonstrated that N–GC matrix, Co, and doped‐N act synergistically in the system according to their special role.…”

An Efficient Co/C Microwave Absorber with Tunable Co Nanoparticles Derived from a ZnCo Bimetallic Zeolitic Imidazolate Framework

“…Hence, we compared the impedance matching of the four composites at a representative thickness of 2 mm. Generally, ideal impedance matching requires the | Z in / Z 0 | value to equal 1.0, which implies the zero‐reflection of incident EM wave at the front surface of absorber . As seen in Figure b, the | Z in / Z 0 | curve of Co50/C composite is close to 1.0 in a wider frequency range compared with other samples, which implies its better impedance matching.…”

Controllable Syntheses of MOF‐Derived Materials

“…To date, considerable research on the calcination of Fe, Co and Ni‐MOFs, have demonstrated that these metal species possess remarkable graphitization effect on the carbon during the thermolysis process at high temperatures . For example, the porous CNTs/Co composite was successfully prepared by the in situ pyrolysis of ZIF‐67 under Ar/H 2 atmosphere, and CNTs were formed by the graphitization of carbon under the catalysis of Co nanoparticles (Figure a) . In addition, due to relatively low boiling points, Zn (907 °C) and Cd (767 °C) particles could be easily evaporated with the gas flow at high calcination temperatures, which leaves porous regions on the carbon matrix .…”

“…e) The fine‐tuning pore structures of MOF‐derived carbon on the basis of pore‐forming agent of Cu particles. Reproduced with permission from references . Copyright American Chemical Society, Wiley and Royal Society of Chemistry.…”