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Cite This: ACS Appl. Mater. Interfaces 2019, 11, 25624−25635
Core−Shell CoNi@Graphitic Carbon Decorated on B,N-Codoped Hollow Carbon Polyhedrons toward Lightweight and High-Efficiency Microwave Attenuation Panbo Liu,*,† Sai Gao,† Yang Wang,† Ying Huang,*,† Yan Wang,*,‡ and Juhua Luo§
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†
MOE Key Laboratory of Material Physics and Chemistry under Extrodinary Conditions, School of Science, Northwestern Polytechnical University, Xi’an 710129, China ‡ School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710021, China § School of Material Science and Engineering, Yancheng Institute of Technology, Yancheng 224051, China S Supporting Information *
ABSTRACT: Lightweight and high-efficiency microwave attenuation are two major challenges in the exploration of carbon-based absorbers, which can be achieved simultaneously by manipulating their chemical composition, microstructure, or impedance matching. In this work, core−shell CoNi@graphitic carbon decorated on B,N-codoped hollow carbon polyhedrons has been constructed by a facile pyrolysis process using metal−organic frameworks as precursors. The B,N-codoped hollow carbon polyhedrons, originated from the calcination of Co-Ni-ZIF-67, are composed of carbon nanocages and BN domains, and CoNi alloy is encapsulated by graphitic carbon layers. With a filling loading of 30 wt %, the absorber exhibits a maximum RL of −62.8 dB at 7.2 GHz with 3 mm and the effective absorption bandwidth below −10 dB remarkably reaches as strong as 8 GHz when the thickness is only 2 mm. The outstanding microwave absorption performance stems from the hollow carbon polyhedrons and carbon nanocages with interior cavities, the synergistic coupling effect between the abundant B−C−N heteroatoms, the strong dipolar/interfacial polarizations, the multiple scatterings, and the improved impedance matching. This study demonstrates that the codoped strategy provides a new way for the rational design of carbon-based absorbers with lightweight and superior microwave attenuation. KEYWORDS: metal−organic frameworks (MOFs), CoNi alloy, carbon nanocages, hollow structure, microwave absorption performance
1. INTRODUCTION
To get an ideal absorber with excellent chemical stability and uniform dispersion, a reasonable design of various structures should be considered.14 Among these structures, core−shell materials are promising candidates to solve these limitations because the magnetic core can be protected by a dielectric shell with better resistance to chemical corrosion, the interfacial polarization of the absorbers can be improved due to the multiple components, the agglomeration of the magnetic particles can be restrained to some extent, and the combination of the dielectric properties, such as carbon or conducting polymer, will solve the problem of high density. So far, tremendous efforts have been devoted to fabricating core−shell absorbers, such as Ni@TiO2,15 Ni@NG/NC,16 Co@C,17 Fe3O4@C,18−20 Fe3O4@ZnO,21 Fe3O4@PPy,22 Fe-Fe3O4@ C,23 γ-Fe2O3@C@α-MnO2,24 and
[email protected],26 For example, Li’s group prepared core−shell Fe3O4@PPy by a sequential process of etching and polymerization; the obtained
With the rapid development and massive usage of wireless communication devices, microwave absorption materials with chemical stability have gained growing attention because they can protect the environment or human beings from the electromagnetic pollution or irradiation. Over the past decades, extensive efforts have been devoted to constructing highefficient microwave absorption materials with easy synthesis, low cost, strong microwave absorption intensity, and wide absorption bandwidth.1−4 Compared with metallic absorbers, carbon materials with low density, adjustable electrical conductivity, and high mechanical stability can be used as microwave absorbers.5−10 With the aim to strengthen the microwave absorption capacity, magnetic constituents are incorporated into carbon materials due to their multicomponents, improved characteristic impedance, and multiple interfacial polarizations.11−13 Unfortunately, the magnetic constituents usually suffer from high density, poor dispersity, and corrosion/oxidization under the operation conditions, which greatly restrict their practical applications. © 2019 American Chemical Society
Received: May 16, 2019 Accepted: June 24, 2019 Published: June 24, 2019 25624
DOI: 10.1021/acsami.9b08525 ACS Appl. Mater. Interfaces 2019, 11, 25624−25635
Research Article
ACS Applied Materials & Interfaces Scheme 1. Schematic Illustration of the Formation Process of CoNi@GC/BN-HCPs
enhanced dielectric loss.36−39 However, the replacement of Co by Zn/Cu species will pull down the magnetic loss to some extent. To achieve high performance, MOF-derived carbon materials incorporated with alloy or ferrite, such as FeCo,40,41 NiCo,42 NiFe,43 and ferrite44 with strong magnetic loss, have been considered. By the introduction of Ni, Chen’s groups synthesized hollow N-doped carbon polyhedrons containing CoNi alloy embedded within N-doped graphene. As an absorber with 35 wt % filler loading, the minimal RL reached −24 dB and the effective bandwidth was 4.32 GHz with a thickness of 2.5 mm.42 The existence of N atoms in MOFderived carbon materials can serve as polarized centers to produce dipolar polarization, resulting in enhanced dielectric loss. Inspired by this advantage, it is documented that the simultaneous codoping of carbon materials by two elements with reverse electronegativity, e.g., B and N, can form a nanojunction and modulate the electronic structure because N atoms introduce electrons and B atoms provide holes and, as a result, microwave absorption performance should be different from that of N-doped carbon materials.45 However, to the best of our knowledge, there are rare literature works on the synthesis of carbon materials codoped by B and N heteroatoms and their microwave absorption performance has not been investigated. Herein, we present a facile annealing route to construct core−shell CoNi@graphitic carbon decorated on B,N-codoped hollow carbon polyhedrons (CoNi@GC/BN-HCPs), in which the CoNi core is beneficial for magnetic loss, the graphitic carbon shell and BN-HCPs contribute to dielectric loss, and the highly porosity can adjust the impedance matching between the absorber and air. When evaluated as an absorber with a filler loading of 30 wt %, the maximum RL of the absorber is up to −62.8 dB at 3 mm and the effective absorption bandwidth exceeding −10 dB ranges from 10 to 18 GHz with a thickness of only 2 mm. Furthermore, with a thickness in the range of 2−5 mm, the effective absorption bandwidth (
