Research ArticleUltrathin self-assembly MXene/Co-based bimetallic oxide heterostructures as superior and modulated microwave absorber
Graphical abstract
Introduction
Electromagnetic (EM) absorbing materials are considered as a promising technology to solve the growing hazard of EM pollution [[1], [2], [3]–4]. There is a general recognition of urgent need for exploring the ultra-lightweight, wide band, low load and efficient absorbing material, which can be suitable for the practical applications in portable electronic devices, aircraft, and spacecraft [5]. A variety of novel nanomaterials and nanostructures based on graphene [6,7], MXene [8,9], g-C3N4 [10] and Metal-organic frameworks [11,12] have been successfully prepared and exhibited potential microwave absorption (MA) properties [13].
Recently, MXene have been vigorously pursued in high-effective absorbing material owing to their versatile functional groups, excellent dielectric loss capability and solution processability [14]. Additionally, MXene holds powerful feasibility as the lightweight absorbers in relatively low percolation threshold due to its large aspect ratio and flexibility [15,16]. However, the excessively high conductivity and limited accessible active surfaces active sites caused by the intrinsic self-stacking are detrimental for their EM absorption properties [17]. In principle, the rational design of multicomponent composites could utilize different constituents for a better synergistic effect, facilitating an improvement in the impedance matching. Pan et al. [18] successfully synthesized multilayer-sandwiched heterostructure MXene/Co nanochains composites, which realized a minimum reflection loss (RLmin) of −46.48 dB at only 1.02 mm. As expected, coupling with the Co nanochains effectively make up for the shortage of EM energy attenuation by a single material, and improve the impedance matching for optimizing the absorbing properties. Li et al. [19] fabricated magnetic CNTs/Ni heterostructure decorated MXene nanosheets via a facile in situ induced growth method, helping to release the double agglomeration of common magnetic nanoparticles and MXene nanosheets. Thus, the MXene-CNTs/Ni hybrid holds a superior MA performance of −56.4 dB at 2.4 mm and 3.95 GHz at only 1.5 mm, demonstrating the effectuality of introducing CNTs/Ni in MXene as dielectric/magnetic modifiers to reasonably optimize its impedance matching condition. Except for the composition optimization, the exquisite design of the microstructure also plays an important role in enhancing impedance matching and microwave absorbing capacity [20,21]. In particular, 3D hierarchical structures containing 1D or 2D cells have been proven to effectively provide the larger specific surface area and higher porosity, resulting in exciting MA performance [22]. Wang et al. [23] obtained hierarchical carbon fiber@MXene@MoS2 (CMM) ternary composites by introducing Ti3C2Tx MXene on the surface of carbon fiber and then anchoring MoS2. The otimal RLmin of −61.51 dB at 3.5 mm and the maximum EAB of 7.6 GHz at 2.1 mm can be effectively achieved based on the core-sheath structure as well as synergistic effects of MXene sheath and MoS2 layer. Cui et al. [24] reported the simple ultrasonic spray method to construct 3D porous MXene/Ni composite microspheres by assembling Ti3C2Tx MXene nanosheets and Ni nanochains. The MXene/Ni composite microspheres exhibit satisfying MA property with the Rlmin of −52.7 dB and the EAB of 3.9 GHz at 1.9 mm, on account of the impedance matching and heterointerface generated in unique microstructure and well-designed 3D porous interconnection network.
Simultaneously, on the basis of the above promising strategies, heterointerface engineering of multicomponent composites will inject a fresh and infinite vitality for designing high-efficiency absorbing materials. Heterogeneous interfaces bring a range of compelling physicochemical properties, such as band alignment, space charge, electron transport, lattice defects, lattice strain, and pinning effects [25]. These properties modulate highly dipole polarization, interfacial polarization, conduction loss and magnetic response, which in turn act on MA properties. Inspired by this idea, we reported a versatile route for the synthesis of flower-like Co-based bimetallic oxide heterostructures and subsequent electrostatic self-assembly of MXene nanosheets to construct a 3D crossing network. Harnessing the inherent surface defect and rich surface functional groups of MXene nanosheets as well as abundant heterostructures, the CoO/MCo2O4/Ti3C2Tx MXene (CMOT, M=Co, Fe, Zn, Cu) composites exhibit a better MA capacity. Besides, the variance of bivalent metal ion in spinel structure MCo2O4 results in diverse defect degree, which will lead to different EM properties of the composites. Notably, the permittivity can be regulated by the introduction of M2+ and decrease gradually in the order of Fe2+, Cu2+, Zn2+. And, different M2+ can subtly modulate the absorbing property with tune absorption peak position and corresponding frequency band. The as-obtained CFOT-12 (10 wt%), CCOT-15 (10 wt%), CZOT-15 (15 wt%) achieve prominent MA capacity with RLmin of –41.06, –52.67, –52.52 dB and corresponding EAB of 3.68, 4.48, 3.92 GHz at 2.10, 1.90, 1.80 mm, respectively. This preliminary work reveals a new methodology for the design of multicomponent heterostructure, opening up a novel approach to tuning the EM parameters and absorbing property, as well as highlights a promising lightweight and highly efficient EM absorber with frequency selective.
Section snippets
Results and discussion
As depicted in Scheme 1, Co2+ and other three bivalent metal ions (Fe2+, Cu2+ and Zn2+) have been introduced to construct Co-based bimetallic nano-flower, named CMM (CFM, CCM and CZM). Subsequently, positively charged nano-flower can couple with Ti3C2Tx MXene nanosheets to construct 3D crossing network through electrostatic self-assembly process. After calcination, the corresponding composites changing the Ti3C2Tx MXene amount are marked as CMOT-x composites, where x (12, 15 and 18 mL) stands
Conclusion
In summary, customized Co-based multiphases nanoflowers with diverse metal components were prepared by facile hydrothermal method, and then combined with MXene by electrostatic self-assembly to obtain the resultant CMOT composites. Intriguingly, the changes in the defects, interfaces and components could be brought by tuning the introduction of different metals, which sequentially affect the electromagnetic properties. Accordingly, the permittivity of CMOT composites demonstrates an increasing
Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos. 52073010 and 21975012). H.Y. Wang thanks the financial support by the program of “Academic Excellence Foundation of BUAA for PhD Students.
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