Low-Temperature Oxidation Induced Phase Evolution with Gradient Magnetic Heterointerfaces for Superior Electromagnetic Wave Absorption

Abstract

Gradient magnetic heterointerfaces have injected infinite vitality in optimizing impedance matching, adjusting dielectric/magnetic resonance and promoting electromagnetic (EM) wave absorption, but still exist a significant challenging in regulating local phase evolution. Herein, accordion-shaped Co/Co3O4@N-doped carbon nanosheets (Co/Co3O4@NC) with gradient magnetic heterointerfaces have been fabricated via the cooperative high-temperature carbonization and low-temperature oxidation process. The results indicate that the surface epitaxial growth of crystal Co3O4 domains on local Co nanoparticles realizes the adjustment of magnetic-heteroatomic components, which are beneficial for optimizing impedance matching and interfacial polarization. Moreover, gradient magnetic heterointerfaces simultaneously realize magnetic coupling, and long-range magnetic diffraction. Specifically, the synthesized Co/Co3O4@NC absorbents display the strong electromagnetic wave attenuation capability of −53.5 dB at a thickness of 3.0 mm with an effective absorption bandwidth of 5.36 GHz, both are superior to those of single magnetic domains embedded in carbon matrix. This design concept provides us an inspiration in optimizing interfacial polarization, regulating magnetic coupling and promoting electromagnetic wave absorption.

1. Introduction

The popularization of wireless communication technology, especially the explosive growth and implementation of 5G technology, greatly promotes the upgrading of global industries and the development of the economy and society [1–3]. However, technological advancements often bring greater challenges. The emergence of electromagnetic (EM) radiation and the responding pollution inevitably affects the normal operation of electronic devices and the health of human beings [4–6]. Therefore, fabricating efficient EM wave absorbents with thin, light, strong absorption and wide broadband has become the promising and effective solution to address these issues [7–11]. Based on these requirements, many strategies have been proposed to construct high-performance EM wave absorbents [12–14]. The magnetic–dielectric synergistic effect is a classic theory which is usually used to elucidate the mechanism of EM wave attenuation [15]. Based on the theoretical research, the focus has gradually shifted to using magnetic and nonmagnetic components to regulate and improve the absorption intensity and effective absorption bandwidth [16–19]. However, among these methods, hydrothermal treatment and etching are usually required, which greatly limit the mass production of materials and introduce more uncertainty.

In recent years, metal–organic frameworks (MOFs) and their derivatives have been considered as the most promising candidates in EM wave absorption due to their tunable chemical composition, mesoporous properties, and diverse microstructures [20–24]. As early as 2015, Du et al. firstly used Prussian blue as a precursor to synthesize Fe/C nanocubes through a one-step pyrolysis method, which opened a new era in the field of EM wave absorption for MOFs derivatives [25]. After that, various morphologies of MOFs derivatives have been employed as EM wave absorbents [26–31]. However, few researchers focus on constructing MOFs derivatives via the manipulation of pyrolysis process, and the mechanism of structural design and EM wave absorption performance has not been clarified. Besides, due to the larger magnetic force between single magnetic nanoparticles, they are preferred to agglomerate to form larger magnetic domains during the pyrolysis process. To address this issue, constructing hollow nanoparticles or yolk–shell structures with coexisting micro- and mesopores has been proposed to reduce material density and improve skin depth. It is well known that the prominence of EM wave absorbing materials prepared through the direct pyrolysis of single MOFs has declined due to the inherent limitations of non-tunability and the singularity of a single-component.