Dual-functional core–shell composites: Integrated microwave absorption and thermal management properties

Abstract

The development of high-performance microwave-absorbing materials with integrated thermal management capabilities is critical for advanced electronic and communication systems. In this study, we synthesized hollow core–shell structured composites through controlled pyrolysis of zeolite imidazolate framework (ZIFs). Structural and compositional characterizations confirm the successful formation of highly graphitized carbon frameworks embedded with metallic nanoparticles (Co or Zn) and a protective mesoporous SiO2 shell. The as-prepared Zn–C@SiO2 exhibits a minimum reflection loss (RLmin) of −23.77 dB with an effective absorption bandwidth (EAB) of 6.24 GHz at 2.0 mm thickness, while Co–C@SiO2 demonstrates superior microwave absorption (RLmin = −51.9 dB, EAB = 5.36 GHz). The enhanced dielectric loss attributed to the interfacial polarization effects was systematically investigated. Additionally, the composites exhibit rapid thermal response, highlighting their dual functionality as microwave absorbers and thermal management materials.

1. Introduction

Driven by the revolutionary advancements in wireless communication systems and miniaturized high-power electronics, microwave-absorbing materials (MAMs) have garnered great attention due to their critical role in mitigating electromagnetic interference and radiation pollution [1–6]. Among various candidates, carbon-based composites, especially those derived from metal–organic frameworks (MOFs), exhibit exceptional dielectric loss and tunable microstructures, making them promising for high-performance microwave absorption [7–12]. However, achieving broadband absorption with thin thickness remains a challenge, necessitating innovative structural designs and composition optimization [11–15].

Recently, MOFs-derived carbon materials, particularly zeolitic imidazolate frameworks (ZIFs), have gained prominence due to their intrinsic properties including ultrahigh porosity, exceptional surface area, and atomic-level metal dispersion uniformity [16–21]. Pyrolysis is the dominant route to produce ZIF derivatives (e.g., ZIF-67 and ZIF-8), widely used in energy storage, catalysis, and electromagnetic wave absorption [22–23]. The process deposits metal species within N-doped carbon frameworks, and the porous structure boosts material performance. Specifically, ZIF-67 (Co) and ZIF-8 (Zn) decompose into magnetic Co nanoparticles and dielectric Zn species, offering a model system to study loss mechanisms. The dual-system strategy generalizes structure–property correlations in electromagnetic (EM) absorbing materials, such as ZIF-derived carbon composites with Co/Zn nanoparticles, which synergize interfacial polarization and conductive loss. The Co/C core–shell composites derived from ZIF-67 exhibited an effective absorption bandwidth (EAB) of 5.80 GHz at a thickness of 2.5 mm [24], while subsequent studies have developed various optimization strategies including heterointerface engineering [25–27], hollow structure engineering [28], and dielectric–magnetic synergistic effects [29], based on MOF-derived materials for designing high-performance MAMs. Nevertheless, the aggregation of metal nanoparticles during pyrolysis often degrades their performance and single-component absorbers typically struggle to achieve broadband absorption [30]. To address this, encapsulating MOFs within protective silica (SiO2) shells has proven effective in preserving structural integrity and enabling adjustable dielectric properties [31].

Herein, we designed two heterostructured absorbers, Co–C@SiO2 and Zn–C@SiO2, via a facile pyrolysis-etching route using ZIF-67@SiO2 and ZIF-8@SiO2 as precursors. The SiO2 coating not only prevents collapse during high-temperature treatment but also introduces abundant heterogeneous interfaces for enhanced polarization loss. Comprehensive characterization confirms the successful formation of hollow carbon frameworks with uniformly dispersed Co/Zn nanoparticles and amorphous SiO2 layers. Notably, the Co–C@SiO2 composite achieves an ultra-strong minimum reflection loss (RLmin) of −51.9 dB at 14.16 GHz with a broad EAB of 5.36 GHz, surpassing most reported MOF-derived absorbers [32]. The superior performance is attributed to the optimized impedance matching and dual loss mechanisms (conductive loss from sp2-carbon and defect-induced polarization). Additionally, the composites exhibit rapid thermal response, highlighting their potential for thermal management in flexible electronic and communication systems.