Synthesis of free-standing carbon nanotube buckypaper films decorated with Fe3O4 nanoparticles and polyaniline as highly effective electromagnetic shielding materials

Abstract

A balance between electrical and magnetic properties is critical for electromagnetic shielding materials to achieve excellent electromagnetic interference (EMI) shielding and attenuation effectiveness across a broad frequency range. We have prepared free-standing buckypaper films (BPFP) decorated with Fe3O4 particles and polyaniline (PANI) by a simple two-step method to meet this requirement. First, buckypaper films decorated with Fe3O4 (BPF) were synthesized by the coprecipitation of Fe2+/Fe3+ ions on buckypaper (BP) which was then coated with a polyaniline layer by the in situ polymerization of aniline monomers. Magnetic characterization revealed that the BPF and BPFP films had saturation magnetization (Ms) values of 14.3 emu g−1 and 13.0 emu g−1, respectively, confirming retention of the magnetic phase. The addition of Fe3O4 nanoparticles and polyaniline to BP (30 μm) increased both the magnetic and dielectric losses due to the increased interfacial polarizations and anisotropy energy. 41 μm-thick BPF and BPFP films had an absorption-dominated shielding effectiveness of 35.1 dB and 36.4 dB, respectively, across the 5.85-18 GHz frequency band. These values are respectively 12.9% and 17.0% greater than that of pristine BP, highlighting the positive effect of Fe3O4-PANI heterostructures on electromagnetic wave dissipation. These films also had the tensile strength, flexibility, and lightness of BP, demonstrating exceptional promise for next-generation electromagnetic shielding materials.

1. Introduction

With the ongoing miniaturization and integration of modern electronic devices, there is an irreversible trend toward developing lightweight and thin shielding materials with high performance that includes broad-spectrum electromagnetic wave absorption[1−2]. The electromagnetic interference (EMI) shielding effectiveness (SE) demonstrates a positive correlation with the conductivity and thickness of the shielding materials[3−4]. More importantly, impedance matching and maximum attenuation at a specific thickness are related to the electrical and magnetic properties of the electromagnetic shielding materials. Electrical permittivity derived from the electric dipoles and magnetic permeability provided by the magnetic dipoles of the composites[5] should be in an optimal balance in order to achieve highly improved EMI shielding and attenuation performance.

Carbon nanotubes (CNTs), encompassing both multi-walled (MWCNTs) and single-walled (SWCNTs) variants, have emerged as a cornerstone of nanotechnology since Iijima’s structural elucidation of MWCNTs in 1991[6]. CNTs exhibit extraordinary electrical, thermal and mechanical properties, and excellent microwave absorbing properties, which meet the requirements of lightweight, broadband and high absorption efficiency for new electromagnetic shielding materials[7–12]. Although considerable efforts have been made toward the development of CNT-based composites for electromagnetic shielding purpose recently, these materials are non-magnetic and preferential to microwave energy absorption mostly attributed to their dielectric loss. Furthermore, the dielectric permittivity and magnetic permeability of CNTs are out of balance, which results in a bad impedance matching characteristic[13]. In order to compensate the magnetic loss and strengthen impedance matching, ingredients with magnetic and dielectric features were frequently used in the preparation of microwave absorbers[14–17]. Among all of the magnetic materials, Fe3O4 nanoparticles are highly favored[13,18−19] owing to their high saturation magnetization, low toxicity and good biocompatibility. In terms of dielectric materials, the applications of graphene[16,20], CNTs[15] and conducting polymers have demonstrated exceptional performance. In previous literature, the evaluation o