Highly Stable 3D Ti₃C₂T_x MXene-Based Foam Architectures toward High-Performance Terahertz Radiation Shielding

Abstract

Terahertz technology promises broad applications, which calls for terahertz electromagnetic interference (EMI) shielding materials to alleviate radiation pollution. 2D transition metal carbides and/or nitrides (MXenes) with metallic conductivity are promising for EMI shielding, but simultaneously realizing light weight, high stability, and foldability in a MXene shielding material to meet the requirements of increasingly popular portable and wearable equipment has remained a great challenge. Herein, an ion-diffusion-induced gelation method is demonstrated to synthesize free-standing, light-weight, foldable, and highly stable MXene foams, in which MXene sheets are cross-linked by multivalent metal ions and graphene oxide to form an oriented porous structure. The method is highly efficient, controllable, and versatile for scalable generation of functional 3D MXene structures with arbitrary shapes and synergistic properties. The distinctive cross-linked porous structure endows the light-weight MXene foam with good foldability, outstanding durability and stability in wet environments, and an excellent terahertz shielding effectiveness of 51 dB at a small thickness of 85 μm. This work not only provides an insight for the on-target design of high-performance terahertz shielding materials but also expands the applications of MXenes in 3D macroscopic form.

MXene hydrogels: fundamentals and applications

“…17 Recently, Lin et al have simultaneously incorporated two crosslinkers, i.e., divalent metallic ions and GO, to prepare MXene-containing hydrogels through an improved gelation process. 12 To initiate the gelation, a metal substrate, e.g., Zn foil, was placed on the surface of an acidified Ti 3 C 2 T x /GO dispersion to release Zn 2+ ions into the dispersion (Fig. 6c).…”

“…Thus far, there are several methods for preparing MXene aerogels including (1) direct freeze-drying of MXene NC dispersions, 16,25,35,36 (2) calcination after freeze-drying of MXene NC dispersions, [37][38][39][40][41] and (3) freeze-drying of MXene hydrogels. 5,6,12,28,[42][43][44][45][46][47] In all these methods, the sublimation of ice crystals from frozen dispersions or hydrogels was necessary for obtaining MXene aerogels. Similar to hydrogels, the resultant micro/nanostructures and mechanical behavior of the obtained aerogels are influenced by the MXene concentration, polymeric molecular weight, freezing methods, and post-processing procedure.…”

“…The highly oriented-layered MXene aerogel skeletons obtained from freeze-drying of MXene hydrogels were found to improve the electromagnetic shielding ability by weakening the reflection of terahertz radiation. 12 The subsequent calcination after freeze-drying was also beneficial for more gas generation and conduction within pure MXene-rGO aerogels, resulting in lower density and larger lamellar size. 37 In addition to aerogels, MXene xerogels have also been reported.…”

“…9a). 12,47 Finally, the inclusion of MXenes in hydrogel systems has patently improved the mechanical properties of the resultant hydrogel and even has brought about brand-new characteristics. In general, It is traditionally thought that the viscoelastic property of hydrogels is a disadvantage for mechanical sensing, as it can cause unstable baseline and fluctuation of signals if the stimulus is faster than the relaxation speed of hydrogels.…”

“…It is worth noting that the MXene-rGO aerogels were not only active within the X-band frequency range, but it also had a good stealth property in the terahertz communication window. 12…”