Three-Dimensional Porous Ti₃C₂T_x MXene-Based Hybrids Formed by Charge-Driven Assembly

Abstract

Functional three-dimensional (3D) structures based on 2D Ti3C2T x MXene nanosheets are promising candidates for high-performance applications. However, the repulsive electrical double layer forces among MXene nanosheets make their 3D assembly challenging. Herein, we demonstrate that the diffusion of positively charged poly­(allylamine hydrochloride) (PAH) into the single-layer MXene suspension allows for a range of free-standing 3D porous structures. The assemblies are developed by the adsorption of PAH chains from an aqueous solution on the MXene surfaces at the interface and their subsequent diffusion into the bulk of MXene suspension. Our morphological analysis shows that an optimum PAH concentration results in smaller and more circular pores. Moreover, 120–200 kDa PAH is found to be more effective than 17.5 kDa in developing MXene assemblies with well-defined pores. A significant change in the porous morphology is observed by manipulating the ionization degrees of the components, illustrating the importance of electrostatic interactions in morphology development. The MXene/PAH hybrids are electroconductive and can be processed into different shapes, including porous fibers that exhibit shape memory properties. Altogether, our results provide a basis for the rational design of hybrid MXene-based macroassemblies with potential applications in electromagnetic shielding, environmental remediation, and tissue engineering.

Tuning the Self-Assembled Morphology of Ti3C2Tx MXene-Based Hybrids for High-Performance Electromagnetic Interference Shielding

“…The flexibility of our interfacial assembly approach allows for the fabrication of MXene/PAH porous structures in the shape of fibers detailed in our previous report . The conductive fibrous structure provides a viable route to control the electron conduction path inside the shields and, accordingly, EMI shielding effectiveness.…”

“…The absence of the Ti 3 AlC 2 characteristic peak in the XRD pattern at 39° coupled with the higher d -spacing of MXene suggests no residual unreacted MAX phase in the MXene film (Figure S3, Supporting Information). We have recently shown that the strong electrostatic interactions between the negatively charged MXene nanosheets and positively charged PAH chains could be regulated by the diffusion-driven assembly to develop integrated MXene macrostructures . The PAH chains act as the physical cross-linker in the MXene phase, leading to the free-standing and integrated assemblies in both wet and dry states, Figure b2, c2, d. These stable free-standing assemblies cannot be gained without PAH chains, Figure b1, c1.…”

“…These 3D assemblies with internal porosities are prepared by the diffusion of PAH chains into the MXene suspension (x = 25, 35, or 45 mg/mL), Figure c2. In our previous study, we described a new approach that allows control of the morphology of MXene/PAH porous assemblies based on the concentration of MXene suspension. This approach is employed in the current study, while the total mass of MXene and the final PAH content are kept constant for different samples.…”

“…Ti 3 C 2 T x MXene is synthesized by selective etching of Al atomic layers from Ti 3 AlC 2 MAX precursor (Carbon-Ukraine), as detailed previously . Briefly, 1 g of Ti 3 AlC 2 powder is added to the etching solution containing 1.5 g of lithium fluoride (99% LiF, Millipore Sigma) in 20 mL of 9 M hydrochloric acid (HCl, Millipore Sigma), and the reaction continues for 28 h at 45 °C.…”

“…Recently, we have shown that controlled self-assembly of negatively charged MXene nanosheets and positively charged poly­(allylamine hydrochloride) (PAH) chains at the liquid–liquid interface creates porous MXene/PAH structures with tunable morphologies . In the current study, we exploit this assembly method to investigate how the positively charged insulating polymer affects the development of integrated MXene networks with different electrical conductivities and EMI shielding effectiveness.…”