No 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.

Ti3C2T X MXene was used for surface modification of membranes by vacuum-assisted filtration. Owing to its higher hydrophilicity, negatively charged surface, and lower molecular weight cutoff, the Ti3C2T X MXene-coated membrane showed great performance for the treatment of organic contaminants. Humic acid (HA)/tannic acid mixtures were selected as the target natural organic matter (NOM). Owing to weakened hydrophobic interaction and improved size exclusion upon using Ti3C2T X MXene, it was difficult for HA to pass through the membrane. Membrane performance was tested for two different charged pharmaceuticals (amitriptyline and ibuprofen) under three pH conditions. The water permeabilities of pure water and both pharmaceuticals showed similar trends. This indicates that separation is affected by electrostatic interactions because the membrane surface is more negatively charged after Ti3C2T X MXene coating. Additionally, the reusability of the Ti3C2T X MXene-coated membrane was evaluated in three filtration cycles for NOM. After the first and second cleanings, recoveries of water permeabilities were 95.5% and 91.6% for HA. Although NOM can act as a foulant, HA caused reversible fouling. These findings indicate that the Ti3C2T X -coated membrane can be engineered to effectively treat various organic contaminants with high water permeability, retention performance, and antifouling capability.

Hybrid materials based on transition metal carbide and nitride (MXene) nanosheets have great potential for electromagnetic interference (EMI) shielding due to their excellent electrical conductivity. However, the performance of final products depends not only on the properties of constituent components but also on the morphology of the assembly. Here, via the controlled diffusion of positively charged poly(allylamine hydrochloride) (PAH) chains into the negatively charged Ti3C2T x MXene suspension, MXene/PAH hybrids in the forms of thin films, porous structures, and fibers with distinguished internal morphologies are obtained. Our results confirm that PAH chains could effectively enhance the oxidation stability and integrity of wet and dry MXene structures. The flexibility to tune the structures allows for a thorough discussion of the relations between the morphology, electrical conductivity, and EMI shielding mechanism of the hybrids in a wide range of electrical conductivity (2.5 to 3347 S·cm–1) and thickness (7.7 to 1900 μm) values. The analysis of thin films shows the direct impact of the polymer content on the alignment and compactness of MXene nanosheets regulating the films’ electrical conductivity/EMI shielding effectiveness. The colloidal behavior of the initial MXene suspension determines the interconnection of MXene nanosheets in MXene/PAH porous assemblies and the final electrical properties. In addition to the internal morphology, examining the laminated MXene/PAH fibers with geometrically different arrangements demonstrates the role of conductive network configuration on EMI shielding performance. These findings provide insights into tuning the EMI shielding effectiveness via the charge-driven bottom-up assembly of electrically conductive MXene/polyelectrolyte hybrids.