Flocculation of MXenes and Their Use as 2D Particle Surfactants for Capsule Formation

Abstract

MXenes, transition metal carbides or nitrides, have gained great attention in recent years due to their high electrical conductivity and catalytic activity, hydrophilicity, and diverse surface chemistry. However, high hydrophilicity and negative ζ potential of the MXene nanosheets limit their processability and interfacial assembly. Previous examples for modifying the dispersibility and wettability of MXenes have focused on the use of organic ligands, such as alkyl amines, or covalent modification with triethoxysilanes. Here, we report a simple method to access MXene-stabilized oil-in-water emulsions by using common inorganic salts (e.g., NaCl) to flocculate the nanosheets and demonstrate the use of these Pickering emulsions to prepare capsules with shells of MXene and polymer. Ti3C2T z nanosheets are used as the representative MXene. The salt-flocculated MXene nanosheets produce emulsions that are stable for days, as determined by optical microscopy imaging. The incorporation of a diisocyanate in the discontinuous oil phase and diamine in the continuous water phase led to interfacial polymerization and the formation of capsules. The capsules were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), confirming the presence of both polymer and nanosheets. The addition of ethanol to the capsules led to the removal of the toluene core and retention of the shell structure. The ability to assemble MXene nanosheets at fluid–fluid interfaces without the use of ligands or cosurfactants expands the accessible material constructs relevant for biomedical engineering, water purification, energy storage, electromagnetic electronics, catalysis, and so on.

Capsules with polyurea shells and ionic liquid cores for CO2 capture

“…Examples of surfactants are amphiphilic small molecules, polymers, and particles (including spherical particles and nanosheets). [3][4][5] Emulsions have a broad range of applications, including drug delivery, [6][7][8][9][10] cosmetics, [11][12][13] biosensors, 14,15 foodstuffs, [16][17][18] external coatings, [19][20][21] and catalysis. 22,23 Emulsions can also be coupled with chemical reactions and polymerizations like interfacial polymerization leading to the formation of capsules with a core of the discontinuous phase.…”

Thermal Stability and Flammability Studies of MXene–Organic Hybrid Polystyrene Nanocomposites

“…After a selective etching by LiF and HCl, the disappearance of the diffraction peak at around 39.0° (104) indicates that the aluminum layer was removed from bulk Ti 3 AlC 2 (red line). In addition, the pronounced peak (002) shifted from a 2 θ angle of 9.6° to a lower 2 θ angle of around 6.5°, which is typical for Ti 3 C 2 T x nanosheets [ 31 , 32 ]. The Supplementary Material includes the AFM image ( Figure S1 ) of Ti 3 C 2 nanosheets, with a thickness of ∼1.6 nm, indicating single-layer nanosheets [ 33 ].…”

Polymer particles armored with cobalt oxide nanosheets for the catalytic degradation of bisphenol A

“…These results are in line with our recent work using salt flocculated MXene nanosheets to stabilize oil-in-water emulsions and may indicate that different cation radius or ''hardness'' dictates the ability to use inorganic nanosheets to stabilize Pickering emulsions. 18 Notably, the difference in ionic strength of 0.005 M solutions for monovalent and divalent cations may also play a role (see Fig. S6, ESI †).…”

“…[7][8][9][10][11][12][13][14][15][16][17] We have also recently demonstrated that transition metal carbide (MXene) and transition metal oxide (cobalt oxide) nanosheets can stabilize oil-in-water emulsions, if first flocculated by simple inorganic salt such as NaCl. 18,19 Compared to GO, these inorganic 2D surfactants are expected to not only provide kinetic stability to the emulsion, but to also impart favorable performance properties to any composite structures formed. Pickering emulsions stabilized by 2D particles have also gained increased popularity for use as templates to access composite structures, leveraging the confinement of reagents.…”