In recent years, MXenes, transition metal carbides or nitrides, have drawn increasing attention due to their high electrical conductivity and catalytic activity, hydrophilicity, and diverse surface chemistry. However, their interfacial assembly is limited due to their high hydrophilicity and high negative ζ potential. Previous examples of modifying the dispersity and wettability of MXenes have focused on using organic ligands, such as alkylamines, or triethoxysilanes for non-covalent or covalent surface modification, respectively. Here, we report a simple method to access Ti3C2Tz MXene-stabilized oil-in-water emulsions and demonstrate the use of these Pickering emulsions to prepare different structured MXene/polymer composites, such as capsules with shells of MXene and polymer and armored polymer particles with MXenes on the surface. The addition of common inorganic salts (e.g., NaCl) to the Ti3C2Tz MXenes dispersion results in the flocculation of nanosheets, enabling their interfacial assembly at oil-water interfaces to form an emulsion that is stable for days, as determined by optical microscopy imaging. Interfacial polymerization in these emulsions was accomplished by the incorporation of a diisocyanate in the discontinuous oil phase and diamine in the continuous water phase, leading to the formation of oil-filled capsules. The armored particles were obtained by polymerization of a dispersed phase in the emulsions. The capsules and armored particles were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), confirming the presence of both polymer and nanosheets. The ability to assemble MXene nanosheets at fluid–fluid interfaces without the use of ligands or cosurfactants expands the accessible material constructs relevant for engineering applications, including water purification, energy storage, electromagnetic electronics, and catalysis.

Pickering emulsions stabilized by inorganic salts flocculated MXene nanosheets and their use for capsules and armored particles formation

ACS Fall 2021

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