Surface Functionalization of Ti₃C₂T_x MXene Nanosheets with Catechols: Implication for Colloidal Processing

Abstract

Precise tailoring of two-dimensional nanosheets with organic molecules is critical to passivate the surface and control the reactivity, which is essential for a wide range of applications. Herein, we introduce catechols to functionalize exfoliated MXenes (Ti 3 C 2 T x ) in a colloidal suspension. Catechols react spontaneously with Ti 3 C 2 T x surfaces, where binding is initiated from a charge-transfer complex as confirmed by density functional theory (DFT) and UV−vis. Ti 3 C 2 T x sheet interlayer spacing is increased by catechol functionalization, as confirmed by X-ray diffraction (XRD), while Raman and atomic force microscopy-infrared spectroscopy (AFM-IR) measurements indicate binding of catechols at the Ti 3 C 2 T x surface occurs through metal−oxygen bonds, which is supported by DFT calculations. Finally, we demonstrate immobilization of a fluorescent dye on the surface of MXene. Our results establish a strategy for tailoring MXene surfaces via aqueous functionalization with catechols, whereby colloidal stability can be modified and further functionality can be introduced, which could provide excellent anchoring points to grow polymer brushes and tune specific properties.

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

“…Postsynthesis treatments, shielding the MXene nanosheets with a protecting layer, and introducing organic functional groups on the MXene surface are proven to be effective in enabling the MXene dispersion in a wide range of organic media, averting the defect/edge-driven oxidation, and improving the performance of the MXenes in specific applications (Figure ). ,,,,− For instance, polyanionic salts (polysilicates, polyphosphates, or polyborates) that can adsorb on to positively charged MXene nanosheet edges were employed to slow down the oxidation kinetics of the MXenes for weeks in an aerated water medium (Figure (a)) . Similarly, l -ascorbate anions were also reported to enhance the oxidation stability of the MXenes in both the aqueous dispersion and dried powder/film forms .…”

Grafting Behavior of Amine Ligands for Surface Modification of MXene

“…), and acidic conditions. , However, completely eliminating the dissolved O atom sources is challenging. In addition, surface modification of MXene using ligands, including catechol, silane, , isocyanate, phosphoric acid, diazonium, , and amine, , has been introduced to prevent the oxidation reaction and improve the processability of MXene in nonpolar organic solvents . These ligands have various elements, including O, N, and S, which interact with the MXene surface through various driving forces (e.g., H bonding, electrostatic interaction, and covalent bonding) …”

Mildly Peeling Off and Encapsulating Large MXene Nanosheets with Rigid Biologic Fibrils for Synchronization of Solar Evaporation and Energy Harvest

“…15−18 Some small organic molecules (e.g., dimethyl sulfoxide, hydrazine, urea, and amines) were added as the intercalation agents to expand their interlayer spaces. 19 Certain antioxidants (e.g., ascorbates 20,21 ) and surface capping agents (e.g., catechols, 22 polyanions, 23 and silk fibroin 24 ) were also introduced to retard oxidation of MXene nanosheets into TiO 2 and carbonaceous particles under aqueous conditions. 25,26 The high-power sonication, though enabling a high production yield of MXene nanosheets up to >80%, 27 meanwhile broke them down into submicrometric sizes or even quantum dots (e.g., ∼5 nm in lateral size), 28,29 and thus sacrificed their sizedependent properties (e.g., electrical and optical), chemical stability and wide applications.…”