Covalent Surface Modification of Hydrophobic Alkoxides on Ti3C2Tx MXene Nanosheets Toward Amphiphilic and Electrically Conductive Inks

Abstract

MXenes have garnered significant interest for use in conductive inks, processed either in aqueous solutions or organic solvents following surface modification. However, maintaining their electrical conductivity during dispersion across a broad range of solvents, particularly non-polar ones, has proven challenging, limiting their potential applications as conductive dispersions. Here, a straightforward method is presented for synthesizing electrically conductive and amphiphilic MXenes via surface modification. Alkoxide groups, such as ethoxide and phenoxide, are covalently attached to Ti₃C₂T_x MXene surfaces using a nucleophilic substitution mechanism, enabling stable dispersion in both polar and non-polar solvents. These alkoxide-functionalized MXenes exhibited an electrical conductivity of up to 2,700 S cm^-1 and dispersibility in non-polar solvents like toluene, surpassing previous modification approaches. Additionally, they demonstrate enhanced oxidative stability and excellent coating performance on substrates with varied surface energies. The electromagnetic interference (EMI) shielding films fabricated with these MXenes exhibited some of the highest performance among surface-modified MXenes and their composites, achieving shielding efficiency comparable to that of pristine Ti₃C₂T_x MXene films, while offering significantly improved durability. These findings may contribute to the development of improved processing approaches for MXenes, paving the way for advancements in printable and wearable electronics while addressing key challenges in MXene processing and modification.

Keywords: MXene; alkoxide; amphiphilic; conductive ink; surface modification.

Figure 1

a) Schematic illustration for the covalent surface modification of Ti₃C₂T _x MXene with sodium alkoxides. b) Proposed grafting mechanism for the surface modification process.

Figure 2

a–c) Photos of MX‐OEt dispersed in toluene at (a) a low concentration and (b, c) a high concentration. d) Top‐view SEM image of a single MX‐OEt sheet. e,f) Photos of (e) pristine Ti₃C₂T _x MXene and (f) MX‐OEt dispersed in various solvents taken at the initial stages and after 5 days of dispersion. g,h) Dispersibility of (g) MX‐OEt and (h) MX‐OPh in toluene synthesized with various alkoxide mixing ratios.

Figure 3

a) Digital photograph of a free‐standing MX‐OEt film. b,c) Water contact angles of MX‐OEt functionalized with 0, 50, 100 and 200 wt. % ethoxide. d–f) High‐resolution XPS spectra for Ti₃C₂T _x MXene, MX‐OEt, and MX‐OPh at the (d) Ti 2p, (e) C 1s, and (f) O 1s core levels. g) Schematic illustration that shows the corresponding chemical bonds detected using XPS for MX‐OEt and MX‐OPh. h) Region‐specified XRD analysis of MXene, MX‐OEt and MX‐OPh films. i) (002) peak positions and d‐spacing derived from the XRD peaks.

Figure 4

a) Electrical conductivities of pristine Ti₃C₂T _x MXene (DMSO solvent), MX‐OEt and MX‐OPh synthesized with various alkoxide mixing ratios. b) Electrical conductivities comparison between surface modified MXenes in relation to solvent polarity index. c) Electrical conductivity of MXene, MX‐OEt and MX‐OPh films over 7 days of accelerated oxidation. d) Photos of MXene, MX‐OEt and MX‐OPh films during water immersion tests. e,f) Photos of various substrates coated with (e) pristine Ti₃C₂T _x MXene aqueous dispersions and (f) MX‐OEt toluene dispersions.

Figure 5

a) EMI shielding performance of MX‐OEt and MX‐OPh at the X‐band and Ka‐band, measured by SE_T, SE_R, and SE_A values. b) EMI SE_T values of MX‐OEt, MX‐OPh compared with other composite materials. c) EMI shielding performance of MX‐OEt and MX‐OPh after 7 days of accelerated oxidation. d,e) Average SE_T values for Ti₃C₂T _x MXene, MX‐OEt and MX‐OPh at the (d) X‐band and (e) Ka‐band during 7 days of accelerated oxidation. f) EMI SE_T retention of Ti₃C₂T _x MXene, MX‐OEt, and MX‐OPh values during 7 days of accelerated oxidation.