We report on the synthesis of the first two-dimensional transition metal nitride, Ti₄N₃-based MXene. In contrast to the previously reported MXene synthesis methods – in which selective etching of a MAX phase precursor occurred in aqueous acidic solutions – here a molten fluoride salt is used to etch Al from a Ti₄AlN₃ powder precursor at 550 °C under an argon atmosphere. We further delaminated the resulting MXene to produce few-layered nanosheets and monolayers of Ti₄N₃T_x, where T is a surface termination (F, O, or OH). Density functional theory calculations of bare, non-terminated Ti₄N₃ and terminated Ti₄N₃T_x were performed to determine the most energetically stable form of this MXene. Bare and functionalized Ti₄N₃ are predicted to be metallic. Bare Ti₄N₃ is expected to show magnetism, which is significantly reduced in the presence of functional groups.

We report on one-step hybridization of silver, gold and palladium nanoparticles from solution onto exfoliated two-dimensional (2D) Ti₃C₂ titanium carbide (MXene) nanosheets. The produced hybrid materials can be used as substrates for surface-enhanced Raman spectroscopy (SERS). An approximate analytical approach is also developed for the calculation of the surface plasmon resonance (SPR) frequency of nanoparticles immersed in a medium, near the interface of two dielectric media with different dielectric constants. We obtained a good match with the experimental data for SPR wavelengths, 440 nm and 558 nm, respectively for silver and gold nanoparticles. In the case of palladium, our calculated SPR wavelength for the planar geometry was 160 nm, demonstrating that non-spherical palladium nanoparticles coupled with 2D MXene yield a broad, significanlty red-shifted SPR band with a peak at 230 nm. We propose a possible mechanism of the plasmonic hybridization of nanoparticles with MXene. The as-prepared noble metal nanoparticles on MXene show a highly sensitive SERS detection of methylene blue (MB) with calculated enhancement factors on the order of 10⁵. These findings open a pathway for extending visible-range SERS applications of novel 2D hybrid materials in sensors, catalysis, and biomedical applications.