Nat. Commun. ｜ Simultaneous regulation of layer spacing and surface groups of MXene using Lewis alkaline halides

Recently, the team of Xiao Xu from University of Electronic Science and Technology of China has made phased progress around the key scientific issues of MXene surface and interface regulation, and published two articles in Nature Communications magazine in two months. Xiao Xu's team proposed that using a large number of free cations and anions in low-temperature eutectic Louis alkaline halides, the - F group on the MXene surface can be replaced by desolvated halogen ions in molten salts through nucleophilic reaction (the treated MXene is named LB MXene), and the cations are inserted into the layers to expand the layer spacing. This method can realize the regulation of MXene layer spacing and surface groups at the same time. It is of great significance for the application of MXene in optoelectronics, energy and other fields.



By adjusting the proportion of AlBr3 in the eutectic molten salt AlBr3-NaBr-KBr, the molten salt system can achieve a leap from Lewis acid to Lewis alkaline. Only under the Lewis alkaline condition can there be a large amount of free desolvated Br ions. Desolvated halogen ions in eutectic molten salts participate in group substitution through nucleophilic reactions. After group substitution, cation charge compensation further expands the layer spacing of MXene. The synergistic effect of halogen group substitution and cation intercalation (a large amount of desolvated Na+and K+) is the reason for the increased interlayer spacing. This method is applicable to various MXenes, including 32/43 phase MXenes, single/double MXenes, and MXenes synthesized by HF or Lewis acid etching.



This achievement was published online in the international journal Nature Communications, with the title: Simulately tuning interlayer spacing and termination of MXenes by Lewis basic halides.

Picture and text guided reading

Fig. 1. Preparation and characterization of LB-Ti3C2Tx. a. Schematic diagram of preparation of LB Ti3C2Tx. After Lewis alkaline halide treatment, Ti3C2Tx was intercalated by desolvated Na+and K+, resulting in an increase in interlayer spacing. At the same time, the - F group on the surface is replaced by the desolvated halogen anion. b. Nucleophilic substitution between desolvated Br ions and F groups. C-d, scanning electron microscopy of multi-layer Ti3C2Tx and LB-Ti3C2Tx. Scale 1 μ m。 e. XRD spectra of multilayer Ti3C2Tx and LB-Ti3C2Tx. f. Atomic resolution high angle annular dark field (HAADF) TEM images and their atomic arrangements. The scale is 1 nanometer. g. Energy spectrum element analysis (line scan) of LB Ti3C2Tx. h. High resolution Br 3d XPS spectra of Ti3C2Tx and LB Ti3C2Tx.

Fig. 2. a-c, the composition of AlBr3/NaBr/KBr molten salt in different proportions. D-e, XRD spectra and high-resolution Br 3d XPS spectra of LB-Ti3C2Tx treated with AlBr3/NaBr/KBr molten salt in different proportions. f. The change trend of bromine group content and layer spacing in LB-Ti3C2Tx treated with AlBr3/NaBr/KBr molten salt of different proportions.

Fig. 3. SEM images of a, d, g, Nb4C3Tx, Mo2Ti2C3Tx and Ti3C2Tx-I before and after Lewis alkaline halide treatment. SCALE 1 μ m。 b. XRD spectra of e, h, Nb4C3Tx, Mo2Ti2C3Tx and Ti3C2Tx-I before and after Lewis alkaline halide treatment. c. High resolution XPS spectra of f, i, Nb4C3Tx, Mo2Ti2C3Tx and Ti3C2Tx-I.

Fig. 4. a. CV curves of Ti3C2Tx and LB-Ti3C2Tx at scanning rate of 2 mV s-1. b. Capacity comparison of Ti3C2Tx and LB Ti3C2Tx at different scanning rates. c. Capacity of LB-Ti3C2Tx under different current densities. d. Cyclic stability of LB Ti3C2Tx at 3A g-1.