MXenes as Emerging Materials: Synthesis, Properties, and Applications

Abstract

Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure-property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.

Keywords: 2D materials; MXenes; MXenes composites; layered materials; max phases.

Figure 3

(a) STEM micrograph of the bulk-etched MAX phase Ti₃AlC₂ for 3 h and the corresponding SAED pattern as inset. Reproduced with permission from ref. [36] Copyright 2021, The American Chemical Society. (b) The SEM micrograph of CoF₃/MAX without any AlF₃·3H₂O impurity. Reproduced with permission from ref. [38] Copyright 2019, The American Chemical Society. (c) TEM micrograph, (d) the corresponding SAED pattern, and (e) HR-TEM micrograph of the MS-Ti₃C₂T_x. Reproduced with permission from ref. [42] Copyright 2022, The American Chemical Society.

Figure 5

TEM images: (a) Side view, (b) bird’s-eye view, and (c) selected area HR-TEM with inset FFT image of h-Ti₃C₂ flakes. Reproduced with permission from ref. [62] Copyright 2018, Elsevier. (d) SEM micrograph of pristine MXene, (e) TEM micrograph, and (f) HR-TEM micrograph of N-MXene QDs. Reproduced with permission from ref. [64] Copyright 2020, Elsevier.

Figure 1

Scheme for the synthesis, properties, and applications of MXenes.

Figure 2

MXenes synthesis routes timeline in last decade. Reproduced with permission from ref. [31] Copyright 2021, Elsevier.

Figure 4

Scheme for the synthesis (a), TEM micrograph (b), and HR-TEM micrograph (c) of the fluoride-free Ti₃C₂T_x MXene. Reproduced with permission from ref. [45] Copyright 2022, The American Chemical Society.

Figure 6

(a) Schematic of the synthesis process, and (b–d) FE-TEM micrographs of the Ti₃C₂T_x nanodots. (e) The SEM micrograph of V2C MXene. (f) The average size of the generated V2C MXene was 4.13 nm, and it was 2.33 nm thick. (g) The lattice fringes with d-spacing of 0.247 nm. Reproduced with permission from ref. [67] Copyright 2017, The Willey.

Figure 7

(a) Schematic for the fabrication of Mo₂C/C nanosheets via molten salt method. (b) SEM micrograph, (c) TEM micrograph, and (d) HR-TEM micrograph with the inset showing the fast-Fourier-transform (FFT) pattern of the Mo₂C/C nanosheets. Reproduced with permission from ref. [74] Copyright 2018, Wiley.

Figure 8

(a) Schematic for the fabrication of Mo₂C-decorated carbon polyhedrons. (b) SEM micrograph of the Mo₂C/C, (c) and TEM micrograph of Mo₂C/C with inset the HR-TEM micrograph of Mo₂C. Reproduced with permission from ref. [75] Copyright 2018, The American Chemical Society.

Figure 9

(a–d) Layered MXenes and their roles in photocatalysis. Reproduced with permission from ref. [118] Copyright 2020, Elsevier.

Figure 10

(a) Schematic for the fabrication of Ti₃C₂T_x MXene and E-Ti₃C₂O_x. SEM micrographs (b) of Ti₃AlC₂, (c) layered Ti₃C₂T_x, (d) layered Ti₃C₂T_x intercalated with DMSO, and (e) E-Ti₃C₂T_x. Reproduced with permission from ref. [141] Copyright 2019, Willey.

Figure 11

(a) SEM micrograph along with structural model, and (b) top view of TEM micrograph with the SAED pattern of the Ti₃C₂ MNSs in the inset. (c) SEM micrograph along with structural model, and (d) TEM micrograph with SAED pattern of the Ti₃C₂ MNRs in the inset. (e) Formation of ammonia and the faradaic efficiency with various electrodes at −0.5 V potential versus the RHE after electrocatalytic tests for 3 h at room temperature. Reproduced with permission from ref. [148] Copyright 2020, Willey.

Figure 12

(a) Schematic for the delamination of V₂CT_x MXene. (b) The compiled resistance variation of the V₂CT_x gas sensor toward 100 ppm gases at room temperature. (c) Sensor response toward 100 ppm of hydrogen sulfide, hydrogen, methane, ammonia, acetone, and ethanol at room temperature. Real-time sensing response of the V₂CT_x sensor toward varying concentrations of different gases: (d) Hydrogen, (e) acetone, (f) methane, and (g) H₂S. Reproduced with permission from ref. [156] Copyright 2019, the American Chemical Society.

Figure 13

(a) Schematic of the fabrication of Ti₃C₂@mMSNs-RGD and the synergetic chemo-PTT against HCC with possible PA-imaging guidance and monitoring. (a) Schematic of the fabrication of Ti₃C₂ sheets. (b) Schematic of the fabrication of Ti₃C₂@mMSNs-RGD. (c) Schematic of the theranostic functions of Ti₃C₂@mMSNs-RGD. Reproduced with permission from ref. [187] Copyright 2018, Willey.