Figure 2.

Definition and characteristics of MXenes. (a) Schematic diagram of the synthesis process from the MAX phase to the MXene nanosheets, and SEM images of the MAX phase (Ti₃AlC₂) before and after hydrofluoric acid (HF) treatment (reprinted with permission from [37]; copyright (2012) American Chemical Society). (b) Crystal structure images of the MAX phase of Ti₃AlC₂, and the low-magnification and atomic resolution high-angle annular dark field (HAADF)-scanning transmission electron microscopy (STEM) images of Ti₃C₂T_x (reprinted with permission from [39]; copyright (2016) American Chemical Society). (c) Schematic image of the MXene/Au nanostructure (NS) SERS substrate fabrication process, XRD pattern, and TEM image of synthesized MXene (Ti₃C₂T_x), and the Raman spectra of R6G on the MXene/Au NSs SERS substrate with different concentration ranges of R6G (reprinted with permission from [45]; copyright (2019) The Royal Society of Chemistry). (d) Schematic image of the MXene-derived quantum dot (MQD) synthesis process using different solvents such as the dimethylformamide (DMF), DMSO, and ethanol (f-MQDs, s-MQDs, and e-MQDs, respectively), and the XRD pattern and FTIR spectra of the e-MQDs (black), f-MQDs (blue), and s-MQDs (red) (reprinted with permission from [41]; copyright (2018) John Wiley and Sons, Inc.).