Systematic Study of the Multiple Variables Involved in V2AlC Acid-Based Etching Processes, a Key Step in MXene Synthesis

The realization ofthe broad range of application of MXenes relieson the successful and reproducible synthesis of quality materialsof tailored properties. To date, most MXenes have been produced makinguse of acid-based etching methods, yet an in-depth understanding ofetching processes is lacking. Herein, we have engaged in a comprehensivestudy of the multiple variables involved in the synthesis of V2CT x with focus on the propertiesof etched materials. Two main sets of experiments were considered,each using a different V2AlC precursor and a range of synthesisvariables including reaction time and temperature, mixing rate, andtype of acid. Correlations of synthesis conditions-materialsproperties were investigated using a broad range of characterizationtechniques including analytical methods, scanning and transmissionelectron microscopy, X-ray diffraction (XRD), and X-ray photoelectronspectroscopy (XPS). Findings indicated the crucial relevance of propertiesof the MAX precursor such as elemental composition, particle size,and crystal structure on etching processes and properties of etchedmaterials. Particularly, depending on the MAX precursor, two etchingpatterns were identified, core-shell and plate-by-plate, thelatter describing a more efficient etching. Combined studies of elementalcomposition, crystal structure, and yield quantification allowed usto evaluate the effectiveness of etching processes. XRD studies revealedkey crystal-structure-type of acid correlations showing advantagesof using a HF/HCl mix over only HF. Analytical methods XRD and XPSdelivered insights into undergoing chemical processes and their influenceon bulk and surface chemistry of etched materials. The relevance forreaction kinetics of highly correlated variables such as reactionvessel dimensions, mixing efficiency, and reaction temperature wasrecognized. For the first time, a MXene synthesis has been investigatedcomprehensively highlighting its multivariable nature and the highvariable intercorrelation, opening up venues for further investigationon MAX and MXene synthesis.

Automated summary

This study comprehensively investigates the synthesis of MXene, with a specific focus on the properties of etched materials. Through different experimental conditions and various characterization techniques, it is found that the elemental composition, particle size, and crystal structure of the MAX precursor are critically relevant to the etching process and properties of etched materials. Additionally, XRD studies reveal the advantages of using a HF/HCl mix over only HF, in terms of crystal-structure-type of acid correlations.