Delamination of MXene Flakes Using Simple Inorganic Bases

Since the discovery of the first MXene, Ti3C2T (z) , in 2011, more than 30new MXene chemistrieshave been reported. A universal method via which all MXenes can besynthesized is by etching the "A" layer from the MAXphase using hydrofluoric acid, HF. After etching, to delaminate theresulting MXene multilayers, MLs, they are typically treated witha surfactant like tetrabutylammonium hydroxide, TBAOH, tetramethylammoniumhydroxide, TMAOH, dimethyl sulfoxide, DMSO, etc. In our earlier work,we found that treating HF-etched Ti3C2T (z) MLs with a base like NaOH renders them ion-exchangeable,similar to the earlier reported treatments using expensive and moretoxic bases like TMAOH or TBAOH. In this work, we study the effectsof sodium hydroxide, NaOH, treatment on Nb2CT (z) and Mo2Ti2C3T (z) MXene MLs. We show that, similar to Ti3C2T z , Na ions alsointercalate in these two MXenes. This was clearly confirmed by X-raydiffraction analysis, which showed an increase in the interlayer spacingpost treatment of HF-etched MXenes with NaOH. This increase in theinterlayer space reduces the van der Waals interaction between theflakes, allowing for their facile delamination to single or few layers.It was also observed that NaOH treatment reduces the flakes'surface oxidation during processing, compared to when TBAOH is used.The surface chemistry and morphology of the MXenes post NaOH and TBAOHtreatments were also analyzed using X-ray photoelectron spectroscopyand scanning electron microscopy, respectively, and compared. Finally,we conclude that inexpensive NaOH can be used to substitute for TBAOHor TMAOH, conventionally used for MXene delamination.