Control of electrical properties of Ti3C2Tx mediated by facile alkalization

The surface functional groups of MXenes make the material group special and play a critical role in determining their electrical properties. In this work, Ti3C2Tx MXene's surface functional groups were adjusted by a facile alkalization method, using NaOH and KOH. The alkalization was effective even at very low alkaline concentrations below 0.1 M. It was disclosed that the interlayer spacing became wider and the crystal quality was improved after alkalization. Molecular characterizations showed a clear transition from F-rich terminations to OH/O-rich terminations as a consequence of alkalization. Hall measurements, which can trace multiple electrical parameters elaborately, were utilized to examine the electrical property change induced by alkalization. An abrupt rise of sheet resistance and a sharp drop of carrier concentration were simultaneously observed for a MXene alkalized with a very low alkali concentration. Temperature-dependent Hall measurements and UV-Vis absorption tests revealed that the alkalized MXene did not behave like a semiconductor. Such electrical property change was explained in relation to the modulation of surface functional groups. The results of this work demonstrate that the electrical properties of Ti3C2Tx MXene can be widely tuned within a metal domain by a simple alkalization method, offering a practical property control technique for the expanded application of MXenes.