Synthesis of two-dimensional Ti3C2Tx MXene using HCl+LiF etchant: Enhanced exfoliation and delamination

Herein, enhanced exfoliation and large-scale delamination of two-dimensional (2D) Ti3C2Tx MXene using etchant of HCl + LiF, instead of HF, in which both etching and intercalation were achieved in exfoliation process, were thoroughly investigated with the focus on the effects of two critical factors, reaction temperature and washing solution. Increasing etching temperature promotes the exfoliation process, i.e., the transformation from Ti3AlC2 to multilayer Ti3C2Tx MXene, whereas simultaneously results in an aggravated surface oxidation of MXene layers formed after the extraction of Al. As a result, delamination ratio increases firstly and then decreases, and the samples etched at 35 °C show the highest delamination ratio. Compared with the distilled water, washing the exfoliation products using ethanol significantly improves the delamination ratio of Ti3C2Tx MXene by co-intercalation of larger alcohol molecule and more impurity ions and a large scale delamination of Ti3C2Tx MXene with a delamination ratio as high as 29.2% was obtained by simple sonication for 1 h, without additional intercalation step required, after washing using ethanol. The possible exfoliation reactions by HCl + LiF solution were proposed. Using the as-fabricated stable suspensions of delaminated Ti3C2Tx flakes, flexible, free-standing Ti3C2Tx papers with tailored thickness, hydrophilic surface and excellent conductivity, typically 2 × 105 S/m at 5 μm in thickness, were prepared. As anode for lithium ion batteries, the delaminated Ti3C2Tx MXene obtained reversible capacities of 226.3 mAh g−1, 137.9 mAh g−1,102.0 mAh g−1 and 47.9 mAh g−1 respectively at the current density of 100, 300, 1000 and 3000 mA g−1, which are superior to those of the Ti3C2 MXene prepared by conventional HF process.