Synthesis of two-dimensional Ti₃C₂T_xMXene using HCl+LiF etchant: Enhanced exfoliation and delamination

Herein, enhanced exfoliation and large-scale delamination of two-dimensional (2D) Ti₃C₂T_xMXene 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 Ti₃AlC₂to multilayer Ti₃C₂T_xMXene, 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 Ti₃C₂T_xMXene by co-intercalation of larger alcohol molecule and more impurity ions and a large scale delamination of Ti₃C₂T_xMXene 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 Ti₃C₂T_xflakes, flexible, free-standing Ti₃C₂T_xpapers with tailored thickness, hydrophilic surface and excellent conductivity, typically 2 × 10⁵S/m at 5 μm in thickness, were prepared. As anode for lithium ion batteries, the delaminated Ti₃C₂T_xMXene obtained reversible capacities of 226.3 mAh g⁻¹, 137.9 mAh g⁻¹,102.0 mAh g⁻¹and 47.9 mAh g⁻¹respectively at the current density of 100, 300, 1000 and 3000 mA g⁻¹, which are superior to those of the Ti₃C₂MXene prepared by conventional HF process.