Abstract:

Two-dimensional transition metal carbides and carbonitrides (MXenes) are the latest additions of the 2D world, which can be obtained by selective etching the a atomic layers from layered MAX precursors. In the traditional method of preparing MXene, the commonly used etchant is hydrofluoric acid. However, the use of concentrated hydrofluoric acid may inevitably bring about safety problems and even the destruction of crystal structure, resulting in the deterioration of intrinsic physical and chemical properties. This article starts from the typical carbide precursor Ti₃AlC₂ and uses NH₄BF₄ as an etchant to effectively reduce the amount of acid used in the system. More importantly, during the reaction process, the A layers were etched accompanied by intercalation of \mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}, by which the interlayer spacing was expanded and interlayer interaction was greatly weakened. High exfoliation efficiency of 2D Ti₃C₂ with intact crystallinities exfoliation was realized by a sequent hand shaking process. The electrochemical performance of as-obtained Ti₃C₂ was further characterized, showing an excellent capacitive electrochemical performance (503 F?g^-1 at a scan rate of 5 mV?s^-1) and cycling stability (the capacitance retention rate is 95.8% at 5 A·g^-1 after 10⁴ cycles). This provides new ideas for the synthesis and application of Ti₃C₂ nanosheets.

Key words: hydrothermal, nanomaterials, synthesis, Ti₃C₂ nanosheets, electrochemistry, MXene

摘要：

二维过渡金属碳/氮化物（MXene）是一种新型二维材料，可通过从MAX相前体中选择性刻蚀 A 原子层获得。在传统制备MXene的方法中，常用的刻蚀剂是氢氟酸。然而高浓度氢氟酸的使用，不可避免会带来安全问题，甚至破坏MXene的晶体结构，从而限制本征物理化学性能。从典型的碳化物前体Ti₃AlC₂出发，使用 NH₄BF₄作为刻蚀剂，有效降低体系中酸的使用量；在反应过程中，刻蚀 A 层的同时，\mathrm{N}{\mathrm{H}}_{\mathrm{4}}^{+}进入堆垛层间，扩大层间距，弱化层间作用力。因此，仅通过简单手摇就可以实现高效剥离，得到具有完整晶体结构的二维Ti₃C₂。进一步测试了Ti₃C₂的电化学性能，结果显示，所得的Ti₃C₂具有优异的性能（扫描速率为5 mV?s^-1时为503 F?g^-1）和循环稳定性（在5 A?g^-1下循环10⁴次后电容保持率为95.8%）。本文为Ti₃C₂纳米片的合成及应用提供了新的思路。

关键词: 水热, 纳米材料, 合成, Ti₃C₂纳米片, 电化学, MXene