Department of Chemistry , Missouri University of Science & Technology , Rolla , Missouri 65409 , United States.
Department of Materials Science & Engineering , Missouri University of Science & Technology , Rolla , Missouri 65409 , United States.
Inorg Chem. 2019 Feb 4;58(3):1958-1966. doi: 10.1021/acs.inorgchem.8b02890. Epub 2019 Jan 16.
Although oxidation was deemed as the main factor responsible for the instability of MXenes in aqueous colloids, here we put forward and test a hypothesis about the central role of water as the primary factor. We show that water and related processes of MXene hydrolysis play the main role in the phenomena leading to complete transformations of 2D titanium carbide MXenes into titania in aqueous environments. To demonstrate the role of water, the stability of two MXenes, TiCT and TiCT , has been systematically studied in aqueous and nonaqueous colloids exposed to oxygen and inert gas atmospheres. The calculated time constant for degradation of TiCT dispersed in anhydrous iso-propanol saturated with pure oxygen exceeds 5 years, in striking contrast to the same MXene dispersed in water, where more than a half of it would transform into titania even in an oxygen-less atmosphere over ∼41 days. A thinner TiCT MXene showed similar behavior, albeit with shorter time constants in both solvents, correspondingly. UV-vis and Raman spectroscopy were used to analyze the oxidation kinetics and composition of fresh and aged MXenes. An intense anatase peak was observed in MXenes stored in aqueous solutions under Ar atmosphere, while no signs of oxidation could be found in iso-propanol solutions of the MXenes stored under O atmosphere over a similar period of time.
虽然氧化被认为是导致 MXenes 在水胶体中不稳定的主要因素，但在这里我们提出并测试了一个假设，即水是主要因素。我们表明，水和相关的 MXene 水解过程在导致二维碳化钛 MXenes 在水相环境中完全转化为二氧化钛的现象中起主要作用。为了证明水的作用，我们系统地研究了两种 MXenes，TiCT 和 TiCT 在暴露于氧气和惰性气体气氛的水相和非水相胶体中的稳定性。在无水异丙醇中分散的 TiCT 在纯氧饱和的情况下，其降解的计算时间常数超过 5 年，这与在水中分散的相同 MXene 形成鲜明对比，在没有氧气的情况下，超过一半的 MXene 在 41 天内就会转化为二氧化钛。更薄的 TiCT MXene 表现出类似的行为，尽管在两种溶剂中的时间常数都更短。我们使用 UV-vis 和拉曼光谱来分析新鲜和老化 MXenes 的氧化动力学和组成。在 Ar 气氛下储存在水溶液中的 MXenes 中观察到锐钛矿的强峰，而在 O 气氛下储存在异丙醇溶液中的 MXenes 在相似的时间内没有发现氧化迹象。
