Fluoride‐Free Molten Salt Hydrate‐Assisted Synthesis of MXene in Air Down to 150 °C
Sin‐Yi Pang, Weng Fu Io, Lok Wing Wong, Xinyue Lao, Qianqian Bai, Kam Lin Chan, Jiong Zhao, Jianhua Hao
Abstract
Abstract The conventional Lewis acid molten salt etching approach for synthesizing MXenes typically necessitates elevated temperatures exceeding 550 °C, in addition to the use of inert gas protection to prevent oxidation. Additionally, delamination of molten salt‐etched MXenes typically requires hazardous intercalating agents. Herein, a scalable and non‐toxic low‐temperature shielded salt (LSS) approach for synthesizing MXene in air is reported, with the use of only a small portion of salts and a low reaction temperature down to 150 °C. Especially, the synergistic effect of the increased diffusion rate by Li + ions and the phase change of magnesium chloride hexahydrate (MgCl 2 ·6H 2 O) enables a redox‐controlled A‐site etching of the parent MAX phase, which even facilitates the synthesis of hard‐to‐etch MXenes. As a proof‐of‐concept demonstration, several theoretically hard‐to‐synthesize MXenes including Cr 2 CT x and Nb 2 CT x are successfully prepared through the LSS technique, where Cr 2 CT x is not achieved by Lewis acidic molten salt yet. Compared to conventional techniques, this low‐temperature shielded salt etching method exhibits unconventional molten behavior while offering several advantages, including a non‐oxidizing environment, shorter processing time, and elimination of highly corrosive washing agents and organic intercalants. These advances render the LSS approach a promising route for synthesizing MXenes with applications toward diverse practical applications.