Fluorine-Free MXenes: Recent Advances, Synthesis Strategies, and Mechanisms

MXenes, an exceptional class of 2D materials, possess high conductivity, adaptable surface chemistry, mechanical strength, and tunable bandgaps, making them attractive for diverse applications. Unlocking the potential of MXenes requires precise control over synthesis methods and surface functionality. Conventionally, fluorine-based etchants are used in MXenes synthesis, posing both environmental concerns and alterations to surface properties, along with the introduction of certain defects. This prompts the exploration of innovative fluorine-free strategies for MXenes synthesis. This review focuses on environmentally friendly, fluorine-free techniques for MXene synthesis, emphasizing mechanisms and recent breakthroughs in alternative etching strategies. The comprehensive coverage includes electrochemical etching, Lewis acid-driven molten salt etching, alkaline/hydrothermal techniques, chemical vapor deposition (CVD), and recent innovative methods. Fluorine-free MXenes synthesis yields terminations such as O, OH, Cl, etc., influencing surface chemistry and improving their properties. The presence of OH groups in NaOH etched MXenes boosts their energy storage, while Cl functionality from Lewis acidic salts optimizes electrochemical performance. Fluorine-free methods mitigate adverse effects of F terminations on MXene conductivity, improving electronic properties and broadening their applications. In addition to traditional approaches, this review delves into novel fluorine-free methods for tailoring MXenes properties. It comprehensively addresses challenges, opportunities, and future perspectives in fluorine-free MXenes. This review spotlights fluorine-free MXenes synthesis methods, including electrochemical etching, molten salt etching, alkaline/hydrothermal etching techniques, and chemical vapor deposition (CVD) synthesis. Diverse terminations, like O, OH, Cl, resulting from these processes enhance MXene properties, broadening their potential for various applications. The review also includes recent innovative fluorine-free MXenes synthesis, addressing challenges and envisioning tailored applications for the future.image

Automated summary

This review focuses on environmentally friendly, fluorine-free techniques for MXene synthesis and explores mechanisms and recent breakthroughs in various etching strategies. Fluorine-free MXene synthesis improves surface chemistry and electronic properties, expanding their applications. In addition, this review delves into novel fluorine-free methods for tailoring MXene properties.