Advanced Max/MXene Synthesis

• MAX/MXene Synthesis

While 30 stoichiometric MXenes and countless solid-solution MXenes have already been synthesized, our group’s work does not currently emphasize MAX/MXene synthesis as a primary topic. However, we continue to explore new approaches that expand the accessible compositions and surface chemistries of MXenes. Our efforts are increasingly focused on novel synthesis tactics that avoid the limitations of traditional wet etching routes.

• Molten Salt Etching

Molten salt etching, which uses a eutectic salt mixture to etch MAX phases, has emerged as a safer and more controlled alternative to HF-based wet chemical etching. This method avoids hydrofluoric acid while producing MXenes with uniform surface terminations, improving consistency in surface chemistry and functional properties.

• Gas-Phase Etching

Gas-phase etching uses corrosive gases to selectively remove A layers from MAX phases. This technique also results in MXenes with uniform surface terminations while eliminating the need for liquid handling, reducing waste and simplifying processing.

• Chemical Vapor Deposition (CVD)

Our group has recently begun working on CVD approaches to MXenes. This bottom-up synthesis involves chemical reactions between gaseous precursors and a substrate, enabling controlled growth of MXenes with uniform surface chemistry. CVD represents a fundamentally different pathway compared to etching-based methods and expands the possible structural and electronic properties of MXenes.

• Wet Chemical Etching (HF-based)

Traditional MXene synthesis relies on HF-based wet chemical etching of MAX phases. While widely used, this route generates toxic and hazardous waste and typically produces MXenes with a mixture of surface terminations. Our group has largely shifted away from this approach in favor of molten salt, gas-phase, and CVD methods, but it remains an important benchmark for comparing newer techniques.

• Delamination Techniques

Delamination is essential for obtaining single- and few-layer MXenes. The newer synthesis routes (molten salt, gas-phase, and CVD) produce MXenes with different surface chemistries compared to HF-etched MXenes, requiring modified delamination tactics. Current strategies remain low-yield, and our group is prioritizing efforts to increase throughput and yield while reducing waste, making scalable MXene production more practical.