Surface Chemistry-Driven Oxidation Mechanisms in Ti₃C₂T _x MXenes

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• Ti3C2Tx is a prominent MXene with diverse applications.
• MXene synthesis involves etching Ti3AlC2, introducing surface terminations (Tx).
• Impurities can arise from synthesis and environmental exposure, affecting MXene properties.

Purpose of the Study:

• To investigate the oxidation process of Ti3C2Tx during heat treatment.
• To understand the influence of synthesis routes and surface chemistry on oxidation products.
• To identify the role of surface terminations in stabilizing specific TiO2 phases.

Main Methods:

• In-situ Raman spectroscopy to monitor structural changes.
• In-situ microwave conductivity measurements to track electronic properties.
• Preparation of Ti3C2Tx using various etching methods (HF, LiF+HCl, HF+HCl).

Main Results:

• A two-step oxidation process was observed: initial inter-layer oxidation followed by TiO2 formation.
• Anatase TiO2 formed at elevated temperatures, with its stabilization influenced by fluoride and oxyfluoride groups.
• Rutile TiO2 formed in the absence of these stabilizing groups.
• Oxidation pathways varied depending on the MXene synthesis route and surface chemistry.

Conclusions:

• The heat treatment of Ti3C2Tx leads to a two-step oxidation process.
• Surface terminations, especially fluoride-containing groups, are crucial for controlling the phase of TiO2 formed.
• Understanding these oxidation mechanisms is vital for tailoring MXene properties for specific applications.