Researchers from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences have proposed an optimized synthesis strategy to obtain defect-free low-layer M₄C₃Tx (M = V, Nb, Ta) MXene nanosheets.

The results were published in Advanced Science.

MXene materials have enormous potential for applications such as energy storage, energy conversion, and electromagnetic shielding due to their excellent physical and chemical properties. M₄C₃Tx (M = V, Nb, Ta) MXenes have received much attention. However, obtaining a pure MAX phase precursor, complete etching for multi-layer M₄C₃Tx MXenes, and strict requirements for intercalation agents and exfoliation operations are all difficulties in the synthesis of these few-layer M₄C₃Tx MXenes. As a result, only a few investigations have focused on the study of thin M₄C₃Tx (M = V, Nb, Ta) MXenes.

In this study, the scientists proposed a roadmap for the synthesis of defect-free few-layer M₄C₃Tx (M = V, Nb, Ta) nanosheets. It included high-temperature calcination, HF selective etching, intercalation, and exfoliation. It produced three distinct defect-free few-layer M₄C₃Tx (M = V, Nb, Ta) nanosheets.

Extensive characterization confirmed their defect-free structure, significant interlayer spacing (ranging from 1.702 to 1.955 nm), diverse functional groups (-OH, -F, -O), and abundant valence states (M⁵⁺, M⁴⁺, M³⁺, M²⁺, M0).

In addition, they fabricated a free-standing film by vacuum filtration of a few-layer M₄C₃Tx (M = V, Nb, Ta) MXene ink, which exhibited remarkable physicochemical properties such as high conductivity, high stability, and hydrophilicity.

"Our work provides detailed guidelines for the synthesis of other defect-free few-layer MXene nanosheets," said HUANG Yanan, a member of the team, "and serves as a catalyst for the extensive exploration of functional applications of M₄C₃Tx (M = V, Nb, Ta) MXene nanosheets in the future."

The preparation steps and the corresponding structure evolution of few-layer M₄C₃Tx (M = V, Nb, Ta) MXenes. (Image by HUANG Yanan) 

The TEM results of defect-free few-layer V₄C₃Tx MXene nanosheets. (Image by HUANG Yanan)