Defect-Free Few-Layer M C T (M = V, Nb, Ta) MXene Nanosheets: Synthesis, Characterization, and Physicochemical Properties.

High-quality few-layer M C T (M = V, Nb, Ta) MXenes are very important for applications and are necessary for clarifying their physicochemical properties. However, the difficulty in etching for themselves and the existence of MC/MC and M-Al alloy impurities in their M AlC precursors seriously hinder the achievement of defect-free few-layer M C T (M = V, Nb, Ta) MXenes nanosheets. Herein, three different defect-free few-layer M C T (M = V, Nb, Ta) nanosheets are obtained by using a universal synthesis strategy of calcination, selective etching, intercalation, and exfoliation. Comprehensive characterizations confirm their defect-free few-layer structure feature, large interlayer spacing (1.702-1.955 nm), types of functional groups (-OH, -F, -O), and abundant valance states (M , M , M , M , M ). M C T (M = V, Nb, Ta) free-standing films obtained by vacuum filtration of few-layer M C T inks show good hydrophilia, high thermostability, and conductivity. A roadmap on synthesis of defect-free few-layer M C T (M = V, Nb, Ta) nanosheets are proposed and three key points are summarized. This work provides detailed guidelines for the synthesis of other defect-free few-layer MXenes nanosheets, but also will stimulate extensive functional explorations for M C T (M = V, Nb, Ta) MXenes nanosheets in the future.