Multi-element mixing boosts exfoliation of layered hexaniobate single crystals

Scalable and green methods to prepare two-dimensional materials are important in the fields of catalysis, electronics, and energy conversion and storage. Existing approaches can be classified as bottom-up and top-down. Mass production through bottom-up approaches is costly, inefficient, and poorly scalable. Herein, we demonstrate a top-down approach based on chemical exfoliation. Without using strong acids or bases, single-crystalline nanosheets were obtained through hydrothermal treatment of multi-element-substituted layered oxides. Layered K₄Nb₆O₁₇ single crystals with multi-element substitution were grown using a flux method. The homogeneous distribution of Ti, Ta, and Sb ions in the niobate framework was confirmed experimentally. Subsequent hydrothermal treatment caused spontaneous exfoliation to form approximately 2.3 nm-thick nanosheets. The weight-based exfoliation efficiency of single crystals after multi-element substitution was five times higher than that of pristine K₄Nb₆O₁₇. Theoretical calculations revealed that substituting Nb with Ti, Ta, and Sb ions induced structural distortion in the octahedral metalate units in the K₄Nb₆O₁₇ framework, facilitating spontaneous exfoliation. By mixing framework elements to exfoliate layered materials efficiently, this methodology can be used for preparing 2D 'inks' through solution-based fabrication techniques.