Deintercalation of Al from MoAlB by molten salt etching to achieve a Mo₂AlB₂ compound and 2D MoB nanosheets

Two-dimensional (2D) MoB metal borides (MoB MBene) have attracted much attention due to their fascinating properties and functional applications. So far, work on the synthesis of 2D MoB nanosheets by acid or alkaline etching of MoAlB has not been very successful. It has been proposed that the 2D MoB MBene may be fabricated by chemical etching of a Mo₂AlB₂ precursor, but further investigations were not performed possibly due to the difficult preparation of the metastable Mo₂AlB₂ compound at high temperatures by solid-state reactions. Here, we report on the successful synthesis of the Mo₂AlB₂ compound and 2D MoB nanosheets by the deintercalation of Al from MoAlB through a ZnCl₂ molten salt etching approach at relatively low temperatures. The influence of etching temperature, etching time, and starting mixtures on the formation of desirable phases have been investigated. A pure Mo₂AlB₂ compound was synthesized at temperatures below 600 ℃, while the 2D MoB MBene nanosheets were obtained at 700 ℃ through the molten salt etching of MoAlB. In addition, the present work further confirms that the MoB MBene can be prepared by etching the as-synthesized Mo₂AlB₂ precursor in LiF–HCl solution. Our work demonstrates that the molten salt etching is an effective method to prepare 2D MoB MBene.