Few-layer Mg-deficient borophene nanosheets: I 2 oxidation and ultrasonic delamination from MgB 2 .

By using I 2 as an oxidant and CH 3 CN as a reaction medium, few-layer Mg-deficient borophene nanosheets (FBN) with a stoichiometric ratio of Mg 0.22 B 2 are prepared by oxidizing MgB 2 in a mixture of CH 3 CN and HCl for 14 days under nitrogen protection and followed by ultrasonic delaminating in CH 3 CN for 2 h. The prepared FBN possess a two-dimensional flake morphology, and they show a clear interference fringe with a d -spacing of 0.251 nm corresponding to the (208) plane of rhombohedral boron. While maintaining the hexagonal boron networks of MgB 2 , the FBN have an average thickness of about 4.14 nm (four monolayer borophene) and a lateral dimension of 500 nm, and the maximum Mg deintercalation rate can reach 78%. The acidity of the reaction system plays an important role; the HCl reaction system not only facilitates the oxidation of MgB 2 by I 2 , but also increases the deintercalation ratio of Mg atoms. Etching of the Mg atom layer with HCl, the negative charge decrease of the boron layer by I 2 oxidation, and the Mg chelating effect from CH 3 COOH due to the hydrolysis of CH 3 CN in an HCl environment led to a high deintercalation rate of the Mg atom. Density functional theory (DFT) calculations further support the result that the maximum deintercalation rate of Mg atoms is about 78% while maintaining the hexagonal layer structure of boron. This research solves the problems of low Mg atom deintercalation rate and hexagonal boron structure destruction when using the precursor MgB 2 to produce borophene nanosheets, which is of great significance for large-scale novel preparation and application of borophene nanosheets.