Tuning the Reaction Chemistry for the Sulfo-Bromination of Bismuth, Leading to Dual-Tapered Bi-Sulfobromide Platelet Nanocrystals and Their Heterostructures

The chemistry of sulfo-bromination of metals leading to dual-tapered 2D-shaped nanostructures is reported. This has been confined to the metal ion Bi(III), whose reduction followed by reionization in the presence of sulfide and bromide precursors leads to the desired bismuth sulfobromide nanocrystals. Initially Bi₁₉S₂₇Br₃ seed rods are taken, where Bi(0) nanocrystals are connected via a redox chemistry, conjugating with secondary metal ions. Then these 1D-shaped Bi₁₉S₂₇Br₃–Bi(0) heterostructures are transformed to dual-tapered 2D-shaped Bi₁₉S₂₇Br₃–Bi(0) nanostructures following a solution–liquid–solid (SLS) growth mechanism. The sulfo-bromination process is initially nucleated on the metal(0) sites but grown on the surface of the substrate seed rods. The size of Bi(0) equilibrates the tapering, whereby the length of the rods is gradually reduced and the width of the rods is slowly widened, leading to the dual-tapered 1D to 2D shape-transferred Bi-chalcohalide nanostructures. Extensive electron microscopic analysis and stepwise synthesis have been carried out to investigate the growth mechanism and to understand the tapering during the shape evolution processes. In addition, these materials of seed rods, intermediate and final nanostructures obtained are further explored as photocatalysts for HER and their activities are compared. The reaction chemistry discussed here enables the controlled incorporation of two anions with Bi(0) ionization, where one end of the nanostructure initiates nucleation, while the other end promotes growth. Overall, the reaction chemistry here provides a pathway for the solution-processed 2D SLS growth process, leading to shape-controlled metal chalcohalide nanostructures.