From One to Two: In Situ Construction of an Ultrathin 2D-2D Closely Bonded Heterojunction from a Single-Phase Monolayer Nanosheet

Abstract

Despite the many attempts to build ultrathin 2D-2D heterojunctions via wet chemical methods, the resulting composite materials reported to date suffer from poor interfacial bonding and/or complexity of the synthetic protocols. Encouraged by the structural compatibility of Bi₂WO₆ and Bi₂O₂S, both of which are 2D semiconductors sharing a rather similar structural unit of a [Bi₂O₂]²⁺ slice in their crystal structures, we have successfully fabricated an ultrathin nanosheet with a tightly bonded 2D-2D heterojunction between the two components by facilely joining the [Bi₂O₂]²⁺ and [S]^2- slices using a simple two-step hydrothermal method. Such a Bi₂WO₆-Bi₂O₂S 2D-2D heterojunction has a five-alternating-layer (Bi₂O₂S-Bi₂WO₆-Bi₂O₂S-Bi₂WO₆-Bi₂O₂S) sandwich structure and a thickness down to ca. 5 nm and was obtained by simply growing the Bi₂O₂S layer in situ on the surface of monolayer Bi₂WO₆ nanosheets. The judicious combination of Bi₂WO₆ and Bi₂O₂S through a 2D-2D heterojunction not only extended light absorption in the visible range but also significantly enhanced photo(electro)chemical water splitting efficiencies in comparison to the bare Bi₂WO₆ nanosheets alone due to the close-bonding-promoted interfacial charge separation. Our findings provide a viable methodology to build a host of nanomaterials with closely bonded 2D nanosheets, which can be used as photocatalysts and electrocatalysts, among others.