• Universitat de València

• Christian Dolle

2D layered materials are of great scientific interest due to their physical and chemical properties. These materials could be promising not only for (opto)electronic applications, but also for catalysis, energy storage or biological applications.

Among all ultra-thin layered materials, those formed by elements of the nitrogen or pnictogen group occupy a prominent place since their properties can complement or even surpass in some cases those of graphene, the best known 2D material. Among these elements, bismuth (Bi) is particularly noteworthy, as it is a semi-metal with very interesting physicochemical properties, for example: it has a high storage capacity for alkali metals, very low toxicity, high spin-orbit coupling and considerable diamagnetism.

However, the generation of these layered materials represents a major challenge as the formation of anisotropic thin films becomes progressively more complicated as one moves down the elements of the periodic table. Existing methods, such as epitaxial growth or liquid-phase exfoliation, lead to the formation of small nanoparticles of different sizes and high polydispersity.

There is, therefore, a need for efficient procedures for the synthesis of high quality 2D pycogenics, and bismuth in particular given its special properties, which allow the growth and morphology of the layers to be controlled and easily scalable.

Research staff at the Universitat de València (ICMOL) have developed a colloidal synthesis method for obtaining 2D bismuth crystals, based on a photocatalytic reduction of an organometallic Bi(III) complex.

This synthesis method allows to obtain a 2D bismuth material, also called bismuthene. The lamellar structure of this material is formed by two outer layers of organic molecules containing sulphur atoms and an inner layer formed by a crystal lattice of Bi(0) atoms. These structures have interesting features for energy storage, medical, catalysis, topological properties and other applications.

Examples of applications for 2D bismuth include:

• In energy, as an electrode in sodium ion batteries.
• In medicine, as a contrast agent.
• In electronic applications, as a material with topological properties.
• In chemical catalysis, as part of the structure in porous materials.

The main advantages of this new synthesis method for 2D bismuth layered materials are:

• Simplicity and ease of production of ultra-thin layered materials.
• The size, thickness and plane orientation of the crystals obtained can be controlled.
• Scalability, allowing 2D bismuth crystals to be obtained in large quantities with reproducible characteristics and properties.

In addition, the resulting material, bismuthene, has several advantages over other layered materials of group 15 elements, such as:

• High stability against oxidation.
• It allows the incorporation of functional groups to its structure, allowing the possibility of new properties and functionalities.

• Patent applied