Among dozens of layered transition metal dichalcogenides (TMDs), VS₂ has attracted particular interest due to its intrinsic magnetism and potential applications as a high-performance functional nanomaterial. The phase stability and electronic properties of the typical crystal structures of both monolayer and bulk VS₂ are carefully investigated based on first-principle calculations. The results reveal that the relative stability between different phases is greatly affected by the thickness of the layers and the temperature. Below room temperature, both bulk and monolayer VS₂ prefer to exhibit the hexagonal (H) structure instead of the trigonal (T) structure. Interestingly, at room temperature, although the H monolayer VS₂ remains more stable than the T-VS₂, the bulk T-VS₂ becomes more stable than H-VS₂. These results reveal that a phase transition between H and T will occur on changing either the thickness of the slab or the temperature. Furthermore, the different crystal structures (H and T) exhibit significantly distinct magnetism: the bulk T-VS₂ has the lowest magnetism (0.31 μ_B), while the monolayer H-VS₂ has the largest magnetism (about 1.00 μ_B) among the structures. Most importantly, our results reveal that the magnetism will increase sharply on the exfoliation of monolayer VS₂ from the bulk at room temperature because of the phase transition from T to H. The present results provide an efficient way to modulate the magnetic moment through controlling the crystal structure and the thickness of the VS₂ nanosheets.

Two-dimensional (2D) materials open up tremendous opportunities for attractive applications in next-generation flexible and transparent nanoelectronic devices. In this work, the structural and electronic properties of 81 single layer structures are systematically examined for the 27 zinc-blende (ZB) materials with the constitutional formula MX by density functional calculations. The calculated results reveal that 38 of them are thermodynamically stable including 12 two-phase coexistence structures. Interestingly, the stable configurations in various MX compounds are correlated with the atomic radius and electronegativity difference of constituent elements X and M. The atomic and electronic properties of novel materials are greatly dependent on the stable phase structures. The stable single-layer ZB structures exhibit versatile electronic properties, such as tunable band gaps, strong optical absorption in the solar spectrum and suitable band edge positions, thus such 2D materials are potential photocatalysts for water-splitting.

Hydrogen is a highly appealing renewable energy resource, while hydrogen generation and storage for practical applications remain a great challenge at present. The proposed porous p-BN has both good hydrogen generation and storage ability which can be dramatically enhanced by C-dopant and Li-decoration.

Charge density of the VBM (green) and CBM (blue) for armchair MoS₂–WS₂ heterostructures, indicating the spontaneous separation of photo-generated electrons and holes, which could strongly enhance the photocatalytic activity due to suppression of the electron–hole recombination.

Two-dimensional graphene-like materials have attracted considerable attention for the further development of nanoscale devices. In this work, the structural, electronic and optical properties of free-standing, graphene-like nitrides XN (X = B, Al and Ga) are studied by density functional calculations with the inclusion of the nonlocal van der Waals correction. The results show that all the studied nitrides are thermodynamically stable and their electronic structures can be easily tuned by forming the heterostructure with MoS₂ monolayer. Although GaN and AlN monolayers retain the indirect band gap of bulk, MoS₂–AlN and MoS₂–GaN heterostructures have suitable direct gaps, complete electron–hole separation and fascinating visible light adsorption, which is promising for solar energy applications. Moreover, the MoS₂–AlN heterostructure is a good candidate for enhanced photocatalytic activity of hydrogen generation from water.