First-Principles Study of Two-Dimensional Layered MoSi2N4 and WSi2N4 for Photocatalytic Water Splitting.

Two-dimensional (2D) materials have attracted increasing interest due to their excellent properties and various applications such as energy storage, sensors, composites and catalysis. Recently, 2D van der Waals (vdW) layered materials, MoSi₂N₄ and WSi₂N₄, have been synthesized successfully by CVD methods. Here, we have investigated the structure, optoelectronic properties and electron–hole excitation characteristics of two-dimensional MoSi₂N₄, MoSi₂P₄, and WSi₂N₄ using first-principles calculations to determine whether they can be applied for photocatalytic hydrolysis. The results showed that replacing N atoms in 2D MoSi₂N₄ with P atoms could not only reduce the bandgap, but also make the band position more negative, while replacing Mo atoms with W atoms could expand and move the bands towards more positive direction. H⁺ ions can obtain electrons to generate H₂ from the conduction band of WSi₂N₄ where the conduction band minimum (CBM) and valence band maximum (VBM) is –0.43 and –2.49 eV, respectively. Time-dependent density functional theory is used to explain that the experimentally measured UV–Vis spectra in which visible light absorption is broader and more intense in WSi₂N₄ than in MoSi₂N₄ and WSi₂N₄ is a promising photocatalyst for H₂ generation from water. [ABSTRACT FROM AUTHOR]