van der Waals heterostructure for photocatalysis: Graphitic carbon nitride and Janus transition-metal dichalcogenides

Converting solar energy into chemical energy by splitting water is a promising method to generate a sustainable and renewable solution without detrimental environmental impact. The two-dimensional semiconductors serve as potential catalysts in this regard, and here we combine Janus transition-metal dichalcogenides (MoXY, X/Y = S, Se, Te) and graphitic carbon nitride in a van der Waals heterostructure. Within the first-principles calculations, we investigate the electronic, optical and excitonic properties that determine the photocatalytic activity. Due to the internal electric field, the photogenerated electrons and holes are separated in the MoXY layers, and also generates high overpotentials for the redox reactions. The high optical absorptions span throughout the entire visible and near ultraviolet regime in these heterostructure nanocomposites. Further, the lower exciton binding, calculated within the two-dimensional hydrogenic model, indicates efficient charge separation. The maximum solar-to-hydrogen efficiency using the entire solar spectrum reaches up to 16.5% in these heterostructures. The present results indicate these heterostructures to be excellent candidate materials for photocatalytic applications and also demonstrate the enormous possibilities in two-dimensional heterostructures that should attract considerable theoretical and experimental attention in future.