Interfacial Control at Janus WSSe/Triazine g-C3N4 Heterostructures in Developing Type-II and Z-Scheme Photocatalysts

Tailoring band gap energies and band alignment types of heterogeneous photocatalysts is critical for their performance in particular applications. Here, by performing calculations in the framework of density functional theory, we study the role of interface in control and tuning band gap and band alignment characteristics of two-dimensional van der Waals (vdW) heterostructures of monolayers of triazine graphitic carbon nitride (tg-C3N4) and Janus tungsten sulfide selenide (WSSe) by varying either S or Se atomic layers. Then we investigate how the vdW heterostructures (i.e., tg-C3N4/SWSe and tg-C3N4/SeWS) over both tg-C3N4 and WSSe surface sides can serve as an efficient water-splitting photocatalyst under sunlight photoirradiation. We also demonstrate that there is a built-in electric field developed across both heterostructures directing from tg-C3N4 to WSSe, which creates Z-scheme tg-C3N4/SWSe (indirect band gap of 1.41 eV) and type-II tg-C3N4/SeWS (direct band gap of 1.56 eV) heterojunctions. Both of these types are appropriate for photocatalytic reactions, thanks to retardation in the recombination rate of the photogenerated charge carriers (electrons and holes), resulting from better spatial separation of conduction band minimum (CBM) and valence band maximum (VBM). Furthermore, we show that both heterostructures exhibit a considerable optical absorption over the visible light photoirradiation. Then, we compare VBM and CBM energy levels of the heterostructured photocatalyst in water oxidation/reduction reactions over both tg-C3N4 and WSSe surfaces in order to determine its potential application in the overall water splitting process. We finally study how to tune both heterostructures for the desired CBM and VBM energy levels as well as types of band alignment and band gap energies to improve activity of the photocatalysts toward water splitting reaction under applied biaxial strain and external electric field.