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

Tailoring band gap energies and band alignment typesof heterogeneousphotocatalysts is critical for their performance in particular applications.Here, by performing calculations in the framework of density functionaltheory, we study the role of interface in control and tuning bandgap and band alignment characteristics of two-dimensional van derWaals (vdW) heterostructures of monolayers of triazine graphitic carbonnitride (tg-C3N4) and Janus tungsten sulfideselenide (WSSe) by varying either S or Se atomic layers. Then we investigatehow the vdW heterostructures (i.e., tg-C3N4/SWSeand tg-C3N4/SeWS) over both tg-C3N4 and WSSe surface sides can serve as an efficient water-splittingphotocatalyst under sunlight photoirradiation. We also demonstratethat there is a built-in electric field developed across both heterostructuresdirecting from tg-C3N4 to WSSe, which createsZ-scheme tg-C3N4/SWSe (indirect band gap of1.41 eV) and type-II tg-C3N4/SeWS (direct bandgap of 1.56 eV) heterojunctions. Both of these types are appropriatefor photocatalytic reactions, thanks to retardation in the recombinationrate 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 bothheterostructures exhibit a considerable optical absorption over thevisible light photoirradiation. Then, we compare VBM and CBM energylevels of the heterostructured photocatalyst in water oxidation/reductionreactions over both tg-C3N4 and WSSe surfacesin order to determine its potential application in the overall watersplitting process. We finally study how to tune both heterostructuresfor the desired CBM and VBM energy levels as well as types of bandalignment and band gap energies to improve activity of the photocatalyststoward water splitting reaction under applied biaxial strain and externalelectric field.