Strain-tunable electronic and optical properties in two dimensional GaSe/g-C3N4 van der Waals heterojunction as photocatalyst for water splitting

Abstract Restacking diverse two dimensional (2D) nanosheets into a bilayer van der Waals (vdW) heterojunction opens up a promising platform for designing high performance photocatalyst. In this work, by employing HSE06 hybrid functional, we have systematically studied the electronic and optical properties of GaSe/g-C3N4 bilayer heterojunction, whose different layers with a interlayer spacing of 3.49 A at equilibrium are bound together through the vdW interaction. Our computations indicate that the GaSe/g-C3N4 heterostructure, whose bandedge positions can stride over the redox levels of water and bandgap is much smaller than that of GaSe monolayer, is suitable for photocatalytic water splitting. By applying strains in the range from 6% pressure to 6% tension, these bandgaps of GaSe/g-C3N4 heterojunction can be narrowed to the range of 1.70–2.84 eV. Particularly, GaSe/g-C3N4 heterojunction with 6% tension, whose conduction band minimum (CBM) and valence band maximum (VBM) are situated at different slabs, can realize the efficient separation of electron–hole pairs. Meanwhile, GaSe/g-C3N4 heterojunction with 6% tension, whose bandgap decreases to 2.31 eV, can make the utmost of the sunlight. In contrast with GaSe and g-C3N4 monolayers, the distinct red shifts of optical absorption appear in GaSe/g-C3N4 heterojunctions with 6% tension, which results in the narrowing of the bandgaps. Even in the VIS region about 460 nm, there is an absorption peak in the optical absorption spectrum of GaSe/g-C3N4 heterojunctions with 6% tension. Therefore, GaSe/g-C3N4 heterojunctions should have promising applications as photocatalysts for water decomposition to generate hydrogen.