First-principles investigation on hydrogen evolution reaction in KNbO3 (100)/g-C3N4 heterojunction

Constructing the two-dimensional (2D) heterojunction photocatalysts is a highly efficient strategy for utilizing solar energy and speeding up the separation rate of photogenerated charge carriers. In this contribution, we systematically investigate the electronic and photocatalytic performances of the 2D KNbO3/g-C3N4 heterojunction using first-principles calculations, along with the origin of the photocatalytic performance. Our results indicate that the KNbO3/g-C3N4 heterojunction is a very promising photocatalytic material for water splitting, particularly for the hydrogen evolution reaction, well consistent with the reported experimental results. The KNbO3/g-C3N4 heterojunction owns a type-II band alignment. Moreover, the density charge difference (DCD) and Mulliken population analysis show that the g-C3N4 monolayer can absorb visible light and effectively improve the optical properties of KNbO3. After g-C3N4 combined with KNbO3 (100) surface, the band gap has been significantly reduced and a red shift occurs in the visible light region. Additionally, the application of an external electric field and biaxial strain have been evident as efficient methods to obtain modulated band gaps for the heterojunction. Interestingly, a linear evolution trend of the band gap is presented for the heterojunction under the compression and tensile strain. Heterojunctions have a tendency to convert from semiconductors to conductors. Overall, these findings provide theoretical support for the research about KNbO3/g-C3N4 heterojunction and pave a way of enhancing the photocatalytic performance under visible light irradiation.