Theoretical Modeling of Direct Z-Scheme B,F-Doped g-C3N4/CoN4 Composites for Promoting Photocatalytic Water Splitting Reaction

Abstract

The Z-scheme mechanism bestows a perfect band alignment for photocatalysis due to the high separation efficiency of the photoexcited electron–hole pair and concomitantly preserves the redox ability toward reduction of electrons and oxidation of holes. However, the challenge of modeling and building of Z-scheme photocatalysts hinges on the correct band alignment and the direction of the inherent electric field. Keeping the efficacy of the advanced metaGGA functional to illustrate the band gap of layered materials in mind, we model a Z-scheme photocatalytic mechanism using density functional theory calculations using R2SCAN method. The type I g-C₃N₄/CoN₄ heterojunction with limited photocatalytic activity is switched into a direct Z-scheme configuration through boron and F doping in g-C₃N₄ and enhances the utilization ratio of visible light for the g-C₃N₄/CoN₄ photocatalyst. The built-in electric field in the B,F-g-C₃N₄/CoN₄ nanocomposite facilitates interface charge transfer and forbids the rapid recombination of photoinduced carriers, causing the B,F-g-C₃N₄ monolayer with a negative charge and the CoN₄ (111) surface with a positive charge. The higher band edge potentials of CoN₄(111) surface compared to that of the B,F-g-C₃N₄ monolayer ensure a stronger redox ability and the built-in electric field along with satisfy the essentiality of B,F-g-C₃N₄/CoN₄ nanocomposite to be a typical Z-scheme heterostructure. In the presence of visible light irradiation, electrons are excited to the conduction band minimum (CBM) of the CoN₄ (111) surface enduring the hydrogen evolution reaction (HER), and the holes remain in the valence band maximum (VBM) of the B,F-g-C₃N₄ monolayer ministering the oxygen evolution reaction (OER). Investigation on the absorption spectra further manifests a large enhancement of the visible light absorption efficiency after boron and fluorine doping. A systematic theoretical analysis of electronic and optical properties, charge transfer, differential charge density distribution, work function, and photocatalytic mechanisms manifests that B,F-g-C₃N₄/CoN₄ is a potential Z-scheme photocatalyst for water splitting reaction under visible light.