Orbital Understanding to the Origin of Site-Specific Band Gap Tuning in Electron-Rich S-Doped and Electron Precise C,S-Dual-Doped Graphitic Carbon Nitride
Mohammed Sadik N. K., Gibu George, Susmita De
Abstract
Elemental doping engineering has proven to be a powerful method for tailoring the physical and chemical properties of two-dimensional materials. However, we still lack an understanding of how to control it for our desired purpose. Graphitic carbon nitride ( g-CN ) is an exciting material that has received much attention for enhanced optical and photo-physical properties due to elemental doping. Sulfur-doped g-S-CN is an interesting example of elemental doping that exhibits both enlarged and narrowed band gaps. Hence, it is necessary to understand the electronic origin of band gap variation with respect to the structure of the doped material. Herein, we aim to provide a systematic theoretical understanding of the enhanced optical properties of electron-rich sulfur-doped g-S-CN and the electron-precise carbon sulfur dual-doped g-CS-CN . In our theoretical investigation, we have successfully shown that a mere change of dopant site alters the electronic structure owing to the geometrical changes at the atomic level in order to maintain proper π-electron delocalization in the system. The prominent effect observed in the replacement of di-coordinated aromatic N-atom by the C-atom is the destabilization of the σ-valence band, while the substitution of tri-coordinated terminal and central N-atom by C-atom destabilizes the π-conduction band as compared to g-S-CN . Considering the suitable position of the bands, band gap, and low substitution energy, the dual-doped pristine g-CN (band gap = 2.80 eV) formed by the substitution of aromatic N-atom with S-atom and terminal/central N-atom with C-atom leads to rather stable systems with Δ E sub(g-CS-CNx) of 0.68 and 0.90 eV, as well as higher photocatalytic reactivity, where the former shows a redshift (2.37 eV) and the latter shows a blueshift (3.09 eV) within the visible region. Thus, promising theoretical understanding about the tuning of band edge levels of these novel C,S-dual doped g-CN can attract more experiments for potential applications to be developed, especially for photocatalysis.