Understanding the influence of single metal (Li, Mg, Al, Fe, Ag) doping on the electronic and optical properties of g-C3N4: a theoretical study

Semi-empirical tight-binding-based quantum chemistry method (GFN2-xTB) has been done to study the influence of single metal (Li, Mg, Al, Fe, Ag) doping on the electronic and optical properties of monolayer corrugated graphitic carbon nitride (g-C3N4). Based on the calculated formation energy and population analysis, we showed that the metal atom is chemically bound to the g-C3N4 surface. The metal doping reduces the vertical ionisation potential and raises the electron affinity and Lewis acidity of g-C3N4. The metal-doped g-C3N4 systems have lower band gap than that of pristine g-C3N4 which is attributed to the electron donating from the metal atom to g-C3N4. Analysis of the lowest unoccupied molecular orbital and the highest occupied molecular orbital shows that for the Fe- and Ag-doped g-C3N4 systems the separation of photo-generated electron-hole pairs is efficient, resulting in the enhancement of photo-catalytic activity.