Theoretical study of the electronic structure of the complexes of gold, silver, and copper mono- and bimetallic nanoclusters decorated on graphitic carbon nitride (g-C3N4): DFT and TD-DFT studies of photocatalytic activity

In this study, the structure and electronic properties of tetratomic metal clusters of Au, Ag, and Cu decorated on graphitized carbon nitride (g-C3N4) were investigated using the density functional theory (DFT) method. The most stable structures of the complexes of Au4, Ag4, Cu4, Au2–Ag2, Au2–Cu2, and Ag2–Cu2 clusters with g-C3N4 were calculated. The molecular orbitals, partial atomic charges, and density of states of the complexes were calculated. It was noted that the HOMO–LUMO energy gap of the complexes varied depending on the type of metal cluster on the g-C3N4. The absorption spectra of the complexes were calculated and compared with the absorption spectrum of the bare g-C3N4. The electronic configurations of the calculated absorption lines in the visible region of the absorption spectrum of each complex were investigated. The absorption lines that were related to the electron excitation from an occupied molecular orbital of the complex, localized on the metal cluster, to an unoccupied orbital of the complex, localized on g-C3N4, were selected for further comparison. The electron–hole recombination rate for this type of absorption line is lower than that of the absorption lines in which the initial and final molecular orbitals are related to the g-C3N4. The prolonged electron–hole lifetime can lead to higher photocatalytic activity.