Computational studies on magnetism and the optical properties of transition metal embedded graphitic carbon nitride sheets

Using density functional theory (DFT), we have explored the structural, electronic, magnetic and optical properties of two-dimensional 3d-transition metal (TM)-embedded graphitic carbon nitride (g-C3N4) sheets. g-C3N4 sheets are structurally modified in different ways depending upon the radius of embedded-TM atoms and the crystal field stabilization energy gained by the corresponding geometry. Bare g-C3N4, which is a wide-gap semiconductor, becomes metallic upon TM inclusion. The d-orbitals of TMs hybridize with the p(pi)-orbitals of the g-C3N4 framework and close the band gap in TM-embedded g-C3N4 (TM-g-C3N4). Interestingly, for V, Cr and Fe embedded g-C3N4, the TM atoms interact ferromagnetically to each other and result in a ferromagnetic ground state. However, Mn couples antiferromagnetically and Cu and Zn are nonmagnetic in the ground state of their corresponding TM-g-C3N4 sheets. Because of structural distortion, Co- and Ni-g-C3N4 do not have a well-ordered magnetic orientation. Performing Heisenberg-model-based Monte Carlo simulations, we predict that V-, Cr- and Fe-g-C3N4 would possess Curie temperatures (T-c) of 205 K, 170.5 K, and 115 K, respectively. Furthermore, these modified g-C3N4 sheets also show prominent absorption at low energy, which evidently confirms their efficient photoabsorption capacity. The present study demonstrates the multifunctional behavior of TM-g-C3N4, which shows significant promise for application in various fields such as in memory devices or for photocatalysis.