A first-principle investigation of NO2 adsorption behavior on Co, Rh, and Ir-embedded graphitic carbon nitride: Looking for highly sensitive gas sensor

First-principle calculations were performed to investigate the adsorption behavior of NO2 gas on the pristine graphitic carbon nitride (gCN) and transition metals (TM)-embedded gCN systems (TM = Co, Rh, and It elements) in order to explore the sensing capabilities of gCN systems as toxic gas sensor. The results of adsorption energy revealed that NO2 gas was physisorbed on the pristine gCN, whereas this gas was strongly chemisorbed on the TM-embedded gCN. Additionally, it was found that the interaction of NO2 gas with Ir-embedded gCN (-4.47 eV) is much higher than those of the Co and Rh-embedded systems, alluding to its suitability as a highly sensitive gas sensor. The obtained results displayed that the electronic and magnetic properties of the gCN systems remarkably modulated by chemisorption of NO2 gas. The strong interactions between the TM-embedded gCN and NO2 gas induced dramatic changes on the conductivity of the systems and led a large reduction in the band gap energy. The results of spin-polarized band structure and density of states indicated that with adsorption of NO2 gas over the Rh- and Ir-embedded gCN, the magnetic moment of these systems remarkably reduced from 0.10 to 0.07 and 0.01 B, respectively. Additionally, the results of partial density of states indicated that with adsorption of NO2 gas over the pristine and TM-embedded gCN systems, the sharp peaks close to the Fermi energy levels of TM-embedded gCN were significantly increased in comparison with the pristine gCN, thanks to the large charge transfer from d-orbitals of the TM atoms to p-orbitals of NO2 gas. Furthermore, the results of optimized structure showed that with embedding Co-, Rh-, and Ir-elements and also adsorption of NO2 gas on the gCN, the initial planar structure of the pristine gCN automatically became wrinkle. Finally, based on the obtained results, it can be concluded that the high adsorption energy and considerable charge transfer between NO2 gas and Ir-embedded gCN make this system as an excellent candidate for NO2 gas sensor applications. (C) 2019 Elsevier B.V. All rights reserved.