Metal-doped graphitic carbon nitride (g-C ₃ N ₄ ) as selective NO ₂ sensors: A first-principles study

In this research, the potential application of metal-doped g-C ₃ N ₄ as highly sensitive molecule sensors for NO ₂ detection was studied using density function theory (DFT) calculations. Various metal-doped (Ag-, Au-, Co-, Cr-, Cu-, Fe-, K-, Li-, Na-, Mn-, Pt-, Pd-, Ti-, V-) g-C ₃ N ₄ sheets were considered. CO, CO ₂ , NH ₃ , N ₂ and NO ₂ molecules were found to adsorb on metal-doped g-C ₃ N ₄ via strong chemical bonds. Chemisorbed gas molecules and metal-doped g-C ₃ N ₄ formed charge transfer complexes with different charges transferring from metal-doped g-C ₃ N ₄ to gas molecules. Pristine and metal-doped g-C ₃ N ₄ sheets were demonstrated as potential capturers for certain gas molecules according to the adsorption energy, isosurface of electron density difference, and density of states analysis. Among the diverse metal-doped g-C ₃ N ₄ sheets, Ag-, K-, Na-, and Li-doped g-C ₃ N ₄ were found to be clearly sensitive to the NO ₂ molecule. The adsorption energies between NO ₂ and Ag-, K-, Na-, and Li-doped g-C ₃ N ₄ were significantly greater than those of the other gas molecules (CO, CO ₂ , N ₂ , and NH ₃ ). The density of states indicates that the NO ₂ adsorption on Ag-, K-, Na-, and Li-doped g-C ₃ N ₄ induced the shift of the total density of state in the positive energy direction. Charge transfer results also demonstrate that chemical interactions existed between NO ₂ and Ag-, K-, Na-, and Li-doped g-C ₃ N ₄ . All these results suggest the strong potential of Ag-, K-, Na-, and Li-doped g-C ₃ N ₄ for application as highly sensitive molecule sensors.