Metal-doped graphitic carbon nitride (g-C3N4) as selective NO2 sensors: A first-principles study

In this research, the potential application of metal-doped g-C3N4 as highly sensitive molecule sensors for NO2 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-C3N4 sheets were considered. CO, CO2, NH3, N2 and NO2 molecules were found to adsorb on metal-doped g-C3N4 via strong chemical bonds. Chemisorbed gas molecules and metal-doped g-C3N4 formed charge transfer complexes with different charges transferring from metal-doped g-C3N4 to gas molecules. Pristine and metal-doped g-C3N4 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-C3N4 sheets, Ag-, K-, Na-, and Li-doped g-C3N4 were found to be clearly sensitive to the NO2 molecule. The adsorption energies between NO2 and Ag-, K-, Na-, and Li-doped g-C3N4 were significantly greater than those of the other gas molecules (CO, CO2, N2, and NH3). The density of states indicates that the NO2 adsorption on Ag-, K-, Na-, and Li-doped g-C3N4 induced the shift of the total density of state in the positive energy direction. Charge transfer results also demonstrate that chemical interactions existed between NO2 and Ag-, K-, Na-, and Li-doped g-C3N4. All these results suggest the strong potential of Ag-, K-, Na-, and Li-doped g-C3N4 for application as highly sensitive molecule sensors.