Single metal (M=Sc, Ti, Fe, Co, Ni) atom anchored in three pyrrolic-N doped graphene for the CO gas-sensing characterization from DFTB algorithm

Based on self-consistent charge density functional tight-binding calculations, this study investigates the adsorption properties of CO on the three pyrrolic-N doped graphene (pyrrolic-type nitrogen tricoordinate doped graphene, N3-G) anchored by a single metal atom. The Co@N3-G structure, formed by anchoring a cobalt atom onto the N3-G framework, exhibits a binding energy as high as 5.23 eV and a significantly reduced energy gap of 0.30 eV. This reduces the energy required for electronic thermal excitation and the barrier for carrier transport. The adsorption energy of the CO molecule (whether the C-end or O-end) on the Co@N3-G substrate reaches as high as 3.5 eV, surpassing that of other configurations. The shortened Co-C and Co-O bond lengths, averaging 1.860 Å and 1.898 Å, respectively, reflect strong bonding interactions driven by higher electron density. In addition, CO adsorption leads to a significant reduction in the energy gap of Co@N3-G by approximately 44.99% and 49.88%. In summary, the low energy gap of Co@N3-G itself and its significant electrical conductivity modulation upon adsorption of trace amounts of CO highlight its potential as a highly sensitive gas-sensing material operable at room temperature.