Density functional theory (DFT) studies at B3LYP/6–31 G (d) level were performed to evaluate the electronic sensitivity of pristine and transition metals (TM) such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu doped in ZnS nanocluster (TM-doped Zn12S12) toward carbon monoxide (CO) molecule. Several parameters, including the adsorption energy (Ead), band gap energy (Eg), atoms in molecules (AIM) results, the distance between the C atom of CO (DX-C), and Mulliken charge transfer (QT), were calculated to estimate the sensitivity of Zn12S12 and its TM-doped forms to CO tracing. Due to their highest Eg change (ΔEg) values after CO adsorption, Ni- and V doped Zn12S12 have the most significant potential for use as CO sensors among the investigated TM-doped Zn12S12. In addition, doping with Cr, Mn, Cu, Co, or Fe reduces sensitivity slightly, whereas doping with Sc or Ti reduces sensitivity significantly. The Eg of V- and Ni-doped Zn12S12 increased significantly after CO adsorption (ΔEg%= 33.73% and 33.35%, respectively). Furthermore, the highest electron density (ρ) values at the C.TM bonds accorded in CO/V-doped Zn12S12 and CO/Ni-doped Zn12S12. It is found that replacing a Zn atom with Mn, Cr, Cu, or Fe atom slightly decreases the sensitivity of the cluster but doping Ni and V atoms significantly increases the sensitivity. Also, Ti or Sc doping greatly reduces the sensitivity.

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