Highly sensitive sensing of CO and HF gases by monolayer CuCl.

Using a first-principles approach, the adsorption characteristics of CO and HF on a CuCl monolayer (ML) are studied with Grimme-scheme DFT-D2 for accurate description of the long-range (van der Waals) interactions. According to our study, CO gas molecules undergo chemisorption and HF gas molecules show a physisorption phenomenon on the CuCl monolayer. The adsorption energy for CO is -1.80 eV, which is quite a large negative value compared to that on other previously studied substrates, like InN (-0.223 eV), phosphorene (0.325 eV), Janus TeSe (-0.171 eV), graphene (P-graphene, -0.12 eV, B-graphene, -0.14 eV, N-graphene, -0.1 eV) and monolayer ZnS (-0.96 eV), as well as pristine hBN (0.21 eV) and Ti-doped hBN (1.66 eV). Meanwhile, for HF, the adsorption energy value is -0.31 eV (greater than that of Ti-doped hBN, 0.27 eV). For CO, the large value of the diffusion energy barrier (DEB = 1.26 eV) during its movement between two optimal sites indicates that clustering can be prevented if many molecules of CO are adsorbed on the CuCl ML. For HF, the value of the DEB (0.082 eV) implies that the adsorption phenomenon may happen quite easily upon the CuCl ML. The transfer of charge according to Bader charge analysis and the variation in the work function depend only on the properties of the elements involved, , their nature, rather than the local binding environment. The work function and band-gap energy variation of the CuCl ML (before and after adsorption) show high sensitivity and selectivity of CO and HF binding with the CuCl monolayer. HF molecules give a more rapid recovery time of 1.09 × 10 s compared to that of CO molecules at a room temperature (RT) of 300 K, which indicates that the necessary adsorption and reusability of the CuCl ML for HF can be accomplished effectively at RT. Significant changes in the conductivity are observed due to the CO adsorption at various temperatures, as compared to adsorption of HF, which suggests the possibility of a modification in the conductivity of the CuCl ML.