Copper oxide monolayers as carbon monoxide gas sensors: a density functional theory study

Using density functional theory calculations (LDA + U and HSE06), we study carbon monoxide (CO) adsorption on experimentally realised copper oxide (CuO) monolayers. A CO molecule is adsorbed exothermically on the CuO monolayer surface for all surface coverages and structural representations examined, with adsorption energies clustered around −0.25 eV, while CO adsorption reduces the band gap from the pristine range of 1.36–1.38 eV to values between 1.10 and 1.35 eV. For the primary CuO monolayer representation considered, with a ratio of one gas molecule per 16 Cu atoms, CO adsorption reduces the band gap to 1.26 eV through modulation of extended lattice states, with less than 1% of the frontier orbital density localised on the CO molecule, while H2O also reduces the band gap to 1.32 eV, and the other common atmospheric gases (CO2, O2, and N2) induce negligible changes to the band gap. However, water binds more strongly (−0.46 eV) and is expected to dominate surface coverage under humid conditions, posing a significant selectivity challenge. These results suggest that band-gap modulation in CuO monolayers may serve as a viable electronic signature for CO sensing, provided that environmental effects such as humidity are properly treated.