Transition metal decorated ZnO monolayer for CO and NO sensing: A DFT plus U study with vdW correction

Based on density functional theory, we study the adsorption of CO and NO gas molecules on transition metal (Fe, Co, Ni, Cu) decorated ZnO monolayer (ZnO ML), with the electronic interactions taken into account by introducing Hubbard potential (U) for d-orbitals and van der Waals interactions corrected using Grimme method. From its electronic properties and adsorption energies, pristine ZnO ML shows weak physical interaction with the gas molecules with adsorption energies of -0.05 eV and -0.07 eV for CO and NO respectively. TM atoms are then placed in their most stable site (top of O atom for all TMs), with their binding energy in the range of 1.002-2.314 eV. Upon TM decoration, CO shows an adsorption energy in the range of -0.3 eV to -1.3 eV, while NO adsorption energies are in the range of -1.7 to -2 eV. Recovery time calculation shows that Fe and Codecorated ZnO ML served as a reusable sensor for CO gas while the rest shows great application prospects in the field of industrial safety monitoring. These results showed that TM-decoration in ZnO ML is an effective way of improving its CO and NO gas sensing properties and adsorption capacities.