Investigating the chemisorption of CO and CO₂ on Al- and Cu-doped ZnO nanowires by density-functional calculations

The chemisorption of CO and CO₂ on zinc oxide triangular nanowires, doped with Al and Cu atoms, was studied using density functional calculations. Adsorption energies for CO on doped nanowires are higher than those for the pristine nanowire. In particular, configurations forming C[sbnd]Al bonds have double the adsorption energies when compared to those in the pristine nanowire. A lower adsorption energy is found when both the CO atoms are bonded to the Al-doped ZnO nanowire. For the Cu-doped nanowire, double-bond configurations have the highest adsorption energies. CO₂ forms tri-dentate structures in the pristine nanowires. In Al-doped nanowires, we observed mono- and bi-dentate modes of adsorption, and only one configuration showed enhancement in the adsorption energy. The CO₂ prefers to bond to a Zn atom in the Cu-doped nanowire. Reductions in the band gap energy and shifts in the stretching frequency due to adsorption are also discussed.