Zinc oxide nanoclusters and their potential application as CH4 and CO2 gas sensors: Insight from DFT and TD-DFT.

Abstract

We have investigated the adsorption of CH4 and CO2 gases on zinc oxide nanoclusters (ZnO NCs) using density functional theory (DFT). It was found that the CH4 tends to be physically adsorbed on the surface of all the ZnO NCs with adsorption energy in the range -11 to -14 kcal/mol. Even though, the CO2 is favorably chemisorbed on the Zn12 O12 and Zn15 O15 NCs, with adsorption energy about -38 kcal/mol at B3LYP/6-311G(d,p) level of theory. When the CH4 and CO2 gases are adsorbed on the ZnO NCs, their electrical conductivities are decreased, and thus the studied ZnO NCs do not generate an electrical signal in the presence of CH4 and CO2 gases. Interestingly, both pure and gas adsorbed Zn22 O22 NC exhibited more favorable electronic and reactive properties than other NCs. Comparison of the structural, electronic, and optical data predicted by DFT/B3LYP and TD-DFT/CAM-B3LYP calculations with those experimentally obtained show good agreement.