CO2 and CO gas sensing using ZnO-based sensors: An experimental-theoretical study

The detection of carbon dioxide (CO 2 ) and carbon monoxide (CO) is critical for environmental and safety applications. This work presents a synergistic experimental and theoretical investigation of zinc oxide (ZnO) films for sensing these gases. ZnO with a hemispherical morphology (103 ± 20 nm) and the wurtzite phase was obtained via an ultrasound-assisted sol-gel route. The sensor exhibited performance at 200 °C, showing a concentration-dependent response to CO 2 from 44.96 % (50 ppm) to 64.94 % (200 ppm), with a sensitivity of 0.137 %/ppm and rapid response/recovery (14.66/71 s). A 50 % response was observed for CO at 130 ppm. Density functional theory (DFT) calculations corroborated these findings, revealing chemisorption on the O-terminated ZnO (0001) surface with adsorption energies of -4.83 eV for CO and -4.74 eV for CO 2 . Electronic structure analysis confirmed that adsorption introduces mid-gap states, facilitating charge transfer and elucidating the fundamental mechanism behind the enhanced electrical response. The high performance is attributed to the synergistic effect of morphology, oxygen vacancies, and the theoretically identified favorable adsorption pathways.