Computational investigation of sensing properties of Ca-doped zinc oxide nanotube toward formaldehyde.

Following an experimental work, we employed density functionals B3LYP, B97D, CAM-B3LYP, BMK, and M06-HF to study the impact of Ca-doping on a ZnO nanotube (ZnONT) sensing performance to the formaldehyde gas. The interaction of the pristine ZnONT with the formaldehyde gas was found to be weak, and the sensing response is 0.7 based on the B3LYP results. Doping a Ca atom into the ZnONT changes the adsorption energy of formaldehyde from - 4.2 to - 36.1 kcal/mol. Energy decomposing analysis indicated that the nature of interaction is partially electrostatic and covalent. The sensing response significantly rises to 4.2 by Ca-doping (experimental value ~ 5.28). A short recovery time of 5.6 s is found for the formaldehyde gas desorption from the Ca@ZnONT surface at 300 °C. Both theory and experiment suggest that Ca-doped ZnONT may be a formaldehyde gas sensor with a short recovery time.