Zinc oxide for gas sensing of formaldehyde: Density functional theory modelling of the effect of nanostructure morphology and gas concentration on the chemisorption reaction

The adsorption of formaldehyde (HCHO) gas on different one-dimensional ZnO nanostructures is examined using density functional theory calculations. The effects of nanostructure shape and gas concentration are investigated to determine how these factors may influence the surface reaction of HCHO for sensing applications. The binding energies, vibrational frequencies, charge transfer and density of states were determined. We show that HCHO associatively chemisorbs in multiple sites and orientations on the ZnO nanowire and facetted-nanotube. The facetted-nanotube offers a greater number of adsorption sites due to its larger surface area and hollow centre where HCHO can also adsorb. HCHO is able to form one or two bonds to the surface, where structures in the latter configuration show greater stability, with HCHO behaving as a charge acceptor. Conversely, HCHO acts as a charge donor in the singly coordinated structures. As the adsorption mechanism of HCHO gas on the surface of ZnO nanostructure is not well understood, this study provides useful insights into the gas-surface reaction that may assist future experimental development of ZnO nanostructures for gas sensing of formaldehyde. (C) 2017 Elsevier B.V. All rights reserved.