Ultraviolet-light-assisted formation of ZnO nanowires in ambient air: Comparison of photoresponsive and photocatalytic activities in zinc hydroxide

Abstract

In ambient air, zinc acetylacetonate hydrate precursor was directly decomposed to fabricate large-area ZnO nanowires on a substrate using ultraviolet-light- (λ = 350-380 nm, I = 76 mW cm-2) assisted thermal decomposition processes at 200 °C. The growing process required 5 min. High-resolution transmission electron microscopy images revealed that the ZnO nanowires consisted of fine single-crystal nanoparticles. The particle size was calculated to be ∼8-9 nm using the Debye-Scherrer equation. The photocatalytic activities of ZnOnonUV (without UV-light assistance) nanowires were found to be superior to those of ZnOUV (with UV-light assistance) nanowires and commercial TiO2 P25 nanoparticles. The oxygen defects (i.e., oxygen vacancies and interstitials) acted as key components for a photodegradation process in the ZnO nanowires. The oxygen defects are attributed to the presence of zinc hydroxide [Zn(OH)2] on the surface of the ZnO nanocrystallites. For the photoresponsive activities, no significant photocurrent-to-dark-current ratio was observed in ZnO nonUV nanowires using UV-light (λ = 365 nm, I = 2.33 mW cm-2), whereas the ratio of ZnOUV nanowires was high, reaching a maximum of 91. As-synthesized ZnOUV nanowires exhibited a relatively good crystallinity and superior photoresponsive properties when compared with ZnOnonUV nanowires based on the characterizations of the materials and sensor properties. Detailed mechanisms of the photoresponsive and photocatalytic properties were investigated. © 2011 American Chemical Society.