LAUSR

We have successfully prepared the ZnO nanowire (nw) thin films which show different surface wettabilities to discuss the correlation between the photocatalytic reactivities and the surface morphologies. When the ZnO(seed)/glass was horizontally placed in the ZnO precursor solution, relatively short and thick ZnO hexagonal cylinders were randomly accumulated on the substrate (denoted as “h-ZnO(nw)/glass”). The h-ZnO(nw)/glass showed high surface wettability (water contact angle: 0°) because liquid water easily went into the micrometer-sized inter-particle voids via capillary effect. In contrast, when the ZnO(seed)/glass was vertically placed in the ZnO precursor solution, relatively long and thin ZnO nanowires perpendicularly grew and aligned on the substrate (denoted as “v-ZnO(nw)/glass”). The v-ZnO(nw)/glass showed high water-repellent property (water contact angle: 100°–143°) because of a lotus effect exhibited by the thin ZnO nanowires. The v-ZnO(nw)/glass had about twice the surface area of the h-ZnO(nw)/glass but did not show sufficiently high photocatalytic reactivity for the decomposition of methylene blue (MB) in aqueous solution because of its water-repellent property. However, the high surface area of the v-ZnO(nw)/glass was useful for the photocatalytic decomposition of acetaldehyde in gaseous phase. The deposition of Ag particles especially improved the photocatalytic reactivity of the h-ZnO(nw)/glass up to 2.8–6 times, because lots of Ag particles were deposited on the sidewalls of the ZnO hexagonal cylinders due to their high surface wettability. However, since the Ag particles were deposited only on the tips of the ZnO nanowires due to the water-repellent property of the v-ZnO(nw)/glass, the photocatalytic reactivity was only improved up to 1.6–2.4 times.