Surface morphology effects on the light-controlled wettability of ZnO nanostructures

Abstract

ZnO nanostructures of diverse morphology with shapes of corrals and cabbages as well as open and filled hexagons and sheaves prepared by APMOCVD technique, are investigated with water contact angle (CA) analysis. The as-grown ZnO nanostructures exhibit pure hydrophobic behavior, which is enhanced with the increase of the nanostructure's surface area. The most hydrophobic structures (CA = 124°) were found to be the complex nanosheaf, containing both the macro-and nanoscale features. It is concluded that the nanoscale roughness contributes significantly to the hydrophobicity increase. The character of wettability was possible to switch from hydrophobic to superhydrophilic state upon ultra violet irradiation. Both the rate and amplitude of the contact angle depend on the characteristic size of nanostructure. The observed effect is explained due to the semiconductor properties of zinc oxide enhanced by increased surface chemistry effect in nanostructures.

Water-resistant surfaces using zinc oxide structured nanorod arrays with switchable wetting property

“…Previous research were dedicated to investigate the ZnO switching behavior from hydrophobicity to under UV light exposition [63,64]. In fact, the illumination of ZnO layers with UV light with photon energy equal or higher than the bang gap of ZnO (3.37 eV) generates electron-hole pairs in the surface of the ZnO layers.…”

Microstructure, wettability and electrical properties of n-ZnO/ZnO-SL/p-Cu2O heterojunction

“…A large number of compact and vertically aligned ZnO nanorods on the Sample 2 result in higher total interface area between water and ZnO nanorods. This leads to an effective increase in light-induced surface oxygen vacancies, which are kinetically more favorable for hydroxyl adsorption than oxygen adsorption [15,16]. Thus, the Sample 2 has the most obvious hydrophobic-to-hydrophilic transition.…”

Smart Membrane Surfaces: Wettability Amplification and Self‐Healing

“…Metal oxides such as zinc or titanium oxide can be patterned in intricate structures combining their semiconductor properties with complex topographies. Indeed, the irradiation of ZnO-based surfaces at a wavelength less than 375 nm, which has an energy more than ZnO band gap, caused a reversible hydrophobic-hydrophilic transition from 124° to 5°, owing to competitive sorption/desorption events [22]. Treatments of smooth TiO 2 sol-gel fi lms with CF 4 plasma and octadecylphosphonic acid (ODP) allowed getting surfaces in a superhydrophobic state as well [23].…”