Effect of Surface and Defect Chemistry on the Photocatalytic Properties of Intentionally Defect-Rich ZnO Nanorod Arrays

Abstract

Due to the abundance of intrinsic defects in zinc oxide (ZnO), the material properties are often governed by same. Knowledge of the defect chemistry has proven to be highly important, especially in terms of the photocatalytic degradation of pollutants. Given the fact that defect-free materials or structures exhibiting only one type of defect are extremely difficult to produce, it is necessary to evaluate what influence various defects may have when present together in the material. In this study, intentionally defect-rich ZnO nanorod (NR) arrays are grown using a simple low-temperature solution-based growth technique. Upon changing the defect chemistry using rapid thermal annealing (RTA) the material properties are carefully assessed and correlated to the resulting photocatalytic properties. Special focus is put on the investigation of these properties for samples showing strong orange photoluminescence (PL). It is shown that intense orange emitting NR arrays exhibit improved dye-degradation rates under UV-light irradiation. Furthermore, strong dye-adsorption has been observed for some samples. This behavior is found to stem from a graphitic surface structure (e.g., shell) formed during RTA in vacuum. Since orange-luminescent samples also exhibit an enhancement of the dye adsorption a possible interplay and synergy of these two defects is elucidated. Additionally, evidence is presented suggesting that in annealed ZnO NRs structural defects may be responsible for the often observed PL emission at 3.31 eV. However, a clear correlation with the photocatalytic properties could not be established for these defects. Building on the specific findings presented here, this study also presents some more general guidelines which, it is suggested, should be employed when assessing the photocatalytic properties of defect-rich ZnO.

Role of Oxygen Defects on Photoelectrochemical Activity of ZnO Nanorods Grown on Transparent Conducting Oxide Thin Film

“…It was further noted that the defects were uniformly distributed throughout the entire nanorods. The structural defects had already been noticed by Kegel et al [4] (a) (b)…”

“…[2,3] Among various metal oxide semiconductors (MOSs), ZnO is a promising MOS for PEC application due to its cost effectiveness, non-toxicity and earth abundant in nature. [4] The deposition of nanostructured ZnO film on different substrates is possible by various techniques, among which hydrothermal growth technique is an effective one. [5] Moreover, one-dimensional (1D) nanostructures such as nanowires and nanorods with direct electron transport capability can also provide large surface area that is beneficial for improving PEC activity of ZnO.…”

Facile fabrication of porous BiVO4hollow spheres with improved visible-light photocatalytic properties

“…[3][4][5] The widely used semiconductor-based photocatalysts include zinc oxide (ZnO) and titanium dioxide (TiO 2 ). 6,7 However, only ultraviolet or near ultraviolet fractions of sunlight can be absorbed by ZnO and TiO 2 because of their broad bandgaps (3.0-3.2 eV). So, the development of photocatalysts with enhanced solar energy utilization efficiency is urgent.…”

Enhanced Photocatalytic Activity of ZnO Toward the Degradation of Methylene Blue Dye: Effects of Fe3+ and Sn4+ Doping

“…Nanometer ZnO is a multifunctional semiconductor material that is widely applied as a photocatalyst . ZnO photocatalyst is used to degrade organic pollutants in industrial wastewater . With the aid of ultraviolet (UV) light, the photogenerated electrons (e − ) and holes (h + ) in ZnO semiconductor can react with O 2 , OH − , and H 2 O to produce active species such as • O 2− and • OH.…”