Enhanced Quality, Growth Kinetics, and Photocatalysis of ZnO Nanowalls Prepared by Chemical Bath Deposition

Abstract

ZnO nanowalls (NWLs) represent a non-toxic, abundant and porous material, with promising applications in sensing and photocatalysis. They can be grown by low-cost solution methods on Al (covered) substrates -Al(OH) 4 -generated in situ is assumed to be responsible for engendering the NWL morphology. Here, we grew ZnO NWLs by chemical bath deposition (at 70-95°C).The roles of pH, concentration of Al(OH) 4 -, and growth time on the thickness and quality of NWL film were experimentally investigated and the growth kinetics was explained in terms of a self-screening model. Increasing the chemical bath pH from 5.7 to 7.4 led to a 40% thicker film and more NWLs per unit area of the substrate -due to increased concentration of Al(OH) 4 --but these were accompanied by the presence of embedded micro/nano particles. We propose the use of anodized Al as a way to enhance the growth rate and density of the NWLs with no detrimental effect on film quality. Compared with non anodized Al, NWL film grown on anodized Al (at the lower pH) showed a higher growth rate, an excellent film quality, and a higher photocatalytic activity in the degradation of toxic methyl orange.

Significant triboelectric enhancement using interfacial piezoelectric ZnO nanosheet layer

“…[23,24]. The growth of all these ZnO nanostructures is known to follow a simple "nucleation and growth"…”

“…substrates alongside HMTA and zinc precursor has been shown to be crucial [24]. It has been previously shown that the binding of Al(OH) 4 -to the Zn 2+ terminated surface is essential for suppressing the ZnO growth along the (0001) direction and promoting lateral growth of ZnO nanosheets [24].…”

“…It has been previously shown that the binding of Al(OH) 4 -to the Zn 2+ terminated surface is essential for suppressing the ZnO growth along the (0001) direction and promoting lateral growth of ZnO nanosheets [24]. The sources for hydroxide ions generated from the electrochemical method and the HMTA in the solution are consumed during the ZnO nanosheet growth through the following reactions:…”

“…This is followed by the absorption of AlO -2 by Zn 2+ which slows down the growth of ZnO along (0002) orientation, resulting in a honeycomb-like network structure [18,24] with a certain amount of Al elements included in the ZnO nanosheets (see Fig. 2).…”

“…The ZnO nanostructures grown by this method on Si substrates (without Al) are typically nanorods with diameters varying from a few nanometres to tens of nanometres, depending on the experimental conditions of concentration, growth temperature etc. [24]. When an Al substrate is used, ZnO nanosheets are typically observed, which are particularly useful for the application in TENGs as the structure provides large surface areas for charge generation.…”