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

ZnO nanowalls (NWLs) represent a nontoxic, 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 degrees 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 NVVLs per unit area of the substrate-due to increased concentration of Al(OH)(4)(-)-but these were accompanied by the presence of embedded micro-/ nanoparticles. 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.