A Comprehensive Secondary Ion Mass Spectrometry Analysis Of Zno Nanowalls: Correlation To Photocatalytic Responses

We report on the visible light induced photocatalytic responses of zinc oxide (ZnO) nanostructures in the form of nanowires and nanowalls grown on aluminum substrates. Morphological and microstructural characteristics of these nanostructures have been analyzed using scanning electron microscopy (SEM) and high resolution electron microscopy (HRTEM). The presence of surface-adsorbed H+, O-2(-), and OH- species on ZnO nanostructures has been established through secondary ion mass spectrometry (SIMS). The relative change in substrate coverage under varying reaction time has also been evidenced through SIMS and is in agreement with SEM observation. Compared to nanowires, oxygen adsorption on ZnO surfaces and subsequent oxygen in-diffusion are found to be prominent for the nanowall-like structures and are seen to be highest for nanowalls grown in lower reaction time. In contrast to nanowires, nanowalls are found to exhibit higher photocatalytic activity and this can be attributed to higher adsorption of oxygen. The photocatalytic activity of the samples under visible light is originated from the native defect-states and the photocatalytic efficiency is largely influenced by the surface-adsorbants. Control of surface adsorption characteristics of the nanowalls upon tuning wall thicknesses can lead to the development of futuristic efficient photocatalytic devices. (C) 2015 AIP Publishing LLC.