Process-dependent photocatalytic performance of quantum sized ZnO nanoparticles

Photocatalytic properties of ZnO nanoparticles (NPs) strongly depend on their electronic characteristics which can be tuned by varying size, crystal defects and dopings. In this work, ZnO NPs were prepared using a simple chemical precipitation method. Effect of some independent process/synthesis parameters (i.e. reaction time and precursor concentration) on size and ROS generation in ZnO NPs was investigated. Based on TEM analysis and UV-vis absorption spectra, the synthesized nanoparticles ranged from 2.3 to 4.0 nm in size with the spherical morphologies. Moreover, XRD and SAED showed mono-crystal structures with noticeable diffraction peak at 2θ = 36.8° attributed to (101) plane. Using response surface methodology, OH−/Zn+ molar ratio, Zn+ concentration and reaction time were shown to have significant impacts on size of ZnO NPs. At fixed Zn+ concentrations, reaction time was found to be the most effective parameter on ROS generation and photocatalytic activity of NPs. Obtained results demonstrated that ROS generation is strongly dependent on synthesis reaction time as an indicator of oxygen deficiency and crystal formation in ZnO NPs. No clear relation was obtained between size of NPs and their ROS generation/photocatalytic activity in this size range.