Suspension of ZnO Nanostructures Synthesized by Hot Water Treatment for Photocatalytic Wastewater Treatment

In this study, zinc oxide (ZnO) nanostructures were synthesized using a simple and chemical additive-free hot water treatment (HWT) method for the photocatalytic degradation of methylene blue (MB). Zinc (Zn) plates were immersed in deionized (DI) water at 75 degrees C for 5 h, resulting in the formation of ZnO nanostructures on the Zn surface and a suspension of ZnO nanostructures in water. The nanostructures were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD), which showed the formation of crystalline and stoichiometric ZnO nanowires. We studied the effects of the ZnO nanostructure load, initial concentration, and pH of MB on its photocatalytic degradation under UV light. We found that a 25 mL of ZnO nanostructure suspension, MB concentration of 1 ppm (mg/L), and pH of 11 gave the best average photocatalytic degradation, most likely due to the optimum light absorption, surface charging, and ROS (center dot OH) generation by the ZnO nanostructures in these conditions. In addition, we investigated the formation of ZnO nanostructures in hot tap-water, and their morphology was not as welldeveloped as in DI-water. However, comparable MB degradation was observed, which is believed to be the combined effect of photocatalysis, and free radicals generated by photolysis of chlorine present in tapwater. Furthermore, the DI-water HWT ZnO nanostructures showed significant photocatalytic activity under a solar simulator. These results indicate that HWT has the potential to be an alternative method for the scalable, cost-effective, and environmentally friendly synthesis of ZnO nanostructures for photocatalytic wastewater treatment applications.

Automated summary

In this study, ZnO nanostructures were synthesized using a simple and chemical additive-free hot water treatment (HWT) method for the photocatalytic degradation of MB. The effects of ZnO nanostructure load, initial concentration, and pH of MB on photocatalytic degradation were studied. The results showed that the ZnO nanostructures exhibited the best average photocatalytic degradation under UV light at a ZnO nanostructure suspension volume of 25 mL, MB concentration of 1 ppm, and pH of 11. The HWT ZnO nanostructures in both DI-water and hot tap water showed significant photocatalytic activity and have potential for scalable and cost-effective synthesis.