Integrated hydrothermal assisted green synthesis of ZnO nano discs and their water purification efficiency together with antimicrobial activity

Abstract

The water microbial contamination is very common and different techniques are in practice for the decontamination purpose. The advance oxidation processes are being employed to mortify pathogens polluting drinking water. Heterogeneous photocatalysis under sunlight irradiation is a cost effective and remarkably proficient method for water purification. Zinc Oxide (ZnO) is a biocompatible material that has promising photo–oxidant activity. In this study, ZnO has been synthesized using Aloe vera (Av) extract assisted with hydrothermal approach. The nano disc structure of ZnO was characterized by XRD SEM, TEM, AFM, EDX, and FTIR techniques. The optical properties of ZnO@Av NDs (nano discs) evaluated by DRS and PL revealed their sunlight harvesting capability, as the calculated band gap value was 2.8 eV. The surface area and surface charge were measured by BET (5.34 m2g-1) and Zeta potential (+7.46 mV). The antibacterial activity of ZnO@Av NDs was studied against Salmonella typhimurium as a function of various process variables i.e., photocatalyst loading, sunlight exposure time, and bacterial inoculum size. The bactericidal reaction parameters were optimized statistically by Response Surface Methodology (RSM) on exposure to direct sunlight (average solar flux was 650 KWh/m2) at pH 7. As optimized conditions, 100 μL initial inoculum concentration of S. typhimurium was treated with 60 μg/mL of ZnO@Av NDs suspension under sunlight irradiation of 5 h, antibacterial index obtained was 6.8. The MIC and MBC for ZnO@Av NDs against S. typhimurium were 50 μL and 100 μL, respectively. It has been observed that ZnO@Av NDs lower the optical density of water that contains S. typhimurium. The photocatalytic purification of water using ZnO@Av NDs is safe and cost-effective method under sunlight irradiation, which could possibly be employed for the wastewater purification.

Keywords

• Zinc oxide
• Green synthesis
• Aloe vera extract
• Photocatalysis
• Response surface methodology
• Antibacterial activity