Bioinspired green synthesis of ZnO structures with enhanced visible light photocatalytic activity

In this present study, a green modified co-precipitation technique has been employed for the synthesis of green ZnO products (Z-ZnO, A-ZnO and P-ZnO) using plant waste extracts of corn (Zea mays) husk, jackfruit (Artocarpus heterophyllus) peel and pomegranate (Punica granatum) peel as well as simultaneously without plant extract (C-ZnO), respectively. All synthesized photocatalysts were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), Brunauer-Emmett-Teller (BET) surface area analysis and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The phytochemical screening analyses showed that the P-ZnO had the highest polyphenol and flavonoid contents. Under visible light irradiation, all green ZnO products demonstrated excellent antibacterial activities against Enterococcus faecalis (E. faecalis) bacteria compared to C-ZnO and commercial ZnO. P-ZnO had the highest photocatalytic antibacterial performance among all green ZnO products. Moreover, the bacterial regrowth examinations were carried out to determine the practicality of this treatment. The FTIR analysis also revealed the damage of bacterial membrane through cellular substance alteration. The radical scavenger experiments presented that hydrogen peroxide (H2O2) played a significant role in photocatalytic antibacterial of E. faecalis. The synthesized P-ZnO also exhibited the highest antioxidant activities against 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenger compared to other tested ZnO.