Photocatalytic degradation of methylene blue with polyphenol rich Citrus limetta (peel waste) facilitated ZnO nanoparticles under sunlight

The present study emphasized an attempt to identify reducing agents (polyphenols/flavonoids/ other bioactive compounds) present in Citrus Limetta peel extract to form stabilized ZnO nanoparticles (ZnO NPs) and its involvement on photocatalytic degradation of textile organic dye. The involvement of anti-oxidant molecules present in Citrus Limetta peel extract before NPs synthesis (BS) and filtrate remained after synthesis of NPs (AS) were monitored by LC-MS analytical method. The observed % RSC, polyphenol and flavonoid contents of BS were greater than AS. Therefore, the anti-oxidant activity and number of identified compounds were lower in AS; signifies the capping of anti-oxidant molecules in BS for the formation of NPs. The synthesized ZnO NPs were characterized by UV-visible spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM) with energy dispersive X-ray (EDX). It was observed that, the synthesized ZnO NPs have wurtzite crystalline structure. The size of the nanoparticles were 41 nm with spherical shape. Complete degradation of MB was observed with synthesized ZnO-NPs from Citrus Limetta peel extract. Small amount (0.9 g/L) of prepared ZnO NPs were effective to degrade textile dye MB solution up to 95% in 150 min. The intermediates produced during photo-degradation for time intervals of 30 min, 90 min and 150 min were also identified by using GC-MS analytical method.