Synthesis of Zinc Oxide Nanoparticles from Azadirachta indica Extract: A Sustainable and Cost-Effective Material for Wastewater Treatment

Nanoparticles are gaining wide application in wastewater treatment owing to their specific properties and large surface area-to-volume ratio. Due to growing environmental concerns, developing environment-friendly methods for synthesizing nanoparticles has attracted great attention of researchers. The present work highlights a "greener strategy" for synthesizing ZnO nanoparticles. The ZnO nanoparticles were synthesized using Azadirachta indica (neem) leaf extract at four different leaf concentrations (G1-5 g, G2-10 g, G3-15 g, and G4-20 g). The effect of concentration on morphological properties was analyzed by transmission electron microscope, SEM-EDS, X-ray diffraction, Fourier-transform infrared, and Brunauer-Emmett-Teller (BET). Optical and luminescence properties were studied using a UV-Visible spectrophotometer and photoluminescence spectra. These studies indicate that leaf extract concentration greatly influences the size, shape, and stability of synthesized ZnO nanoparticles. An attempt was made to identify and quantify the leaf extract's phytochemicals, and the formation mechanism of nanoparticles was also proposed. A cost calculation study was performed to understand the cost-effectiveness of the green method over the chemical synthesis method. From the study, it was found that the chemical method was 3.22 times costlier than the green method of synthesis. To study the applicability of green-synthesized nanoparticles in wastewater treatment, their potential toxicity against the bacteria Escherichia coli and the photocatalytic efficiency for the removal of emerging contaminants, acetaminophen (AMP) and sulfadiazine (SDZ), was investigated. The photocatalytic efficiency was compared with that of commercially purchased ZnO nanoparticles. More than 71% reduction in the bacterial count was observed using green-synthesized ZnO nanoparticles. In the photocatalytic study, 69% and 64% reduction rates were observed for acetaminophen and sulfadiazine at the end of 15 min of irradiation using UV lamps. This study reveals that zinc oxide nanoparticles synthesized from neem leaf extract exhibit excellent antimicrobial properties and function as a high-performing, sustainable, low-cost material for removing emerging contaminants.