Bio-and Chemically Synthesized ZnO Nanoparticles for Textile Wastewater Treatment and Phytotoxicity Alleviation in Vigna radiata

Abstract

Textile effluents are a global concern as they contain dyes, heavy metals, and other organic pollutants and pose serious risks to crop production, particularly when reused for irrigation. This study reports the development of biologically and chemically synthesized zinc oxide nanoparticles (ZnO-NPs) using the leaf extract of Conocarpus erectus and sodium hydroxide, respectively. The morphology, functional groups, and crystalline nature of the ZnO-NPs were evaluated using SEM, FTIR, and XRD. The performance of ZnO-NPs was evaluated for the photocatalytic treatment of synthetic azo dyes solution and real textile wastewater. Furthermore, they were assessed for mitigation of phytotoxicity in Vigna radiata. The results revealed that a lower catalyst dose of ZnO(B)-NPs showed higher efficiency for decolorizing Congo red as compared to ZnO(C)-NPs. However, dye concentration, light sources (sunlight and UV) and reducing agents had a significant effect on decolorization rates. When applied in real textile industry wastewater, ZnO(B)-NPs reduced the pH, EC, TDS, sulphate, phosphate, color intensity and COD more efficiently as compared to ZnO(C)-NPs, showing enhanced remediation potential. Subsequently, phototoxicity studies revealed significant improvements in seed germination, growth parameters, photosynthetic content, and antioxidative enzymatic activity of Vigna radiata under wastewater stress. On the other hand, ZnO(B)-NPs reduced the levels of oxidative stress indicators such as hydrogen peroxide and malondialdehyde, and increased the superoxide dismutase, catalase, and peroxidase activities. Multivariate analyses further validated the consistent and better performance of ZnO(B)-NPs in wastewater remediation and plant stress alleviation response metrics. Overall, this work suggested that Conocarpus derived ZnO-NPs offer green and sustainable high-performance material to mitigate textile effluent toxicity and improve crop performance under stress conditions.