Biosynthesis of copper nanoparticles using Bacillus flexus and estimation of their potential for decolorization of azo dyes and textile wastewater treatment

In many underdeveloped countries, textile industries discharge their effluents without any treatment. The untreated textile wastewater consists of both azo dyes and heavy metals which not only change the physicochemical and biological properties of soil and water but also affect human health. In recent years, copper-based nanomaterials have attained worldwide attention because of their unique properties and potential for decolorization of azo dyes and wastewater treatment. The present study demonstrates the bacterial synthesis of copper nanoparticles (Cu-NPs) using Bacillus flexus strain isolated from a textile wastewater followed by their application for photocatalytic degradation of various azo dyes and treatment of actual wastewater. The FT-IR analysis confirmed the presence of various functional groups including proteins on Cu-NPs which improved their stability. The scanning electron microscopy (SEM) images revealed the spherical shape of Cu-NPs with a size of range between 17–34 nm. Similarly, the XRD analysis of biosynthesized Cu-NPs showed various diffraction peaks at 44.5°, 51.5°, 74.75 which confirmed the crystalline nature of nanoparticles. While studying the photocatalytic decolorization of azo dyes by Cu-NPs, it was observed that 88.164 ± 0.19 %, 88.452 ± 1.89 %, 90.433 ± 1.81 %, 64.770 ± 1.02 %, 46.774 ± 1.61 %, and 67.274 ± 2.89 % of reactive black-5, congo red, malachite green, methylene blue, reactive red-2 and blue direct, respectively, were decolorized after 4 h of solar irradiation at 50 ppm concentration. Additionally, the biosynthesized nanoparticles also resulted in reduction of various parameters like EC, pH, TDS, COD, color intensity, sulphates, and phosphates in the textiles wastewater. The reduction of COD, sulfates, and phosphates was about 39.659 %, 43.157 %, and 49.493 %. The results of current work suggest that biosynthesized copper nanoparticles might serve as a potential green solution for the decolorization of various dyes including wastewater treatment.