Characterization of metallic nanoparticles synthesized via green synthesis from Viola odorata and their application in azo-dye biodegradation: A circular economy approach

The study aimed to synthesize nanoparticles from Viola odorata extract to biodegrade azo-dyes, enabling a circular economy approach to waste management in industries that utilize these dyes. The study utilized UV–visible spectroscopy and scanning electron microscopy (SEM) to confirm the synthesis and analyze the characteristics of the nanoparticles. The stability of the nanoparticles was assessed through the examination of four factors: the impact of NaCl, storage conditions, temperature, and pH. Plant-based nanoparticles were mixed with dye solutions, incubated, and analyzed for dye degradation using UV–Vis spectroscopy. Antibacterial and antifungal activity were assayed by disc diffusion method. UV–Vis spectrum confirms the synthesis of Ag-NPs at 450 nm, Au-NPs 533 nm, Co-NPs 246, Fe-NPs 255 nm. Ag-NPs had an average size of 18.2, Co-NPs 22.86 nm, Au-NPs 14. 9 nm and Fe-NPs 43 nm and all nanoparticles are spherical in shape. The nanoparticles exhibited excellent stability under varying temperature, pH, salt concentrations, and during six-months storage, these stable nanoparticles degraded methyl orange absorbance from 2.7 to 1.5. Methyl red was also degraded and its absorbance decreased from 2.8 to 1.25. The study found that all the synthesized nanoparticles displayed good antibacterial activity against both Gram-negative and Gram-positive bacteria. However, the gold nanoparticles (Au-NPs) demonstrated the highest potency, particularly against Pseudomonas aeruginosa, with an inhibition zone diameter nearly matching that of the commercial antibiotic Streptomycin. Similarly, the antifungal assay revealed that the Au-NPs exhibited the strongest activity against the tested fungal strains compared to the other nanoparticle types.