Biogenic Synthesis of Silver Nanoparticles by <i>Deinococcus radiodurans</i> for Efficient Photocatalytic Biotransformation of Dyes

In this study, we report biogenic synthesis of silver nanoparticles (AgNPs) using polyextremophile bacteria Deinococcus radiodurans. Optical and structural properties of the green synthesized silver nanoparticles were investigated by various techniques, including Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive x-ray (EDX) spectroscopy, and UV-visible (UV-Vis) absorption spectroscopy. The AgNPs were entrapped in calcium alginate beads and were used for photo decolorization of various charged pollutant dyes, under solar irradiation. In this study, cationic (methylene blue [MB], methyl green [MG]) and anionic (methyl orange [MO]) dyes were used as model dyes. Both AgNPs in suspension and those entrapped in beads could degrade all the three dyes with 100% degradation efficiency in suspension and slightly lower efficiency with beads. The photocatalytic activity of immobilized AgNPs in fabricated column model demonstrates potential application for the removal of dyes from effluents, contributing ultimately to ecological cleanup process and facilitated in recovery and reprocessing. The nanocomposites retained a significant amount of photocatalytic efficiency even after four reuse cycles, and the degradation efficiency followed the order: MB > MO > MG. Additionally, phytotoxicity and cytotoxicity assay was performed to show significant reduction in toxicity of nanoparticle (NP)-assisted degraded cationic and anionic dyes, thereby substantiating the nontoxic nature of the degraded dye. The efficiency of beads entrapped silver NPs as a viable option, for the degradation of harmful organic dyes from the environment, is established in the present study.