Biogenic Synthesis of Iron Oxide Nanoparticles Using Enterococcus faecalis : Adsorption of Hexavalent Chromium from Aqueous Solution and In Vitro Cytotoxicity Analysis.

The biological synthesis of nanoparticles is emerging as a potential method for nanoparticle synthesis due to its non-toxicity and simplicity. In the present study, a bacterium resistant to heavy metals was isolated from a metal-contaminated site and we aimed to report the synthesis of Fe 3 O 4 nanoparticles via co-precipitation using bacterial exopolysaccharides (EPS) derived from Enterococcus faecalis _RMSN6 strains. A three-variable Box-Behnken design was used for determining the optimal conditions of the Fe 3 O 4 NPs synthesis process. The synthesized Fe 3 O 4 NPs were thoroughly characterized through multiple analytical techniques such as XRD, UV-Visible spectroscopy, FTIR spectroscopy and finally SEM analysis to understand the surface morphology. Fe 3 O 4 NPs were then probed for the Cr(VI) ion adsorption studies. The important parameters such as optimization of initial concentration of Cr(VI) ions, effects of contact time, pH of the solution and contact time on quantity of Cr(VI) adsorbed were studied in detail. The maximum adsorption capacity of the nanoparticles was found to be 98.03 mg/g. The nanoparticles could retain up to 73% of their efficiency of chromium removal for up to 5 cycles. Additionally, prepared Fe 3 O 4 NPs in the concentration were subjected to cytotoxicity studies using an MTT assay. The investigations using Fe 3 O 4 NPs displayed a substantial dose-dependent effect on the A594 cells. The research elucidates that the Fe 3 O 4 NPs synthesized from EPS of E. faecalis _RMSN6 can be used for the removal of heavy metal contaminants from wastewater.