Removal of Cr(VI) by magnetic iron oxide nanoparticles synthesized from extracellular polymeric substances of chromium resistant acid-tolerant bacterium Lysinibacillus sphaericus RTA-01.

BACKGROUND: Extracellular polymeric substances (EPS) from Cr(VI) resistant acid-tolerant biofilm forming bacterium (CrRAtBb) Lysinibacillus sphaericus RTA-01 was used for synthesis of magnetic iron oxide nanoparticles (MIONPs) in removal of Cr(VI).
METHODS: MIONPs synthesized in EPS matrix were characterized by UV-Vis, DLS, ATR-FTIR, XRD, FESEM, HRTEM and VSM. Primarily, the synthesis of MIONPs was established by the formation of black-colored precipitate through surface plasmon resonance (SPR) peak in between 330 and 450 nm.
RESULTS: The size of the spherical MIONPs with diameter range 13.75-106 nm was confirmed by DLS, XRD and FESEM analysis. HRTEM study confirmed the size of the MIONPs in the range of 10-65 nm. Moreover, the EDX and SAED confirmed the purity and polycrystalline nature of MIONPs. The ATR-FTIR peaks below 1000 cm-1 designated the synthesis of MIONPs. Also, the magnetic property of MIONPs was confirmed for separation from the aqueous solution. MIONPs were further checked for the adsorption of Cr(VI) with initial concentration range of 50-200 mg L-1. An adsorption isotherm and thermodynamic study were also carried out and the experimental data was best fitted in Langmuir isotherm model with maximum adsorption percent of 1052.63 mg g-1 of Cr(VI). Post interaction with Cr(VI), the surface characteristic of MIONPs in EPS matrix was evaluated by zeta potential, EDX, ATR-FTIR and XRD.
CONCLUSION: This study ascertained the adsorption of Cr(VI) over EPS stabilized MIONPs whereas the zeta potential and XRD analysis confirmed the presence of reduced Cr(IV) on the adsorbent surface. © Springer Nature Switzerland AG 2019.