Mycosynthesized magnetic iron-oxide nanoparticles for the remediation of heavy metals – An insight into the mechanism of adsorption, process optimization using algorithmic approach and its application for the treatment of groundwater

Abstract

In the present study, mycosynthesized magnetic iron-oxide (γ-Fe2O3) nanoparticles (IO-NPs) were synthesized using manglicolous fungi isolated from the sediment samples of Indian Sundarbans. Out of the 15 strains isolated from the sediment samples, cell-free filtrate of Corynespora cassiicola – CNMP1 reduced the Fe(NO3)3 solution leading to the formation of IO-NPs (100 nm). It was observed that the fungal extracellular biomaterial embedding the IO-NPs provided stability to the IO-NPs in the aqueous suspension. The mycosynthesized IO-NPs were employed to adsorb heavy metals, viz. Pb, Ni, Cu, Zn, Cd, and Cr from water. Studies on adsorption isotherms delineated the energetically heterogeneous nature of IO-NPs. Batch adsorption studies showed that 1 g/L of IO-NPs at 313 K temperature and pH 6 is able to remove more than 90% of Pb, Ni, Cu, and Zn ions from the 10 mg/L solution. However, more than 90 % removal efficacy was obtained for Cr with a pH of 2, keeping the other adsorption parameters the same. Thermodynamic studies laid bare the spontaneity and endothermic nature of the adsorption process for each studied heavy metal. A multi-metric approach involving response surface methodology (RSM), and artificial neural network (ANN) analysis was used to validate the adsorption of heavy metals by IO-NPs, and it was observed that 1 g/L of IO-NPs at 313 K temperature and pH 6.1 can adsorb 92.86% of Pb, 94.93% of Ni, 95.92% of Cu, 98.11% of Zn, 98.91% of Cd and 82.12 % of Cr from water with an initial metallic concentration of 11.96 mg/L. Further, with the optimized IO-NP dose and temperature, the IO-NPs were able to remove 94 % of Cr from Cr-rich groundwater (12.68 mg/L) collected from a region around chromite ore processing residues (COPR) dumping. The magnetic nature of the IO-NPs eased their separation from the treated water.