A novel nano zero-valent iron biomaterial for chromium (Cr⁶⁺ to Cr³⁺) reduction

This research work aims to develop a biomaterial entrapped with iron nanoparticles by green synthesis method in which biomass act as both reducing and capping agent. Iron nanoparticles embedded in Citrus limetta peels were characterised using ICP-MS for determination of metal loading, XRD, XPS for crystallinity and oxidation states, TEM followed by FESEM-EDS for particle size and morphology. Sizes of nanoparticles were found to be in the range of 4-70 nm. Batch experiments were conducted to study the effect of different parameters such as contact time, amount of biomaterial and volume of chromium(VI) solution for 2500 mg L^-1 of Cr(VI). Complete reduction was attained for a contact time of 5 min with 1.5 g of biomaterial for initial concentration of 2500 mg L^-1. The experimental results inferred that 1 g of biomaterial completely reduced 33 mg of hexavalent Cr to trivalent Cr. XRD and XPS revealed that iron nanoparticles are in amorphous form while XPS confirms Fe⁰ state. The transition of Fe⁰ to Fe²⁺/Fe³⁺ during the treatment with chromium solution confirms the reduction of Cr⁶⁺ to Cr³⁺.