Green synthesis of iron nanoparticles using red peanut skin extract: Synthesis mechanism, characterization and effect of conditions on chromium removal

Green synthesis of nanoparticles is becoming increasingly popular as a simple and environmentally friendly method. In this study, iron-based nanoparticles (Fe-NPs) were successfully prepared using a peanut skin extract, where the peanut skin as an agricultural waste product was easy to obtain in large quantities, relatively inexpensive and also environmentally friendly. The average particle size of the produced Fe-NPs changed with their post-synthesis drying conditions. Under vacuum drying at 60 ⁰C, the smallest average particle size obtained was 10.6 nm. The synthesized Fe-NPs had a core shell-like structure, inwhich the core was composed of Fe⁰, and the shell was a layered coating composed of biomolecules(e.g. anthocyanins, flavonols, phenolic compounds, epicatechin), iron oxides, Fe coordination compounds and iron-carbon alloys. Thereafter Fe-NPs (2 g L⁻¹) prepared under different drying conditions were evaluated for their ability to remove Cr(VI) from aqueous solutions at pH of 4.7 and 25 ⁰C. Fe-NPs obtained under vacuum drying at 60 ⁰C performed the best, removing 100% of Cr(VI), from a 10 mg L⁻¹ aqueous solution of Cr(VI) in just one min. Desorption and reuse experiments show that the desorption rate of Cr using 16 M hydrochloric acid and the recycling rate reached 70.2 and 59.9%, respectively. A potential mechanism for Fe NP synthesis involving the formation of intermediate complexes, an electron transfer reaction and adsorption of non-reducing organic macromolecules at the solid-liquid interfaces was proposed. Refereed/Peer-reviewed