One-step green synthesis of hybrid Fe-Mn nanoparticles: Methodology, characterization and mechanism

Recently green synthesized hybrid iron-manganese nanoparticles (Fe–Mn NPs) have attracted considerable research attention due to their potential to remove contaminants from wastewater. However, the exact mechanism involved in the green synthesis of Fe–Mn NPs and the influence that synthetic conditions have on the contaminant removal efficiency of the produced materials is still unclear. In this study, Fe–Mn NPs were systematically green synthesized via a one-step process using green tea extracts and a response surface methodology. This was done to optimize synthetic conditions to maximize the reactivity of Fe–Mn NPs for the removal of Sb species, where a 100% Sb(III) and an 83.1% Sb(V) removal were obtained under the optimized synthetic conditions which included a Fe: Mn ratio of 3:1, a pH of 3.0 and a reaction temperature of 80 °C. Advanced characterizations revealed that Fe–Mn NPs were well dispersed with biomolecules intimately associated with the nanoparticle surface, and where during synthesis Fe(III) was reduced to Fe(II), and Mn(VII) was reduced to Mn(III) and Mn(IV). The function of these biomolecules during Fe–Mn NPs formation was further elucidated using Fourier transform infrared spectroscopy, gas chromatography-mass spectrometer and liquid chromatography-mass spectrometer. This analysis found theses biomolecules had different roles during synthesis. Polyphenols and flavonoids acted mainly as reducing agents, acids were the main dispersing agents, and polyphenols and unsaturated olefins were the main capping agents. Finally, a mechanism for the green synthesis of Fe–Mn NPs was proposed, involving a combination of reduction, complexation, dispersion and end-capping reactions.