Mechanistic insight into the one step green synthesis of hybrid rGO/Fe NPs

Recently, the green synthesis of iron nanoparticles and associated hybrids using plant extracts has attracted much attention due to its low cost, simplicity and environmental friendliness . However, the exact formation mechanism is still unclear. In this study, the one step green synthesis of hybrid rGO/Fe NPs by a tea extract was examined using a response surface methodology (RSM) to obtain a high activity of rGO/Fe NPs. The results showed that the best conditions for synthesis were an extract concentration = 35 g/L, pH = 7, and temperature = 30 °C. The optimized hybrid produced could remove 99.9% of mitoxantrone (MTX) compared to only 78.9% when unoptimized. To better understand the formation process, characterizations by SEM , TEM, AFM , FTIR, XRD , Raman, and XPS were performed. Theses characterizations showed that the Fe NPs produced had a particle size of 25 nm which were deposited randomly across the rGO nanosheet with a thickness of approximately 1.5 nm, indicating that stable hybrid rGO/Fe NPs were successfully synthesized, where the green tea extract exhibited both reducing and capping/stabilizing behavior. Furthermore, the specific biomolecules in the green tea extract responsible for bio-reduction and stabilization were identified by GC-MS and LC-MS, which showed that catechins were the main reducing agents, while alkaloids, amino acids and phenolic acids were the main capping/stabilizing agents. Finally, a mechanism for synthesizing rGO/Fe NPs was proposed, where the polyphenols successfully reduced GO and complexed with iron ions to form amorphous ferric (and ferrous) polyphenol complex nanoparticles.