Iron and silver nanostructures: Biosynthesis, characterization and their catalytic properties

Finding suitable plant extracts that exert precise control over both the shape and size of nanoparticles remains a challenge in the synthesis of metal nanoparticles. In this study, iron (Fe) nanoparticles with uniform sizes and shapes, and silver (Ag) nanoparticles with unique morphology and phases were synthesized from aqueous plantain peel extracts. The effect of temperature and concentration of the starting metal salts on the size and shape of the synthesized nanoparticles were investigated. The catalytic effectiveness of the metal nanoparticles was also assessed based on their ability to mediate the degradation of methylene blue dye in the presence of sodium borohydride (NaBH₄) as the reducing agent. Phytochemical analysis of the plantain peel extract revealed the presence of polyhydroxy compounds: tannins, flavonoids, glycosides, saponins, and terpenoids. The presence of these compounds in the extract was confirmed by Fourier transform infra-red analysis. Microstructural analysis showed that the Fe nanoparticles had uniform cylindrical shapes with 70.0 ± 0.4 nm diameters, whereas the Ag nanoparticles exhibited multi-shaped, single and polycrystalline phases with a varying size range. UV–Vis spectroscopic analysis indicated that Ag nanoparticles exhibited maximum plasmon absorbance at 440 nm typical of nanoscale silver while X-ray diffraction studies showed that the Fe and Ag nanoparticles were highly crystalline. The study indicated that Ag can be synthesized at all temperatures, whereas the Fe nanoparticles formed only above room temperature with plantain peel extract. Both Fe and Ag nanoparticles exhibited dose-dependent degradation of methylene blue dye, suggesting their potential use as bio-catalysts, although the Fe nanoparticles showed a better catalytic efficiency. This study demonstrates an eco-friendly approach to synthesizing uniformly shaped and sized Fe and Ag bio-catalysts for potential use in effluent waste treatment in cosmetics, food, pharmaceuticals, plastics, paper industries, and in general environmental remediation.