Nano-Structures & Nano-Objects 22 (2020) 100453 Contents lists available at ScienceDirect Nano-Structures & Nano-Objects journal homepage: www.elsevier.com/locate/nanoso Iron and silver nanostructures: Biosynthesis, characterization and their catalytic properties Peter O. Ohemeng a , Enock Dankyi a , Samuel Darko b , Abu Yaya c , Ali A. Salifu d , Charles Ahenkorah e , Vitus A. Apalangya e,∗ a Department of Chemistry, School of Physical and Mathematical Sciences, College of Basic and Applied Sciences, University of Ghana, Legon, Accra, Ghana b Department of Physics and Engineering, Benedict College, 1600 Harden Street, Columbia, SC 29204, USA c Department of Materials Science and Engineering, School of Engineering Sciences, College of Basic and Applied Sciences, University of Ghana, Legon, Accra, Ghana d Department of Mechanical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA e Department of Food Process Engineering, School of Engineering Sciences, College of Basic and Applied Sciences, University of Ghana, P.O. Box LG 77, Legon, Accra, Ghana article info Article history: Received 14 September 2019 Received in revised form 14 March 2020 Accepted 19 March 2020 Keywords: Silver Iron Biosynthesis Nanoparticles Green synthesis Catalysis Plantain abstract 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 (NaBH 4 ) 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. © 2020 Elsevier B.V. All rights reserved. 1. Introduction There is tremendous interest in metal nanostructures due to their useful and versatile application in many fields [1–5]. Silver (Ag), and iron (Fe) are noteworthy as they are applied in catalysis, remediation, water purification, food packaging, as nano-fluids in heat exchangers, medical imaging and diagnosis [6–13]. Nanos- tructures with specific morphologies and sizes are of particular interest as they enhance the performance efficiency of their final ∗ Corresponding author. E-mail address: vapalangya@ug.edu.gh (V.A. Apalangya). products [10,14]. Thus, there are physical and chemical synthetic approaches and conditions which tailor nanostructures to various sizes and shapes [15,16]. However, physical methods are cost prohibitive as they re- quire intricate process controls, and high energy to maintain the non-standard temperature and pressure conditions necessary in tailoring materials at the atomic scale to specific sizes and mor- phologies [17,18]. Moreover, most chemical methods use toxic and non-biodegradable chemicals as reducing agents, stabilizers and solvents, burdening the environment and posing serious risks to biological systems [19,20]. https://doi.org/10.1016/j.nanoso.2020.100453 2352-507X/© 2020 Elsevier B.V. All rights reserved.