Synthesis of Metal/Metal Oxide Nanoparticles by Green Methods and Their Applications

Abstract

Nanotechnology is an exciting field of research; numerous versatile nanoparticles can be synthesized into a range of sizes, shapes, and chemical compo- sitions, ultimately offering extensive applications for humans. Correct synthesis, manipulation, and use of metal NPs grant them with unique thermal, optical and electronic properties. In material science, ‘green’ synthesis has been considered a reliable, sustainable and environmentally-friendly protocol. Non-toxic and environmentally- friendly methods have been developed for synthesis of metal/ metal oxide NPs. These techniques use live organisms such as bacteria, fungi, yeast, algae, and plants and their tissues and extracts. The biomolecules of natural extracts, such as enzymes, flavonoids, phenols, and terpenoids can be used as reducing agents of metal ions to metal NPs. Whilst the physical and chemical techniques used in traditional synthesis methods have raised environmental concerns due to use of haz- ardous chemicals and their possible emissions to the environment, green methods have made it possible to develop a simple, rapid, and environmentally-friendly means of synthesizing NPs. NPs produced by green methods are usually more sta- ble and do not require application of chemical stabilizers; as a result, toxic residues do not enter the environment. Green-synthesized NPs have extensive applications for their antibacterial and antifungal properties and may be used as either plant growth stimulators or inhibitors, depending on their type, size, and shape, as well as the specific plant species.