Green Synthesis of Metal, Metal Oxide Nanoparticles, and Their Various Applications

Abstract

Nanotechnology is emerging as an important field of research since last decades, and nanoparticles are considered to be the basic element of nanotechnology as they are the primary source of several nanostructured devices or materials. Nanomaterials can be obtained either naturally or incidentally or can be manufactured. Metal nanoparticles (NPs) are among the several nanomaterials found to have vast applications in various fields of science and technology, including electronics to structural engineering and agriculture to medicine. Conventionally, metal NPs were synthesized by physical and chemical methods such as hydrothermal, flame spray pyrolysis, sonochemical, microwave, sol-gel, coprecipitation, and so on using different chemical agents as reducing and stabilizing agents which later on become accountable for various biological and environmental risks due to the toxicity of used chemicals. Biological synthesis is emerging as another green and safe method for synthesis of metal/metal oxide nanoparticles using plants and microbes as a source of precursor material. However, the use of plant extract for this purpose is advantageous over microbes due to ease of use and less biohazard. Moreover, it reduces the cost of maintaining microorganism isolation and their culture media, thus enhancing cost competency over the use of microbes. The ideal protocol should provide better control of shapes, sizes, and dispersivity of metal/metal oxide nanoparticles and reduce the need for purification of the manufactured nanoparticle, which in turn eliminates the use of extensive amounts of organic solvents and manipulation of nanoparticles that are hazardous to the environment. Synthesis of NPs by utilizing the plant extract aqueous solution has gained more attention of the researchers toward the green approach and also without any adverse effect on the environment. These nanoparticles have played a pivotal role in many fields especially biomedical and photocatalysis. Due to its small size and free radical scavenging properties, it also shows its application in catalyst, sensor, solid oxide fuel cells, sunscreen cosmetics, bioimaging, biotransformation, antioxidant, and antibacterial activity. In this chapter, authors tried to explore the green synthesis of metal/metal oxide nanoparticles (Ag, Cu, ZnO, CeO2, Au, etc.), various characterization techniques, and properties along with their applications.