Developing a rapid, reliable and eco-accommodating methodology for the synthesis of metal/metal oxide nanoparticles (NPs) is an important step in the area of nanotechnology. Cobalt oxide nanoparticles (Co3O4 NPs) have been widely studied due to their potential applications including, antibacterial, antifungal, electrochromic sensors, heterogeneous catalysis, and energy storage devices. Due to the large rate of perilous chemicals employed in the physical and chemical production of these NPs, green methods employing the use of plants, fungus, algae, and bacteria have been adopted. However, plant-mediated synthesis of metal NPs has been developed as a substitute to defeat the restrictions of conventional synthesis approaches such as physical and chemical methods. Biomolecules, such as tannins, saponins, proteins, amino acids, steroids, enzymes, flavonoids, and vitamins from several plant extracts have been used as a stabilizing and reducing agents for the synthesis of Co3O4 NPs. Recently, several attempts were made to develop plant-mediated synthesis methods to produce stable, cost-effective, and eco-accommodating Co3O4 NPs. In this review, a comprehensive study was conducted on synthesis, characterization, and various applications of Co3O4 NPs produced using various plant sources. Journal of Chemical Reviews (JCR)

Development of reliable and environmentally gracious routes for the fabrication of metal oxide nanoparticles is a crucial step in nano-biotechnology. Among the all zirconia nanoparticles (ZrO2 NPs) draws more attention due to its significant biocompatible, electrical, mechanical, and optical properties. Many natural biomolecules in plant extracts such as alkaloids, amino acids, enzymes, proteins, polysaccharides, polyphenols, steroid, and vitamins could be involved in bioreduction, formation, and stabilization of ZrO2 NPs. In the last decade, numerous efforts were made to develop ecofriendly methods of synthesis to avoid the hazardous byproducts. In this review, green synthesis of ZrO2 NPs, their characterization techniques, and miscellaneous applications were discussed. Journal of Chemical Reviews (JCR)