Green Synthesis of Hierarchically Structured Metal and Metal Oxide Nanomaterials

Scientific and technological innovations are rapidly occurring in today’s world. These innovations include development of numerous functional nanomaterials among which hierarchically structured nanomaterials (HSNs) are most important owing to their enormous applications in different fields like biomedical, wastewater management, energy storage, sensing, and so on. Alternative to conventional synthesis methods which can cause harmful effects to human health and environment, several green chemical, physical and biological methods are known for producing different metal and metal oxide-based HSNs. It is to be noted that adoption of these methods is increasing as these methods are environmentally sustainable. Green chemical and physical methods involve use of environmentally benign solvents and reagents. In some cases, these are also energy efficient. Additionally, several biological materials including microorganisms, plants, biomolecules are known to be well accepted as befitting reactants/templates for synthesizing several HSNs. However, these methods further need an in-depth mechanistic realization toward large-scale production for practical applications. This chapter is mainly focused upon an understanding of green chemistry-based methodologies for the synthesis of metal and metal oxide HSNs and their potential applications. Finally, the present challenges and future prospect of the methodologies toward making biocompatible and environmentally sustainable HSNs with useful functional properties for advanced applications are discussed briefly.