Nanomaterials and their Synthesis for a Sustainable Future

Nanomaterials are structured materials whose dimensions lie in the nanoscale, at least in one dimension. Their small size and high surface area lead to properties not observed in their bulky state, some of which have revolutionized different fields in the last decades. While it is acknowledged that nanomaterials have been obtained or created since ancient times, with little or no knowledge about nanotechnology itself, it was not until this century that the development of nanomaterials was done on purpose, achieving a high level of sophistication in terms of fine-tuning the nanomaterial’s properties, including size, shape, chemical composition, and structure. As such, nanomaterials are used in many industries as advanced materials with high strength while being light, superhydrophobicity, and antimicrobial properties, to name a few. Some of the nanomaterials with high value, given their outstanding properties, are quantum dots (superior luminescence properties), gold nanoparticles (localized surface plasmons), layered perovskites (optimal band gaps for materials like solar cells), and carbon nanotubes (very high tensile strength, electrical conductivity). Consequently, there has been a tremendous boom of nanomaterials in the industry, so they have been introduced into our daily lives. Despite the little knowledge available about their impact on the environment and our health, such intensified use has raised some concerns about the safe use of nanomaterials. Furthermore, due to the extended use of resources and current pollution levels, given that access to energy, food, clean water, and health is not guaranteed to future generations, the concept of “sustainability” and the transition from a linear to a circular economy is becoming more important in the manufacturing of products. As a result, society is making efforts to implement the 3Rs ‘reduce’, ‘reduce’, and ‘recycle’ in our community. In addition, other Rs are of utmost importance: ‘Recover’, ‘Redesign’, ‘Remanufacture’, etc., so that products, materials, and resources are maintained in the economy for as long as possible, and the generation of waste is minimized. This book chapter tackles all these aspects for nanomaterials and “nano-products” (nanomaterials already introduced in specific markets or industries). In particular, it analyzes and collects data available in the literature, where it was possible to implement the sustainability concept in different steps of the life-cycle of nanomaterials: from their synthesis to subsequent remanufacturing processes. In this line, this chapter discusses the ‘green’ synthesis of nanomaterials, which are environmentally friendly processes that take place in natural environments (i.e., processes where nanoparticles are produced by microorganisms), or techniques that eliminate toxic reagents, minimize waste, reduce energy consumption and use ecological solvents. In addition, a section of the chapter covers reported strategies where the recovery, reuse, and recycling of nanomaterials were successful. The chapter has been structured into five parts. First, a general introduction to nanomaterials is provided. Then, different green synthesis methods are described, focusing on the biosynthesis of metal/metal-based oxide nanoparticles. After, the definition and classification of nanowastes are given, as well as a general overview of nano-toxicity and the different management procedures applied to nanomaterials after their end-of-life. Then, the book chapter covers the reuse and recycling of nanomaterials. In the fourth section of the book chapter, we provide data on ‘safe- and sustainable-by-design’ (SSbD) synthesis methods of nanomaterials. SSbD is a key concept for implementing a circular economy on nanomaterials. Finally, we provide some conclusions and final remarks about nanomaterials and their synthesis for a sustainable future.