Eco-friendly and Green Synthesis of Carbon Nanostructures

Nanotechnology is undoubtedly one of the most scientific breakthroughs of the twenty-first century. However, developing an environmentally friendly process is essential due to environmental concerns. Carbon nanoparticles represent a group of nanoparticles that have attracted attention due to their properties. This group includes graphene, graphene quantum dots, carbon dots, carbon nanotubes, etc. The applications of carbon nanoparticles are countless and include environmental protection, biomedical applications, automotive, etc. However, conventional synthesis approaches are not environmentally friendly. For these reasons, developing eco-friendly synthesis represents a new trend in addressing environmental concerns. Among the carbon nanoparticles, carbon dots that were firstly synthesized in 2004 have attracted attention. Carbon dots are a new group of carbon nanostructures that present applications in the environmental, biomedical, and agricultural fields due to their excellent properties, such as biocompatibility, photostability, fluorescence emission, etc. Nevertheless, the conventional synthesis approach for these nanoparticles could be more eco-friendly. For these reasons, the search for green processes to obtain carbon dots in the last years represents much interest. Green synthesis is the most interesting for synthesizing carbon dots compared to conventional methods due to reducing toxic and expensive carbon precursors, reducing solvents, etc. These nanoparticles are greenly obtained by applying several precursors, such as plant biomass, algae, microorganisms, liquid, solid waste from domestic activities, etc., in hydrothermal and solid-state phases. The results are promising; however, until now, it is difficult to obtain larger quantities of carbon dots, limiting the scalability of the process. Furthermore, few works combine the green synthesis of carbon dots and flow synthesis protocols. Therefore, this chapter gives a general outlook regarding carbon nanoparticles’ eco-friendliness with special emphasis on carbon dots.