Bottom-up approaches for the preparation of carbon dots

Recently, carbon dots (CDs) have been emerged as one of the potential nanomaterials in the interdisciplinary research areas of physics, chemistry, biology, and materials science due to its unique physicochemical properties like aqueous solubility, biocompatibility, photoluminescence, high resistance to photobleaching, and ease of surface functionalization. Due to its ease of fabrication and fascinating properties, the role of CDs has been explored in wide variety applications including bioimaging, theranostic, sensing, photo-catalysis, light-harvesting devices, etc. In general, bottom-up and top-down approaches have been utilized for the preparation of CDs. Bottom-up approaches include the assembling of molecular precursors from smaller carbon units such as carbohydrates, organic acids, polymers, natural products, and biomass via hydrothermal, carbonization, microwave, solvothermal, pyrolysis, and thermal decomposition techniques, whereas top-down approach includes breaking down of wide variety of carbon nanomaterials (graphite, carbon soot, carbon nanotubes, activated carbon, and nanodiamonds) into smaller carbon nanoparticles via laser ablation, chemical and electrochemical oxidation, arc-discharge, and ultrasonication techniques. Moreover, the size and properties of the CDs can be altered by controlling the reaction condition and time. Hence, the selection of effective synthesis route is an important factor for controlled preparation of CDs with uniform size and surface passivation. However, top-down approaches always require sophisticated instruments, harsh reaction condition, and longer reaction time, which limit their use for large-scale production of CDs as compared to the bottom-up approaches. In this chapter, various bottom-up routes for the precise fabrication of CDs have been briefly summarized and discussed.