Properties, synthesis, and applications of carbon dots: A review

Carbon dots (CDs) refer to a class of carbon-based nanoparticles with various subgroups based on their crystallinity and morphology. CDs offer tuneable physical, chemical, and optical properties, which can be controlled using simple one-pot synthesis techniques. In addition, their non-toxicity, biocompatibility, chemical and physical responsiveness, resistance to photo- and chemical-bleaching and low cost pave the way to a wide range of applications. The synthesis of CDs can be achieved via two approaches: (i) the top-down methods, and (ii) bottom-up methods. These two approaches can be designed to generate the intended chemical structures with specific band gap, hetero-atom doping, and chemical functionality. Further ongoing research enables us to understand the relationship between structural and optical properties of CDs. The photoluminescence of CDs depends on various parameters including synthesis methods, starting materials, surface states, and heteroatom doping etc. Herein, we review the various synthesis approaches and the properties of CDs such as the optical, physical, chemical, and structural properties resulting from the particles synthesis design. Also, proposed applications of CDs such as biomedicine, light emitting diodes, anticounterfeiting, and sensing are presented, where the main challenges in sensing applications and strategies to overcome these challenges are introduced.