Carbon dots (C-dots) are a developing subclass of nanomaterials which are characterized by a typical diameter of less than 10 nm. C-dots are a type of core–shell composites that feature a surface passivation with various functional groups, including amine, carboxyl, hydroxyl group, and a carbon core. Green C-dots, which have drawn a lot of interest from researchers due to their superior water solubility, excellent biocompatibility, and environmental-friendly behavior when compared to chemically generated C-dots, can be made from a variety of low-cost and renewable materials. Since green C-dots have heteroatoms on their surface in the form of carboxyl, amine, hydroxyl, or other functional groups, which can enhance their physicochemical characteristics, quantum yield (QY), and likelihood of visible light absorption, further surface passivation is not necessary. Green C-dots may find use in the areas of biosensing, catalysis, bioimaging, and gene and drug delivery. In this paper, the creation of C-dots was outlined, and its fluorescence process examined. This review represents the summary of synthesis, mechanism, properties, characterization, and applications of C-dots. This article aims at the green chemistry strategies for C-dot synthesis. Furthermore, a discussion on the applications of C-dots produced with green approaches is presented. The paper may help the researchers in the field to develop new C-dots with potential features to attract the attention of new applications.

A study on the development of C-dots via green chemistry: a state-of-the-art review
    Abstract
        Graphical Abstract
    1 Introduction
    2 Synthesis methods of carbon dots
        2.1 Top-down method
        2.2 Bottom-up method
    3 Synthesis of carbon dots via green methods
        3.1 Pyrolysis
        3.2 Hydrothermal method
        3.3 Microwave irradiation
        3.4 Heating
        3.5 Carbonization
        3.6 Hydrothermal carbonization
    4 Various sources for synthesis of carbon dot
        4.1 From green precursors
        4.2 From natural or food sources
        4.3 From rice husk
        4.4 From the ash of the eggshell membrane
        4.5 From diesel engine exhaust
        4.6 From waste food
        4.7 Beverages as carbon source
        4.8 From bagasse
        4.9 From the juice of Saccharum officinarum
        4.10 From the leaves of coriander
        4.11 From frying oil waste
    5 Properties of carbon dots
        5.1 Composition and morphology
        5.2 Resilience and sensitivity of carbon dots
        5.3 Luminous mechanism
            5.3.1 Quantum effects
            5.3.2 Surface state
        5.4 Biocompatibility properties
        5.5 Optical characteristics
    6 Carbon dots characterization techniques
        6.1 Ultraviolet–visible spectroscopy technique
        6.2 Fourier-transform infrared spectroscopy
        6.3 Electron microscopy approaches
        6.4 X-ray diffraction
        6.5 Quantum yield analysis
    7 Applications
        7.1 Biomedical and biotechnological applications
            7.1.1 Antiviral and antimicrobial effects
            7.1.2 Gene and drug delivery
            7.1.3 Sensors
            7.1.4 Biomedicine
            7.1.5 Bioimaging
        7.2 Biosensing
            7.2.1 pH sensing
            7.2.2 Amino acid sensing
            7.2.3 Chemical sensing
        7.3 Catalysis
        7.4 Quality control
    8 Future perspective and conclusion
    Acknowledgements 
    References

• Nazia Tarannum(Department of Chemistry, Chaudhary Charan Singh University Meerut, Meerut 250004, India)
• Km. Pooja(Department of Chemistry, Chaudhary Charan Singh University Meerut, Meerut 250004, India)
• Manvi Singh(Department of Chemistry, Chaudhary Charan Singh University Meerut, Meerut 250004, India)
• Anurag Panwar(Department of Chemistry, Chaudhary Charan Singh University Meerut, Meerut 250004, India)