The carbon-based nanostructures are in limelight due to their widespread applications in nano-to-micro-scale technologies. The carbon dots are known for their unique physical, electrical, optical, chemical and biological properties. The carbon dots (CDs) are being produced through several well-developed synthesis methods, one of which is the green sonochemical. This method is preferred over others because it is a green source of energy, facile, fast, low-temperature process, non-toxic and less expensive. Despite the fact of using 90% less energy than other methods, this method has been overlooked in the published literature. It is possible to prepare pure and doped CDs of low toxicity and controlled physicochemical properties through sonochemical method. In recent years, sonochemically produced CDs have been tuned and characterized for a variety of applications. This review has explored the merits and demerits of sonochemical method in comparison to the other methods for the synthesis of pure CDs and their nanocomposites. The role of multiple factors in tailoring the specific parameters of CDs for their application in antibacterial, polymerization, tissue engineering, catalysis, bio-imagining, supercapacitors, drug delivery and electric devices is also elaborated in this review. This review also concludes on future directions in the applications of sonochemically produced CDs.

    Abstract
    1 Introduction
    2 Preparation of carbon dots
        2.1 Quantum yield
        2.2 Mechanism of formation of carbon dots
    3 Chemical structure of CDs
    4 Effects of sonication process parameters
        4.1 Effect of solvent
        4.2 Effect of power of ultrasound
        4.3 Effect of ultrasound frequency
        4.4 Effect of sonication time
        4.5 Effect of precursors and catalysts
    5 Advantages of ultrasonic synthesis of CDs
    6 Applications of CDs
        6.1 Antimicrobial and anti-parasitic
        6.2 Use in catalysis
        6.3 Polymerization
        6.4 Use in bioimaging
        6.5 Neural tissue engineering
        6.6 Superconductivity
        6.7 Preparation of biofuels
        6.8 Use in supercapacitors
    7 Conclusion
    Acknowledgements 
    References

• M. Saleem(Department of Physics, University of Agriculture)
• M. Y. Naz(Department of Physics, University of Agriculture)
• S. Shukrullah(Department of Physics, University of Agriculture)
• M. A. Shujah(Department of Physics, University of Agriculture)
• M. Akhtar(Department of Physics, University of Agriculture)
• Sami Ullah(Department of Chemistry, College of Science, King Khalid University)
• S. Ali(Department of Chemistry, University of Agriculture)