Carbon quantum dots (CQDs) as a rising class of carbon family have gained widespread attention in view of their multiple properties such as great photoluminescence (PL) properties, facile synthesis route, needing economical and cheap raw material, high physiochemical stability, and simple functionalization. This makes CQDs highly versatile and with potential for different applications. To date, CQDs-enabled photocatalysts are regarded as one of the most efficient technologies to degrade pollutants in water; however, poor activity under visible light and the recombination of photogenerated electron and hole pairs hinder getting an ideal performance that may be applied on a large scale. Conventional techniques have been modified via a new advanced method. In this review, we highlighted the strategies to improve the activity of conventional semiconductor photocatalysis via coupling with CQDs, and strategies to improve the photocatalytic activity such as functionalization, doping, and Z-scheme heterojunctions were discussed in detail. This review also covered the CQDs heterojunction application in pollutant degradation and discussed several examples with high-performance photocatalytic activity.

    Abstract
    1 Introduction
    2 Role of CQDs in photocatalytic water splitting
    3 CQDs as a surface modifier for functionalization of photocatalyst
    4 CQDs-modified heterojunction photocatalysts
    5 The degradation of pollutants by CQDs-based heterojunctions
    6 Conclusion
    Acknowledgements 
    References

• Noureen Syed(School of Material Science and Engineering, International S&T Cooperation Foundation of Shaanxi Province, Xi’an Key Laboratory of Green Manufacture of Ceramic Materials, Shaanxi University of Science and Technology)
• Jianfeng Huang(School of Material Science and Engineering, International S&T Cooperation Foundation of Shaanxi Province, Xi’an Key Laboratory of Green Manufacture of Ceramic Materials, Shaanxi University of Science and Technology)
• Yongqiang Feng(School of Material Science and Engineering, International S&T Cooperation Foundation of Shaanxi Province, Xi’an Key Laboratory of Green Manufacture of Ceramic Materials, Shaanxi University of Science and Technology)