Developing the high-performance semiconductor photocatalytic materials is an eternal topic under the background of the current energy and environment requirements. In recent years, single-atom photocatalysts (SAPCs) have been brought a lot of attention in energy conversion and environmental purification because of their unique characteristics and properties, including the unique coordination patterns, outstanding atomic utilization, quantum confinement effects, high catalytic activity, etc. Hence, this critical review focuses on the summarized various synthetic methods and the recent important applications of SAPCs, including photocatalytic H2 evolution (PHE) from water splitting, photocatalytic CO2 reduction, photodegradation of organic pollutants, etc. The prospects and challenges for future research topics of SAPCs with excellent activity and stability for various photocatalytic applications are prospected at the end of this review. We sincerely expect that this critical review can promote deep-level insight into the SAPCs subject for the future significant applications in other fields.

Recent advance of single atom-based photocatalysts for energy conversion and environmental purification
    Abstract
    1 Introduction
    2 Synthesis strategies for SAPCs
        2.1 Metal ion absorption synthesis
        2.2 High temperature pyrolysis synthesis
        2.3 Photodeposition synthesis
        2.4 Other synthesis strategies
    3 Application of SAPCs
        3.1 PHE from water splitting based on SAPCs
        3.2 Photocatalytic CO2 reduction based on SAPCs
        3.3 Photodegradation of organic pollutants based on SAPCs
        3.4 Other photocatalytic applications based on SAPCs
    4 Conclusions and outlook
    Acknowledgements 
    References

• Yaling Niu(Baicheng Normal University, Baicheng 137000, People’s Republic of China)
• Chengcai Yue(Baicheng Normal University, Baicheng 137000, People’s Republic of China)
• Shuqi Li(Baicheng Normal University, Baicheng 137000, People’s Republic of China)
• Guangbo Che(Baicheng Normal University, Baicheng 137000, People’s Republic of China, Key Laboratory of Preparation and Application of Environmental Friendly Materials, Ministry of Education, Jilin Normal University, Changchun 130103, People’s Republic of China)
• Nan Su(Institute of Green Chemistry and Chemical Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China)
• Hongjun Dong(Institute of Green Chemistry and Chemical Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China)
• Chunmei Li(Institute of Green Chemistry and Chemical Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, People’s Republic of China)