This study details the synthesis and characterization of phosphorus-sulfur co-doped graphitic carbon nitride quantum dots (PSQ) and their integration into g-C3N4 (CN) to form PSQ/CN composites for the enhanced photocatalytic reduction of Cr(VI) and fluorescence detection. Incorporating PSQ into CN was found to significantly improve light absorption, narrow the band gap, and enhance charge separation efficiency. Notably, the composite material exhibits superior photocatalytic performance, especially in acidic environments. Photocatalytic assessments utilizing Cr(VI) demonstrated that the PSQ/ CN composite outperformed both undoped and singly doped materials, indicating its superior photocatalytic activity. Additionally, phosphorus-sulfur co-doping markedly increased the fluorescence quantum yield of PSQ. The fluorescence intensity exhibited a linear decrease with increasing Cr(VI) concentrations, enabling sensitive and selective detection of Cr(VI) with a detection limit as low as 1.69 μmol/L. Collectively, the PSQ/CN composite and PSQ highlight their potential for photocatalysis and fluorescence-based detection of Cr(VI), providing high sensitivity, selectivity, and synergistic interactions within the composite material.

Phosphorus-sulfur co-doped carbon nitride quantum dots for enhanced photocatalytic reduction and fluorescence detection of Cr (VI)
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Preparation of materials
        2.3 Characterization
        2.4 Photocatalytic detection
        2.5 Photoluminescence measurement
    3 Results and discussion
        3.1 XRD
        3.2 Structure
        3.3 FT-IR
        3.4 XPS
        3.5 UV–Vis DRS
        3.6 PL spectrum
        3.7 Electrochemical properties
        3.8 Photocatalytic performance
        3.9 Photocatalytic mechanism
        3.10 Fluorescence performance
    4 Conclusion
    Acknowledgements 
    References

• Zhiyuan Ren(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Wei Chang(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Ke Tian(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Peiqi Yao(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Bin Liu(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Yunfeng Li(Xi’an Key Laboratory of Textile Chemical Engineering Auxiliaries, School of Environmental and Chemical Engineering, Xi’an Polytechnic University, Xi’an 710600, People’s Republic of China)
• Runze Zhang(Xi’an Wonder Energy Chemical Co., Ltd, Xi’an 710600, People’s Republic of China)