Photodegradation of Organic Pollutants Coupled with Simultaneous Photocatalytic Evolution of Hydrogen Using Quantum-Dot-Modified g‑C₃N₄ Catalysts under Visible-Light Irradiation

Carbon quantum dots/CdS quantum dots/g-C₃N₄ (CDs/CdS/GCN) photocatalysts have been designed and prepared. Systematic characterization such as XRD, SEM, TEM, UV, and XPS, were done to confirm the composite catalysts of CDs/CdS/GCN. The simultaneous photocatalytic production of hydrogen coupled with degradation of organic contaminants (p-chlorophenol, bisphenol A, and tetracycline, called 4-NP, BPA, and TTC, respectively) was efficiently realized over the resultant CDs/CdS/GCN composites. The as-prepared 3% CDs/10% CdS/GCN exhibits high efficiency of photocatalytic hydrogen evolution from water splitting and photodegradation rates of organic pollutants in aqueous solutions of 4-NP, BPA, and TTC under visible-light illumination since the formation of interfaces between CdS quantum dots and GCN nanosheets leads to an efficient charge separation efficiency. Furthermore, as compared to that in a pure water system, the photocatalytic evolution rate of H₂ over the 3% CDs/10% CdS/GCN catalyst in the presence of 4-NP solution is decreased, while the H₂ evolution rates increase when BPA or TTC solution were used instead of 4-NP solution under visible-light irradiation. Consequently, 4-NP shows higher photodegradation efficiency than do BPA and TTC in the simultaneous photocatalytic oxidation and reduction system. Aiming at making clear the relationship between the photocatalytic H₂ production and the photocatalytic pollutants degradation, density functional theory (DFT) calculations, and liquid chromatography mass spectrometry (LC-MS) were used for a systematic investigation. The present work reports a plausible mechanism of photodegradation of different organic contaminants with synchronous photocatalytic H₂ evolution from water and the photocatalytic enhancement of the CDs/10% CdS/GCN catalysts.