Bifunctional Carbon Nitride Exhibiting both Enhanced Photoactivity and Residual Catalytic Activity in the Post-Irradiation Dark Period

Graphitic carbon nitride (CN) as an environmental photocatalyst works under continuous illumination and stops under the dark condition. Here, we develop a bifunctional CN (4-phenoxyphenol-functionalized alkalinized carbon nitride (PP-ACN)) that exhibits not only enhanced photoactivity but also residual catalytic activity in the post-irradiation dark period by grafting 4-phenoxyphenol (PP) moieties onto the polymeric alkalinized CN framework and demonstrate the successful performance of the sequential photocatalysis–dark reaction process. The modified CN catalyst can degrade organic compounds (or inactivate bacteria) and concurrently generate and accumulate H2O2 (up to 40–60 μM) in the solution under visible light illumination. In the following dark period, it decomposes the accumulated H2O2 to generate •OH and continues to work for hours even in the absence of light. PP-ACN in the presence of H2O2 shows both the peroxidase-like activity and the dark Fenton-like activity in a wide range of pH (3–9), which is clearly different from the conventional photocatalysts. It exhibits an intrinsic radical character and a high selectivity for sequential three-electron reduction of O2 under irradiation and a single-electron reduction of H2O2 in the dark that lead to the generation of •OH radical. The present strategy of combining the photocatalytic activity and the post-illumination (dark) catalysis utilizing in situ H2O2 in series should be a versatile platform of photon utilization in the overall process.