Constructing a Z-scheme heterojunction photocatalyst I-ABN-C3N4@CDs/ BiOI by synergistically in situ modified g-C3N4 via carbon dots and copolymerization for BPA degradation

The rapid recombination of photogenerated carriers and the narrow absorption range of visible light greatly limit the photocatalytic activity of graphite carbon nitride (g-C3N4). Herein, g-C3N4 was jointly modified by carbon dots (CDs) and copolymerization via in situ co-calcining of three precursors (urea, glucose and 2-amino-5-iodobenzonitrile (I-ABN)), and named as I-ABNx-C3N4@CDsy. Then, solid-state Z-scheme photocatalysts PC1-PC9 with CDs as the electron mediators were prepared via in situ growth of BiOI on the surface of I-ABNx-C3N4@CDsy through solvothermal method. The optimal proportion of each component was explored through orthogonal experiments. The existence of CDs act as an electron transport medium to accelerate the transportation rate of photogenerated carriers, improve the light absorption capacity. The copolymerization with I-ABN introduce benzene rings and I- to g-C3N4, which enhance the light absorption capacity and photoelectric efficiency. The Zscheme heterojunction effectively suppresses the recombination of photogenerated electron-hole pairs. Therefore, PC1-PC9 presented excellent performance for the degradation of BPA due to the synergistic effects of the above three points. Among them, PC6 showed the best photocatalytic activity, which completely degraded BPA (15 mg/L) within 40 min, and whose rate constant (0.091 min-1) was 22.8 times that of bulk g-C3N4. The active radical trapping experiment determined center dot O2- and h+ were the main active radicals. Finally, the BPA degradation mechanism by PC6 was proposed. This study provides new insights for the combination of heterojunction, carbon dots, and copolymerization to rationally design efficient photocatalysts to restore the environment.