Fabrication of a Perylene Tetracarboxylic Diimide–Graphitic Carbon Nitride Heterojunction Photocatalyst for Efficient Degradation of Aqueous Organic Pollutants

Metal-free g-C3N4 is a promising candidate for the next-generation visible light-responsive photocatalyst; however, high recombination probability of the photogenerated charge carriers on g-C3N4 limits its photocatalytic activity. To further increase the intrinsic photocatalytic activity of g-C3N4, here, perylene tetracarboxylic diimide–g-C3N4 (PDI/GCN) heterojunctions are prepared by one-step imidization reaction between perylene tetracarboxylic dianhydride (PTCDA) and g-C3N4 in aqueous solution. By the combination of various testing results, it is confirmed that the surface hybridization of PTCDA and g-C3N4 in the PDI/GCN heterojunctions via O═C–N–C═O covalent bonds occurs at lower PTCDA-to-g-C3N4 weight percentage. By selecting p-nitrophenol (PNP) and levofloxacin (LEV) as the target organic pollutants, the visible-light photocatalytic performance of the PDI/GCN heterojunctions is studied. It shows that the PDI/GCN heterojunction prepared at a PTCDA-to-g-C3N4 weight percentage of 1% exhibits remarkably higher visible-light photocatalytic degradation and mineralization ability toward aqueous target pollutants as compared with g-C3N4 and Degussa P25 TiO2. On the basis of the experimental results including photoelectrochemistry, indirect chemical probe, and electron spin resonance spectroscopy, it is verified that the surface hybridization in the heterojunctions is responsible for this enhanced photocatalytic activity via accelerating the migration and separation of the photogenerated charge carriers, causing to produce more active species like •O2–, hVB+, and •OH for deep oxidation of PNP or LEV to CO2 and inorganic anions.