Facile construction of porous intramolecular g-C3N4-based donor-acceptor conjugated copolymers as highly efficient photocatalysts for superior H2 evolution

Graphitic carbon nitride (g-C3N4) is an emerging polymeric visible-light photocatalyst with a high stability, but it continues to exhibit low photocatalytic efficiency. Herein, novel intramolecular g-C3N4-based donor-acceptor (D-A) conjugated copolymers with a porous structure and large specific surface area, have been facilely prepared by copolymerizing urea with melamine-formaldehyde (MF) resin, which is strategically used for promoting the photocatalytic performance of pure g-C3N4. The experimental results indicate that the as-prepared porous intramolecular g-C3N4-MFx D-A conjugated copolymers not only enlarge the light utilization but also accelerate the separation of charge carriers because of the enhanced electron-accepting ability due to the introduction of MF resin. In addition, compared to the pure g-C3N4, the specific surface area of g-C3N4-MF100 is clearly increased, and the conduction band is significantly shifted up. As expected, the porous g-C3N4-MF100 D-A conjugated copolymer achieves the best photocatalytic hydrogen evolution (PHE) activity (3612.65 μmol h−1 g−1), which is over 8.87 times higher than that of pure g-C3N4, and outperforms the majority of the previously reported g-C3N4-based D-A conjugated polymers and porous g-C3N4. In addition, the apparent quantum yield (AQY) of the porous intramolecular g-C3N4-MF100 D-A conjugated copolymer reaches 8.6% at 420 nm. This work provides a new design idea of effectively combining the porous and intramolecular D-A conjugated structures of g-C3N4 to achieve a remarkably enhanced PHE activity and light utilization.