Construction of porphyrin-based two-dimensional covalent organic frameworks for photocatalytic hydrogen production

With rapid industrial development, the increasing energy consumption has led to severe environmental pollution. Photocatalytic hydrogen production from water splitting has been regarded as a plausible solution to the energy crisis. However, highly-efficient photocatalytic hydrogen evolution remains a great challenge. Therefore, there is an urgent need to develop novel photocatalysts with broad visible absorption, stable structure, elevated photoinduced photon separation and transfer rates, and strong reduction power. Two-dimensional covalent organic frameworks (2D COFs) may present an ideal platform for highly-efficient photocatalytic hydrogen production due to their structural designability, which allows the integration of light-sensitive organic monomers, and their long-range ordered molecular arrangement that can facilitate interlayer electron transfer over amorphous materials. In this study, we design and synthesize two porphyrin-based 2D COFs, namely, TPB-TAPP-COF and TFPPY-TAPP-COF that have a similar structure but different cores with distinct conjugation levels. The photocatalytic hydrogen production efficiencies of TPB-TAPP-COF and TFPPY-TAPP-COF materials are investigated. Our results indicate that the photocatalytic hydrogen production efficiency is 4244.2 μmol g⁻¹ h⁻¹ for TPB-TAPP-COF and 8700.2 μmol g⁻¹ h⁻¹ for TFPPY-TAPP-COF, suggesting that the degree of conjugation of COFs strongly affects the efficiency of charge transport and photocatalytic hydrogen evolution. The results provide valuable insights into the rational design of photocatalytic materials with high efficiency in photocatalytic hydrogen evolution.