Porphyrin-based COF nanosheet arrays with donor-acceptor structure for solar-driven water purification

Solar interface evaporation technology can effectively draw fresh water from the abundant seawater by utilizing green and clean solar energy. Advanced photothermal conversion materials play a crucial role in solar interface evaporation. As an emerging class of crystalline conjugated polymers, COFs (Covalent Organic Frameworks) provide an ideal molecular platform for the design of photothermal conversion materials. However, the mechanisms in which COF nano-morphologies promote photothermal conversion and the interface evaporation process remain unclear. In this work, we take advantage of the highly designable structure and functionality of COFs and develop porphyrin squaric acid-based COF membranes by controlling the nucleation and growth of COF crystal templated by porphyrin self-assemblies. These membranes feature an intramolecular donor-acceptor (D-A) heterojunction structure favorable for photothermal conversion and a unique nanosheet array structure. The arrayed COF nanosheets enhance light absorption and reduce the enthalpy of water evaporation, thereby increasing the evaporation rate. The membrane achieves an evaporation rate of 2.32 kg m −2  h −1 and an evaporation efficiency of 85.7 %. The COF membrane enables solar-driven desalination and demonstrates long-term salt resistance. This work provides a practical approach for constructing interface evaporation materials with unique micro/nanostructures.