In-situ polarization of covalent organic frameworks in seawater enables enhanced photocatalytic hydrogen evolution under visiblelight irradiation

Photocatalytic hydrogen(H_(2))production from seawater over a photocatalyst is of great significance for the utilization of the earth’s abundant seawater resources and the storage of inexhaustible solar energy with low-energy density.However,the designation of efficient photocatalytic systems by using seawater usually suffers from activation decline when replacing pure water with seawater.Herein,we synthesized threeβ-ketoenamine-linked covalent organic frameworks(COFs),demonstrating their promotion in the photocatalytic decomposition of seawater relative to pure water under visible-light irradiation.The target COFs were synthesized via a microwave assisted solvothermal method by using 1,3,5-triformylphloroglucinol(Tp)as the aldehyde monomer to react with diamino units with different numbers of benzene rings.By surveying the building blocks,the constructed COF with a high density ofβ-ketoenamine units exhibited the so far highest photocatalytic H_(2) evolution rate(41.3 mmol·g^(−1)·h^(−1))in seawater,about 1.66 times higher than that in pure water.Theβ-ketoenamine units allowed the in-situ polarization of the COF framework through the adsorption of metal salts when proceeding with the photocatalytic H_(2) production in seawater.This polarization effect significantly increases the dielectric constant of the organic semiconductor to lower exciton dissociation energy and thus enhances the charge separation and transfer to promote the H_(2) photoproduction in seawater.