In-situ polarization of covalent organic frameworks in seawater enables enhanced photocatalytic hydrogen evolution under visible- light 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 three beta-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 of beta-ketoenamine units exhibited the so far highest photocatalytic H(2 )evolution rate (41.3 mmolmiddotg(-1)middoth(-1)) in seawater, about 1.66 times higher than that in pure water. The beta-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.

Automated summary

Photocatalytic hydrogen production from seawater is enhanced by using beta-ketoenamine-linked covalent organic frameworks (COFs) as catalysts under visible-light irradiation. Among the constructed COFs, the one with a high density of beta-ketoenamine units exhibits the highest photocatalytic H2 evolution rate in seawater, about 1.66 times higher than in pure water. The beta-ketoenamine units allow in-situ polarization of the COF framework, resulting in increased dielectric constant and enhanced charge separation and transfer for promoting H2 photoproduction in seawater.