Microporous Confinement of One-Dimensional Covalent Organic Frameworks for Surface-Regulated Photocatalytic Hydrogen Evolution.

Covalent organic frameworks (COFs) have gained attention as an advanced platform for photocatalytic hydrogen evolution. Previously reported COF-based photocatalysis focused on the molecular design of donor-acceptor motifs and bandgap engineering, while quantifying the contribution of active sites located on different surfaces remains underexplored. Herein, we construct three one-dimensional COFs with identical backbone structures but distinct active-site distributions to systematically investigate their impact on exciton migration. By leveraging hydroxyl-functionalized linkers, we introduce active sites on either the inner or outer surfaces of the COFs. Among them, 2-OH-COF, featuring inner-surface hydroxylation, exhibits a superior hydrogen evolution rate in both pure water and seawater systems, significantly outperforming its structural analogues. Extensive characterization reveals that the hydroxylated surface of the micropores plays a pivotal role in promoting exciton dissociation and facilitating the adsorption of water molecules and platinum precursors. This confinement effect within the micropores enables optimized catalytic microenvironments and efficient two-step photoreduction. This research provides insights into the surface engineering of COFs and highlights the effects of active site localization on optimizing photocatalytic performance.