Hydroxy functional groups modulate S-scheme MIL-125-NH2@COF heterojunctions for regulated photocatalytic production of hydrogen peroxide

Abstract

Covalent organic frameworks (COFs) and metal–organic frameworks (MOFs) possess crystalline porous structures and tunable assembly properties, making them promising for photocatalytic H2O2 production. However, single-component systems suffer from limited redox ability and fast carrier recombination. To address this, an S-scheme heterojunction was constructed by integrating hydroxyl-functionalized triazine-based COFs with aminated MIL-125-NH2 (designated as MIL@COF-nOH, where n ranges from 0 to 3). The number of hydroxyl groups in the COF layers has varying degrees of influence on tautomerization in COF-nOH. This, in turn, determines the band alignment of the heterojunction and subsequently impacts the charge separation efficiency and steers the performance of photocatalytic hydrogen peroxide. Specifically, MIL@COF-3OH exhibits the highest ratio of keto/enol tautomerism, and the ketone form acts as an electron trap, photoexcitation can induce ultrafast populating the enol-imine form, which may facilitate proton-coupled electron transfer event. Under visible light, the optimized heterojunction achieves a production rate of 2916 μmol g−1 h−1. This work demonstrates the great potential of a hydroxyl-functionalized COF/MOF-based S-scheme heterojunction for efficient photocatalytic H2O2 production, providing deep mechanistic insights into the role of functional groups in regulating charge dynamics.