Proton Reservoir in Covalent Organic Framework Compensating Oxygen Reduction Reaction Enhances Hydrogen Peroxide Photosynthesis.

The water oxidation reaction (WOR) with sluggish kinetics usually fails to adequately furnish protons to oxygen reduction reaction (ORR), which ultimately constrains the overall efficiency of photocatalytic synthesis of H2O2, particularly in the absence of sacrificial agents. Herein, a class of hydroxyl groups (─OH) functionalized covalent organic framework (COF) is reported as a proton reservoir to compensate ORR for greatly improving the efficiency of H2O2 photosynthesis. It has been demonstrated that the incorporation of ─OH into the TFBP-DHBD (TFBP: 1,2,4,5-tetrakis-(4-formylphenyl)benzene, DHBD: 3,3'-dihydroxybenzidine) COF can achieve a 3.3 times higher H2O2 photosynthetic activity than that of TFBP-BD (BD: benzidine) COF without ─OH groups. Isotope labeling experiments and in situ infrared spectroscopy analysis demonstrate that the proton reservoir can donate protons for ORR and subsequently regain the released protons from WOR. Theoretical calculations further confirm that the ─OH functionalized COF provides the protons for the formation of *OOH intermediate and reduces its energy barrier, thereby facilitating the photosynthesis of H2O2. A novel COF loaded with Al2O3 spheres-based streamlined microreactor is built that can simultaneously achieve production of H2O2 and elimination of bacteria over 1.3 × 104 CFU mL-1, superior to the reported continuous flow photocatalytic reactors.