Enhanced photocatalytic hydrogen peroxide production activity of imine-linked covalent organic frameworks via modification with functional groups

Solar-driven photocatalytic H2O2 production with water and O-2 is an environmentally friendly process for producing H2O2, an important chemical. Compared with traditional photocatalysts, covalent organic frameworks (COFs) have received extensive attention due to their tuneable composition and photoelectric structure at the molecular and nanoscale levels. Ligand functionalisation is an efficient strategy to modulate the properties and stability of COFs. Here, we synthesized a series of functionalised TAPB-PDA-X with various functional groups (X = H-2, OH, OCH3, and CH3) for photocatalytic H2O2 production under visible light and investigated their morphology, light-absorption intensity, stability, catalytic activity and band gap. We found that the hydroxyl functional group modification TAPB-PDA-X can further improve its photocatalytic H2O2 production abilities. The photocatalytic H2O2 evolution over the TAPB-PDA-OH catalyst reached 2117.6 mu mol g(-1) h(-1), and the apparent quantum yield (AQY) was 2.99% at 420 nm. The hydroxyl group in TAPB-PDA-X can enhance visible-light absorptions and improve the stability of photocatalytic H2O2 production. Mechanistic experiments illustrate that photocatalytic H2O2 evolution is a two-step single-electron reduction process. Our results offer new ideas for developing solar-driven metal-free photocatalysts.