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

Abstract

Solar-driven photocatalytic H₂O₂ production with water and O₂ 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 = H₂, 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 μmol 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.