π-Bridge Modulation in Three-Motif Covalent Organic Framework for Efficient H₂O₂ Photosynthesis From Water and Air

Area of Science:

• Materials Science
• Photocatalysis
• Organic Chemistry

Background:

• Developing high-performance photocatalysts requires integrating photosensitive units and active sites.
• Uncontrolled charge transfer hinders efficiency in complex photocatalyst designs.

Purpose of the Study:

• To synthesize and investigate novel imine-bonded covalent organic frameworks (COFs) for photocatalysis.
• To explore the structure-activity relationship of COFs with varying electron-donor and acceptor motifs.

Main Methods:

• Synthesis of imine-bonded COFs (USTB-65 to USTB-68) with triphenylamine (donor) and benzothiadiazole/triphenyltriazine (acceptor) units.
• Incorporation of a π-bridge in USTB-66 to create a D-A-π-A structure.
• Photophysical investigations and theoretical calculations to study charge transfer dynamics.
• Evaluation of photocatalytic activity for H₂O₂ production from water and air.

Main Results:

• USTB-66, with its D-A-π-A structure, exhibited enhanced exciton dissociation and stepwise charge transfer.
• Achieved a H₂O₂ production rate of 11.2 mmol g⁻¹ h⁻¹, apparent quantum yield of 27.3% at 550 nm, and solar-to-chemical efficiency of 2.71%.
• Under solar concentration in a flow reactor, H₂O₂ production increased to 33.8 mmol g⁻¹ h⁻¹ over 24 hours.

Conclusions:

• The D-A-π-A architecture in USTB-66 effectively facilitates charge separation and transfer.
• USTB-66 demonstrates significant potential as a highly efficient photocatalyst for H₂O₂ production.
• The study highlights the rational design of COFs for advanced photocatalytic applications.