Gradient Polarization Induces Three-Dimensional Asymmetric Electron Distribution in Covalent Organic Frameworks for...

Area of Science:

• Materials Science
• Photocatalysis
• Chemistry

Background:

• Donor-acceptor (D-A) based covalent organic frameworks (COFs) show promise for photocatalysis.
• Spatial conformation in COFs presents trade-offs between in-plane and interplane carrier transport.
• Enhancing photocatalytic efficiency requires overcoming limitations in charge transport.

Purpose of the Study:

• To introduce a spatial gradient polarization strategy in COFs to improve photocatalytic efficiency.
• To investigate the effect of distinct electronegativities on electron distribution and polarization within COFs.
• To break traditional D-A intramolecular polarization limitations and enhance carrier transport.

Main Methods:

• Fabrication of COFs with distinct (NH)2─C═S and C═O groups.
• Utilizing a spatial gradient polarization strategy to create 3D asymmetric electron distribution.
• Mechanistic studies to analyze interlayer dipole rearrangement and polarization fields.
• Evaluating photocatalytic performance for nitrogen conversion under visible light and natural sunlight.

Main Results:

• A cooperative in-plane and out-of-plane polarization field was established, driving anisotropic charge transfer.
• The polarized microenvironment activated N≡N bonds and stabilized intermediates for sequential nitrogen conversion.
• The synthesized SBO COFs achieved record yields for NH4+ (11.59 mg g-1 h-1) and NO3- (7.18 mg g-1 h-1) under visible light.
• Unprecedented NH4+ (87.17 mg m-2 h-1) and NO3- (73.63 mg m-2 h-1) yields were observed under natural sunlight.

Conclusions:

• The spatial gradient polarization strategy effectively decouples carrier transport constraints in COFs.
• This approach optimizes the molecular structure-material relationship for enhanced spatial carrier migration.
• The developed COFs represent a significant advancement in photocatalytic nitrogen conversion.