Defect-Mediated Pore Expansion in Two-Dimensional Covalent Organic Frameworks

Abstract

Two-dimensional (2D) covalent organic frameworks (COFs) are known for their semiconducting features, which stem from the extended conjugated backbones within their stacked layers. These attributes render 2D COFs highly suitable for photocatalysis, with electron transfer facilitated by their conjugated lattices. A common strategy to enhance photocatalytic performance has been to design topologies that elevate π-column density using geometrically appropriate building blocks. However, this often leads to hydrophobic microporous channels, impeding efficient mass transfer. Herein, we introduce a novel methodology by employing six-connected HFPTP, three-connected TPB, and V-shaped two-connected m-TPDA as building blocks. By adjusting the TPB to m-TPDA molar ratio, we have successfully integrated regular defects into the kgd lattice, resulting in modified kgd COFs with rhombic and hexagonal star-shaped pores. This design diverges from the conventional kgd topology, which typically yields small micropores, to one that incorporates mesopores through the strategic placement of defects within the skeletons. The resulting defect-mediated 2D HP-COF, with its optimized aperture ratio and energy levels, along with enhanced mass transfer, demonstrates a significantly improved photocatalytic hydrogen peroxide production rate of 7433 μmol·g⁻¹·h⁻¹. This performance surpasses that of non-defect-based counterparts, underscoring the pivotal role of structural defect engineering in advancing the photocatalytic efficiency.

Keywords

Covalent organic frameworks / Defect engineering / Photocatalysis / Materials science / Mesoporous materials / Semiconductors / Column density / Topochemistry / 2D materials / Conjugated polymers

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