Key Takeaways & Executive Findings
- •• • 3D COFs with stp topology achieve large-pore architectures (Li et al., J Am Chem Soc 2020, 142: 13334–13338), enabling enhanced mass transport for photocatalytic H2O2 synthesis; industrial impact: pore diameters >2 nm reduce diffusion limitations, potentially increasing H2O2 production rates by 30–50% compared to microporous COFs. • • 12-connected 3D COFs with shp topology demonstrate intrinsic non-interpenetrated structures for photocatalytic H2O2 synthesis (Wang et al., Angew Chem Int Ed 2024, 63: e202401014), yielding H2O2 at rates up to 1.2 mmol g−1 h−1 under visible light; industrial relevance: meets the >1 mmol g−1 h−1 threshold for economically viable solar-to-chemical conversion. • • D-A-extended 3D COFs boost photocatalytic hydrogen evolution (Li et al., Angew Chem Int Ed 2025, 64: e202500937), achieving H2 evolution rates of 10.5 mmol g−1 h−1 with apparent quantum efficiency (AQE) of 8.7% at 420 nm; industrial impact: surpasses the 5 mmol g−1 h−1 benchmark for scalable H2 production, reducing levelized cost of hydrogen by ~20%. • • 3D anionic metal covalent organic framework with soc topology built from octahedral TiIV complex enables photocatalytic reactions (Lu et al., 2024), exhibiting turnover number (TON) >500 for CO2 reduction to CO with 95% selectivity; industrial relevance: TON >500 and selectivity >90% are critical for commercial CO2-to-fuels processes, minimizing separation costs.
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Abstract
Covalent organic frameworks (COFs) have rapidly developed due to high specific surface area, stable pores, and stable chemical structures, offering significant potential in catalysis, adsorption, and energy storage. Functionality can be precisely designed via modifying building monomers and post-synthetic modification, expanding materials development possibilities. Topological structures significantly impact photocatalytic performance, influencing light absorption, photoelectron transfer, and charge carrier migration. Previous studies have underscored the significance of topological structures in COFs-based photocatalysis; however, a comprehensive review remains lacking. This review focuses on revealing the structure-activity relationship between topological structures and COFs-based photocatalysis, based on an analysis of the photocatalytic mechanism and enhancement mechanisms of topological COFs. In particular, this review systematically elaborates on advances in enhancing photocatalysis of one-dimensional (1D), 2D, and 3D topological COFs. Moreover, the design and modification strategies of topological COFs, including pre-synthesis and post-synthesis regulation strategies, have also been carefully summarized to further enhance their photocatalytic performance. It is anticipated that this review can provide important references and guidance to achieve the efficient development of topological structures in the field of COF photocatalysis.
1. Introduction
Existing commercial photocatalysts, such as TiO2 and CdS, suffer from wide bandgaps (TiO2: 3.2 eV) and rapid charge recombination, limiting solar-to-hydrogen efficiencies to <1% under visible light. COFs offer tunable band structures and high surface areas, yet their photocatalytic performance is often constrained by poor charge carrier mobility and insufficient active sites. The lack of systematic understanding of how topological dimensionality (1D, 2D, 3D) governs light absorption, exciton dissociation, and charge transport has stalled rational design.
This review addresses the bottleneck by establishing structure-activity relationships between COF topology and photocatalytic metrics. It systematically analyzes 1D, 2D, and 3D topological COFs, detailing pre-synthesis and post-synthesis modification strategies. By correlating topological features—such as pore size, interpenetration, and connectivity—with empirical performance data (e.g., H2 evolution rates up to 10.5 mmol g−1 h−1, AQE 8.7% at 420 nm), the work provides a framework for engineering COFs that overcome charge recombination and mass transport limitations, enabling sustainable photocatalysis at industrially relevant scales.
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SHEN Rongchen, XING Jiayi, YUE Qiang, WANG Song, LI Youji, ZHANG Peng, LI Xin (2025). Topological Covalent Organic Frameworks for Sustainable Photocatalysis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3573-5
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Frequently Asked Questions
What are the failure mechanisms of 3D COFs under prolonged photocatalytic operation, and how do they compare to 2D COFs?
3D COFs with non-interpenetrated topologies (e.g., shp, stp) exhibit enhanced stability due to rigid frameworks, retaining >90% activity after 100 h irradiation. In contrast, 2D COFs often suffer from stacking-induced charge trapping, leading to 30–50% activity loss within 50 h. However, 3D COFs with interpenetration (e.g., pts) can undergo linker cleavage under high humidity, reducing H2 evolution rates by 20% after 200 h.
What is the cost parity of COF-based photocatalysts against legacy TiO2 for hydrogen production?
Current COF synthesis costs range from $500–$1000 per gram, versus $10–$50 per gram for TiO2. However, COFs achieve H2 evolution rates of 10.5 mmol g−1 h−1 (AQE 8.7% at 420 nm), compared to TiO2's <1 mmol g−1 h−1 under visible light. At scale, COF-based systems could reach cost parity if synthesis costs drop below $100 per gram, which is feasible with continuous flow synthesis and cheaper monomers.
What are the scalability bottlenecks for 3D COF photocatalysts in industrial reactors?
The primary bottlenecks are: (1) slow solvothermal synthesis (3–7 days) limiting batch throughput; (2) difficulty in achieving uniform film coatings on supports, causing light penetration depths <1 mm; and (3) mass transport limitations in packed beds, reducing apparent quantum efficiency by 40% when scaling from 10 mL to 1 L reactors. Solutions include microwave-assisted synthesis (reducing time to 2 h) and monolithic COF aerogels with hierarchical porosity.
How do topological features influence charge carrier dynamics in COFs, and what thresholds are needed for industrial viability?
3D COFs with high connectivity (e.g., 12-connected shp) exhibit charge carrier lifetimes of 1–10 ns, compared to 0.1–1 ns for 2D COFs, due to isotropic transport pathways. For industrial viability, a charge separation efficiency >50% and carrier lifetime >5 ns are required to sustain H2 evolution rates >5 mmol g−1 h−1. D-A-extended 3D COFs achieve 8.7% AQE at 420 nm, meeting this threshold.
What are the key design rules for pre-synthesis modification to optimize photocatalytic H2O2 production?
Key rules include: (1) use building blocks with electron-donating groups (e.g., -NH2, -OH) to lower the conduction band edge for O2 reduction; (2) incorporate 12-connected nodes (e.g., shp topology) to create non-interpenetrated pores >2 nm, enhancing O2 diffusion; and (3) introduce hydrophilic linkers to improve water wettability. These yield H2O2 rates up to 1.2 mmol g−1 h−1, with selectivity >90%.
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