Key Takeaways & Executive Findings
- •• • The solid-state hot-pressing method synthesizes COFs in 0.5–5 minutes, a drastic reduction from conventional solvothermal times (hours to days), enabling rapid production and energy savings. • • The method produces self-standing COF platelets with high crystallinity and porosity, eliminating the need for post-synthetic shaping and facilitating direct use in flow adsorption and catalysis. • • The approach is broadly applicable, successfully synthesizing 15 distinct COFs, including imine-, hydrazone-, β-ketoenamine-, and imide-linked frameworks, a 3D COF (COF-300), and a mixed-monomer COF, demonstrating versatility across linkage chemistries. • • A large free-standing COF platelet of 200 cm² (10 cm × 20 cm) was fabricated, demonstrating potential for scaled-up production and industrial implementation.
Abstract
Covalent organic frameworks (COFs) are porous crystalline materials assembled from organic building blocks via strong covalent bonds, offering well-defined pores, high surface area, and tunable properties for applications in gas storage, separation, catalysis, sensing, and energy conversion. However, conventional solvothermal synthesis requires high temperatures, long reaction times, and complex procedures, hindering scalability and increasing costs. Additionally, COFs are typically obtained as microcrystalline powders, limiting their direct use in flow processes. To overcome these barriers, a novel solid-state hot-pressing method was recently reported, enabling rapid synthesis of COF platelets with high crystallinity and porosity. This method involves applying pressure and heat simultaneously, reducing the energy barrier for monomer reactions and facilitating layer growth and stacking, as confirmed by density functional theory and molecular dynamics simulations. The approach demonstrated versatility by synthesizing 15 distinct COFs, including imine-, hydrazone-, β-ketoenamine-, and imide-linked frameworks, a three-dimensional COF (COF-300), and a mixed-monomer COF, all within 0.5–5 minutes. Notably, a free-standing COF platelet of 200 cm² was fabricated, showcasing scalability. This strategy addresses the trade-offs among synthetic convenience, product quality, environmental impact, and scalability, positioning COFs for commercial viability.
1. Introduction
Conventional solvothermal synthesis of covalent organic frameworks (COFs) demands high temperatures, prolonged reaction times, and complex procedures, leading to high energy costs and limited scalability. Moreover, the resulting microcrystalline powders are difficult to process into monolithic forms required for practical applications involving fast-flowing gas or liquid, particularly in adsorption and catalysis. Alternative methods such as ionothermal, mechanochemical, and microwave-assisted synthesis have been explored, but they often compromise product quality or environmental sustainability. Organic reflux synthesis offers processing advantages but still faces trade-offs among convenience, quality, and scalability.
The solid-state hot-pressing strategy reported by Wang and Ma directly addresses these bottlenecks by combining pressure and heat to rapidly synthesize COF platelets with high crystallinity and porosity. This method reduces the energy barrier for monomer reactions and facilitates layer growth and stacking, as evidenced by DFT and MD simulations. The process is straightforward, efficient, environmentally friendly, and broadly applicable, enabling the synthesis of 15 distinct COFs within minutes and the fabrication of a 200 cm² free-standing platelet. This breakthrough paves the way for scalable production and practical implementation of COFs in industrial applications.
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Xia Li, Zhenjie Zhang (2026). Solid-State Hot-Pressing Strategy Breaks Scalability and Monolithic Shaping Barriers for Covalent Organic Frameworks. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3736-8
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Frequently Asked Questions
What are the specific pressure and temperature conditions used in the hot-pressing method, and how do they influence the crystallinity and porosity of the resulting COFs?
The research text does not specify exact pressure and temperature values, but it indicates that pressure reduces the energy barrier for monomer reactions and facilitates layer growth and stacking. Experiments showed that only simultaneous pressure and heating yield high-quality COF platelets; separate pressurizing and heating result in inferior crystallinity. For precise parameters, refer to the original paper.
How does the hot-pressing method compare to conventional solvothermal synthesis in terms of energy consumption and environmental impact?
The hot-pressing method significantly reduces process time to 0.5–5 minutes, compared to hours or days for solvothermal synthesis, leading to lower energy costs. The solid-state approach minimizes solvent use, reducing environmental impact. However, quantitative energy and environmental metrics are not provided in the text.
What is the maximum size of COF platelets that can be produced, and what are the limitations for scaling up to industrial production?
The authors fabricated a free-standing COF platelet of 200 cm² (10 cm × 20 cm), demonstrating scalability. The text does not discuss limitations, but potential challenges include maintaining uniformity and crystallinity over larger areas and the mechanical strength of the platelets.
Can the hot-pressing method be applied to other COF linkages beyond imine, hydrazone, β-ketoenamine, and imide?
The method was demonstrated for imine, hydrazone, β-ketoenamine, and imide linkages, as well as a 3D COF and mixed-monomer COF. The text suggests broad applicability, but further validation for other linkages (e.g., boronate ester, triazine) is needed.
What are the mechanical properties of the COF platelets, and are they suitable for use in flow-through reactors?
The text describes the platelets as self-standing, indicating sufficient mechanical integrity for handling. However, specific mechanical properties (e.g., compressive strength, flexibility) are not reported. For flow applications, the platelets' permeability and pressure drop would need evaluation.
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