MOFs vs. COFs: What’s the Difference and Why it Matters

 

Metal-Organic Frameworks (MOFs) were first developed in the 1990s by Professor Omar Yaghi, and consist of metal ions (such as zinc, copper or zirconium) connected by organic linkers to form three-dimensional structures with exceptionally high surface area often exceeding 10,000 m² per gram.  As a result, one gram of MOF material can have a surface area as large as a football field. Their high surface area, and tailorable surface features, allow MOFs to adsorb large volumes of gas or liquid, making them particularly effective for capturing industrial CO₂ emissions and harvesting water from humid air.

 

One of the most notable aspects of MOFs is their structural tunability. By choosing different metal nodes and organic linkers, scientists can tailor the physical and chemical properties of these materials and optimize them for particular applications. This adaptability has made MOFs an invaluable tool in industrial gas separations, CO₂ mitigation, water harvesting, and even drug delivery.

 

Key benefits of MOFs:

 

• Selective Adsorption: MOFs can be engineered to selectively capture specific molecules, such as CO₂ or H₂O, making them ideal for carbon capture applications.

 

• High Capacity: Due to their high surface area, MOFs can store significant amounts of gases or liquids within their pores, enabling efficient climate technology solutions. 

 

• Customizable Design: The choice of metal ions and organic linkers provides flexibility in designing MOFs for various functions, making them adaptable for both industrial and environmental applications. 

Covalent Organic Frameworks (COFs) are another class of reticular materials. In contrast to MOFs, COFs are composed entirely of lightweight elements like carbon, hydrogen, nitrogen, and oxygen. They rely on covalent bonds – strong chemical links formed when atoms share electrons – rather than metal ions, giving them high thermal and chemical stability, which makes them useful in extreme conditions such as high temperatures or acidic environments.

 

COFs selectively capture and filter out specific molecules based on size, shape, and affinity for the COF surface. This quality is particularly advantageous for gas separations, allowing COFs to be designed to target specific molecules. For example, recent advances have also shown that COFs, like COF-999, are highly effective in capturing CO₂, even under humid conditions. Filtration of CO₂ in the presence of humidity is significant because water typically interferes with adsorption in many materials. This makes COFs promising candidates for carbon capture and separation applications.

 

Key benefits of COFs:

 

• Thermal and Chemical Stability: COFs can be designed to be stable in high temperature environments, in chemical aggressive conditions, and over many adsorption cycles because they are comprised of covalent bonds.

 

• Porosity and Structure: COFs provide porosity and tailorable surfaces without the use of a metal structural support.

 

• Efficient Gas Permeability: COFs facilitate fast gas permeability, allowing for efficient capture and release cycles, ideal for continuous processes like water and CO₂ capture.

While MOFs and COFs share certain similarities as reticular materials, such as their high porosity and customizable design, their key differences lie in their composition and bonding:

 

• MOFs contain metal ions, which make them highly versatile and tunable but can sometimes reduce stability in highly acidic or basic conditions.

 

• COFs, with their purely covalent bonds, are highly stable, making them ideal for applications requiring chemical resistance and structural durability.

The unique characteristics of MOFs and COFs make them pivotal in the field of climate technology. Their customizable structures and high porosity allow for the efficient capture and storage of various molecules, addressing environmental challenges in a scalable way.  Additionally, the controlled tunability of these materials is simply not possible in traditional adsorbent materials such as zeolites, carbons, or silicas.

• Carbon Capture: Both MOFs and COFs can be used to capture CO₂ from industrial emissions or the ambient environment, and both offer unique methods of accessing tailorable surface chemistry and adsorption sites. For MOFs the design of the adsorption site centers around metal and linker selection. For COFs the full suite of organic chemistry can be used to build a unique covalently bound adsorption surface. The selection of one or the other depends on the conditions upon which the carbon is being captured, allowing for tailored solutions to customer needs.

 

• Water Harvesting: MOFs have been demonstrated to capture water vapor from low-humidity air, offering a new solution for water-scarce regions. Similarly, COFs are suitable for water harvesting because of their stable structure and tunability.

 

• Energy Storage and Gas Separation: MOFs are being used to store hydrogen and methane, supporting clean energy solutions. COFs, with their precise pore structure, are advantageous for gas separation tasks where molecular precision is critical, enabling efficient filtration and purification in gas processes.

 

The ongoing development of MOFs and COFs offers exciting opportunities for addressing climate challenges through materials science. At Atoco, our Advanced Mixed Gas Characterization Lab leverages state-of-the-art capabilities and expertise to analyze and optimize these reticular materials under real-world mixed-gas environments. Our laboratory enables us to design cutting-edge technologies using MOFs and COFs and positions us at the forefront of highly efficient, tailored solutions to meet pressing environmental challenges.

Atoco is a leader in climate technology and was founded by Professor Omar Yaghi, the inventor of Reticular Chemistry. Atoco utilizes reticular materials such as Metal-Organic Frameworks (MOFs) and Covalent Organic Frameworks (COFs) to develop breakthrough solutions for carbon capture and atmospheric water harvesting. These technologies, designed with atomic precision, are engineered to tackle the world’s most pressing challenges: climate change and water scarcity.

 

Atoco’s solid-state PCC and DAC technologies tackle the challenges of carbon capture by using highly efficient reticular materials. This approach allows for reduced energy consumption and scalable deployment across industries, making it a vital tool in addressing global carbon emissions and fighting climate change.