Nobel Prize for porous materials relevant to the water sector

The Nobel Prize in Chemistry awarded on Wednesday 8 October recognizes the development of porous materials with potential applications for water purification and water availability. The Royal Swedish Academy of Sciences announced that the Nobel Prize in Chemistry goes to Susumu Kitagawa, Richard Robson, and Omar Yaghi for the development of metal-organic frameworks (MOFs). These molecular storage boxes can capture substances as PFAS from water and water from air.

MOFs are porous, crystalline materials composed of metal ions and organic linkers. By adjusting the combination of metals and organic bridges of varying lengths, the pore size can be fine-tuned so that specific molecules fit inside. Over the past 35 years, increasing numbers of studies have shown that metal-organic frameworks can be used for CO₂ storage, adsorption of specific contaminants from water, and harvesting water from the atmosphere.

This all traces back to an idea Richard Robson had in the late 1980s when he was at the University of Melbourne crafting wooden molecular models for his students. He devised a recipe for porous organometallic polymers and succeeded in constructing ‘hollow diamonds’. He also demonstrated that the metal ions in what later became known as a MOF could be exchanged with other metals by dissolving MOF powder in a solution containing a different metal than the one used in the original framework.

At the time, many chemists considered the invention pointless, but Kitagawa (in Japan) and Yaghi (in the United States) each recognized its potential. Working independently throughout the 1990s and 2000s, they built on Robson’s work. Kitagawa’s guiding belief has always been that scientific research does not necessarily need a specific goal. His early MOF constructions therefore had no defined application. Funding agencies considered Kitagawa’s work aimless, which meant his grant applications were often rejected.

MOFs can change shape

Funding bodies at the time also reasoned that there were already very useful porous materials available (zeolites), which are still widely used today in applications such as air purification. A familiar example is cat litter. However, unlike zeolites, which are typically rigid, Kitagawa demonstrated that flexible MOFs could be created by incorporating mobile organic linkers. He produced a MOF that changes shape when filled with water or methane. When the pores are emptied (the material is “regenerated”), the MOF returns to its original form.

Capturing Water in the Desert

Meanwhile, on the other side of the world, Omar Yaghi (Arizona State University) demonstrated the vast design freedom of MOFs. Through rational design, Yaghi created MOFs with high thermal stability and large storage cavities. Just a few grams of his famous MOF-5 have an internal surface area equivalent to a football field, proving the added value of metal-organic frameworks over zeolites, which generally have much lower adsorption capacities. Yaghi also showed that MOFs can be used to capture water from the atmosphere. In the Arizona desert, his research group succeeded in storing water vapor in MOFs overnight and harvesting the condensed water the next morning as the rising sun warmed the material.

Relevant for the water sector

After this trio laid the scientific foundation for MOFs, research on these materials took off in laboratories around the world. According to a literature review by the Dutch KWR Water Research Institute, by 2020 more than 90,000 different MOFs had already been reported. In 2021, and again in 2023 in collaboration with Dutch water utilities, KWR investigated the possible applications and current status of MOFs for water treatment.

Due to their high adsorption capacity, MOFs are being extensively studied for their potential to remove pollutants such as PFAS from wastewater. MOFs are characterized by large internal surface areas (up to about 4500 m² per gram), significantly higher than those of activated carbon for example (about 720 to 1710 m² per gram).

Other potential roles for MOFs in water purification include:

• Selective removal of specific ions, such as phosphate, nitrate, ammonium, sulfide, and sulfate;
• Selective removal of heavy metals, such as lead, cadmium, and chromium;
• Separation of monovalent ions (such as potassium, sodium, and lithium) from divalent ions (such as calcium and magnesium);
• Adsorption of salts from water in the dark, followed by release upon exposure to (sun)light;
• Degradation of organic micropollutants such as pharmaceutical residues through (photo)catalytic oxidation;
• Enhancement of pressure-driven membrane processes such as reverse osmosis, forward osmosis, and nano-, ultra-, and microfiltration. MOFs can improve membrane performance through higher water flux, better separation, or increased salt rejection.

An important requirement for using MOFs in water purification applications is that the material must be regenerable or that the MOF, including its adsorbed content, can be easily separated from the wastewater. To achieve this, various approaches are being explored, including MOF-based hydrogels, hydrophobic MOFs, and regeneration methods based on organic solvents, pH switches, (photo)chemical or thermal treatments, vacuum treatment, activation with supercritical CO₂, and freeze-drying.

Potential for freshwater treatment

According to KWR’s 2021 report, the implementation of MOFs for drinking water purification was not yet considered likely at the time. However, MOFs may have potential for concentrate streams derived from relatively fresh sources such as surface water, groundwater bank- and dunefiltrate. Most MOFs described in the literature are currently only available at laboratory scale. According to KWR, the field is developing rapidly, and more and more MOFs are becoming commercially available.

MOF production in Europe

One of the larger MOF producers in Europe today is BASF in Germany, which collaborates with the Canadian company Svante Technologies. According to its website, BASF can produce MOFs on a multi-ton scale as of 2025. The company also holds a patent for a MOF capable of extracting water from the air.

This article was published first by the Dutch platform for water professionals H2O Magazine