Swiss watch on damaging emissions

Swiss chemical engineers may have taken an important step in finding the best way to strip damaging carbon dioxide (CO2) from the flue gases expelled by factories and power plants.

Writing in the journal Nature, they describe using algorithms and an approach common to the pharmaceuticals industry to work out which materials are likely to be best cut out for the job.

There is great interest in the performance and potential of Metal-Organic Frameworks (MOFs), which are porous and flexible and have shown the ability to capture and store carbon.

However, the Swiss team says, most MOFs require “wet” flue gas to be dried first, which is technically feasible but very expensive and thus not commercially appealing.

The problem, they add, is that the materials that are good at capturing CO2 are even better at capturing water, which makes them of little use. The CO2 and water compete for the same adsorption sites – areas in the material’s structure that capture the target molecule.

Now, Berend Smit from Ecole Polytechnique Fédérale de Lausanne (EPFL) and colleagues have designed a new material they say prevents this competition, is not affected by water, and can take the CO2 out of wet flue gases more efficiently than current materials.

In what Smit calls “a breakthrough for computational materials design”, they narrowed down the field by using an approach common to drug discovery.

When pharmaceutical companies search for a new drug candidate, he says, they first test millions of molecules to see which ones will bind to a target protein that is related to the disease in question. 

The ones that do are then compared to determine what structural properties they share in common. A common motif is established, and that forms the basis for designing and synthesizing actual drug molecules.

Using this approach, the EPFL scientists computer-generated 325,000 MOF materials whose common motif is the ability to bind CO2 then looked for their common structural motif – an ability to bind well with CO2 but not water. 

This subclass was then further narrowed down by adding parameters of selectivity and efficiency, until their MOF-generation algorithm settled on 35 materials they say show better CO2 capturing ability for wet flue gas than commercially available materials.

“What makes this work stand out is that we were also able to synthesise these materials,” says Smit. 

“That allowed us to work with our colleagues to show that the MOFs actually adsorb CO2 and not water, actually test them for carbon capture, and compare them with existing commercial materials.” 

This part of the study was carried out in collaboration with the University of California Berkeley, US, the University of Ottawa, Canada, Heriot-Watt University in the UK, and the Universidad de Granada in Spain.

“The experiments carried out in Berkeley showed that all our predictions were correct,” says Smit. “The group in Heriot-Watt showed that our designed materials can capture carbon dioxide from wet flue gasses better than the commercial materials.”

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