U.S. Develops a "Sponge" for "Eating" CO2

U.S. Develops a "Sponge" for "Eating" CO2

When the yellow MOF crystals are filled with carbon dioxide, the indicator molecules turn red.

Recently, a novel research result appeared in the industry's field of vision. The chemistry team at Northwestern University in the United States has successfully developed a material that can “eat” carbon dioxide. The material is an all-natural nanostructure that can completely absorb carbon dioxide just like a sponge.

In fact, as early as a year ago, the chemistry team published one of their scientific achievements: New nanostructured materials based on sugar, salt, and alcohol. The "sponge" they are developing is actually a compound that can effectively detect, trap and store carbon dioxide, and the compound itself is carbon neutral.

According to the US "Daily Science" report, the team was led by Fraser Stoddart, a professor of chemistry at Northwestern University. The research report has been published in the Journal of the American Chemical Society.

According to Stoddart, the "sponge" is actually a so-called metal organic framework (MOFs), but compared with other MOFs, it is not only a pure natural component, but also a simple manufacturing process, which is also its greatest advantage.

Although conventional MOFs can also effectively absorb carbon dioxide, their raw materials are usually derived from crude oil and often contain toxic heavy metals. Stoddart said that the MOFs still have many unique features. When they completely “eat” carbon dioxide, they will turn red and the capture process will be reversible.

In fact, MOFs were born around 1999. It is an ordered, lattice-framed crystal made of organic molecules connected to nodes. Nodes are usually copper, zinc, nickel or cobalt. In their large pores, MOFs can effectively store gases such as hydrogen or carbon dioxide, which have unique uses in engineering science.

It is reported that the main ingredient of this novel MOFs is gamma-cyclodextrin, which is a renewable sugar molecule derived from corn starch. Then, using sugars such as potassium benzoate or rubidium hydroxide, these sugar molecules are fixed, and the precise arrangement of sugar molecules in crystals is the key to carbon dioxide capture.

In fact, uniform symmetry is very important in MOFs. Natural materials usually do not have uniform symmetry, so it is difficult to crystallize into highly ordered and multi-space frame materials. However, gamma-cyclodextrin solves this problem: it consists of eight asymmetrical glucose residues arranged in a ring structure, which in itself forms a symmetry. The gamma-cyclodextrin and potassium salts are dissolved in water and the evaporation of water and alcohol crystallizes the mixture.

"It turns out that when we put these sugar molecules close to each other in an alkaline environment, something unexpected happened. They started to react with carbon dioxide, and the process was similar to carbon fixation, which is the process of sugar formation." The first author, Jeremiah Gassensmith, said: "This reaction causes carbon dioxide to be tightly bound in the crystal, but then we can still recover it very easily."

The unusual reaction from MOFs and carbon dioxide can detect whether the crystal has reached full capacity. The team placed an indicator molecule in each crystal that could detect the change in pH (which represents the activity of the hydrogen ion) by color change. When the yellow MOFs are filled with carbon dioxide, they turn red.

This new type of MOFs is not only low-cost, but also green and environmentally friendly, which makes them more likely to become candidates for commercialization. Dr. Ronald A. Smaldone, a member of the team added: "I think this is the best proof that simple chemistry can be successfully applied to carbon capture and sensor technology."

It is reported that the National Natural Science Foundation of the United States, the U.S. Department of Energy, the British Engineering and Physical Sciences Research Council, the King’s University of Science and Technology, and the Korea Advanced Institute of Science and Technology are all supporters of this research. (Wang Lin)

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