All-natural nanosponge captures CO2

NORTHWESTERN (US) — Nanostructures made of sugar, salt, and alcohol are able to effectively detect, capture, and store carbon dioxide—and are themselves carbon-neutral.

Because the porous crystals—known as metal-organic frameworks (MOFs)—are made from all-natural ingredients and are simple to prepare, they have a significant advantage over other MOFs that, while also effective at adsorbing carbon dioxide, are usually prepared from materials derived from crude oil and incorporate toxic heavy metals.

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“We are able to take molecules that are themselves sourced from atmospheric carbon, through photosynthesis, and use them to capture even more carbon dioxide,” says Ross S. Forgan, a postdoctoral fellow in the lab of Fraser Stoddart, professor of chemistry at Northwestern University.

“By preparing our MOFs from naturally derived ingredients, we are not only making materials that are entirely nontoxic, but we are also cutting down on the carbon dioxide emissions associated with their manufacture.”

The findings are published in the Journal of the American Chemical Society.

The main component, gamma-cyclodextrin, is a naturally occurring biorenewable sugar molecule that is derived from cornstarch and held in place by metals taken from salts such as potassium benzoate or rubidium hydroxide. It is the precise arrangement of the sugars in the crystals that is vital to their successful capture of carbon dioxide.

“It turns out that a fairly unexpected event occurs when you put that many sugars next to each other in an alkaline environment—they start reacting with carbon dioxide in a process akin to carbon fixation, which is how sugars are made in the first place,” says Jeremiah J. Gassensmith, lead author of the paper and also a postdoctoral fellow in Stoddart’s lab.

“The reaction leads to the carbon dioxide being tightly bound inside the crystals, but we can still recover it at a later date very simply.”

The fact that the carbon dioxide reacts with the MOF, an unusual occurrence, led to a simple method of detecting when the crystals have reached full capacity. The researchers place an indicator molecule, which detects changes in pH by changing its color, inside each crystal.  When the yellow crystals of the MOFs are full of carbon dioxide, they turn red.

The simplicity of the new MOFs, allied with their low cost and green credentials, have marked them as candidates for further commercialization.

“I think this is a remarkable demonstration of how simple chemistry can be successfully applied to relevant problems like carbon capture and sensor technology.” says Ronald A. Smaldone, another postdoctoral fellow in Stoddart’s group and co-author of the paper.

The research that was supported by the National Science Foundation, the U.S. Department of Energy, the Engineering and Physical Sciences Research Council in the U.K., the King Abdulaziz City of Science and Technology in Saudi Arabia, and the Korea Advanced Institute of Science and Technology.

More news from Northwestern University: www.northwestern.edu/newscenter