Sponges already clean up kitchen spills and soap scum, now they may start cleaning up the atmosphere.
A newly-developed synthetic sponge made of salt, sugar, and alcohol soaks up carbon dioxide. It's non-toxic, reusable, and carbon neutral. In a pinch, you can even make a meal of it.
Northwestern University chemists developed this special sponge, known as a metal-organic framework (MOF). Other MOFs soak up carbon dioxide too, but are usually made from crude oil and contain more toxic heavy metals than Beavis and Butthead's record collection.
The new sponges don't pollute the environment while cleaning it up. In fact, their manufacture could reduce the amount of greenhouse gas in the air, since they contain sugar made by plants which themselves pull carbon dioxide out of the air.
“We are able to take molecules that are themselves sourced from atmospheric carbon, through photosynthesis, and use them to capture even more carbon dioxide,” said Ross Forgan, a co-author of the sponge study published in Journal of the American Chemical Society, in a press release.
“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,” said Forgan.
The main ingredient is gamma-cyclodextrin, a type of sugar derived from corn, held together in a crystalline structure by metals, such as potassium benzoate and rubidium hydroxide, derived from salts.
Despite the intimidating names of its ingredients, the MOF carbon sponge is actually edible. But don't sit down to a sponge lunch just yet, the carbon-hungry sponges can be cleaned and reused.
“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,” said Jeremiah J. Gassensmith, lead author of the paper, in a press release.
“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,” Gassensmith said.
The MOF sponges suck in the carbon dioxide and converts it to carbonate. But when exposed to an atmosphere with low concentrations of carbon dioxide, the gas is released.
Unlike other methods of carbon capture, little extra energy is needed to release the carbon dioxide.
"In our material, the CO2 is converted into a solid, most likely by reacting with the sugar, but if you blow a stream of nitrogen over the material, the CO2 spontaneously pops off and will go wherever you blow it, and the material is reused and thus recyclable.
"It is thus a very, very green way of trapping CO2," Gassensmith said.
The sponges could be used to scrub emissions or the air itself. The excess carbon can then be used in other industrial processes or stored somewhere.
The sponge even lets people know when it's ready for a cleaning.
The researchers included methyl red, a common chemical pH indicator, in the sponges to let them know when the sponge has soaked up all the carbon it can. A pH shift within the sponge causes the color to change from yellow to red when it is full of carbon.
Since the MOF carbon sponges are cheap and easy to manufacture, not to mention eco-friendly, Northwestern plans to pursue commercialization opportunities.
“I think this is a remarkable demonstration of how simple chemistry can be successfully applied to relevant problems like carbon capture and sensor technology,” said Ronald A. Smaldone, a co-author of the paper.
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