The Northwestern filter changes color when full of carbon
dioxide, then changes back after being emptied
As concerns continue to rise over man-made carbon dioxide
entering the atmosphere, various groups of scientists have begun
developing
filters that could remove some or all of the CO2 content
from smokestack emissions. Many of these sponge-like filters
incorporate porous crystals known as metal-organic frameworks
(MOFs). Unfortunately, most MOFs are derived from crude oil,
plus some of them contain toxic heavy metals. Researchers from
Illinois' Northwestern University, however, recently announced
that their nontoxic MOF sponge - made from sugar, salt
and alcohol - is fully capable of capturing and storing CO2. As
an added bonus, should you be really hungry, you can eat the
thing.
The main ingredient in the edible MOF is gamma-cyclodextrin,
which is a biorenewable naturally-occurring sugar derived from
corn starch. Metals taken from salts such as potassium benzoate
and rubidium hydroxide hold the sugar molecules in place, those
molecules' precise arrangement within the crystals being
essential to the capture of CO2.
"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 postdoctoral fellow Jeremiah J.
Gassensmith. "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."
Not only can the filters be emptied of CO2 and reused, but
they also have a way of letting people know when they can't hold
any more. Each crystal has an indicator molecule placed inside
of it, which changes color according to the surrounding pH. When
the whole sponge changes from yellow to red, that means that it
has reached capacity. After being emptied, its color returns to
yellow.
The
Northwestern research was recently published in the
Journal of the American Chemical Society.
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