How a crystalline sponge sheds water molecules
Scientists use advanced techniques to observe how a specific crystalline sponge changes shape as it loses water molecules

Date:
July 29, 2020
Source:
University at Buffalo
Summary:
How does water leave a sponge? In a new study, scientists answer
this question in detail for a porous, crystalline material
made from metal and organic building blocks -- specifically,
cobalt(II) sulfate heptahydrate, 5-aminoisophthalic acid and
4,4'-bipyridine. Using advanced techniques, researchers studied how
this crystalline sponge changed shape as it went from a hydrated
state to a dehydrated state.



FULL STORY ==========================================================================
How does water leave a sponge?

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In a new study, scientists answer this question in detail for a porous, crystalline material made from metal and organic building blocks - - specifically, cobalt(II) sulfate heptahydrate, 5-aminoisophthalic acid
and 4,4'-bipyridine.

Using advanced techniques, researchers studied how this crystalline sponge changed shape as it went from a hydrated state to a dehydrated state. The observations were elaborate, allowing the team to "see" when and how
three individual water molecules left the material as it dried out.

Crystalline sponges of this kind belong to a class of materials called
metal- organic frameworks (MOFs), which hold potential for applications
such as trapping pollutants or storing fuel at low pressures.

"This was a really nice, detailed example of using dynamic in-situ
x-ray diffraction to study the transformation of a MOF crystal," says
Jason Benedict, PhD, associate professor of chemistry in the University
at Buffalo College of Arts and Sciences. "We initiate a reaction -- a dehydration. Then we monitor it with x-rays, solving crystal structures,
and we can actually watch how this material transforms from the fully
hydrated phase to the fully dehydrated phase.

"In this case, the hydrated crystal holds three independent water
molecules, and the question was basically, how do you go from three
to zero? Do these water molecules leave one at time? Do they all leave
at once?


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"And we discovered that what happens is that one water molecule leaves
really quickly, which causes the crystal lattice to compress and twist,
and the other two molecules wind up leaving together. They leak out at the
same time, and that causes the lattice to untwist but stay compressed. All
of that motion that I'm describing -- you wouldn't have any insight into
that kind of motion in the absence of these sort of experiments that we
are performing." The research was published online on June 23 in the
journal Structural Dynamics. Benedict led the study with first authors
Ian M. Walton and Jordan M.

Cox, UB chemistry PhD graduates. Other scientists from UB and the
University of Chicago also contributed to the project.

Understanding how the structures of MOFs morph -- step by step --
during processes like dehydration is interesting from the standpoint
of basic science, Benedict says. But such knowledge could also aid
efforts to design new crystalline sponges. As Benedict explains, the
more researchers can learn about the properties of such materials, the
easier it will be to tailor-make novel MOFs geared toward specific tasks.

The technique the team developed and employed to study the crystal's transformation provides scientists with a powerful tool to advance
research of this kind.

"Scientists often study dynamic crystals in an environment that is
static," says co-author Travis Mitchell, a chemistry PhD student in
Benedict's lab.

"This greatly limits the scope of their observations to before and after a particular process takes place. Our findings show that observing dynamic crystals in an environment that is also dynamic allows scientists to
make observations while a particular process is taking place. Our group developed a device that allows us to control the environment relative to
the crystal: We are able to continuously flow fluid around the crystal
as we are collecting data, which provides us with information about how
and why these dynamic crystals transform." The study was supported by
the National Science Foundation (NSF) and U.S.

Department of Energy, including through the NSF's ChemMatCARS facility,
where much of the experimental work took place.

"These types of experiments often take days to perform on a laboratory diffractometer," Mitchell says. "Fortunately, our group was able
to perform these experiments using synchrotron radiation at NSF's
ChemMatCARS. With synchrotron radiation, we were able to make measurements
in a matter of hours."

========================================================================== Story Source: Materials provided by University_at_Buffalo. Original
written by Charlotte Hsu.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ian M. Walton, Jordan M. Cox, Shea D. Myers, Cassidy A. Benson,
Travis B.

Mitchell, Gage S. Bateman, Eric D. Sylvester, Yu-Sheng Chen,
Jason B.

Benedict. Determination of the dehydration pathway in a
flexible metal- organic framework by dynamic in situ x-ray
diffraction. Structural Dynamics, 2020; 7 (3): 034305 DOI:
10.1063/4.0000015 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200729124419.htm

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