Tech Briefs Magazine - August 2021 - 44

Sustainable Technology
ed together in long chains. The attractive
forces between the imides gives the
polymer its characteristic strength and
thus an advantage over mechanically
weak zeolites. But the dehumidification
properties of the polyimide material
needed enhancement.
The researchers first created a film by
applying polyimide molecules on a few
nanometers-wide alumina platforms.
Next, they put this film in a highly concentrated
sodium hydroxide solution,
triggering a chemical process called hy -
drolysis. The reaction caused the imide
molecular groups to break and become
hydrophilic. When viewed under a highpowered
microscope, the researchers
uncovered that the hydrolysis reactions
lead to the formation of water-attractive
percolation channels, or highways, within
the polyimide material.
When the team tested the enhanced
material for dehumidification, it found
that the polyimide membrane was very
permeable to water molecules - the
membrane was capable of extracting
excess moisture from the air by trapping it
in the percolation channels. These membranes
could be operated continuously
without the need for regeneration since
the trapped water molecules leave from
the other side by a vacuum pump that is
installed within a standard dehumidifier.
For more information, contact Professor
Hae-Kwon Jeong at hjeong7@tamu.edu;
979-862-4850.
Desalination Process Removes Toxic Metals
The desalination method produces clean water while, at the same time, potentially capturing
valuable metals such as gold.
University of California, Berkeley
D
esalination - the removal of salt -
is only one step in the process of producing
drinkable water from ocean or
wastewater. Either before or after the
removal of salt, the water often has to be
treated to remove boron, which is toxic
to plants, and heavy metals like arsenic
and mercury, which are toxic to humans.
Often, the process leaves behind a toxic
brine that can be difficult to dispose of.
Chemists have discovered a way to simplify
the removal of toxic metals, like
mercury and boron, during desalination
to produce clean water, while at the same
time potentially capturing valuable metals
such as gold.
The new technique, which can easily be
added to current membrane-based elec -
trodialysis desalination processes, removes
nearly 100% of these toxic metals, producing
a pure brine along with pure water and
isolating the valuable metals for later use
or disposal. Desal ination or water treatment
facilities typically require a long
series of high-cost pre- and post-treatment
systems that the water must go through.
The new process enables several of the
steps to be done at once.
The chemists synthesized flexible polymer
membranes, like those currently
used in membrane separation processes,
but embedded nanoparticles that can be
tuned to absorb specific metal ions -
gold or uranium ions, for example. The
membrane can incorporate a single type
of tuned nanoparticle if the metal is to
be recovered, or several different types,
each tuned to absorb a different metal or
ionic compound if multiple contaminants
need to be removed in one step.
The polymer membrane laced with nano -
particles is very stable in water and at
high heat, which is not true of many
other types of absorbers including most
metal-organic frameworks (MOFs) when
embedded in membranes.
The researchers hope to tune the nano -
particles to remove other types of toxic
chemicals including a common groundwater
contaminant - polyfluoroalkyl (PFA)
substances - found in plastics. The new
process, called ion-capture electrodialysis,
also could potentially remove radioactive
isotopes from nuclear power plant effluent.
The polymer membranes are highly
effective when incorporated into membrane-based
electrodialysis systems -
where an electric voltage drives ions
through the membrane to remove salt and
metals - and diffusion dialysis, which is
used primarily in chemical processing.
While reverse osmosis and electrodialysis
work well for removing salt from highsalinity
water sources, such as seawater, the
concentrated brine left behind can have
high levels of metals including cadmium,
chromium, mercury, lead, copper, zinc,
gold, and uranium.
A flexible polymer membrane incorporating nanoparticles of PAF selectively absorbs nearly 100%
of metals such as mercury, copper, or iron during desalination, more efficiently producing clean,
safe water. (UC Berkeley photo by Adam Uliana)
44
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Calculations suggest that a kilogram of
the polymer membrane could strip essentially
all of the mercury from 35,000 liters
of water containing 5 parts per million
(ppm) of the metal before requiring
regeneration of the membrane. The membranes
can be reused many times - at
least ten but likely more - without losing
their ability to absorb ionic metals. And
membranes containing PAFs tuned to
absorb metals easily release their absorbed
metals for capture and reuse.
For more information, contact Robert
Sanders at rlsanders@berkeley.edu; 510643-6998.
Tech
Briefs, August 2021

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Tech Briefs Magazine - August 2021

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