selves caused the reaction. But the reaction was limited
to water as droplets only. Thus, water droplets act
“very different” than bulk water, Zare says—a principle that opens up the possibility of green chemistry to
The chemical industry, for example, is very interested in methods that eliminate the possibility of
contamination. In the future, this green method could
also be used to create synthetic compounds, and Zare
believes it could serve the pharmaceutical industry
well, moving the drug discovery process along in a
faster, easier and cleaner fashion.
At this time, it’s still unclear how water microdroplets can serve as adequate replacements for reducing
agents. One possibility is that transforming the water
into microdroplets greatly increases its surface area,
creating the opportunity for a strong electric field to
form at the air-water interface, which may promote
the formation of gold nanoparticles and nanowires.
For example, the surface area of microdroplets can be
as much as 3,000x larger than the surface area of that
same amount of bulk water.
Zare and his team are currently working on and
completing follow-up research to their accidental discovery. But for now, the latest in the field of on-droplet
chemistry could not only lead to more environmentally
friendly ways to produce gold and metals nanoparticles,
it may also help usher in a new era of green chemistry.
While Stoddart and Zare’s serendipitous approaches to
green chemistry are unique, there are plenty of researchers that set out with green alternatives at the forefront of
their minds. One such researcher is Joel Ager, a scientist at
Lawrence Berkeley National Laboratory.
At the end of last year, Ager and his team turned de-
cades of carbon dioxide research on its head when they
discovered a way to recycle CO2 into valuable chemi-
cals and fuels in an economical and efficient way—all
through a single copper catalyst.
Copper has something called “active sites,” which is
where electrocatalysis takes place: electrons from the cop-
per surface interact with carbon dioxide and water in a
sequence of steps that transforms them into products like
ethanol fuel, ethylene and propanol. Ever since copper’s
catalyst potential was first realized in the 1980s, scientists
have assumed the chemical end-product didn’t matter.
In other words, copper could be used as a catalyst for
many carbon-based chemicals, and the unwanted, resid-
ual chemicals formed during the intermediate stages of a
reaction were par for the course, albeit unfortunate.
This didn’t sit well with Ager, especially given that one
of the main tenants of green chemistry is to complete
a project without any waste products. Thus, Agar and
Yanwei Lam, a UC Berkeley Ph.D. student in Ager’s lab
at the time, theorized that if copper’s active sites were
actually product specific, they could trace the chemicals’
origins through carbon isotopes.
After Lum ran dozens of experiments on an Agilent
GCMS, Thermo Fisher Scientific HPLC and Bruker NMR
that Agar describes as “crucial” to the study, the scientists
found that three of the products—ethylene, ethanol and
propanol—had different isotopic signatures showing that
they came from different sites on the catalyst.
“Ethylene is the building block for much of the
chemical industry, while polyethelyne, which is in all
plastic bags, is a polymer of ethylene,” Ager explained
to Laboratory Equipment. “Propanol, which is one of
the products we can turn into propylene, is a material
used in plastic bottles. This can unlock, if you want to
be visionary, the green chemistry of the future, if we can
harness the process and make it efficient, and most im-
While this breakthrough in catalysis directly affects
green chemical manufacturing, it also has implications
for the nation’s energy grid—specifically in relation
to solar cells. One of the largest challenges solar energy
faces today is how to provide power at night, or other
times when the sun is not available. But Ager’s new green
process has the potential to addresses this.
“This type of process that we're talking about can be
used to do chemical conversions at times when there's
excess power in the grid,” Ager said. “This is a big
change in the way we think about introducing renewable
intermittent sources into the grid, because it gives you a
reason to keep manufacturing solar panels, even when
you reach the point where they already provided enough
power at noon to supply all of the region's electricity
Gold nanoparticles are attached to threads of gold nanowires.
Both structures were formed using a novel redox reaction
involving water microdroplets. Image: Courtesy of Jae Kyoo Lee