Pulsed lasers in liquids speed up hunt for effective catalysts

Date:
August 2, 2021
Source:
University of Rochester
Summary:
Researchers document how the technique quickly produces arrays of
highly active, carefully tuned nanoparticles with remarkably uniform
properties that can be compared and tested for use as catalysts,
far more quickly than traditional wet lab methods.



FULL STORY ========================================================================== Chemical catalysts are the change agents behind the production of
just about everything we use in our daily lives, from plastics to
prescription drugs. When the right catalysts are mixed with the right
chemical compounds, molecules that would otherwise take years to interact
do so in mere seconds.


========================================================================== However, developing even one catalyst material to trigger this precise choreography of atoms can take months, even years, when using traditional
wet chemistry procedures that use only chemical reactions, often in the
liquid phase, to grow nanoparticles.

University of Rochester researchers say there is a way to shorten that
process dramatically -- by instead using pulsed lasers in liquids to
quickly create carefully tuned, systematic arrays of nanoparticles that
can be easily compared and tested for use as catalysts.

The process is described in a Chemical Reviews article by Astrid Mu"ller,
an assistant professor of chemical engineering at the University of
Rochester who has adapted the technique for her work on sustainable
energy solutions. Three PhD students in her lab -- coauthors Ryland
Forsythe, Connor Cox, and Madeleine Wilsey -- conducted an exhaustive
review of almost 600 previous papers involving the use of pulsed lasers in liquids. As a result, their article is the most comprehensive, up-to-date survey of a technology that was first developed in 1987.

Pulsed lasers in liquids an 'indispensable tool' for discovering catalysts
So how does pulsed-laser-in-liquid synthesis work?
* A pulsed laser is directed at a solid material immersed in
liquid. This
creates a high-temperature, high-pressure plasma near the surface
of the solid.

* As the plasma decays, it vaporizes molecules in the surrounding
liquid,
leading to a cavitation bubble. Within the bubble, chemical
reactions begin to occur between particles from the liquid and
particles that were ablated, or knocked loose, from the solid.

* After periodic expansions and contractions, the cavitation bubble
violently implodes, causing shock waves and rapid
cooling. Nanoparticles from the bubble condense in small clusters
that are injected into the surrounding liquid and become stable.



==========================================================================
The pulsed-laser-in-liquids technique offers multiple advantages over traditional wet-lab synthesis of nanomaterials. According to Mu"ller:
* Because the reactions are confined primarily within the cavitation
bubble, the resulting nanoparticles have remarkably uniform
properties.

"Every particle that is made is created under the same conditions,"
she says.

* The properties of the nanoparticles can be easily fine-tuned
by adjusting
the laser pulses and the chemical compositions of the solid and
surrounding fluid.

* Laser-made nanocatalysts are intrinsically more active than those
obtained by wet chemistry methods. Metastable nanomaterials
with non- equilibrium structures and compositions can easily be
produced. Such materials cannot be made under moderate temperatures
and pressures.

* Laser synthesis can be controlled remotely, increasing the
potential for
large-scale industrial applications.

* Pulsed-laser-in-liquids synthesis of nanomaterials is also far
more rapid
than traditional methods. The technique can prepare bulk quantities
of a nanoparticle in an hour or less. Systematic arrays of 70
materials can be made in a week.

"These advantages make this an indispensable as a tool for discovery,"
says Mu"ller, whose background includes work in lasers, materials, and electrocatalysis. "You often have people who know lasers and materials,
or maybe electrocatalysis and materials, but you very rarely get someone
with expertise in all three." She says, "This is what compelled us
to write this paper, because the Mu"ller group can bring together the perspectives of all three fields." How catalysts can combat climate
change While working as a staff scientist at Caltech, Mu"ller pioneered
an adaption of the laser-in-liquids technique to prepare nonprecious water-splitting electrocatalysts that liberate oxygen from water to
produce clean hydrogen. At Rochester, the Mu"ller group expands on
her expertise to study laser-made electrocatalysts as a way to turn climate-damaging carbon dioxide (CO2) into a closed cycle of useful
liquid fuels, such as methanol or ethanol.

"If you were to burn these fuels again, you make CO2 again, so you go
round and round. The carbon always stays within the cycle, and does not contribute to more climate change," Mu"ller says. "For that to work we
need catalysts, and no one knows yet what those catalysts would be --
what would work and why, and why other catalysts don't work." Hence her interest in using pulsed-laser-in-liquid synthesis to accelerate the
process. "It is hugely important because we can't just sit and hope for
the best with climate change; we need to work on successor technologies
now," she says.

So far, pulsed-laser-in-liquid synthesis has had only limited commercial
use.

The start-up cost of investing in laser technology is a stumbling block
for many companies, Mu"ller says. "But that will change as this method
gets more and more traction," she believes.

Thanks to Mu"ller's lab, pulsed-laser-in-liquids synthesis is certainly
getting more attention. Their paper has become a catalyst of its own by
being downloaded more than 2,400 times.

========================================================================== Story Source: Materials provided by University_of_Rochester. Original
written by Bob Marcotte. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ryland C. Forsythe, Connor P. Cox, Madeleine K. Wilsey, Astrid M.

Mu"ller. Pulsed Laser in Liquids Made Nanomaterials for Catalysis.

Chemical Reviews, 2021; 121 (13): 7568 DOI:
10.1021/acs.chemrev.0c01069 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210802114956.htm

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