Researchers from Stony Brook University led by Alexander Orlov — in collaboration with scientists at the Air Force Research Lab (AFRL) and Brookhaven National Lab — have produced catalytically active gold nanoparticles in an ultra-high vacuum chamber with temperatures approaching absolute zero. A paper describing the first catalyst ever produced using their new method, called Helium Nanodroplet Deposition (HND), was recently published in the Journal of Physical Chemistry Letters.
Orlov, an associate professor in the Department of Materials Science and Chemical Engineering, states that HND works by boiling gold atoms in a vacuum to produce a vapor. The vaporized gold is then “picked up” by an extremely cold jet stream of liquid helium droplets that act to literally strike gold clusters against a solid collector downstream. Upon striking the collector, the liquid helium droplets instantly evaporate releasing helium gas and leaving behind unprecedentedly pure and stable gold nanoparticles.
“This new method to produce active nanoparticles offers unique opportunities to create materials with unprecedented properties to solve energy and environmental problems,” Orlov added. “Our Brookhaven and AFRL collaborators made it possible for our students to access the most unique facilities in the world, which made all the difference in our research.”
Qiyuan Wu, a graduate student working in Orlov’s laboratory and first author on the paper, performed much of the work to develop the method. Michael Lindsay and Claron Ridge of AFRL provided state-of-the-art facilities at Eglin Air Force Base, one of only a few places in the world with the capabilities required to generate the gold nanoparticles using the new technique. And a team at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, used advanced imaging and characterization tools to study the nanoparticles’ catalytic activity.
SBU graduate student Qiyuan Wu and BNL staff scientist Dmitri Zakharov study samples at BNL’s Titan Environmental Transmission Electron Microscope (photo courtesy of BNL).
Brookhaven scientists Eric Stach and Dmitri Zakharov of the CFN and Shen Zhao, then a postdoctoral fellow working under Stach, developed a method to deposit the gold nanoparticles onto a “catalyst support” structure they use for characterizing the stability of other nanomaterials. They then studied the characteristics of the nanoparticles, including their stability under reaction conditions, using the Titan Environmental Transmission Electron Microscope at the CFN. Further characterization by Zhao and CFN staff member Dong Su using aberration-corrected Scanning Transmission Electron Microscopy allowed the Stony Brook researchers to understand how the droplets form.
Nanoparticles are of high research interest due to their improved properties compared to bulk materials. They have revolutionized technologies aimed at improving sustainability such as fuel cells, photocatalysts and solar panels. The gold nanoparticle catalysts produced in this study are capable of converting poisonous carbon monoxide gas into carbon dioxide gas, an essential reaction that occurs in the catalytic converters of cars to reduce pollution and lower impacts on the environment.
According to Orlov, the HND method is not limited to the production of gold nanoparticles, but can be applied to nearly all metals and can even produce challenging multi-metallic nanoparticles. The technique’s versatility and ability to produce clean and well-defined samples make it a powerful tool for the discovery of new catalysts and studying factors that affect catalyst performance.
The collaboration is now researching how the parameters of HND can be adjusted to control catalyst performance.
This research was funded by the Division of Materials Research at the National Science Foundation and the Air Force Office of Scientific Research. The work at CFN was funded by the DOE Office of Science.