Maria Sazonova ’26

Figure 1: Electron micrograph scan of hexagonal gold nanowire array

Gold nanoparticles can effectively convert carbon monoxide from harmful waste products into usable fuels. Alexander Orlov and his research team, in collaboration with Brookhaven National Lab scientists and U.S. Air Force Laboratory, conducted a study to explore how gold nanoparticles (Au NPs), widely studied for their high catalytic activity, can accelerate the chemical reaction of carbon monoxide oxidation. They hypothesized that a combination of both charge transfer and electric field formation at the metal-oxide support junction are the major driving forces for the incredible reactivity of gold nanoparticles. 

The researchers designed a model system consisting of gold nanoparticles on a well-controlled oxide support. The nanoparticles were synthesized via the helium droplet deposition method: gold atoms were condensed into nanoparticles within helium droplets – generated by supersonic expansion of helium gas – which were then deposited on oxide-covered silicon wafers (SiO₂/Si). The helium droplets were subsequently evaporated, leaving behind only ultra-clean nanoparticles – highly uniform catalysts – on the substrates. At the junction between Au and SiO₂/Si, the charge transfer to the nanoparticles was controlled by varying the thickness of the SiO₂ substrate. This allowed for the analysis of charge transfer and electric field, the main factors affecting onset temperature of CO oxidation. Numerical simulations used X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) to show distributions of charge density and electric field. Charge transfer is often regarded as the primary reason for Au nanoparticles’ improved catalytic activity in CO oxidation, whereas the role of a strong electric field is often overlooked.  

The simulations showed lower activation barriers for CO oxidation due to the electric field. Additionally, these simulations demonstrated a large negative charge accumulation on the surface of Au nanoparticles where the SiO₂ layer was thinner, resulting in a stronger net electric field. Using TPD, samples of variable SiO₂ layer thickness were studied to determine their effect on catalytic performance. The researchers concluded that both electric field and negative charge on the surface of gold nanoparticles decrease the onset temperature of CO oxidation and principally contribute to the dependence of catalytic reactivity on SiO₂ thickness. These findings have significant implications for designing the next generation of nanocatalysts that aid in solving environmental problems inextricably linked to the high onset temperature of CO oxidation. Further research can investigate the reactivity of the created system under dynamic reaction conditions and the mechanisms of CO adsorption.  

Works Cited

[1] H. Yang, J., et al., Enhancing CO oxidation activity via tuning a charge transfer between gold nanoparticles and supports. The Journal of Physical Chemistry C. 126, 10 (2022). Doi: 10.1021/acs.jpcc.1c10072

[2] Image retrieved from: https://www.flickr.com/photos/40137058@N07/3790862760