In situ ETEM uncovers that deep-ultraviolet plasmons have the ability to drive endothermic reactions at room temperature

Original article by Canhui Wang, Wei-Chang D. Yang, David Raciti, Alina Bruma, Ronald Marx, Amit Agrawal and Renu Sharma

Plasmonic nanoparticles of certain metals, like gold, silver and aluminium, have the unique capability of harvesting and scattering light. These nanoparticles can harvest energy from a light source and transfer it to adsorbed gas molecules, ultimately reducing the temperature needed to drive the chemical reaction. Most of the reactions reported in research are exothermic, and only H-D bond formation has been successful at room temperature. However, for the first time in research, scientists from the NIST and IREAP in Maryland, U.S., find that endothermic reactions can be achieved at room temperature using localized surface plasmons (LSP) in the deep-UV range. Without the DENSsolutions Climate Air in situ system, this revolutionary finding would be awaiting its indispensable discovery. 


The DENSsolutions Climate system

When light excites the conduction electrons of certain metallic nanoparticles, it causes these electrons to undergo oscillation, generating localized surface plasmons (LSP). This resonant oscillation, called surface plasmon resonance (SPR), is essentially why these plasmonic nanoparticles have this exceptional ability to absorb and scatter light. 

In this in situ experiment, the reduction of CO₂ on a graphite sample to CO was realized at room temperature by exciting multiple LSP modes of aluminum nanoparticles using high-energy electrons. An ETEM is used to excite and characterize the aluminum LSP resonances and concurrently measure the spatial distribution of the carbon gasification around the nanoparticles in a CO₂ environment. Although this experiment took place in an ETEM, the ETEM was only used to provide an electron beam to generate the localized surface plasmons. It was the Climate Sample Holder that enabled the introduction of the CO₂ gas towards the sample.

In order to detect CO as a reaction product, the Climate Sample Holder containing the Climate Nano-Reactor was coupled to a gas chromatograph-mass spectrometer (GCMS). Four nanoreactor environments were analyzed, represented by the lines in the figure below: 1) Pure CO₂, 2) 0.01% CO added to the CO₂ gas flow, 3) Pure graphite heated at 900°C without aluminum nanoparticles, and finally 4) Illumination of aluminum on graphite in CO₂ at room temperature using an e-beam.

Detection of CO as a reaction product using the GCMS

Measurable CO was detected only in the latter three cases but not in pure CO₂. However, it was particularly in the last case where a CO-peak was realized when the electron beam was switched on to generate LSPs. Typically, a standard ETEM will produce CO concentrations that are far below the detection threshold of the GCMS. Yet, because the Climate Nano-Reactor in the Climate Sample Holder has a small volume, high pressure environment, the CO concentration in the CO₂ gas could rise high enough to enable the GCMS to detect it. This experiment demonstrates the unique stability and integrity of the Climate Nano-reactor over long periods of time. 

Novelty in findings

This novel finding not contributes highly on an academic front, paving the way for scientists to explore other industrially relevant chemical processes initiated by plasmonic fields at room temperature, but also globally by providing an alternate route for CO₂ reduction. Aluminium, Earth’s most abundant metal, presents itself as an ideal candidate for channelling energy from light to perform large-scale CO₂ reduction. This common and inexpensive metal therefore has ample potential to aid in the relentless fight against climate change.

Dr. Mihaela Albu

“The Climate Nano-Reactor proved to be essential for taking the reaction product of this LSP experiment out of the ETEM specimen chamber. Due to its unique low-volume, high-pressure design, the CO concentration in the carrier gas was still high enough to be detected ex situ.”

Ronald Marx
Senior Technical Consultant | DENSsolutions

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