Unexpected discovery may offer new industrial applications

Newly discovered chemistry involving water-soluble particle surfaces is now being presented in a new study in Science. Initiated by a team from the University of Gothenburg, this study may be useful in the future for sewage treatment, for example.

Gases and aerosol particles play important roles for the chemistry in the atmosphere. Their interactions affect clouds and the climate. Typical examples of aerosols are smoke, fog and air pollution.
Aerosol particles are especially important, even if they are not visible, because they have surfaces in an atmosphere that otherwise consists only of gases. A new study has now found evidence that when these surfaces begin to absorb water and dissolve, new and previously undiscovered chemistry can take place.

Surprising discovery of new chemistry

In the new article in the journal Science, the researchers describe that when a surface of ammonium sulphate dissolves, it promotes sulphate-reducing ammonium oxidation.

The discovery is surprising, because this reaction ordinarily requires extra energy to overcome a barrier and therefore does not occur spontaneously.

“It was a surprise to see the reaction occur, but we came to understand that the water-soluble salt surface made the reaction possible. This has led us to rethink the catalytic effects of surfaces, where some reactions actually can be promoted in the right conditions,” says Xiangrui Kong, researcher at the University of Gothenburg and lead author of the study.

Possible benefits for cost-effective industrial and environmental applications

The research has ramifications for our understanding of the atmospheric sulphur cycle and the occurrence of other important compounds involved in many chemical reactions in the atmosphere.

The sulphate-reducing ammonium oxidation reaction that was observed may also be useful for sewage treatment, for example, and other industrial applications. Biocatalysts or other expensive methods are currently required to activate such reactions. According to the researchers, the new mechanism indicates that cost-effective applications may be developed based on this new knowledge.

“As we began to realise our results, it took us quite some time to understand what we were observing and why, but the result is exciting and motivates us to dig deeper into how surface phase transitions can change the chemical environment,” says Erik S. Thomson, senior lecturer at the University of Gothenburg and one of the authors behind the study.

The new study is the fruit of a collaboration between researchers from the University of Gothenburg and researchers from the Paul Scherrer Institute in Switzerland and the Qatar Environmental and Energy Research Institute. The observations were made at the Swiss Light Source research facility in Switzerland and theoretical calculations support the experimental observations and the proposed reaction mechanism.

Facts
Aerosols are small particles suspended in a gas. The particles can be solid or liquid, and the aerosol consists of both the gas and the particles. The word aerosol comes from the Greek aer, meaning air, and the Latin solutio, meaning solution.

The study was initiated by a team from the University of Gothenburg with researchers Xiangrui Kong, Dimitri Castarède, Erik S. Thomson and Jan B.C. Pettersson, all from the Department of Chemistry and Molecular Biology, Atmospheric Science division (https://www.gu.se/en/chemistry-molecular-biology/our-research/atmospheric-science).

The measurements were carried out at the X07DB In Situ Spectroscopy beamline, Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI), Switzerland (https://www.psi.ch/en/sls/nanoxas), with the help of researcher Luca Artiglia. The research at SLS was supported by the research departments Energy and Environment (https://www.psi.ch/en/ene) and Photon Science (https://www.psi.ch/en/psd).

The beamline team included colleagues from the Surface Chemistry Laboratory at PSI (https://www.psi.ch/en/luc/surface-chemistry) led by Markus Ammann and including Anthony Boucly and Luca Artiglia.

Molecular simulations were conducted by partner Ivan Gladich with the help of the new computer cluster (HPCC) at Qatar Environment and Energy Research Institute (QEERI)/HBKU and the HPCC at Texas A&M University at Qatar, founded by Qatar Foundation for Education, Science and Community Development.