Virginia Tech studies reveal reaction pathways for ozone on organic surfaces

Virginia Tech chemistry researchers have made a discovery about how ozone degrades organic surfaces such as biological surfactants and polymeric coatings.

The research will be presented at the 231st American Chemical Society (ACS) national meeting being held in Atlanta on March 26-30.

John Morris' group is studying the reactions of small molecules found in pollution of surfaces. Morris, associate professor of chemistry in the College of Science, and his students are looking specifically at hydrochloric acid (HCl) and triatomic oxygen (O3, a toxic form of oxygen), pollutants known to play a major role in atmosphere chemistry. They are using functionalized self-assembled monolayers (thin films – one molecule thick) to simulate organic surfaces. "It gives us control of the surface structure and chemical functionality so we can study how those aspects of a surface influence the fate of important gas-surface collisions," Morris said.

The experiments have led to a detailed understanding of the reaction mechanisms of HC1 and ozone on organic surfaces, which is what Morris will present in the paper authored by graduate student Larry R. Fiegland, Morris, and graduate student B. Scott Day.

A major finding is that ozone reacts with carbon-carbon double bonds to form crosslinked networks within the thin film. Carbon-carbon double bonds are the very strong forces that link carbon atoms together to help form long-chain molecules -- major components of many polymeric materials found in everyday life. "The formation of crosslinked networks is a new discovery – that provides a fundamental understanding of how, on the molecular level, organic surfaces degrade with prolonged exposure to ozone, a major atmospheric pollutant," Morris said. "Understanding the reaction mechanism may someday lead to more robust films for organic coatings, or polymeric coatings, such as paints."

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The paper, "Reaction dynamics of HCl and O3 in collisions with omega-functionalized self-assembled monolayers" (COLL 515), will be presented at 3:30 p.m. at the OMNI at CNN Center International Ballroom F as part of the Division of Colloid and Surface Chemistry symposium honoring ACS Adamson Award Winner Steven Bernasek.

Morris' National Science Foundation Career Award funds the research.

ACS Abstract
The objectives of this work are aimed at elucidating the atomic-scale mechanisms of interfacial bonding, diffusion, and reactions that govern gas-surface interactions on model organic materials. This presentation will focus on recent molecular beam scattering studies of HCl and O3 collisions with self-assembled monolayers (SAMs). The gases represent two important atmospheric species and the SAMs are chosen to mimic the surface of surfactant-covered organic aerosols that are also prevalent in the environment. These studies reveal how the atomic-scale nature of organic surfaces determine the extent of energy transfer, thermal accommodation, and subsequent reaction pathways for the gas-surface collisions. The experiments involving HCl impinging on OH-terminated SAMs have revealed that HCl can form 24 kJ/mol hydrogen-bonds with the monolayer, but the interaction is not significant enough to result in proton-transfer reactions. In the case of O3 colliding with an olefin-terminated SAM, reactions produce carboxylic-acid anhydride groups that crosslink adjacent SAM chains.

Learn more about John Morris' research at www.chem.vt.edu/chem-dept/jmorris/index.htm


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