Electrical discharges in gases that operate near room temperature and at atmospheric pressure can be interfaced with aqueous solutions to serve as a gaseous, metal-free electrode and mediate electrochemical reactions. In particular, the injection of gas-phase electrons into solution to generate solvated electrons, one of the strongest chemical reducing species, has been demonstrated, and applied to the synthesis of metal nanoparticles, the electroreduction of carbon dioxide to oxygenates, and the electroreduction of molecular nitrogen to ammonia.<br/>For the most part, these plasma-liquid studies have been limited to water as the solvent. Expanding the solvent system to organics would open up new chemical applications such as small molecule transformations and controlled depolymerization/degradation of engineered plastics. In this work, we investigated two such examples: 1) the conversion of anisole and 2) the degradation/depolymerization of polystyrene (PS) and polyoxymethylene (POM). In order to avoid the need for an electrolyte, the experiments were performed with a remote plasma configuration where the afterglow of the discharge was in contact with the surface of the organic solvent. Following treatment of the solvents containing the precursor, a suite of analytical techniques were used to characterize the products including nuclear magnetic resonance (NMR) spectrometry, high-pressure liquid chromatography (HPLC), gas chromatography mass spectrometry (GC-MS), and liquid chromatography mass spectrometry (LC-MS). We found that anisole was converted to new aromatic compounds. In the case of POM, we found depolymerization at much lower temperature than its thermal degradation temperature to formadehyde, and in the case of PS, there were a wide range of small molecules. These findings suggest that non-thermal plasma can trigger molecular transformation in catalyst free conditions and expand chemical and electrochemical processes involving organic and polymeric molecules.

Plasma electrochemistry for molecular transformation

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.