Efficient aqueous degradation of fluoranthene using non-thermal plasma treatment

Abstract

Fluoranthene (FLT), a polycyclic aromatic hydrocarbon (PAH) classified as a Priority Hazardous Substance, is recognised for its persistence in the environment. This is due to its complex molecular structure and low aqueous solubility, making it particularly challenging to degrade. This study investigated a pin-to-water non-thermal plasma (NTP) reactor for the efficient degradation of FLT in aqueous environments. The Results showed that NTP eliminated FLT rapidly with 100 % degradation in less than 5 min. A linear correlation was observed between the pseudo-first-order reaction rate constant and the applied voltage, with energy efficiency reaching up to 110 mg/kWh. The stable species and physicochemical parameters measured in the liquid phase show varying changes over time, both in the presence and absence of FLT. For instance, the pH of the solution decreased from around 6.6 to 4.5 while the oxidation-reduction potential (ORP) increased steadily as the discharge time increased. H₂O₂ concentrations revealed its consumption during the first 10 min of plasma exposure, indicating H 2 O 2 contribution to FLT degradation. Additionally, LC-ESI-MS/MS analysis identified nine by-products, primarily resulting from nitration and hydroxylation reactions. Both LC-ESI-MS/MS analysis and Fukui function indices determined through Density Functional Theory calculation provided insights into the reaction mechanism. Overall, this study highlights the effectiveness and potential of NTP for the treatment of PAH-contaminated waters. • Non-thermal plasma degraded 100 % of fluoranthene in less than 5 min. • Rate constants increased with voltage at a rate of 0.133 min −1 /kV. • High energy efficiency with a yield of 110 mg/kWh was attained. • Hydroxyl radicals and nitrogen species were responsible for FLT degradation. • Radicals attack carbons either shared between neighboring rings or at the edges.