Non-thermal dielectric barrier discharge plasma for the degradation of microplastics suspended in water: Evidence from CO2 quantification and spectroscopic analysis

The persistence of microplastics (MPs) in aquatic environments poses a significant challenge due to their resistance to conventional remediation strategies. In this study, the direct application of atmospheric dielectric barrier discharge (DBD) non-thermal plasma (NTP) was investigated for the mineralization of polyvinyl chloride (PVC), polystyrene (PS), and polypropylene (PP) microplastics suspended in water. Treatments were carried out using air or pure oxygen as process gases, and degradation efficiency was quantitatively assessed by continuous CO₂ monitoring via in-line mass spectrometry. A key innovation of this work lies in the direct plasma treatment of MP-contaminated water combined with real-time CO₂ evolution tracking and internal temperature measurement using a fiber optic probe. Although temperature increases during the treatment, this approach enables the evaluation of the relative contributions of thermal effects and plasma-induced chemical degradation mechanisms. Results show that using oxygen as the process gas significantly enhances degradation performance compared to air, with PVC exhibiting the highest CO₂ release due to dehydrochlorination followed by oxidation. PS showed intermediate reactivity, whereas PP was the least responsive under plasma treatment. Structural and morphological changes were characterized by SEM, FTIR, and Raman spectroscopy, revealing polymer-specific surface modifications induced by plasma treatment. These findings provide new insights into selective microplastic degradation mechanisms and highlight non-thermal plasma as a promising tool for advanced oxidation processes under mild operating conditions.