Energy-Efficient Degradation of Sulfamethoxazole in Water Using Nanosecond-Pulsed Underwater Plasma Bubbles

Non-thermal plasma-liquid systems provide a promising route for water treatment via reactive oxygen and nitrogen species, though achieving high efficiency with low energy input remains challenging. A nanosecond-pulsed underwater plasma bubble reactor was developed for efficient sulfamethoxazole degradation, achieving ~90% removal within 20 min and a high energy yield of ~860 mg·kWh⁻¹. Optical emission spectroscopy indicated enhanced oxygen-related reactive species under air and O₂ plasmas, correlating with improved degradation performance. Solution chemistry showed increased oxidation-reduction potential and acidification during treatment. Electron spin resonance confirmed short-lived radicals (OH, ONOO⁻) and long-lived species (H₂O₂, NO₂⁻, NO₃⁻). Mechanistic analysis suggests that indirect oxidation pathways dominate via hydroxylation, bond cleavage, and aromatic ring opening, highlighting the importance of plasma chemistry regulation and reactor design.