Long-lived RONS effects on plasma-activated water physicochemical properties

Abstract Plasma-activated water (PAW) is enriched with reactive oxygen and nitrogen species (RONS), which significantly alter its physicochemical properties and expand its applicability in fields like materials science, biomedicine, and agriculture. This study investigates the specific contributions of key long-lived RONS—hydrogen peroxide (H 2 O 2 ), nitrate ions (NO 3 − ), and ozone (O 3 )—to the physicochemical properties of PAW. PAW was produced using a pin-to-liquid plasma system, and its properties were characterized using UV–Vis spectroscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy, and measurements of pH, electrical conductivity, total dissolved solids (TDS), and oxidation-reduction potential (ORP). To isolate the effects of individual RONS, aqueous solutions containing H 2 O 2 , NO 3 − , O 3 , and a composite solution with the three species at concentrations equivalent to those measured in PAW were prepared and analyzed using the same characterization techniques. The individual RONS solutions revealed specific influences on the physicochemical parameters: H 2 O 2 led to slight acidification and increased conductivity; NO 3 − ; significantly increased conductivity and TDS; and O 3 had minimal effect on the measured properties. The composite solution is the only one that has a positive ORP; it is an oxidant. However, none of the individual solutions replicated the comprehensive alterations observed in PAW. The composite solution containing all three RONS showed more pronounced changes but still did not fully match PAW’s properties. This difference hints to the presence of unidentified long-lived reactive species in PAW, possibly originating from electrode degradation, as spectroscopic analyses indicate. Understanding the individual and combined effects of long-lived RONS is crucial for optimizing PAW generation and tailoring its properties for specific applications.