The role of different plasma forming gases on chemical species formed in plasma activated water (PAW) and their effect on its properties

Abstract

The present work showed the role of plasma-forming gases (air, nitrogen (N2), argon (Ar), helium (He), and their mixture with oxygen (O2)) on the properties of plasma-activated water (PAW). Electrical diagnosis and optical emission spectroscopy were performed to characterize plasma and identify plasma radicals/species. The PAW is characterized by studying its physicochemical properties and dissolved reactive oxygen-nitrogen species (RONS) concentration in it. The results showed introducing O2 in N2, Ar and He plasma suppresses the emission lines intensity of NOϒ band in N2 plasma, OH band in Ar and He plasma, and N2 second positive system in He plasma. Also, adding O2 to Ar and He plasma changes the plasma discharge characteristic from glow discharge to filamentary micro-discharge. The PAW prepared by air and its mixture with O2 showed improved physicochemical properties and RONS concentration in it compared to other plasma forming gases and their mixture with O2. In addition, increasing plasma-water exposure time significantly affects the physicochemical properties and RONS concentration in PAW. Therefore, plasma forming gas and plasma-water exposure time gives better control over the properties of PAW. Hence, these parameters play a significant role in deciding the applications of PAW.

Methotrexate degradation in artificial wastewater using non-thermal pencil plasma jet

“…These interact with the solution, changing its chemical properties. The formation of various species and radicals in the solution due to plasma-water interaction has been shown in previous studies (41,43,44,48). The presence of these species is significant in the degradation of pollutants present in wastewater.…”

“…These species collectively have the potential to degrade the complex structure of these chemotherapy drugs. As the plasma-liquid interaction time increases, more and more reactive species are generated, as shown in supplementary material Table S2 (41)(42)(43)(44)48).…”

“…The species/radicals formed during air discharge in the NT-PPJ setup were identified by recording the optical emission spectra of air plasma using an optical fiber and spectrophotometers (maker StellarNet Inc. model no. EPP2000-UV (wavelength range 200 to 600 nm) and maker ASEQ instruments model UVH-1 (wavelength range 300 to 900 nm, spectra not shown in Figure 1(c))) (43,44).…”

“…The air plasma optical emission spectra is shown in Figure 1 (see supplementary Figure S3 for details of emission lines) (44,(47)(48)(49)(50). These generated species/radicals are the major contributors that change the physicochemical properties of the solution as well as responsible for degradation of organic impurities present in wastewater.…”

“…The change in the physicochemical properties of methotrexate solution with increasing plasma treatment time is shown in Figure 2. These changes occur due to the dissolution of various short-lived and long-lived species in the methotrexate solution (41,43,44,48). As the plasma treatment time with methotrexate solution increases, a continuous decrease in pH and an increase in ORP, TDS, and EC are observed.…”