Cold atmospheric microplasma jet-water interactions: physicochemical analysis and growth effects in flowering plants

TL;DR

This work addresses how cold atmospheric plasma jets can activate water to form plasma-activated water (PAW) rich in reactive species and nitrates, and how PAW influences flowering-plant growth. The authors use a He–air (14:1) micro-plasma jet in a ring-to-ring configuration, characterize the discharge with optical emission spectroscopy, optimize PAW chemistry via water volume, treatment time, and gas composition, and quantify nitrate formation using ion chromatography. Under optimized conditions (12 mL water treated for 40 min), PAW contains up to ~$NO_3^-$ of about 10 ppm and high ORP/EC, correlating with enhanced Chrysanthemum sapling height and soil fertility after two weeks. These findings suggest PAW as a scalable, environmentally friendly nutrient solution for sustainable horticulture of flowering plants.

Abstract

Cold atmospheric pressure plasma jets (APPJs) are non-equilibrium plasmas, that are capable of producing reactive oxygen and nitrogen species (RONS) at near-room temperature. Their interaction with water leads to the formation of plasma-activated water (PAW), whose chemical activity depends on discharge conditions. In this work, a helium-air (14:1) micro-plasma jet operated in a ring-to-ring electrode configuration is used to generate PAW and study its influence on the growth of Chrysanthemum saplings. Optical emission spectroscopy (OES) confirms the presence of $N_2$ bands and He lines, with the He-air mixture providing more chemically active discharge (in terms of favoring the generation of nitrates in PAW) as compared to pure helium. The physicochemical characteristics of PAW such as pH, electrical conductivity (EC), oxidation-reduction potential (ORP), and total dissolved solids (TDS) are analyzed as a function of plasma treatment time and water volume. The optimum condition for PAW generation is found to be 12 ml of de-ionized (DI) water treated for 40 minutes, which yields the highest ORP and nitrate concentration with a reduced pH. Comparative growth experiments over two weeks show that PAW-treated Chrysanthemum saplings exhibit significantly greater height (10.2 cm) and soil fertility (2580 $μ$S/cm) than those watered with same amount of DI water or tap water. The results highlight the potential of PAW for sustainable enhancement of growth of flowering plants.

Figures (7)

• Figure 1: (a) Atmospheric pressure plasma jet setup (ring-to-ring electrode configuration) barman2020characteristics, (b) digital picture of plasma jet, and (c) digital picture of plasma activation of water
• Figure 2: Chronology of optimization (a) quantity and treatment time for TAP water ; green color indicates the optimized quantity and time, and (b) Nitrate presence in plasma-activated TAP and DI water
• Figure 3: Optimization of (a) plasma treatment time for 20 ml of water and (b) water quantity for 8 min treatment time (TAP Water)
• Figure 4: Ion chromatography results of nitrate presence for 20 ml of tap water in case of (a) pure helium (3000 sccm), (b) mixture of He (3000 sccm) and Air (220 sccm), and (c) 12 ml of DI water treated with mixture of He (3000 sccm) and Air (220 sccm)
• Figure 5: Optical Emission spectra of (a) Pure He (3000 sccm) and (b) Mixture of He (3000 sccm) + Air (220 sccm), where some principle lines are mentioned