Non-thermal plasma has emerged as an effective treatment system against the latest class of highly recalcitrant and toxic environmental pollutants termed emerging contaminants (ECs). In the present work, a detailed experimental study is carried out to evaluate the efficacy of a non-thermal plasma jet with two dyes, Rd. B and Met. Blue, as model contaminants. The plasma jet provided a complete dye decoloration in 30 min with an applied voltage of 6.5 kV_p−p. ·OH, having the highest oxidation potential, acts as the main reactive species, which with direct action on contaminants also acts indirectly by getting converted into H₂O₂ and O₃. Further, the effect of critical operational parameters viz, sample pH, applied voltage (4.5‒6.5 kV_p−p), conductivity (5‒20 mS cm⁻¹), and sample distance on plasma treatment efficacy was also examined. Out of all the assessed parameters, the applied voltage and sample conductivity was found to be the most significant operating parameters. A high voltage and low conductivity favored the dye decoloration, while the pH effect was not that significant. To understand the influence of plasma discharge gas on treatment efficacy, all the experiments are conducted with argon and helium gases under the fixed geometrical configuration. Both the gases provided a similar dye decoloration efficiency. The DBD plasma system with complete dye removal also rendered maximum mineralization of 73% for Rd. B, and 60% for Met. Blue. Finally, the system’s efficiency against the actual ECs (four pharmaceutical compounds, viz, metformin, atenolol, acetaminophen, and ranitidine) and microbial contaminant (E. coli) was also tested. The system showed effectivity in the complete removal of targeted pharmaceuticals and a log2.5 E. coli reduction. The present systematic characterization of dye degradation could be of interest to large communities working towards commercializing plasma treatment systems.

The rise in multidrug-resistant (MDR) ESKAPE bacteria have become a major therapeutic challenge globally. Recently, novel cold atmospheric pressure plasma (CAP) as an antimicrobial is becoming popular. In this study, an indigenously developed AC cold atmospheric pressure plasma jet (CAPJ) fed with argon gas was used to evaluate its antimicrobial efficacy on these bacteria isolated from clinical specimens such as urine, blood, and sputum in a tertiary care hospital in India. The difference in CAP’s antimicrobial activity on Gram-negative bacilli (MDR E. coli) and Grampositive cocci (MDR S. aureus) was observed with various input parameters, such as microbial concentration, CAP exposure time, and exposure distance. It was observed that oxidative stress induced by reactive oxygen and nitrogen species (O2-, NO+, OH., H2O2, ONOO-, NO., NO2., HO2., O3-,etc.) and electrostatic stress by ions (Ar+, O+, O2-, OH-, NO+,OH+, NO3-, NO2-, O3-, etc.) might play a crucial role in microbial inactivation. In addition to this, a decrease in adenosine triphosphate concentration post-CAP exposure in a liquid media suggested an efficient microbial inactivation effect. The outcome of this research would be extremely beneficial to multidisciplinary researchers in this field.

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse-modulated 13.56 MHz radio frequency (RF) power source. This helical structure is observed in open ambient air, which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse-modulated RF (2 kHz modulation frequency) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters, viz., duty cycle, gas flow rate, and RF power, of the modulated pulse on the formation of a helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species) as these are involved in an increase in air entrainment into the ionization region desired for various plasma applications.

The effect of pulse-modulated sub-RF range (100 kHz–1 MHz) excitation on atmospheric pressure argon plasma jet characteristics is studied. For this, a suitable power supply is developed, offering a sub-µs rise time with control of different parameters, such as voltage amplitude, pulse modulation frequency in the range of 1–30 kHz, and an oscillation frequency of ∼520 kHz, which can affect the plasma behavior. Plasma characteristics, such as reactive species generation, ionic composition, plasma plume length, and gas temperature, are evaluated qualitatively and quantitatively by employing diagnostics such as optical emission spectroscopy, molecular beam mass spectrometry, and optical imaging. Experimental observations indicate that the gas temperature of the plasma jet and plume length increase with the applied voltage for all pulse modulation frequencies, with a maximum value of ∼(325 ± 2 K) and a maximum length of ∼(23 ± 3 mm), respectively, at 30 kHz and 9 kVpp. The emission intensities of OH• and O• lines show an incremental behavior with the applied voltage across all pulse modulation frequencies. The relative yield of different positive (OH+, O+, etc.) and negative (OH−, O−, etc.) ions also increases with the applied voltage for all pulse modulation frequencies with maximum values of ∼(7.6%, 9.9%) and (3.9%, 9.4%), respectively; these are relatively close to RF excited ionic concentrations reported previously. Attaining a high plasma length and species yield signify the features of both kHz and RF atmospheric plasmas. This study offers significant insights and flexibility into exploring the impact of different RF frequency regimes on plasma characteristics.

This article provides a concise methodology for the development of a cold atmospheric pressure plasma jet and its characterization. To optimize the plasma jet parameters for biological and industrial applications, it is highly necessary to thoroughly understand its characteristics. The major emphasis of this work is to utilize simple and advanced diagnostics systematically with low complexity in the post-data analysis and to obtain in situ information of plasma jet parameters. The detailed optimization methods and the effect of the applied voltage and gas flow rate to achieve the stable plasma jet of the desired dimensions are discussed. In addition, the effects of the gas flow rate on the discharge current profiles and filament behavior are provided. Moreover, optical techniques, such as optical emission spectroscopy and time-resolved fast imaging, are used for the characterization of plasma parameters, i.e., Texc and ne, in a simple way. The gas temperature along the length of the plasma jet is estimated using a K-type thermocouple. The discussed simple characterization techniques and range of parameters of our designed plasma source will be useful for the development and optimization of plasma jet sources for various biological and industrial applications. Furthermore, we have also discussed various applications where we can use the discoursed diagnostics for the system development as well as for characterization. As the characterization of cold atmospheric pressure plasma jets is a multiphysics study, this concise characterization report on the cold atmospheric pressure plasma aims to provide necessary information for early researchers.