Nowadays, increasing concentration of CO₂ in the atmosphere is a major threat for the environment and is a main reason for global warming. Variation in gas temperature and dissociation of CO₂ into its by-products (CO and O) in a home-made dielectric barrier discharge (DBD) reactor have been reported as a function of discharge parameters, i.e., applied voltage and gas flow rate. To estimate the dissociation fraction of CO₂ in the DBD reactor, the optical emission actinometry technique is employed in which 5% N₂ is used as an actinometer. Emission lines of the Angstrom band of CO at 451.09 nm $\left(B^1\sum {}^{+}{v}^{\prime }=0-A^1\pi ,\hspace{0.17em}{v}^{″}=0\right)$ and the 2nd positive system of N₂ at 337.01 nm $\left(C^3{\pi }_u{v}^{\prime }=0-B^3{\pi }_g,v^{″}=0\right)$ are used for actinometry measurements. To estimate the rate coefficients used in actinometry measurements, gas temperature is measured using the Boltzmann plot technique, from the rotational spectra of the Q-branch of the Angstrom band CO (0–1). To avoid discrepancy in gas temperature measurements, rotational temperature of the 2nd positive system, the N₂ (0–1) band, is also measured. For this, synthetic spectra have been fitted over the experimentally recorded spectrum of the N₂ (0–1) band. A slight difference in gas temperature has been noted for the Angstrom band of CO and the 2nd positive system of nitrogen. Conversely, an increasing trend in the dissociation fraction of CO₂ with an increase in the applied voltage is noted. About 34% dissociation fraction is achieved for 10 kV applied voltage at a flow rate of 25 SCCM. With an increase in the gas flow rate (25–200 SCCM), a decrease in the dissociation fraction of CO₂ from 34% to 11% is noted.

Fabrication of non-functionalized gold nanoparticles is interesting owing to their potential applications in sensing and biomedicine. We report on the synthesis of surfactant-free gold nanoparticles (AuNPs) by Plasma-Liquid Interaction (PLI) technique, using micro-atmospheric pressure D.C. plasma. The effects of discharge parameters, such as discharge current, precursor concentration and gas flow rates on the structure and morphology of AuNPs have been investigated. Optical Emission Spectroscopy (OES) was employed to estimate the UV radiation intensity and OH radical density. Scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) optical spectroscopy were employed to study the morphology and structure of AuNPs. The normalized intensities of UV radiation and OH radical density found to increase with increase in discharge current. We observed that the particle size can be tuned by controlling any of the following parameters: intensity of the UV radiation, OH radical density, and concentration of the Au precursor. Interestingly, we found that addition of 1% Ar in the feedstock gas results in formation of relatively uniform size distribution of nanoparticles. The surfactant-free AuNPs, due to their bare-surface, exhibit excellent surface-enhanced Raman scattering (SERS) properties. The SERS study of Rhodamine 6G using AuNPs as substrates, shows significant Raman enhancement and fluorescence quenching, which makes our technique a potentially powerful route to detection of trace amounts of dangerous explosives and other materials.

Atmospheric pressure plasma jets are gaining a lot of attention due to their widespread applications in the field of bio-decontamination, polymer modification, material processing, deposition of thin film, and nanoparticle fabrication. Herein, we are reporting the disinfection of Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli bacteria using plasma jet. In this regard, Ar-O₂, Ar-N₂, and Ar-O₂-N₂ mixture plasma is generated and characterized using optical and electrical characterization. Variation in plasma parameters like electron temperature, electron density, and reactive species production is monitored with discharge parameters such as applied voltage and feed gas concentration. Results show that the peak average power consumed in Ar-O₂, Ar-N₂, and Ar-O₂-N₂ mixture plasma is found to be 4.45, 2.93, and 4.35 W respectively, at 8 kV. Moreover, it is noted that by increasing applied voltage, the electron temperature, electron density, and reactive species production also increases. It is worth noting that electron temperature increases with increase in oxygen concentration in the mixture (, while it decreases with increase in nitrogen concentration in the mixture (Ar-N₂). Similarly, a decreasing trend in electron temperature is noted for Ar-O₂-N₂ mixture plasma. On the other hand, a decreasing trend in electron density is noted for all the mixtures. Reduction in viable colonies of Pseudomonas aeruginosa, Staphylococcus Aureus, and Escherichia coli were confirmed by the serial dilution method. The inactivation efficiency of pulsed DC plasma generated, in the Ar-N₂ mixture at 8 kV and 6 KHz, was evaluated against P. aeruginosa, S. aureus and E. coli bacteria by measuring the number of surviving cells versus plasma treatment time. Results showed that after 240 s of plasma treatment, the number of survival colonies of the mentioned bacteria was reduced to less than 30 CFU/mL.

Non-equilibrium argon-nitrogen mixture plasma generated at 13.56 MHz is characterized by optical emission spectroscopy and Langmuir probe techniques. The excitation and vibrational temperature are studied as a function of argon percentage in the mixture, at 30-Pa filling pressure and input RF powers of 200 and 300 watt, to find out their role in dissociation of N₂ molecules. In this work, the excitation temperature is determined from Ar-I emission line intensities by using the simple Boltzmann plot method and is found to increase with argon mixing in nitrogen plasma. In similar fashion, the vibrational temperature of second positive system has been determined and is found to also have increasing trend with argon addition. The effect of excitation and vibrational temperature on the nitrogen molecular dissociation level is also monitored. It is observed that N/N ₂ ratio increases with increase in excitation and vibrational temperature and falls slightly at the end.

Low pressure capacitively coupled He–O ₂ /Ar mixture plasma is investigated using optical emission spectroscopy and Langmuir probe (LP) techniques and the effects of discharge parameters i.e. radio frequency (RF) power, filling gas pressure and oxygen concentration on electron density ( n _e ), electron temperature ( T _e ), excitation temperature ( T _exc ), plasma potential ( V _p ) and electron energy probability function (EEPF) are monitored. It is noted that n e increases with increase in RF power and filling gas pressure, while it decreases with increasing O ₂ concentration. The LP technique and Boltzmann plot method are employed to determine T e and T e x c . T e and T e x c estimated by both methods shows similar decreasing trend with increasing RF power and filling gas pressure. A sudden increase in n e and decrease in T e is noted with RF power, indicating a mode transition i.e. from alpha α to the gamma γ mode. The threshold RF power for the γ mode shifts from higher to lower value (150–120 W) with increasing gas pressure (0.3–0.5 mbar). This trend reverses and shifts from lower to higher RF value i.e. from 110 W (pure helium) to 150 W (8% O ₂ ) with increase in O ₂ concentration. Investigation of EEPF profile states evolution from Druyvesteyn-like to bi-Maxwellian distribution with increase in RF power and filling gas pressure; due to mode transition and decrease in the height of high energy tail of EEPF. Similarly, the effect of O ₂ mixing on the shape of EEPF is also investigated. It is noted that in pure helium discharge the EEPF is bi-Maxwellian in nature, while addition of O ₂ in the mixture results in the broadening of the EEPF. Moreover, the height of high energy tail of EEPF also increases. Finally, an increasing trend in atomic oxygen density O is noted with increase in RF power, pressure and O ₂ concentration.