Pressure Glow Discharge Research Articles

Plasma Grafting of Reactive Β-Cyclodextrin Onto the Cotton Fabric

-Cyclodextrin (β-CD) is capable of forming inclusion complexes, but it cannot form a direct covalent bond with textile materials, hence some cyclodextrin derivatives have been synthesized with reactive groups to allow them to chemically bind to various substrates. In this research, the modified β-CD with itaconic acid (CDI) was grafted on to the cotton fabric by applying plasma technologies. Two methods of plasma techniques, atmospheric pressure plasma reactor (APPJ) and atmospheric pressure glow discharge (APGD) were applied for the graft treatments. The grafting copolymerization of the reactive cyclodextrin (CDI or CDI/Acrylic Acid) on the surface of cotton fabric was studied and the performance (accessibility of cyclodextrin cavities for molecular encapsulation) of -cyclodextrin fixed onto the surface cotton was evaluated. The effect of each plasma treatment method on the characteristics of the cellulosic fabric was investigated. The results showed that plasma activation was occurred on the surface of cellulose and free radicals can easily react to CDI/AA without any degradation on the polymeric chains of cellulose. The presence of anchored CD nanoparticles on the surface of the fibers was demonstrated by using SEM as well as the ability of the attached CDs to form inclusion complexes.

Production of antimicrobial silver nanoparticles modified by alkanethiol self‐assembled monolayers by direct current atmospheric pressure glow discharge generated in contact with a flowing liquid anode

AbstractDirect current atmospheric pressure glow discharge (dc‐APGD) generated in contact with a flowing liquid anode (FLA) is used for continuous synthesis of size‐defined silver nanoparticles (AgNPs) modified by a (11‐mercaptoundecyl)‐N,N,N‐trimethylammonium chloride (TMA) alkanethiol self‐assembled monolayer. The impact of the operating parameters (concentration of Ag(I) ions, solution flow rate, discharge current) on the size of TMA‐AgNPs is examined. Design of experiments along with response surface methodology reveals that it is possible to obtain size‐defined TMA‐AgNPs, the smallest being 1.21 ± 0.80 nm. Furthermore, the reactive species involved in formation of TMA‐AgNPs are identified using optical emission spectrometry. TMA‐AgNPs are characterized by several other experimental techniques, which confirm production of approximately spherical, well‐dispersed TMA‐AgNPs. Additionally, attenuated total reflection Fourier transform infrared spectroscopy and UV/Vis absorption spectrophotometry confirmed that the surface of Ag nanostructures is covered by TMA. TMA‐AgNPs display antimicrobial activity toward multiple human pathogens (Escherichia coli, Staphylococcus aureus, and Candida albicans) with minimal bactericidal concentrations or minimal fungicidal concentrations of 3.90 ± 0.15, 7.79 ± 0.30, and 3.90 ± 0.15 mg/L, respectively.

Enhancement of emission from indium in flowing liquid anode atmospheric pressure glow discharge using organic media

The effect of addition of low molecular weight organic compounds, i.e. acids, salts and alcohols, on the emission measured from In with flowing liquid anode atmospheric pressure glow discharge optical emission spectrometry (FLA-APGD-OES) was studied. It was revealed that a small addition of CH3OH or C2H5OH (0.5%, v/v) enhanced the intensity of In 451.1 nm atomic line over 30-times. The observed boosting of emission was caused both not only by promotion of the analyte transport efficiency from the liquid sample to the plasma phase (increased from 19% to 35%) but also due to some other factors, presumably the improvement of atomization/excitation conditions. The developed FLA-APGD-OES method offered a very low detection limit of In which was 0.21 μg L−1 (using a miniaturized spectrometer) or even 0.030 μg L−1 (using a high-resolution spectrometer). Furthermore, it was demonstrated that addition of alcohols significantly reduced the matrix effects from several interfering species, e.g. Ag, Cu, Pb and Zn, and only in case of Na, the anti-interference effect was observed. The intensity improvement which resulted from the addition of alcohols, was observed for In only and it did not occur for other elements such as Ag, Cd, Hg, Pb, Tl and Zn.

Effect of discharge time on the size control of AgNPs prepared by non-thermal atmospheric plasma discharge

In this work, well-controlled and high stability colloidal silver nanoparticles (AgNPs) were attained via atmospheric-pressure plasma glow discharge in AgNO3 aqueous solution by controlling the discharge time. DC glow discharge with (6 kV) applied voltage and (1.8 mA) discharge current for discharge time (5, 10 and 15 min) was carried out in home–made cell at room temperature to prepare specific sizes and form of (AgNPs). Atmospheric pressure plasma between stainless steel capillary tube cathode electrode above the (AgNO3) electrolyte solution and platinum disk as an anode immersed in an (AgNO3) electrolyte solution for fast generation of colloidal nanoparticles. Structural properties of Ag NPs layer were examined via studying of field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) pattern. Optical properties of (AgNPs) were characterized by a UV–Vis beam spectrophotometer. The obtained results showed that (AgNPs) were uniformly distributed on the silicon substrate. Grain size and specific surface area of AgNPs intensely be influenced by the discharge time.

Development of atmospheric pressure glow discharge plasma assisted CVD system for the deposition of SiOx coatings

A novel, unique and self-designed radio frequency-based atmospheric pressure glow discharge plasma assisted chemical vapor deposition system (APGD-PACVD) has been developed indigenously for the deposition of SiOx coatings. The developed system has been evaluated for continuous, stable and low temperature plasma source for the deposition of adherent and uniform SiOx thin films on silicon substrates using a plasma of argon, helium and hexamethyldisiloxane (HMDSO) gases. The SiOx films deposited on silicon substrates were characterized by Fourier transform infrared spectroscopy (FTIR), field emmision scanning electron microscopy (FESEM) and energy dispersive x-ray analysis (EDXA) for confirmation of chemical structure of the coating. The results demonstrate the deposition of uniform and adherent SiOx films on silicon.

A Convenient Method to Realize Large-Area APGD for Wool Surface Modification

In this paper, a method of realizing large-area atmospheric pressure glow discharge (APGD) plasma in ambient air was investigated. The dielectric barrier discharge (DBD) type was adopted, and the electrode arrangement of a tubular array was designed to achieve large-area APGD (about $1000 \times 60$ mm $^{2}$ ). Optical emission spectroscopy (OES) was used to identify active particles and calculate gas temperature. The results show that the seed electrons can react with N2, O2, and H2O in the air to produce N2 (C-B), N2+, OH, and O3. The gas temperature was calculated to be 410 K–514 K, which is suitable for low-added-value materials treatment. The homogeneity of the plasma temperature was also verified by an infrared camera. Furthermore, a prototype for the wool surface modification was also investigated. The scanning electron microscope (SEM) micrographs and wettability test were adopted, which shows that the plasma can damage the squamae of the natural wool to improve the wettability greatly without burning the wool fiber.

A pulsed electrolyte cathode discharge used for metal element analysis by atomic emission spectrometry

In this paper, a pulsed electrolyte cathode discharge is generated for the purpose of detecting metal elements by atomic emission spectrometry in atmospheric air. The discharge image, and the waveforms of voltage and current are obtained for studying the discharge mode. To understand the mechanisms of metal atomic excitation, the plasma temperature and the electron density of discharge are obtained by the spectra of N2 (C-B, Δν = −2) and Hβ (486.1 nm), respectively. Also, the effects of the solution pH, solution flow rate, discharge gap, and discharge voltage on the emission intensities of Cu and Fe are discussed to acquire the optimal experimental conditions. It is found that the pulsed electrolyte cathode discharge is a kind of atmospheric pressure glow discharge, and it can analyze metal elements accurately and sensitively. The gas temperature and electron density play important roles in the improvement of emission intensities of metal elements.

The effect of APGD plasma treatment on silk fabric

ABSTRACTIn this study, silk fabrics were treated with Atmospheric Pressure Glow Discharge (APGD) plasma in the air at a discharge voltage of 35 kV and frequency of 20 kHz. C.I. (Color Index) Natural Yellow 3 was used as a natural dye. The effect of APGD plasma treatment time on the dyeability and colour fastness of silk fabrics has been investigated. The influence of plasma treatment on the surface morphology of silk fabric was characterised using Scanning electron microscopy. X-ray photoelectron spectroscopy measurement showed that the content of nitrogen and oxygen increased with the increasing APGD plasma treatment time. Attenuated Total Reflection Fourier Transform Infrared spectroscopy was used to characterise the functional groups such as –OH, –NH and –COOH on the surface of silk fabrics. The dyeability of silk fabrics was increased obviously after APGD plasma treatment, and the colour fastness of the dyed samples was satisfactory.

Characterization of Atmospheric-Pressure Helium–Oxygen Dual-Frequency Glow Discharges Using Optical Emission Spectroscopy

In this paper, the dual-frequency atmospheric-pressure glow discharge is operated in helium with a small amount of oxygen. It is found that the plasma density increases, but the reactive atomic oxygen density decreases with high-frequency (HF) power. The plasma density also increases with low-frequency (LF) power, but it is weak as with HF power. However, the reactive atomic oxygen density increases with LF power. It shows that HF power is in favor of excited helium, but LF power is in favor of producing reactive O, N2, and OH. The discharge intensity decreases with oxygen gas admixture in working gas due to its electronegative nature. The generation rate of reactive oxygen atom has a trend of increasing first and then decreasing after 0.3% oxygen gas admixture.

Sheathing of the liquid sampling – Atmospheric pressure glow discharge microplasma from ambient atmosphere and its implications for optical emission spectroscopy

The use of a borosilicate glass cylinder to sheath the operational area of the liquid sampling-atmospheric glow discharge (LS-APGD) microplasma from ambient atmosphere and its effects on optical emission spectroscopy (OES) is described. A positive influence of the glass sheath on analyte and background emission characteristics is realized, along with minor drawbacks in terms of analytical performance (i.e., repeatability) and physical restraint. Sheathing the plasma significantly reduces the ambient atmosphere background spectral contributions, especially those of nitrogen species, resulting in improved measurements of interfered Pb (I) and Ag (I) transitions. Qualitatively, the background reduction by means of glass sheathing is comparable to that of a post-acquisition, mathematical background subtraction method. In addition, the noise associated with atmospheric background species is reduced as well, unlike what is observed in the post-acquisition background correction. Limits of detection (LOD) improvements for silver, lead, and cadmium are observed, while those of sodium and lithium were compromised. By virtue of the alleviation of N2 emission from the background, the LOD of lead improved by multiple orders of magnitude after sheathing the plasma. Future development will be focused toward both improving the analytical performance of the LS-APGD-OES and better understanding the mechanism of the improvements seen by sheathing the plasma.

Comparison of deionized and tap water activated with an atmospheric pressure glow discharge

Liquid-cathode discharge at atmospheric pressure has been excited by a direct current voltage above the surfaces of deionized and tap water. Gap voltage decreases with increasing discharge current, which suggests that the discharges above both the liquids belong to a normal glow regime. For a given discharge current, gap and power voltages of the discharge above deionized water are higher than those above tap water. The optical spectrum obtained from the water surface reveals that there are abundant active species related to oxygen, nitrogen, and water vapor, which leads to changes in the pH value, conductivity, and concentrations of NO3−, NO2−, and H2O2 in liquid. Therefore, these parameters are investigated in the two liquids as functions of discharge current and plasma activation time. For both of them, the results show that the pH value decreases, while conductivity increment and concentrations of NO3−, NO2−, and H2O2 increase with increasing discharge current or activation time. Compared to activated tap water, deionized water has a lower pH value, while higher conductivity increment and concentrations of NO3−, NO2−, and H2O2 are observed after the same activation time and discharge current. Finally, these parameters are compared for different salt types and salt concentrations after plasma activation.

Characteristics of a radio-frequency cold atmospheric plasma jet produced with a hybrid cross-linear-field electrode configuration

Cold atmospheric plasma (CAP) jet has wide applications in various fields including advanced materials synthesis and modifications, biomedicine, environmental protection and energy saving, etc. Appropriate control on the volume, temperature and chemically reactive species concentrations of the CAP jet is of great importance in actual applications. In this paper, an radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma generator with a hybrid cross-linear-field electrode configuration is proposed. The experimental results show that, with the aid of the copper mesh located at the downstream of the traditional co-axial-type plasma generator with a cross-field electrode configuration, a linear field between the inner powered electrode of the traditional plasma generator and the copper mesh can be established. This liner-field can, to some extent, enhance the discharges at the upstream of the copper mesh, resulting in small increments (all less than 12.5%) of the species emission intensities, electron excitation temperatures and gas temperatures by keeping other parameters being unchanged. And due to the intrinsic transparent and conducting features of the grounded copper mesh to the gas flowing, electric current and heat flux of the plasma plumes, a plasma region with higher concentrations of chemically reactive species and larger plasma plume diameters is obtained at the downstream of the grounded copper mesh on the same level of the gas temperature and electron excitation temperature compared to those of the plasma free jet. In addition, the charged particle number densities at the same downstream axial location of the grounded copper mesh decrease significantly compared to those of the plasma free jet. This means that the copper mesh is also, to some extent, helpful for separating the chemically reactive neutral species from the charged particles inside a plasma environment. The preceding results indicate that the cross-linear-field electrode configuration of the plasma generator is an effective approach for tuning the characteristics of the RF-APGD plasma jet in order to obtain an appropriate combination of the plasma jet properties with higher chemically reactive species concentrations, especially relative higher number densities of neutral species, larger plasma volumes and lower gas temperatures.

Effect of a novel cold atmospheric plasma jet treatment with different temperatures on resin-dentin bonding

To investigate the effect of different treatment temperatures of a novel cold atmospheric plasma jet treatment on the resin-dentin bonding. (1) Fifty-two freshly extracted, non-carious and intact third molars were collected. The occlusal one-third of the crown was removed by means of a water-cooled low-speed Isomet saw. One dentin disc [(900 ±100) μm] was prepared for each tooth. The fifty-two dentin discs were randomly divided into control group and experimental groups, of which four were in control group, and forty-eight were divided into four experimental groups according to the different treatment temperatures (4 °C, 10 °C, 20 °C and 30 °C) of the novel radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma jet, twelve in each group. Each experimental group was divided into three subgroups according to different treatment time (10 s, 20 s and 30 s), with four in each subgroup. The occlusal one-third of the crown was removed by means of a water-cooled low-speed Isomet saw. The morphology of demineralized dentin surfaces was analyzed using field emission scanning electron microscopy. (2) Twenty unerupted, non-carious and intact third molars were randomly divided into five groups, four in each group: control group, untreated; 4 °C, 10 °C, 20 °C and 30 °C experimental groups, each group was treated with the RF-APGD plasma jet for 20 s. The micro-tensile resin dentin bond strength was tested after 20 s RF-APGD plasma jet treatment with different temperatures, using a universal mechanical machine. (1) The field emission scanning electron microscopy results indicated that when compared with the control group, a 10 s RF-APGD plasma jet treatment with 30 °C and 20 °C collapsed the collagen scaffold. Collagen fibrils maintained an uncollapsed three-dimensional structure after the 4 °C RF-APGD plasma jet treatment for even 30 s treatment. (2) The microtensile resin dentin bond strength results of the 4 °C RF-APGD plasma jet treatment group (57.8±0.7) MPa were significantly higher than that of the control group [(47.4±0.5) MPa] and 10 s, 20 s and 30 s RF-APGD plasma treatment group [(51.9±0.7) MPa,(29.7±1.0) MPa and (22.2±1.5) MPa] with statistically significant difference (P<0.05). Compared with the control group, the micro-tensile bond strength increased about 21.9% and 9.5% after 4 °C and 10 °C RF-APGD plasma jet treatment, respectively. Compared with other treatment temperatures, this novel RF-APGD plasma jet treatment with the temperature of 4 °C can preserve the three-dimensional morphology of demineralized dentin better, and can improve the resin-dentin bonding.

Monochromatic spatial imaging of the liquid sampling – Atmospheric pressure glow discharge: Effects of gas flow on spatial profiles of analyte and background species

The liquid sampling – atmospheric pressure glow discharge (LS-APGD) microplasma was paired with a monochromatic imaging spectrometer (MIS) to interrogate relevant plasma species/elements. The coupling of the LS-APGD source to the MIS allows for the generation of spatial emission profiles at specific analyte and background species' wavelengths. A major goal of this work was to utilize these emission profiles to gain an understanding of the species' location in the plasma as well as the effects of plasma gas flow on these emission profiles. It was found that as sheath gas and counter gas flow rates were increased, there were visible differences in intensity and distribution of emission from the monitored species in the plasma. Silver was used as the representative (test) analyte for this work due to its good sensitivity, wavelength positioning, and ability to provide continuity for comparison to previous works. The majority of analyte emission was found to occur at the tip of the solution electrode, where solutes are introduced to the plasma, whereas various background species emitted throughout the plasma. In addition to aiding in the understanding of plasma operation based on spatial emission characteristics, these studies also aided in optimizing the gas flow parameters for analyte emission intensity, signal-to-background (S/B), and signal-to-noise (S/N) values. The optimized gas flow parameters were found to be 0.7 and 0.1 L min−1 for the sheath and counter gas respectively.

In-situ generation of Ag, Cd, Hg, In, Pb, Tl and Zn volatile species by flowing liquid anode atmospheric pressure glow discharge operated in gaseous jet mode – Evaluation of excitation processes and analytical performance

The use of flowing liquid anode atmospheric pressure glow discharge (FLA-APGD) operated with the aid of a gaseous jet as an efficient and novel excitation source for optical emission spectrometry (OES) was evaluated in details. Although about 50 elements have been tested by introducing respective standard solutions into a discharge system, only emission lines of Ag, Cd, Hg, In, Pb, Tl and Zn have been identified. In this arrangement, the surface of solution was bombarded by electrons resulting in generation of volatile species of mentioned elements. After penetrating the plasma, they were excited and extraordinary atomic emission was observed for these elements. It was found that the use of the Ar or He jet provided beneficial excitation conditions, while reduction of the discharge gap led to suppression of the intensity of interfering diatomic molecular bands like NO, OH and N2. Under optimal operating conditions of the discharge system, detection limits (DLs) assessed for Ag, Cd, Hg, In, Pb, Tl and Zn were respectively 0.001, 0.006, 0.16, 0.093, 0.076, 0.007 and 0.018 µg L−1, and they were on average by 10-times better as referred to earlier FLA-APGD constructions operated without the gaseous jet. In addition, the discharge was characterized by greater stability and precision of measurements (< 2%). Dynamic ranges of calibration curves covered between 3.5 (Cd, In, Zn) and over 5 orders of magnitude (Ag, Tl). The biggest weakness of the developed system turned out to be high susceptibility to matrix interferences. It was found that presence of foreign ions (at concentrations of 1–10 mg L−1) suppressed emission from studied elements on average by 20–60%. To clarify the reason for extremely high sensitivity of emission lines of Ag, Cd, Hg In, Pb, Tl and Zn, efficiency of transport of these elements from the liquid phase to the plasma was determined. It was established that from 5% to 70% of analytes presented in sample solutions were released, whereas evaporation of water was merely 5–15%. Since the FLA-APGD plasma was enriched with analytes atoms, it was concluded that such processes like electrospray formation or solution evaporation do not make a major contribution to transport of analytes from the liquid phase to the discharge, and that it was mainly due to plasma-induced volatile species generation processes.

Atmospheric pressure glow discharge for CO2 conversion: Model-based exploration of the optimum reactor configuration

We investigate the performance of an atmospheric pressure glow discharge (APGD) reactor for CO2 conversion in three different configurations, through experiments and simulations. The first (basic) configuration utilizes the well-known pin-to-plate design, which offers a limited conversion. The second configuration improves the reactor performance by employing a vortex-flow generator. The third, “confined” configuration is a complete re-design of the reactor, which encloses the discharge in a limited volume, significantly surpassing the conversion rate of the other two designs. The plasma properties are investigated using an advanced plasma model.

Synthesis of MoO3 by glow discharge in contact with water

An atmospheric pressure glow discharge was ignited between a molybdenum anode and the water surface of a cathode for the synthesis of MoO3 powders. The action of glow discharge leads to the non-equilibrium evaporation of water, sputtering of the metal anode and formation of molybdenum (VI) oxide, which deposited on the anode. The chemical composition and morphology of the obtained powder were performed by using x-ray diffraction spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. It was found that the synthesized powders are pure α-MoO3. The possible mechanism of the formation of molybdenum trioxide during glow discharge treatment was described. The photocatalytic performance of MoO3 was estimated through the degradation of Rhodamine B under dark and UV irradiation conditions. Orthorhombic MoO3 exhibited the best photocatalytic activity for the photodegradation of Rhodamine B of 100% under UV irradiation for 15 min.

Determination of antimony in water samples by hydride generation coupled with atmospheric pressure glow discharge atomic emission spectrometry

A low power (∼10 W), miniaturized atmospheric pressure glow discharge (APGD) source was coupled with a hydride generation (HG) system for sensitive determination of antimony in water samples with atomic emission spectrometry (AES).

A miniaturized atmospheric pressure glow microdischarge system generated in contact with a hanging drop electrode – a new approach to spectrochemical analysis of liquid microsamples

A newly developed atmospheric pressure glow discharge (APGD) microplasma system generated in contact with a hanging drop electrode (HDE) was investigated here in detail.

Measurements of the Potential Profiles of Glow Discharges Using an Emissive Probe

Glow discharges are produced in air in a ~1-m-long glass vacuum tube under the pressure of 12-113 mtorr. We present the full potential profiles throughout the glow discharge regions characterized using a cold emissive probe with the current-bias method. Secondary electron emission from the probe likely determines the local plasma potential, which replaces the role of thermionic emission that fails in relatively high-pressure plasmas. The measured potential profiles show good agreement with the theoretical expectations. A large potential drop is measured in the cathode dark space followed by a potential plateau through the negative glow and Faraday dark space regions. Striations in the positive column are shown as stair-step-like multiple potential double layers with a potential step close to the ionization energy. This cold emissive probe method can be used for characterizing potentials in even higher pressure (>1 torr) glow discharges that are not yet well understood.