Non-thermal Plasma Technology Research Articles

Effect of Plasma Activated Water (PAW) on Fruits and Vegetables

In recent time, the consumption of fruits and vegetables has raised, the variety of pathogens of fresh fruits and vegetables has enhanced, and it's believed that pathogens are capable to resisting the stress conditions that are major causes of fresh produce related food-borne ill health. In order to ensure microbial safety and reduce nutrient loss, non-thermal plasma technology has received increasing attention in food preservation applications. Non-thermal plasma has high reactivity and has potential applications in food safety, nutritional quality and environmental safety. Plasma activated water (PAW) abundant source of reactive oxygen species (ROS) and reactive nitrogen species, which can inactive the microorganisms. In addition to its bactericidal activity, it can also be used to degrade pesticide residues and antibiotic residues in water and packaging materials. Non-thermal plasma is applied to water to generate plasma-activated water, potentially applied in fruits and vegetables in recent years. PAW has been successfully applied as washing agent or disinfect agent in fruits and vegetables. In addition, it can inactivate food-borne pathogens on fruit and vegetable contact surfaces and on fruits and vegetables without adverse effect on the environment and human health. Reported findings indicates that plasma activated water has the least affect the sensory parameters and quality of fruits and vegetables. Therefore, it can be potentially applied in fruits and vegetables industry as substitute of traditional washing agent i.e. chlorinated water, quaternary ammonium salts etc. Furthermore, High bactericidal ability and easy to produce plasma activated water function can be used in every food field, such as meat, dairy products, fruits and vegetables and grains. However, the chemistry of PAW is taken into account to be extraordinarily complicated, and controlling the reaction is one in all the challenges for future analysis. Furthermore, it also requires from regulatory agencies to generally recognize as a safe (GRAS) status.

Nonthermal Plasma Induced Fabrication of Solid Acid Catalysts for Glycerol Dehydration to Acrolein

The feasibility of fabricating better solid acid catalysts using nonthermal plasma (NTP) technology for biobased acrolein production is demonstrated. NTP discharge exposure was integrated in catalyst fabrication in air or argon atmosphere. The fabricated catalysts were characterized by Brunauer–Emmett–Teller surface area analysis, temperature-programmed desorption of ammonia, X-ray powder diffraction and Fourier-transform infrared spectroscopy of pyridine adsorption, in comparison to regularly prepared catalysts as a control. Further, kinetic results collected via glycerol dehydration experiments were compared, and improvement in acrolein selectivity was displayed when the catalyst was fabricated in the argon NTP, but not in the air NTP. Possible mechanisms for the improvement were also discussed.

Non-thermal atmospheric plasma reactor design for fine powder processing and starch modification

In this article, non-thermal plasma technology at atmospheric pressure for fine powder processing was investigated. A common potato starch was modified within Argon plasma to produce a commercial well-known modified starch known as HT drilling starch. A theoretical model was developed for possible future scale-up of the designed suitable plasma reactor in the emerging field of plasma modification of starch. The model predicts the incipient condition for full fluidization of the solid particles within the plasma fluid. This condition led to maximum interaction between the plasma species and the starch granules. The predicted incipient full fluidization velocity in the model was in consistent with required experimental flow conditions for producing the desired modified starch. Since the plasma modified starch was used as an adhesion additive, the known characteristics in the oil & gas-well drilling fluid such as Fluid-Loss (F.L) and viscosity were reduced more than 30% and 10%, respectively.

Applying a large-scale device using non-thermal plasma for microbial decontamination on shell eggs and its effects on the sensory characteristics

Concerns related to foodborne pathogens such as Salmonella enterica serovar Enteritidis (SE) necessitate the decontamination of eggs. Multiple studies have successfully demonstrated the use of non-thermal plasma (NTP) technology in inactivating SE on artificially inoculated shell eggs. However, the NTP devices abovementioned were operated in the batch mode and small scale. The present study is the first attempt to evaluate the effectiveness of a large-scale device using NTP for egg decontamination. The designed NTP was operated at 400 W (power), 30 slm (Ar flow rate), 5 and 10 eggs/min (speed of conveyor belt), and 4 cm (distance between the plasma jets and egg samples). Conducting a two-round treatment for the egg samples at 400 W-30 slm-5 eggs/min-4 cm achieved the highest reduction of SE populations (3.57 log CFU/egg). SEM observation revealed less damage on the surface of the plasma-treated eggs than the commercial-washed eggs. Overall, NTP treatment can maintain the freshness quality and sensory characteristics until 15-day storage. This study demonstrated a large-scale NTP system was able to effectively achieve a significant reduction of pathogenic SE without adversely affecting egg quality properties. These results suggested the readiness of this NTP device for industrial applications.

Simple approach for the plasma treatment of polymeric membranes and investigation of the aging effect

AbstractThe modification of the surface characteristics after treatment with plasma in polymeric materials, such as the aging phenomenon, calls the attention of research in the area of nonthermal plasma technology. In this work, a direct treatment with dielectric‐barrier discharge plasma was used on the surfaces of ultrafiltration membranes. The measurements of the contact angle with water, attenuated total reflectance accessory, zeta potential, atomic force microscopy and scanning electron microscopy‐MEV were performed on the surfaces to verify changes after plasma treatment and to understand the occurrence and timing of the plasma aging effect. In the analysis of the membrane performance, hydraulic permeation and protein retention tests were performed. The results showed an improvement in wettability and hydrophilic properties in the post‐treated membranes. The study of reversibility/aging of the post‐plasma surface is important for research that deals with the modification of polymeric membranes. Changes in surface morphology, topography and wettability of the membranes were observed up to seven days after treatment, with a tendency to return to the initial characteristics of the membranes.

Abatement of gas-phase VOCs via dielectric barrier discharge plasmas.

Non-thermal plasma (NTP) technology is regarded as promising method for abatement of volatile organic compounds (VOCs) and has gained substantial interests in the fields of air purification. In this present work at atmospheric pressure, dielectric barrier discharge (DBD) plasma has been employed and utilized to evaluate feasibility of toluene, benzene, and m-xylene degradation in a parallel plate type DBD reactor taking argon as a carrier gas. The composition of post-plasma-treated by-products is studied by various spectroscopic techniques such as GC, GCMS, and FTIR, and the corresponding computational work is carried out by Gaussian software. The by-products obtained are analyzed in order to ascertain their structure and stability. The degradation of the VOCs to CO and CO2 has been affirmed from the GC and GCMS analyses. Furthermore, the probable degradation pathway for the degradation of the aforementioned VOCs has been deciphered and the most feasible path is suggested. Additionally, DFT calculations have been performed to have an idea about the energies of the pathways involved. This research work has been carried out without use of any catalyst. Surprisingly, the degradation observed is much higher than the reported values. These findings would be helpful towards the abatement of VOCs by the use of non-thermal plasma.

Surface-Functionalized Boron Nanoparticles with Reduced Oxide Content by Nonthermal Plasma Processing for Nanoenergetic Applications.

The development of an in situ nonthermal plasma technology improved the oxidation and energy release of boron nanoparticles. We reduced the native oxide layer on the surface of boron nanoparticles (70 nm) by treatment in a nonthermal hydrogen plasma, followed by the formation of a passivation barrier by argon plasma-enhanced chemical vapor deposition (PECVD) using perfluorodecalin (C10F18). Both processes occur near room temperature, thus avoiding aggregation and sintering of the nanoparticles. High-resolution transmission electron microscopy (HRTEM), high-angular annular dark-field imaging (HAADF)-scanning TEM (STEM)-energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) demonstrated a significant reduction in surface oxide concentration due to hydrogen plasma treatment and the formation of a 2.5 nm thick passivation coating on the surface due to PECVD treatment. These results correlated with the thermal analysis results, which demonstrated a 19% increase in energy release and an increase in metallic boron content after 120 min of hydrogen plasma treatment and 15 min of PECVD of perfluorodecalin. The PECVD coating provided excellent passivation against air and humidity for 60 days. We conclude in situ nonthermal plasma reduction and passivation lead to the amelioration of energy release characteristics and the storage life of boron nanoparticles, benefits conducive for nanoenergetic applications.

Effect of non-thermal plasma on carbon dioxide reforming of methane to hydrogen

Methane (CH4) and carbon dioxide (CO2) are widely acknowledged as the major greenhouse gases. Theoretically speaking, the mixture of methane and carbon dioxide would reform into gas fuels like hydrogen (H2) and carbon monoxide (CO) under certain treatment conditions. However, the traditional conversion of methane and carbon dioxide requires a high temperature, which can cause carbon deposition and deactivate the catalyst. Non-thermal plasma technology can alleviate this problem. In this research, a method of hydrogen production from greenhouse gases by non-thermal plasma was studied. We discussed the influence of plasma on the reforming of methane and carbon dioxide into hydrogen as functions of different parameters like power input, electrode gaps, total gas fluxes and methane/carbon dioxide ratios in customized single and double dielectric reactors. Meanwhile, the potential mechanism for the reforming has also been discussed. As a result, it was observed higher power input, smaller electrode gap and total gas flux would contribute to better performance of reforming. Based on the results of Fourier transform infrared spectroscopy and emission spectrum analysis, the mechanism of different reforming products such as carbon monoxide, hydrogen, other organic by-products and carbon deposition is discussed based on numerous free radicals including ·C, ·CHx, ·CO, ·H, and ·O in the discharge zone.

Recent progress of non-thermal plasma material surface treatment and functionalization

Plasma technology plays an important role in preparing and processing materials nowadays. This review focuses on the applications of non-thermal plasma (NTP) in the surface treatment and functionalization of materials, including the plasma sources for generating plasmas, NTP techniques and specific application fields. The plasma sources include inductively coupled plasma, capacitively coupled plasma, electron cyclotron resonance plasma, surface wave plasma, helicon wave plasma, atmospheric pressure plasma jet, and dielectric barrier discharge plasma. The NTP techniques for material surface treatment and functionalization include plasma surface grafting and polymerization, plasma enhanced chemical vapor deposition, plasma assisted atomic layer deposition, plasma enhanced reactive ion etching, and plasma assisted atomic layer etching. Specific applications of plasma surface treatment and functionalization cover hydrophilic/hydrophobic surface modification, surface micro-nano processing, biological tissue surface treatment, and catalyst surfaces treatment. Finally, the application prospects and development trends of NTP technology for material surface treatment and functionalization are proposed.

Decomposition of VOCs using serial surface dielectric barrier discharge reactors

ABSTRACT Decomposition of two typical volatile organic compounds (VOCs): toluene and methyl ethyl ketone (MEK), was investigated by introducing the complete energy yield (i.e. amount of VOCs totally converted to CO and CO2 for every 1 kWh of electrical usage) and specific energy density (SED) for the non-thermal plasma technology. Three dielectric barrier discharge reactors of which SED range was 55 J/L to 283 J/L at a flow rate of 1 L/min were connected in a 3-reactor arranged in series using interconnecting tubes in the inlets and outlets. As a result of the serial reactor design, the energy efficiency of the system improved, and in particular, 7% of increase was found in at the same level of energy consumption. The mixed phase of VOCs (toluene and MEK) showed MEK as a limiting species in this study. As the inlet concentration rose from 20 to 100 ppmv, both energy yield and complete energy yield increased from 0.8 to 9.2 g/kWh and from 0.8 to 2.3 g/kWh, respectively.

Non-Thermal Plasma Coupled with Catalyst for the Degradation of Water Pollutants: A Review

Non-thermal plasma is one of the most promising technologies used for the degradation of hazardous pollutants in wastewater. Recent studies evidenced that various operating parameters influence the yield of the Non-Thermal Plasma (NTP)-based processes. In particular, the presence of a catalyst, suitably placed in the NTP reactor, induces a significant increase in process performance with respect to NTP alone. For this purpose, several researchers have studied the ability of NTP coupled to catalysts for the removal of different kind of pollutants in aqueous solution. It is clear that it is still complicated to define an optimal condition that can be suitable for all types of contaminants as well as for the various types of catalysts used in this context. However, it was highlighted that the operational parameters play a fundamental role. However, it is often difficult to understand the effect that plasma can induce on the catalyst and on the production of the oxidizing species most responsible for the degradation of contaminants. For this reason, the aim of this review is to summarize catalytic formulations coupled with non-thermal plasma technology for water pollutants removal. In particular, the reactor configuration to be adopted when NTP was coupled with a catalyst was presented, as well as the position of the catalyst in the reactor and the role of the main oxidizing species. Furthermore, in this review, a comparison in terms of degradation and mineralization efficiency was made for the different cases studied.

Gas-phase isopropanol degradation by nonthermal plasma combined with Mn-Cu/-Al2O3.

In this study, the dielectric barrier discharge (DBD) induced by nonthermal plasma (NTP) technology was used for isopropanol (IPA) degradation. IPA, intermediate, final product, and ozone concentrations were analyzed using GC-MS, carbon dioxide detector, and ozone detector. The experimental flow rate and concentration were fixed to 1 L/min and 1200 ppm ± 10%, respectively. Different reaction procedures were proposed for self-made metal catalyst combined with a plasma system (plasma alone and γ-Al2O3 combined with plasma, Cu (5 wt%)/γ-Al2O3 combined with plasma, Mn (3 wt%)-Cu (5 wt%)/γ-Al2O3 combined with plasma). In addition, the effect of the carrier gas oxygen content (0%, 20%, and 100%) on IPA conversion and intermediate and carbon dioxide selectivity was also investigated. The results revealed that the Mn (F)-Cu/γ-Al2O3 combined with plasma exhibited more efficient IPA conversion. In the 100% oxygen environment, the IPA conversion rate increased from 79.32 to 99.99%, and carbon dioxide selectivity increased from 3.82 to 50.23%. IPA was completely converted after 60 min of plasma treatment with the acetone selectivity, carbon dioxide selectivity, and tail ozone concentration of 26.71% ± 1.27%, 50.23% ± 0.56%, and 1761 ± 11 ppm, respectively. This study proved that the current single planar DBD configuration is an effective advanced treatment technology for the decomposition of VOCs.

Degradation of cefixime antibiotic in water by atmospheric plasma bubbles: Performance, degradation pathways and toxicity evaluation

• Underwater plasma bubbles were used to degrade cefixime in water. • Complete cefixime degradation with high-energy yield of 1.5 g/kWh. • Degradation of cefixime was conducted by reactive species, especially short-lived OH radicals. • Degradation pathways of cefixime were proposed by intermediates identified by LCMS. • Plasma treatment leads to the loss of antibacterial activity and cytotoxicity of cefixime. Excessive use and indiscriminate discharge of antibiotics inevitably lead to their accumulation in the environment, posing significant ecological and physiological risks. Non-thermal plasma (NTP) is receiving increasing attention as a sustainable technology for the efficient breakdown of these antibiotics as well as other contaminants. However, implementation of NTP technology still faces several hurdles, particularly the maximization of the reactive plasma effects and the practical scaling approaches. In this study, we generated NTP inside forming bubbles with enlarged gas-liquid interfacial areas for efficient delivery of reactive plasma species to target cefixime antibiotic molecules in aqueous solution. The degradation of cefixime was largely dependent on the different number of microholes, air flow rate, discharge power, plasma exposure time and solution properties. Results show that a high-performance degradation was achieved in the 10-microhole reactor with an energy yield of 1.5 g/kWh, after 30 min of plasma treatment. Based on LC-MS analysis, an NTP-initiated cefixime degradation pathway was proposed. Cytotoxicity studies demonstrated that the antibiotic activity of cefixime was effectively and wholly deactivated by the plasma process, and that no toxic effects of the 30 min-treated water were observed toward human cell lines. Furthermore, considering that air was employed as the inducer gas, which results in the formation of reactive nitrogen species in the water, the treated water was able to enhance seedling growth, further contributing to the societal and economic benefits of this plasma-based antibiotic degradation strategy.

Material extrusion additively manufactured alumina monolithic structures to improve the efficiency of plasma-catalytic oxidation of toluene

Abstract Non-thermal plasma (NTP) technology is one of the strategies with the most potential for the degradation of volatile organic compounds. Exploring the combination of plasma and catalysts in one system is of considerable significance to improve energy efficiency and decrease harmful by-products. The current geometrical design of monolithic catalysts is not optimal due to the limitations of traditional manufacturing processes. Here, the use of material extrusion additive manufacturing, followed by debinding and sintering to construct alumina monolithic catalysts with two-dimensional channels is suggested. A new feedstock material was adapted to the additive manufacturing process, and Al2O3 structures with unique axial and radial channels coated with Mn-Co nanospheres were successfully prepared for the plasma-catalytic degradation of toluene. The monoliths with radial and axial channels considerably increased energy efficiency with a minor increase in by-products. This work demonstrates the advantages of using additive manufacturing and provides a general strategy for the design and fabrication of monolithic catalysts with two-dimensional channel structures for heterogeneous catalysis.

Applications of nonthermal plasma technology on safety and quality of dried food ingredients.

Cold plasma technology is an efficient, environmental-friendly, economic and noninvasive technology; and in recent years these advantages placed this novel technology at the centre of diverse studies for food industry applications. Dried food ingredients including spices, herbs, powders and seeds are an important part of the human diet; and the growing demands of consumers for higher quality and safe food products have led to increased research into alternative decontamination methods. Numerous studies have investigated the effect of nonthermal plasma on dried food ingredients for food safety and quality purposes. This review provides critical review on potential of cold plasma for disinfection of dried food surfaces (spices, herbs and seeds), improvement of functional and rheological properties of dried ingredients (powders, proteins and starches). The review further highlights the benefits of plasma treatment for enhancement of seeds performance and germination yield which could be applied in agricultural sector in near future. Different studies applying plasma technology for control of pathogens and spoilage micro-organisms and modification of food quality and germination of dried food products followed by benefits and current challenges are presented. However, more systemic research needs to be addressed for successful adoption of this technology in food industry.

A Review about the Recent Advances in Selected NonThermal Plasma Assisted Solid-Gas Phase Chemical Processes.

Plasma science has attracted the interest of researchers in various disciplines since the 1990s. This continuously evolving field has spawned investigations into several applications, including industrial sterilization, pollution control, polymer science, food safety and biomedicine. nonthermal plasma (NTP) can promote the occurrence of chemical reactions in a lower operating temperature range, condition in which, in a conventional process, a catalyst is generally not active. The aim, when using NTP, is to selectively transfer electrical energy to the electrons, generating free radicals through collisions and promoting the desired chemical changes without spending energy in heating the system. Therefore, NTP can be used in various fields, such as NOx removal from exhaust gases, soot removal from diesel engine exhaust, volatile organic compound (VOC) decomposition, industrial applications, such as ammonia production or methanation reaction (Sabatier reaction). The combination of NTP technology with catalysts is a promising option to improve selectivity and efficiency in some chemical processes. In this review, recent advances in selected nonthermal plasma assisted solid–gas processes are introduced, and the attention was mainly focused on the use of the dielectric barrier discharge (DBD) reactors.

Removal of bromoamine acid in dye wastewater by gas-liquid plasma: The role of ozone and hydroxyl radical

As a widely used anthraquinone dye intermediate, bromoamine acid (BAA) exists extensively in dye wastewater. In this study, the gas-liquid discharge non-thermal plasma technology was employed to degrade BAA. Efficient removal was achieved by the system within 15 min treatment. Besides, the effects of input power, working gas flow rate and solution pH value on BAA removal efficiency were investigated. BAA removal rate increased with higher input power and lower pH value, while too high or too low working gas flow rate could lead to the decrease of BAA removal. The existence of BAA caused significant decline of aqueous ozone concentration while enhanced the production of H2O2, indicating that the aqueous ozone participated in BAA degradation. The contributions of main active species were investigated. H2O2 and UV produced by discharges showed little effects on BAA degradation individually, however led to synergistic effect by producing OH. Over 60 % removal of BAA was attributed to OH oxidation, while direct molecular ozone contributed around 20 % degradation. The second-order rate constants of BAA reacting with ozone and OH were determined to be 1.22 × 103 M−1 s−1 and 4.06 × 109 M−1 s−1, respectively. A kinetic model was established to predict BAA degradation. 12 degradation intermediates were detected by HPLC-Q-ToF-MS, GC–MS and HPLC-UV. The degradation was mainly caused by hydroxylation, bond cleavage and addition of OH on double bonds.

Evaluating the Performance of a Lab-Scale Water Treatment Plant Using Non-Thermal Plasma Technology

In this study, a lab-scale plant was designed to treat water in continuous flow condition using non-thermal plasma technology. The core was an electrode system with connected high-voltage (HV) pulse generator. Its potentials and limitations were investigated in different experimental series with regard to the high-voltage settings, additions of oxygen-based species, different volume flow rates, and various physical-chemical properties of the process water such as conductivity, pH value, and temperature. Indigo carmine, para-Chlorobenzoic acid, and phenol were chosen as reference substances. The best HV settings was found for the voltage amplitude Û = 30 kV, the pulse repetition rate f = 0.4–0.6 kHz, and the pulse duration tb = 500 ns with an energy yield for 50% degradation G50, which is of 41.8 g∙kWh−1 for indigo carmine, 0.32 g∙kWh−1 for para-Chlorobenzoic acid, and 1.04 g∙kWh−1 for phenol. By adding 1 × 10−3 mol∙L−1 of oxygen, a 50% increase in degradation was achieved for para-Chlorobenzoic acid. Conductivity is the key parameter for degradation efficiency with a negative exponential dependence. The most important species for degradation are hydroxyl radicals (c ≈ 1.4 × 10−8 mol∙L−1) and solvated electrons (c ≈ 1.4 × 10−8 mol∙L−1). The results show that the technology could be upgraded from the small-scale experiments described in the literature to a pilot plant level and has the potential to be used on a large scale for different applications.

Continuous Generation of HgCl2 by Dielectric Barrier Discharge Nonthermal Plasma. Part II: Influences of the Cl Source

This study is the first investigation on the effects of the Cl source on Hg0 oxidation by dielectric barrier discharge (DBD) nonthermal plasma technology in a self-developed DBD reactor under atmos...

Real diesel engine exhaust emission control: indirect non-thermal plasma and comparison to direct plasma for NOX, THC, CO, and CO2.

Recently, diesel engine exhaust emission control by non-thermal plasma (NTP) technology has been shown to be promising. However, carbon and soot deposition on the inner surface of the NTP reactor for direct plasma processing decreased the efficiency of the plasma process throughout the experiments. In the present work, the feasibility of indirect plasma processing was investigated as an innovative and novel method compared to direct plasma processing. Air was directed through an NTP at an applied voltage of VP-P = 7kV and a flow rate of 1-4L/min, and then, it was combined with engine exhaust gas at a flow rate of 5L/min. In this case, the maximum conversion of NOX was 64.9% at 4L/min. However, for direct plasma processing at 5L/min, NO conversion was 58%, which proves that the indirect NTP process can decrease NOX concentration effectively. The maximum conversion for unburned hydrocarbon (UHC), carbon monoxide (CO) and carbon dioxide (CO2) was obtained as 2%, 4% and 0.7% at 4, 2 and 3L/min in indirect plasma processing; While their remove rate for direct plasma processing was 16.3%, -0.5% and 13.2%, respectively.