Plasma Pretreatment Research Articles

Catalyst‐free pretreatment of raw wheat straw by atmospheric‐pressure pulsed air discharge for enhancement of sugar production

AbstractThis study presents atmospheric‐pressure plasma as a novel catalyst‐free pretreatment method for raw wheat straw (RWS) biomass. The work explores the effects of processing parameters, such as milled particle size, moisture content of RWS, and plasma generations, on pretreatment efficiency. To understand the mechanisms behind the enhanced pretreatment efficiency, various analysis techniques were used to analyze the physical and chemical properties of RWS before and after pretreatment. The analysis reveals that plasma pretreatment significantly damages the surface smoothness of RWS and enhances the decomposition of lignocellulosic structures. These effects are primarily attributed to the reactive species generated by the pulsed discharge, rather than the accompanying UV radiation, acidification, or heating actions during plasma pretreatment.

Effects of cold plasma pretreatment before different drying process on the structural and functional properties of starch in Chinese yam

This article compared the effects of hot air drying (HAD), infrared drying (IRD), and cold plasma (CP) as a pretreatment on the structure, quality, and digestive characteristics of starch extracted from yam. As the most commonly used drying method, HAD was used as a control. SEM and CLSM images showed that all treatments preserve the integrity of the yam starch. CP caused some cracks and breaks in the starch granules. IRD did not destroy the crystal structure of starch molecules, but made the spiral structure tighter and increased short-range orderliness. However, CP led to the depolymerization and dispersion of starch molecular chains, resulting in a decrease in average molecular weight and relative crystallinity. These molecular conformation changes caused by different processes led to differences in solubility, swelling power, pasting parameters, digestion characteristics, and functional characteristics. This study provided an important basis for the reasonable drying preparation and utilization of yam starch.

Enhancement of rosehip bioactive compounds by cold plasma pretreatment and application of its extract as a functional ingredient in ketchup

The effect of cold plasma (CP) was investigated on rosehip characterization for 1,2.5, and 5 min. All of the samples that were treated with CP had higher amounts of total phenolic content (TPC), antioxidant activity, vitamin C, and lycopene compared to the control (P < 0.05). The extract obtained by rosehip pretreated for 1 min had the highest antioxidant activity as well as bioactive compounds (except anthocyanin) and was selected for application in ketchup. Utilizing the CP-treated rosehip extract (RE) in ketchup successfully enhanced TPC (by 1.44 times), flavonoids (by 1.31 times), antioxidant activity (by 1.21 times), carotenoids (by 1.74 times), lycopene (by 1.11 times), vitamin C (by 1.6 times), and anthocyanins (by 2.46 times) compared to the control (P < 0.05). Moreover, the phenolic profile demonstrated that the highest increase belonged to catechin. Therefore, the RE pretreated by CP has the potential to develop a functional ketchup with high bioactive substances.

Artificial neural networks (ANNs) and response surface methodology (RSM) for optimizing wetting and anti-bacterial properties of woven fabric

This study aims to enhance woven fabric’s antibacterial properties by coating with betel leaf extract using immersion and plasma pre-treatment techniques. It explores nano surface modification and develops mathematical models for inhibition zone values using response surface methodology (RSM) and artificial neural networks (ANNs). We divided the RSM into two groups based on the inputs, model A and model H, and then used artificial neural networks to compare the models. We analyzed fabric treatments using SEM, wetting tests, FT-IR spectrometry, and disc diffusion (Kirby-Bauer) with Staphylococcus aureus to assess nano surface modification and antibacterial properties of fabric-treated with discharged plasma. We compared the optimal inhibition zone values for polyester fabrics with plasma treatment, anti-bacterial coatings, and anti-bacterial and plasma treatment. Fabrics treated with antibacterial coating, plasma treatment, or both exhibited inhibition zones of 2.30 ± 0.50 mm, 3.00 ± 0.50 mm, and 6.40 ± 0.50 mm, respectively. Using RSM model A, wetting properties were predicted with SSE, R-squared, and RMSE values of 0.2402, 0.9999, and 0.2451, respectively. Model A also forecasted inhibition zones for different fabric treatments with R-squared values of 0.899 and 0.9579, and SSE values of 0.8038 and 0.0782, respectively. Additionally, inhibition zones were modeled using RSM model H and ANNs, yielding R-squared values of 0.9128 and 0.97724, respectively. We found that the inhibition zone value using the ANNs model had a better predictive ability than RSM. The new technique can, therefore, be used to enhance the anti-bacterial properties and absorbency of 100% polyester fabrics.

Drying kinetics and moisture migration mechanism of yam slices by cold plasma pretreatment combined with far-infrared drying

The aim of this study was to evaluate the effects of a cold plasma (CP) pretreatment on the energy consumption, drying characteristics, and physicochemical parameters of yam slices at different temperatures during the far-infrared drying (IRD) process. The outcomes demonstrated that CP greatly increased drying efficiency while consuming less energy. At 60 °C, the drying time of yam slices with thicknesses of 3 mm, 5 mm, and 7 mm was shortened by 16 min, 24 min, and 32 min respectively. 5 mm thick yam slices during cooperative drying at 60 °C showed improved color retention which △E was only 5.09, the retention of bioactive components improved 20.5%. The loss of free water predominated and the degree of binding between moisture and material tightened as the drying time increased. MRI images showed that the proton density of the cooperative drying method disappeared faster, the moisture dropped rapidly from the center of the yam slice, followed by the edge of the yam. In general, the results showed that IRD + CP had a broad potential in improving the drying efficiency and product quality of the food industry.

Hydrophobization of Cold Plasma Activated Glass Surfaces by Hexamethyldisilazane Treatment.

The objective of this study was to investigate the modification of glass surfaces by the synergistic combination of cold plasma and chemical surface modification techniques. Glass surface hydrophobicity was obtained as a result of various plasma and deposition operational conditions. The mechanisms governing the hydrophobization process were also studied. Glass plates were activated with plasma using different gases (oxygen and argon) at different treatment times, ranging from 30 to 1800 s. Then, the plasma-treated surfaces were exposed to hexamethyldisilazane vapors at different temperatures, i.e., 25, 60, and 100 °C. Complete characterization, including contact angle measurements, surface free energy calculations, 3D profilometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy, was accomplished. It was found that the extent of the hydrophobicity effect depends on both the plasma pre-treatment and the specific conditions of the hexamethyldisilazane deposition process. Plasma activation led to the formation of active sites on the glass surface, which promoted the adsorption and reaction of hexamethyldisilazane species, thereby inducing surface chemical modification. Longer plasma pre-treatment resulted in stronger modification on the glass surface, resulting in changes in the surface roughness. The largest water contact angle of ≈100° was obtained for the surface activated by argon plasma for 1800 s and exposed to hexamethyldisilazane vapors at 25 °C. The changes in the surface properties were caused by the introduction of the hydrophobic trimethylsilyl groups onto the glass surface as well as roughness development.

Mathematical modeling of extraction kinetics from black chokeberries enhanced by cold plasma pretreatment

The application of cold plasma as a pretreatment for extraction process is a recent development. This research investigates the impact of cold plasma (CP) treatment on the extraction process of bioactive compounds from black chokeberry samples. Utilizing a 12-h maceration process, various analyses, including total phenolic content (TPC), antioxidant capacity (DPPH, ABTS+, CUPRAC assays), total monomeric anthocyanin content (TMA), color parameters, and comprehensive mathematical modeling, were employed to assess the effectiveness of CP treatment. The kinetic modeling with Peleg, Power Law, Elovic's, and Two-site Kinetic Models emphasized the critical role of CP treatment duration in the extraction process. This study indicates that the power-law kinetic model provided the best fit for the experimental data from CP-treated samples, suggesting that this model most accurately describes the extraction kinetics under the conditions tested. In summary, this investigation underlines the crucial role of mathematical modeling in understanding the dynamics of bioactive compound extraction under CP treatment.

Cold plasma‐assisted extraction of anthocyanin from purple corncobs and its antioxidant activity

AbstractIn this study, a novel radio‐frequency cold plasma‐assisted extraction (CPAE) process was developed for the extraction of anthocyanins from a type of agricultural biomass waste, purple corncob. The effects of cold plasma pretreatment on anthocyanin extraction were investigated, and this process was further optimized using response surface methodology. The components of purple corncob anthocyanins (PCAs) were analyzed by super‐high performance liquid chromatography‐mass spectrum. The antioxidant activity of PCAs was evaluated through 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and 2′‐azinobis‐(3‐ethylbenzthiazoline‐6‐sulfonate) (ABTS) scavenging capacity assays in vitro and physiological behaviors in vivo for Caenorhabditis elegans. The results showed that the optimal conditions of cold plasma pretreatment were discharge power 127 W, working pressure 150 Pa, and the treatment time 75 s. The maximum yield of PCAs was about 4.05 ± 0.05 mg/g corncob, much higher than that of the conventional solvent extraction and ultrasonic‐assisted extraction. PCAs were mainly composed of pelargonidin‐3‐galactoside (66.02 wt.%), cyanidin‐3‐galactoside (25.95 wt.%), cyanidin (8.02 wt.%), and petunidin‐3‐galactoside (0.02 wt.%). The extracted anthocyanins reflected the superior antioxidant activity. In terms of in vitro antioxidant ability, the half maximal inhibitory concentration (IC50) of PCAs for DPPH and ABTS were slightly lower than those of ascorbic acid. Meanwhile, C. elegans exhibited positive effects on several physiological behaviors by feeding PCAs, including a 29.25% increase in lifespan, and increases in antioxidant capacity, superoxide dismutase, and catalase (CAT) activity of 26.28%, 28.93%, and 22.24%, respectively. The CPAE process is therefore a highly competitive candidate for the realization of industrial PCAs extraction, combining some additional advantages of cold plasma treatment such as green process, low cost, short treatment time, and scale‐up production.Practical applicationsAgricultural biomass wastes (e.g., corncob, straws, and husks) contain a large number of high value‐added natural active ingredients (e.g., polysaccharides, anthocyanins, and polyphenols). However, a highly efficient extraction of these natural active ingredients is always sought, as the protection of lignocellulosic cell walls hinders the extraction of intracellular products. In this work, the cold plasma‐assisted extraction (CPAE) process showed a comparatively higher anthocyanin yield than the conventional solvent extraction and ultrasonic‐assisted extraction processes. This was due to the fact that the high‐energy helium plasma attack readily broke down the lignocellulosic structure of the plant cell walls, resulting in the rapid release of intracellular purple corncob anthocyanins into the extraction medium. This study suggests that the CPAE process will become an emerging application for the industrial extraction of high value‐added natural active ingredients from agricultural biomass wastes.

Low-Temperature Plasma Pretreatment Enhanced Cholesterol Detection in Brain by Desorption Electrospray Ionization-Mass Spectrometry Imaging.

Cholesterol is a primary lipid molecule in the brain that contains one-fourth of the total body cholesterol. Abnormal cholesterol homeostasis is associated with neurodegenerative disorders. Mass spectrometry imaging (MSI) technique is a powerful tool for studying lipidomics and metabolomics. Among the MSI techniques, desorption electrospray ionization-MSI (DESI-MSI) has been used advantageously to study brain lipidomics due to its soft and ambient ionization nature. However, brain cholesterol is poorly ionized. To this end, we have developed a new method for detecting brain cholesterol by DESI-MSI using low-temperature plasma (LTP) pretreatment as an ionization enhancement. In this method, the brain sections were treated with LTP for 1 and 2 min prior to DESI-MSI analyses. Interestingly, the MS signal intensity of cholesterol (at m/z 369.35 [M + H - H2O]+) was more than 2-fold higher in the 1 min LTP-treated brain section compared to the untreated section. In addition, we detected cholesterol, more specifically excluding isomers by targeted-DESI-MSI in multiple reaction monitoring (MRM) mode and similar results were observed: the signal intensity of each cholesterol transition (m/z 369.4 → 95.1, 109.1, 135.1, 147.1, and 161.1) was increased by more than 2-fold due to 1 min LTP treatment. Cholesterol showed characteristic distributions in the fiber tract region, including the corpus callosum and anterior commissure, anterior part of the brain where LTP markedly (p < 0.001) enhanced the cholesterol intensity. In addition, the distributions of some unknown analytes were exclusively detected in the LTP-treated section. Our study revealed LTP pretreatment as a potential strategy to ionize molecules that show poor ionization efficiency in the MSI technique.

Optimization of Water-Repellent Finishing of Polyester/Viscose Fabric by Plasma Pretreatment Using Response Surface Methodology

Optimization of Water-Repellent Finishing of Polyester/Viscose Fabric by Plasma Pretreatment Using Response Surface Methodology

Improving quality of AlN films on GaAs substrate via in-situ plasma pre-treatment in plasma enhanced atomic layer deposition

Using plasma-enhanced atomic layer deposition (PEALD), we achieved the low-temperature growth of aluminum nitride (AlN) films on GaAs substrate. The effect of in-situ plasma pre-treatment on AlN films growth has been thoroughly investigated in detail. After in-situ plasma pre-treatment, the surface roughness closely matched that of the substrate, the interfaces between AlN films and GaAs substrate were extremely sharp, and the film density increased from 3.05 g/cm3 to 3.15 g/cm3. Additionally, the oxygen content in the AlN films decreased from 35.5 % to 18.8 %. This indicates that in-situ plasma pre-treatment is an effective method for reducing impurity content and improving film quality.

Direct deposition of Ti/MgF2 photoabsorber on PTFE membrane with enhanced robustness via plasma pretreatment for photothermal membrane distillation

Deposition of metal-dielectric hybrid composite on the polymer based membrane is important for the electrochemical, photochemical and photothermal reactions on the membrane surface. The hydrophilic reactants such as catalysts and photothermal materials are not easy to be deposited directly on the hydrophobic membrane surface, so in most cases, binder material has been adapted to stably combine them. In this study, commercial PTFE membrane and Ti/MgF2 photothermal layers were combined without any binder. Ar plasma pretreatment was applied to a membrane surface before depositing optimized Ti/MgF2 stacks to fabricate a mechanically robust photothermal membrane. The successful fabrication of Ar plasma pretreated Ti/MgF2 photothermal membrane was demonstrated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), atomic force microscope (AFM) characterization. Through Ar plasma pretreatment, an increase in Ti/MgF2 photothermal membrane heating temperature of 40.5 % was achieved under 1 sun condition compared with unpretreated membrane. This membrane showed improved performance and reduced energy loss in solar desalination. Utilizing these membranes in a membrane distillation system, water flux increased by up to 26.9 %, performance ratio (PR) increased by 18.9 % and thermal efficiency improved by 21.9 %. After 24-h stress test, the Ar plasma pretreated Ti/MgF2 photothermal membranes demonstrated durability and maintained thermal efficiency.

Enhancing starch functionality through synergistic modification via sequential treatments with cold plasma and electron beam irradiation

The impact of dual sequential modifications using radio-frequency (RF) plasma and electron beam irradiation (EBI) on starch properties was investigated and compared with single treatments within an irradiation dose range of 5–20 kGy. Regardless of sequence, dual treatments synergistically affected starch properties, increasing acidity, solubility, and paste clarity, while decreasing rheological features with increasing irradiation dose. The molecular weight distribution was also synergistically influenced. Amylopectin distribution broadened particularly below 10 kGy. Amylose narrowed its distribution across all irradiation doses. This was due to dominating EBI-induced degradation and molecular rearrangements from RF plasma. With the highest average radiation-chemical yield (G) and degradation rate constant (k) of (2.12 ± 0.14) × 10−6 mol·J−1 and (3.43 ± 0.23) × 10−4 kGy−1, respectively, upon RF plasma pre-treatment, amylose underwent random chain scission. In comparison to single treatments, dual modification caused minor alterations in spectral characteristics and crystal short-range order structure, along with increased granule aggregation and surface irregularities. The synergistic effect was dose-dependent, significant up to 10 kGy, irrespective of treatment sequence. The highest synergistic ratio was observed when RF plasma preceded irradiation, demonstrating the superior efficiency of plasma pre-treatment in combination with EBI. This synergy has the potential to lower costs and extend starch's technological uses by enhancing radiation sensitivity and reducing the irradiation dose.

Dielectric barrier discharge plasma pre-treatment to facilitate the acetylation process of corn starch under heating/cooling cycles

The objective of the current work was to evaluate the impacts of dielectric barrier discharge plasma and repeated dry-heat treatments on the acetylation process of corn starch. The combined modification resulted in a higher substitution degree of acetate groups on starch chains compared to the acetylation treatment alone. This outcome was linked to the increase in surface area and structural organization level of granules achieved through the application of plasma and heating/cooling cycles, respectively. The successful esterification of starch structure was verified through FTIR (1710 cm−1) and 1H NMR (2 ppm). With the increase in plasma treatment duration up to 20 min, gelatinization enthalpy increased (10.81 J/g) due to the cross-linking reaction. Starch acetate produced through the combined treatment could find the application in the development of low-calorie food formulations due to its high resistant starch (70.5 g/100 g) and low viscosity (43 mPa s).

Effects of corona discharge plasma pretreatment on the drying kinetics and quality attributes of lily (Lilium davidii var. unicolor) bulbs

The objective of this study was to examine the impact of corona discharge plasma (CDP) treatments of different durations (1, 3, 5, and 10 min) on the drying kinetics and quality attributes of lilies, including color, enzyme activities, total phenols content (TPC), and antioxidant activity. The microstructure of lilies under different CDP conditions were also investigated. As a result, all CDP treatments enhanced the drying rate relative to untreated lilies, and the shortest drying time of 7 h was obtained at CDP-3 minute samples. CDP treatment led to a higher retention in the TPC of dried lilies. Microstructural analysis revealed the formation of irregular micropores on the surface of the lilies after CDP treatment, which was closely associated with the accelerated drying rate and improved bioactive substances of the dried product. In conclusion, CDP has emerged as a novel and beneficial pretreatment technique that accelerates the drying process and enhances the nutritional qualities of dried lilies.

Processing of hemp and cannabis residue into non-adhesive chipboards and wall panels

As woods are dwindling and agriculture waste burning causes severe air pollution and releases greenhouse gases, processing Hemp and lignocellulosic surplus materials into chipboards and other construction elements may substitute timber and reduce environmental pollution. The presented environmental-friendly technology can potentially process hemp and recycle residual materials into industrial woodchip boards and structural elements without the use of hazardous expensive resins. By applying cold plasma pre-treatment followed by the pressing stage acceptable wood chip standard physical properties are achieved. The irradiation dosage is probably optimal since once exceeding the dosage applied, wood disintegration starts; the process improvement may be related to the pressing configuration. Since the pressing temperature and duration are probably higher than required, the element that may still be aligned is the pressing pressure. Moreover, the positive correlation between sample strength and pressing pressure did not reach a steady state value even when pressing the sample to the maximum possible pressure allowed in the existing equipment (5.5 tons). It is suggested that a significant strength improvement will be attained by increasing the pressing pressure and decreasing the pressing temperature. It is assumed that 20 tons/m2 pressing pressure will be sufficient to attain the desired properties.

Effects of Cold Plasma Pretreatment and Cultivar on the Drying Characteristics, Biochemical, and Bioactive Compounds of 'Tropica' and 'Keitt'Mangoes

PurposeMango is a well-known and widely consumed fruit for its savoury taste and nutritional benefits. However, a lack of efficient postharvest handling prior to its storage could gradually lead to undesirable changes that cause postharvest losses. Dehydration techniques such as hot air drying have shown to minimize the water activity thereby preserving fruit shelf-life. Pretreatment prior drying has the advantage of shortening the drying times, consuming less energy, substituting chemical use, and maintaining the quality attributes of agricultural products. Therefore, the main purpose of this research is to assess the application of cold plasma (CP) as a pretreatment step before drying ‘Tropica’ and ‘Keitt’ mango slices.MethodsThe effect of low-pressure cold plasma pretreatment duration (5 and 10 min) and mango cultivar differences was investigated on drying properties, quality attributes, and microbial load. Thin layer mathematical models fitted were fitted to the data collected to describe the drying behaviour.ResultsMango cultivars behaved differently during drying as ‘Keitt’ samples had a shorter drying time (10 h) compared to ‘Tropica’ samples (12 h). Logarithmic model best predicted the drying behaviour with a determination coefficient R2 of 0.99 and RMSE of 0.0664. Change in bioactive compounds, antioxidant capacity, and microbial load of ‘Tropica’ and ‘Keitt’ mango slices were significantly affected by CP pretreatment and drying (p < 0.05).ConclusionThe findings of this study showed that cold plasma improved the drying rate of dried mango slices. Total phenolic and antioxidant activity were improved with cold plasma treatment of 10 min. In summary, cold plasma improves drying kinetics and the quality attributes of mango fruit.

Cold Plasma Deposition of Tobramycin as an Approach to Localized Antibiotic Delivery to Combat Biofilm Formation.

Hospital-acquired infections (HAIs) remain a significant factor in hospitals, with implant surfaces often becoming contaminated by highly resistant strains of bacteria. Recent studies have shown that electrical plasma discharges can reduce bacterial load on surfaces, and this approach may help augment traditional antibiotic treatments. To investigate this, a cold atmospheric plasma was used to deposit tobramycin sulphate onto various surfaces, and the bacterial growth rate of K. pneumoniae in its planktonic and biofilm form was observed to probe the interactions between the plasma discharge and the antibiotic and to determine if there were any synergistic effects on the growth rate. The plasma-deposited tobramycin was still active after passing through the plasma field and being deposited onto titanium or polystyrene. This led to the significant inhibition of K. pneumoniae, with predictable antibiotic dose dependence. Separate studies have shown that the plasma treatment of the biofilm had a weak antimicrobial effect and reduced the amount of biofilm by around 50%. Combining a plasma pre-treatment on exposed biofilm followed by deposited tobramycin application proved to be somewhat effective in further reducing biofilm growth. The plasma discharge pre-treatment produced a further reduction in the biofilm load beyond that expected from just the antibiotic alone. However, the effect was not additive, and the results suggest that a complex interaction between plasma and antibiotic may be at play, with increasing plasma power producing a non-linear effect. This study may contribute to the treatment of infected surgical sites, with the coating of biomaterial surfaces with antibiotics reducing overall antibiotic use through the targeted delivery of therapeutics.

High-performance ultrathin solution-processed SnO2 top-gate thin-film transistors by constructing high-quality dielectric/channel interface

In this work, we developed a low-thermal-budget approach to realize high-performance solution-processed oxide thin-film transistors (TFTs). To construct high-quality dielectric/channel interface, the corrosion-resistant SnO2 channel and further O2 plasma pre-treatment were adopted to minimize the problematic interface defects. With this strategy, the afforded solution-processed SnO2 TFTs exhibited improved electrical performance and stability, including a descent field-effect mobility (μFE) of 21.4 cm2/V·s, high on/off ratio (Ion/Ioff) of 109, positive threshold voltage (Vth) of 0.39 V, steep SS of 94.7 mV/dec, and small ΔVth of 0.08 and −0.03 V under PBS and NBS, respectively. This work demonstrates a promising fabrication approach for solution-processed oxide TFTs towards advanced applications.

Enhanced methane recovery from anaerobic membrane bioreactor coupled with cold plasma pretreatment for rapid hydrolysis and nitrogen removal

Research to increase biomethane recovery efficiency from thickened sewage sludge (TSWS) using sustainable anaerobic digestion (AD) in municipal wastewater treatment plants is ongoing. Pretreating substrates is known to increase organic biodegradation and biomethane conversion rates in AD. Cold plasma (CP), a recently adopted advanced oxidation processes (AOP) has emerged as an alternative to accelerate pretreatment times under different operation variables. This study assessed raw and CP-pretreated TSWS in an anaerobic sequencing batch reactor (ASBR) and anaerobic membrane bioreactor (AnMBR). The effects of incremental organic loading rates (OLR) and nitrogenous compounds concentration on enhanced CH4 bioconversion efficiency were evaluated. We found that the AnMBR outperformed the ASBR, with an overall chemical oxygen demand (COD) conversion rate of 67%, lower total nitrogen (T–N) accumulation (594 mg L−1), and an overall methane yield of 0.24 L CH4 g−1 COD. CP pretreatment improved TSWS AD, resulting in more efficient COD removal and methane recovery. This study suggests that CP technology is a promising pretreatment to improve AD when treating TSWS.