Solution Plasma Process Research Articles

Preparation and synthesis of carbon nanomaterials from 1-hexanol by solution plasma process with Ar/O2 gas bubbles

This study presents the simple and catalyst-free methods for synthesizing carbon nanomaterials from 1-hexanol alcohol by using stable solution plasma process by varying the argon (Ar), oxygen (O2), and Ar and O2 mixtures plasma working gas bubble. The structural characteristics of carbon nanomaterials are measured by transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. The discharge characteristics are examined based on the discharge voltage, current, and optical emission spectrometer (OES) techniques. By using the external Ar gas bubble discharge during solution plasma process, the size of carbon nanoparticle and discharge voltage are decreased compared to the no gas case and the discharge current is increased, which would be due to the increase of plasma energy and enhancement of the square of plasma-liquid contact to plasma volume. By using the external O2 gas bubble discharge during solution plasma process, whereas, the size of carbon nanoparticle is increased compared to the no gas case and the discharge voltage and current are decreased, which would be due to the production of relatively high amounts of oxygen radicals, resulting in the flame synthesis. Raman spectra results show that the degree of graphitization of the carbon nanomaterials synthesized with external Ar 150 and O2 50 standard cubic centimeter per minutes (sccm) mixtures gas bubble during solution plasma process is observed to be greater than that of the carbon nanomaterials synthesized with the only Ar or O2 gas bubble. This solution plasma process by varying the plasma working gas mixtures can potentially be used for the precise nanomaterial synthesis.

Solution plasma process: An option to degrade bisphenol A in liquid-phase to non-toxic products

Bisphenol A (BPA) is a potential endocrine disruptor. It causes hormonal imbalances and also affects aquatic organisms when discharged in untreated form into the ecosystems. Many attempts have been made to degrade BPA in the liquid phase using chemical and or biological methods, which often require multiple steps and are not effective to any great extent. In this study, solution plasma process (SPP) was adopted for the degradation of BPA in liquid phase. BPA at a constant concentration (100 mg·mL−1) was degraded using SPP at various of discharge times (0–45 min) and various pH (3–6). Physical conditions for SPP were voltage at 800 V, frequency 35 kHz with bandwidth of 2 μS and unipolar and bipolar power supplies were used. The degraded BPA was extracted and investigated for the degradation adopting Gas chromatography-Mass Spectroscopy (GC–MS). During SPP, intermediates were formed at 15 min of treatment, and degradation was achieved to a maximum of 86% at 18 min. The GC–MS results revealed that dimethyl ester (91%), hydroxyl‑bicyclooctenone (56%), imidazole (23%), pyridine (10%) and benzene (9%) fragments were formed abundantly due to plasma treatment. Plasma-treated BPA was not toxic to aquatic fern, Lemna minor as revealed in relative growth rate (RGRarea) analysis. SPP causes release of free radicals, which are actively involved in BPA degradation without any additive chemicals. The approach in this study could be projected as an effective SPP-based clean-technology for degradation of toxicants in the aquatic ecosystems and also for effective wastewater treatment.

Production of reducing sugar from cassava starch waste (CSW) using solution plasma process (SPP)

The cassava starch processing plays an important role in food industries. During starch processing stage, a large amount of cassava starch waste (CSW) which mainly contains lost starch product and solid residue such as cassava bagasse are produced. Starch and cassava bagasse can be hydrolyzed into fermentable sugar such as glucose. In the present study, the solution plasma process (SPP) is used to treat CSW to prepare reducing sugar. The investigated parameters are treatment time, solvent concentration, applied pulsed frequency, and CSW concentration. The %yield of total reducing sugar (TRS) and glucose were calculated by DNS method and glucose assay kit, respectively. The chemical structure, morphology, and crystal structure of plasma-treated CSW were investigated. The results showed that the %yield of TRS was greatly enhanced by SPP treatment compared to that of acid hydrolysis. The CSW powder completely broke down into pieces after SPP treatment was applied. The amorphous and crystalline regions of CSW were destroyed during SPP treatment. SPP treatment of CSW with light sulfuric acid concentration of 0.08 M, applied pulsed frequency of 30 kHz, and CSW concentration of 0.5%w/v provided 99.0% TRS and 47.9% glucose.

Effect of Electrolyte Concentration during Solution Plasma on Copper Nanoparticle Size

This research was conducted to investigate the effect of electrolyte concentration of solution plasma on copper nanoparticles size. Copper nanoparticles with the size between 1-100 nm have received a huge interest because of their optical, catalytic and electrical conducting properties. Electrolysis via solution plasma method has many advantages such as its cost effectiveness, simplicity, eco-friendliness, and less energy requirements compared to other methods. To synthesize copper nanoparticles via solution plasma, two wires of copper and platinum as cathode and anode respectively were immersed in a glass beaker of 300 ml of two electrolyte solution (K2CO3 and NaOH) with three different concentrations (0.1 M, 0.5M and 1M), and electrical current was applied similar to an electrolysis process. The images of the nanoparticles were obtained using scanning electron microscopy and their sizes were analyzed using ImageJ software. It was found that when the concentration of K2CO3 increased, the size of copper nanoparticle also increased. However, the size of copper nanoparticles decreased when the concentration of NaOH was increased. This research shows the potential of easily controlling size of copper nanoparticles by changing the electrolyte concentration used during solution plasma process.

Effect of solution plasma process with hydrogen peroxide on the degradation of water-soluble polysaccharide from Auricularia auricula. II: Solution conformation and antioxidant activities in vitro

Synergistic degradation of water-soluble Auricularia auricula polysaccharide (AAP) by solution plasma process (SPP) in the presence of hydrogen peroxide (H2O2) was investigated. The effects of H2O2 concentration, AAP concentration and the distance between the electrodes on the degradation of AAP were evaluated. The results showed that higher H2O2 concentration, lower AAP concentration and narrower distance between the electrodes were favorable for the degradation effect. Particle size, congo red (CR), scanning electron micrographs (SEM) and atomic force microscopy (AFM) results confirmed that SPP irradiation with H2O2 improved significantly the flexibility of the conformation. The degraded AAPs exhibited greater metal chelating effects and DPPH radical scavenging effect than the original AAP. It concluded that the combined SPP/ H2O2 method could be used for preparation of low-molecular-weight AAP.

Solution plasma mediated formation of low molecular weight chitosan and its application as a biomaterial

Low molecular weight (LMW) chitosan has been a great attention in bio-molecular chemistry, medicine, and drug delivery system in particular. Depolymerization of high molecular weight (HMW) chitosan to LMW chitosan was achieved by solution plasma process (SPP) without affecting its chemical structures. Chitosan in solution was depolymerized by discharging plasma at 800 V with 35 kHz for various times (15–120 min). Gel permeation chromatography analysis revealed that molecular weight of chitosan decreased from 3.0 × 105 Da to 7.8 × 103 Da in 30 min plasma treatment, and further to 4.6 × 103 Da in 90 min. Dynamic light scattering and zeta potential studies confirmed formation of chitosan nano-aggregates. Interestingly, the LMW chitosan samples showed antimicrobial activity against Escherichia coli, Staphylococcus aureus, and Candida albicans with minimal inhibitory concentration of 80–1200 μg·mL−1. They also exhibited an excellent antioxidant activity (58–75%) and swelling ratio of 0.2–2.0 mg·mg−1. LMW chitosan was likely to have potential for sustainable usage as carrier molecules, biomaterials, and biomedical applications.

A novel effective approach of nanocrystalline cellulose production: oxidation–hydrolysis strategy

In this work, we have applied, for the first time, solution plasma processing of cellulose-containing material to produce cellulose nanocrystals (CNC). The CNC samples produced in three different modes of solution plasma treatment were characterized using methods of dynamic light scattering, infrared spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The proposed method of CNC production comprising the oxidation–hydrolysis strategy has proved to be effective and allowed us to reduce significantly the time of acid hydrolysis and to increase considerably the total CNC yield.

Effect of solution plasma process with hydrogen peroxide on the degradation and antioxidant activity of polysaccharide from Auricularia auricula

Solution plasma process (SPP) in combination with hydrogen peroxide (H2O2) were adopted to the degradation of Auricularia auricula polysaccharide (AAP). The results showed that SPP irradiation with H2O2 was effective for the AAP degradation. The intrinsic viscosity ([η]) of AAP solution decreased exponentially with increase in irradiation time. The degradation reaction closely fitted to the first order kinetics. The degradation rate constant after SPP irradiation with H2O2 was approximately 4.2 times that with SPP irradiation alone. GPC analysis showed that the molecular weight distribution of AAP was narrowed during degradation. FTIR and 13C NMR analysis revealed that primary structure of APP was not changed by the combination method. In vitro antioxidant activity of the polysaccharides was evaluated by determining their reducing power and radical (ABTS radical and superoxide radical) scavenging abilities. It was found that the degraded AAP possessed the higher antioxidant activity. The results suggested that SPP with H2O2 was an effective means for AAP degradation.

Narrowing band gap energy of defective black TiO2 fabricated by solution plasma process and its photocatalytic activity on glycerol transformation

Defective black titania (TiO2) was synthesized by the solution plasma technique at ambient temperature and pressure. The effects of the electrolyte solution medium type (KCl and HNO3) and concentration (0.3 and 3.0 mM) as well as the plasma discharge time (1–4 h) with a Ti electrode were investigated. The 3.0 mM HNO3 solution provided the highest energy per second discharging into the plasma, resulting in both a high synthesis rate of black TiO2 and a high degree of defective structures, as monitored in terms of the Ti3+/Ti4+ ratio, which can shorten the band gap energy (Eg) of the obtained black TiO2. A long plasma discharge time (4 h) induced the formation of large particles of black TiO2, which appeared as a highly defective structure. Overall, the black TiO2 prepared by discharged plasma for 4 h in 3.0 mM HNO3 solution (BTN-304) provided the highest photocatalytic activity for glycerol conversion (58.49% at 24 h) and 4.85, 3.32, 2.11, 2.15, 39.15 and 26.61% yield of glyceraldehyde, dihydroxyacetone, hydroxypyruvic acid, glycolic acid, glycolaldehyde and formaldehyde, respectively. Pathway of glycerol conversion and product distribution over black TiO2 was attempted to propose. Finally, the reusability of the best black TiO2 was explored.

Synthesis of Hierarchical Micro/Mesoporous Carbon Foams by a Solution Plasma Process and NaOH Activation for Use in Supercapacitors

Synthesis of Hierarchical Micro/Mesoporous Carbon Foams by a Solution Plasma Process and NaOH Activation for Use in Supercapacitors

One-pot synthesis of purple benzene-derived MnO2-carbon hybrids and synergistic enhancement for the removal of cationic dyes

MnO2-carbon hybrid (MnO2-C-PBz) was simultaneously synthesized by a one-step solution plasma process (SPP) using a single precursor referred to as “purple benzene”, which was derived from the K+(dicyclohexano-18-crown-6 ether) complex. To clarify the synergistic effects on the cationic dye removal, MnO2-free carbon and carbon-free MnO2 samples were concurrently investigated. The results of adsorption for cationic dyes (methylene blue (MB) and rhodamine B (Rh B)) and anionic dye (methyl orange (MO)) revealed remarkably high affinity for cationic dyes. In particular, MnO2-C-PBz exhibited the highest adsorption capacity for MB, i.e., ~3 times greater than that of the others. In addition, MnO2-C-PBz exhibited a rapid, high decolorization ability at C0 = 10 mg L−1 (within a few seconds, ~99%) and at C0 = 100 mg L−1 (within 30 min, ~81%), and the theoretical maximum monolayer adsorption capacity was 357.14 mg g−1 as calculated from the Langmuir adsorption isotherm equation. Furthermore, compared with carbon-free MnO2, MnO2-C-PBz exhibited quite a good cyclic stability. We expect that our findings give rise to the understanding of the synergistic effects of MnO2-carbon hybrid, as well as role of each components for the cationic dye adsorption, and may open an innovative synthesis approach to inorganic-organic hybrid materials.

Synthesis of Pt nanoparticles as catalysts of oxygen reduction with microbubble-assisted low-voltage and low-frequency solution plasma processing

In the preparation of metallic nanoparticles by conventional solution plasma (SP) techniques, unstable plasma emission becomes an issue when the voltage and frequency of the waves applied between two electrodes placed in solution are lowered to avoid the boiling of the solution. In this study, we confirm that, in the presence of microbubbles, plasma is generated stably at low voltage (440 V) and low frequency (50–100 Hz) and small-size (≤10 nm) Pt nanoparticles (PtNPs) are synthesized in succession using a flow cell. The smallest PtNPs, ∼3.3 nm in diameter, are obtained using half-wave rectification, a tungsten wire anode, and a platinum wire cathode. The PtNPs are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimeter-differential thermal analysis. The oxygen reduction reaction (ORR) is investigated in 0.1 M HClO4 solution on carbon-supported PtNPs using a rotating ring-disk electrode. The catalytic activities per initial electrochemical active surface area of the carbon-supported PtNPs synthesized employing the low-voltage, low-frequency (LVLF)–SP technique is higher than that of the commercially available 20 wt% Pt on Vulcan XC-72R. These results indicate that the LVLF-SP technique is a promising approach to producing carbon-supported PtNPs that catalyze ORR with low energy consumption.

Antioxidant potentials of nanoceria synthesized by solution plasma process and its biocompatibility study

Nanoceria were synthesized by discharging plasma at 800 V with a frequency of 30 kHz for 0–25 min using a pulsed unipolar power supply into solutions containing 1 or 2 mM of Ce(NO3)2. UV–Vis spectroscopy showed a characteristic absorbance maxima at 304–320 nm for the nanoceria with increase in the intensity of the peaks as the concentration of Ce(NO3)2 increased. The peaks exhibited transition red shift due to nanoceria formation. High resolution transmission electron microscopy revealed that spherical nanoparticles with an average size of 7.0 ± 0.2 nm were formed by discharging plasma for 15 min. The nanoceria showed excellent pH dependent antioxidant properties in hydroxyl and superoxide anion radical scavenging assays. Effect of the nanoceria on cell viability in vitro and inhibition of reactive oxygen species (ROS) by the nanoceria were examined using HeLa cell lines. As the results, no toxic effect was found up to 1600 μg mL−1 of nanoceria and they had an effective antioxidant property. Therefore, the nanoceria synthesized by one-step solution plasma process without employing hazardous chemicals have potential for utilization as antioxidant biomaterials and sustained release in the stream to scavenge ROS in the modern medicine.

Solution Plasma Process-Derived Defect-Induced Heterophase Anatase/Brookite TiO2 Nanocrystals for Enhanced Gaseous Photocatalytic Performance.

We report a simple room-temperature synthesis route for increasing the reactivity of a TiO2 photocatalyst using a solution plasma process (SPP). Hydrogen radicals generated from the SPP chamber interact with the TiO2 photocatalyst feedstock, transforming its crystalline phase and introducing oxygen vacancy defects. In this work, we examined a pure anatase TiO2 as a model feedstock because of its photocatalytic attributes and well-characterized properties. After the SPP treatment, the pure anatase crystalline phase was transformed to an anatase/brookite heterocrystalline phase with oxygen vacancies. Furthermore, the SPP treatment promoted the absorption of both UV and visible light by TiO2. As a result, TiO2 treated by the SPP for 3 h showed a high gaseous photocatalytic performance (91.1%) for acetaldehyde degradation to CO2 compared with the activity of untreated TiO2 (51%). The SPP-treated TiO2 was also more active than nitrogen-doped TiO2 driven by visible light (66%). The overall photocatalytic performance was related to the SPP treatment time. The SPP technique could be used to enhance the activity of readily available feedstocks with a short processing time. These results demonstrate the potential of this method for modifying narrow-band gap metal oxides, metal sulfides, and polymer composite-based catalyst materials. The modifications of these materials are not limited to photocatalysts and could be used in a wide range of energy and environment-based applications.

Comparative study of nanocarbons synthesized between electrodes in liquid phase by solution plasma

For several decades, the development of synthesis processes and designs for carbon materials such as graphites, carbon nanotubes, and graphenes has been continuous because of their superior physicochemical properties. The liquid-phase electric discharge process, known as the solution plasma process (SPP), has emerged as a potential synthesis process for carbon materials; however, liquid discharge in organic solutions has not yet been thoroughly investigated. In this study, plasma discharges in benzene (C6H6) and pyridine (C5H5N) were conducted. During the discharge, two types of nanocarbons with different crystallinities were synthesized simultaneously in different reaction fields: between electrodes and in a liquid phase. The nanocarbons grown between electrodes were collected and then compared with the nanocarbons produced in the liquid phase after discharge. All carbon samples were measured using various techniques such as transmission electron microscopy (TEM), the nitrogen absorption–desorption method, X-ray diffraction (XRD), Raman spectroscopy, CHN elemental analysis, and X-ray photoelectron spectroscopy (XPS). Nanocarbons grown between electrodes in benzene or pyridine were found to be graphite structures, while the nanocarbons produced in the liquid phase were amorphous carbons. On the basis of the results obtained, the formation and growth of the two types of nanocarbon materials synthesized by SPP and their dependence on the position of the reaction field in plasma in the liquid phase are discussed.

Synthesis of silicon–carbon black composite as anode material for lithium ion battery

Silicon has been attracting attention as an anode material that can be used for the design of high-capacity lithium ion batteries (LIB). However, the long-term cycling performance of silicon is limited owing to exfoliation from the current collector, resulting from volumetric expansion upon alloying with lithium in the charging process. However, carbon black is an agglomerate of primary particles that form a network and can incorporate a sufficient void space between network structures to accommodate the volumetric expansion of silicon. In this study, we propose the possibility of preventing the volume expansion and exfoliation of silicon by capturing silicon nanoparticles in the void space of the carbon black network. A silicon–carbon black composite material with this structure was successfully synthesized by solution plasma processing.

Simple introduction of carboxyl head group with alkyl spacer onto multiwalled carbon nanotubes by solution plasma process

A simple method of fabricating carboxyl-terminated multiwalled carbon nanotubes (MWCNTs) with alkyl spacers was developed to improve the dispersion quality of MWCNTs in aqueous solutions using solution plasma (SP) in a 6-aminocaproic acid solution. The formation of SP in the solution led to better dispersion of MWCNTs in aqueous solutions. Fourier transform infrared spectroscopy (FT-IR) results indicate that a carboxyl group with an alkyl spacer can be introduced by SP treatment in the 6-aminocaproic acid solution. Sedimentation tests show that the SP-treated MWCNTs in the 6-aminocaproic acid solution retained their good dispersion quality in aqueous solutions of pHs 5, 6, and 9. The alkyl spacer plays an important role in the preservation of dispersion states particularly at pH 6.

Preparation of Au nano-particle dispersed water solution without surfactant for surface-enhanced Raman scattering platform

ABSTRACTGold nano-particle (AuNP) dispersed water solution was prepared directly from high-purity Au electrodes in hydrogen peroxide (H2O2) water solution by solution plasma (SP) processing. With 5 min SP treatment, about 0.01 wt% of AuNP dispersed water solution of about 50 mL was obtained. The average diameter of AuNP was estimated to be about 14 nm from transmission electron micrograph images. AuNPs kept dispersed state in water solution for 4 weeks without addition of any surfactant. The zeta potential of AuNP resulted in between −36 and −51 mV, and it was suggested the strong negative charge on the AuNP surface prevented AuNPs from binding each other. Vaporization of water by heating brought us the concentration increase of the AuNP dispersed water solution to be about 1 wt%, and this allowed us to make easily Au thin films as a plat form of surface-enhanced Raman scattering.

Facile preparation of defective black TiO2 through the solution plasma process: Effect of parametric changes for plasma discharge on its structural and optical properties

Defective TiO2 or black TiO2 nanoparticles (NPs) are remarkably attractive for photocatalytic applications, since the defect-disordered structure crucially affects the optical properties. In this work, high visible light-active black TiO2 NPs were synthesized by an innovative solution plasma process (SPP) with a titanium (Ti) electrode in HNO3 solution. The effects of the plasma operating parameters, in terms of the pulse frequency (20–80 kHz) and pulse width (0.5–2.0 μs) under two different HNO3 concentrations (0.3 mM and 3.0 mM) on the morphology, structural and optical properties of the obtained black TiO2 NPs were explored. Increasing the pulse frequency, pulse width and concentration of HNO3 all increased the input energy per pulse and energy per second, which induced an increased volume-based particle size, synthesis rate and Ti3+/Ti4+ ratio, but decreased the rutile mass fraction, the Ti-OH/TiO ratio and the band gap energy of the obtained black TiO2 NPs. Among all the prepared black TiO2 NP samples, those prepared at a pulse frequency of 20 kHz, pulse width of 2 μs (energy input per second of 17.3 J) in 3.0 mM HNO3 exhibited the highest visible-light absorption capability (the lowest band gap energy of ∼2.44 eV). The variation in the band gap energy was more strongly dependent on the Ti3+/Ti4+ ratio than the Ti-OH/TiO ratio in the structure of black TiO2 NPs.

Synthesis of Carbon Nanoparticles from Used Motor Oil and Benzene via Solution Plasma Process

Carbon nanoparticles (CNPs) were successfully synthesized from the mixture of used motor oil and benzene via a solution plasma process (SPP). The synthesis was achieved within a single step at room temperature and atmospheric pressure. The effects of mixing ratio between used motor oil and benzene on the physical and chemical properties of CNPs were investigated by means of field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy. The results revealed that there were no significant changes in morphological feature and chemical functional groups on CNPs at different mixing ratios. The CNPs exhibited the aggregates of fine particles with the diameter of about 20–30 nm. The crystallinity of CNPs was found to be slightly increase when synthesized under the presence of used motor oil, possibly due to the effect of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in used motor oil. We expect that the conversion of used motor oil into CNPs by SPP could be another attractive way to add the value to used motor oil prior to disposing.