Microwave-induced Plasma Research Articles

Multielemental determination in lubricating oil samples by microwave-induced plasma optical emission spectrometry after extraction induced by emulsion breaking

Extraction induced by emulsion breaking (EIEB) was studied as a strategy for the determination of Al, Cr, Cu, Fe, Mg, Mn, Mo, Ni, and Pb in used lubricating oil via microwave-induced plasma optical emission spectrometry (MIP OES). No spectral or nonspectral interferences were observed in the developed method. These were evaluated as a function of the emission intensity of natural molecular species in the N2 plasma and different atomic and ionic emission lines. The time required for extraction was evaluated, and the best sensitivity for all the elements was obtained at 40 min of contact between the sample and the extraction solution in the presence of the surfactant. Doehlert matrix response surface methodology was employed to study the effects and interactions between the nitric acid (extractor) and surfactant (emulsifier) concentrations during sample preparation. The recommended conditions for 3.0 g of sample were as follows: 5.0 mL of extraction mixture consisting of 2.8 mol/L nitric acid and 3.0 % (v v−1) of the surfactant Triton X-114. The limits of quantification obtained were 2.9 (Al), 43 (Cr), 4.0 (Cu), 17 (Fe), 4.0 (Mg), 3.7 (Mn), 7.0 (Mo), 9.2 (Ni) and 45 (Pb) µg kg−1. The method developed was applied in the analyses of lubricating oil samples. The following concentration ranges (mg kg−1) were found: 2.5–106 (Al), 2.8–24.8 (Cr), 3.5–21.4 (Cu), 16.9–199 (Fe), 33.4–64.0 (Mg), 0.57–9.7 (Mn), 4.7–43 (Mo), 1.6–11.1 (Ni) and 2.0–12.6 (Pb).

Multi-energy calibration and induced plasma optical emission spectrometry (MEC-MIP OES) as an alternative method for the multi-elemental determination of essential elements in cocoa.

The challenge of combining MEC-MIP OES arises from the limited number of emission lines available in this analytical technique. For the MEC-MIP OES optimization, the emission line wavelengths, sample dilution, proportion sample:standard for preparing MEC solutions, and nebulizer gas flow rate were studied. Then, the use of multi-energy calibration (MEC) and microwave-induced plasma optical emission spectrometry (MIP OES) was proposed as an alternative method for the determination of essential elements (Ca, K, Mg, Mn, and Na) in cocoa. In the optimized conditions, the method presented adequate analytical performance, with recoveries of 94-104% and relative standard deviations lower than 5%, showing adequate precision. The limits of detection (mg kg-1) were 12 for Ca, 2 for K, 3 for Mg, 3 for Mn, and 6 for Na. The proposed method was applied to analyze cocoa samples cultivated in Brazil and Ecuador after acid decomposition. The results were in the range (mg kg-1) of 409-1530 for Ca, 5520-13300 for K, 1460-3210 for Mg, 16-34 for Mn, and 28-61 for Na. Samples cultivated in Ecuador presented higher metal concentrations than the Brazilian samples. The proposed procedure was an easy and reliable approach for determining metals in cocoa samples, enabling multi-elemental determination with a lower cost and simplified calibration to be applied in routine applications.

Optical Analysis of Dry Reforming of Methane in Microwave-Induced Plasma at Atmospheric Pressure

Optical Analysis of Dry Reforming of Methane in Microwave-Induced Plasma at Atmospheric Pressure

Microwave-induced plasma optical emission spectrometry (MIP-OES) analysis of the major elements in woody biomass ash following microwave acid digestion

The increasing use of woody biomass for sustainable heat and power is generating large amounts of woody biomass ash (WBA), which needs to be safely disposed of or recycled. In this study, the utility of Microwave-induced plasma optical emission spectrometry (MIP-OES) with microwave-assisted acid digestion for simplifying analyses of the major elements of WBA was investigated. Calibration curves exhibited good linearity (R2 > 0.999). Internal standardization using three emissions lines (324.754 nm of Cu, 451.131 nm of In and 371.029 nm of Y) showed that calibration with Cu (324.754 nm) correction resulted in the best linearity. Physical effects, even the presence of hydrofluoric acid or boric acid in mixed acids used for digestion, were of trivial influence with internal standard recoveries were within 0.95 to 1.05 times those of the blank sample. The limit of detection of MIP-OES for seven measured elements was 0.85–89 μg/L, 0.23–2.8 times higher than that of inductively coupled plasma optical emission spectrometry (ICP-OES). The recovery of elements in a certified fly ash reference material as determined by MIP-OES was 0.80–1.08. Elemental quantification of WBA samples by MIP-OES showed a strong correlation with that by ICP-OES. However, in a Welch's t-test, the MIP-OES values were significantly higher for K and significantly lower for Al and Ca in a majority of the samples. Nonetheless, considering the good correlation between their results, MIP-OES can replace ICP-OES for the analysis of WBA.

Microwave-induced plasma on spherical flame dynamics of spark-ignited hydrogen-air under water dilution

Microwave-assisted spark ignition (MAI) offers a commercially feasible way to enhance conventional spark ignition performance under extreme conditions. While previous studies suggested microwave pulses had no obvious effect on self-sustained flame from the perspective of energy deposition, the hydrodynamic effect of microwave plasma remained under-explored. This study experimentally investigated the effect of the microwave-induced plasma on lean hydrogen flame dynamics (Lewis number ∼ 0.35), examining the influence of water content (rH2O) in this process under different pulse repetition frequency (PRF) and pressures. Using a linear high-speed shadow imaging system coupled with electrical diagnostics, we synchronously recorded the flame and plasma morphology evolution while monitoring spark and microwave energy. Results revealed that microwave pulses during spark ignition generated wrinkles and perturbances accelerating the cracking and cellularization of the subsequent self-sustained flame. This effect intensified with increasing PRF from 1 to 10 kHz, particularly at high rH2O. The overall microwave impact on early flame development was more pronounced at high rH2O, attributed to stronger interactions between the microwave plasma jet and flame front due to reduced distance. Interestingly, electrical diagnostics showed an inversed relationship between total absorbed microwave energy and rH2O, highlighting the crucial role of the first microwave pulse at 1 kHz PRF. This study demonstrates that early microwave pulses can influence hydrogen flame dynamics even in the self-sustained stage, offering new insights into MAI mechanisms. These findings open avenues for research into active control of self-sustained flame dynamics, potentially leading to improved ignition strategies in challenging combustion environments.

Increasing the production of high-quality graphene nanosheet powder: The impact of electromagnetic shielding of the reaction chamber on the TIAGO torch plasma approach

Microwave-induced plasmas (MIPs), and specifically the TIAGO device (Torche à Injection Axiale sur Guide d’Ondes), offer a streamlined, cost-effective, and environmentally friendly technique for producing high-quality graphene powder in a reaction chamber by a single-step process through ethanol decomposition. To optimize graphene synthesis process, a pivotal move involves minimizing energy dissipation through radiation to maximize the available microwave energy input. Including a metallic shielding around the reaction chamber, essentially creating a Faraday cage, is proposed. The shielding strategy prevents radiation losses and results in a remarkable increase in solid material formation up to 22.8 %. This value, along with the emitted gases proportions and plasma volume increase, shows a correlation with conditions associated with higher input power. Crucially, the shielding of the reaction chamber does not modify graphene growth kinetics in the plasma, as confirmed by Optical Emission Spectroscopy. The synthesized material undergoes a thorough examination, employing diverse techniques like Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller (BET) analysis. These analyses underscore a consistent quality of graphene, unaffected by the shielding implementation. Therefore, electromagnetic shielding of the TIAGO torch discharge not only leads to a remarkable increase in solid material formation, thus energy yield, but does so without compromising the intrinsic properties and quality of the synthesized graphene.

Determination of toxicological relevant arsenic species in urine by hydride generation microwave-induced plasma optical emission spectrometry

An analytical method for the determination of toxicological relevant species of arsenic in urine was developed and validated using hydride generation microwave-induced emission spectrometry (HG-MP-AES). This strategy can be used as an alternative to HG-HPLC-ICP-MS considered as a reference technique for arsenic speciation. This procedure is notably less expensive than other techniques and sample preparation and requires only a few steps.•Hydride generation with MP-AES detection has proven to be an effective technique for measuring arsenic metabolites in urine, which is relevant for occupational monitoring and health risk assessment purposes.•This method offers simplicity and cost-effectiveness, serving as an alternative to classical analytical procedures typically used for arsenic analysis in urine.•The methodology has been successfully applied for the purpose of workers' health surveillance.

Determination of Fe, Cu, and Pb in edible oils using choline chloride:ethylene glycol deep eutectic solvent-based dispersive liquid-liquid microextraction associated with microwave-induced plasma optical emission spectrometry

A new simple, fast and environmentally friendly deep eutectic solvent based dispersive liquid-liquid microextraction (DES-based DLLME) methodology assisted by vortex is presented for the separation and preconcentration of three elements (i.e., Fe, Cu and Pb) from edible oil samples (i.e., soybean, sunflower, rapeseed, sesame, and olive oil) prior to the determination by microwave-induced plasma optical emission spectrometry (MIP-OES). The deep eutectic solvent selected as extractant (i.e., choline chloride and ethylene glycol, 1:2) is synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR) and differential scanning calorimetry (DSC), and the extraction conditions are optimized by a two steps experimental design. Under the optimum extraction conditions (i.e., diluted sample weight: 8.6 g; DES volume: 100 μL; extraction time: 1 min; centrifugation time and speed: 3 min and 3000 rpm; and dispersion system: vortex) the analytical method presents excellent linearity (i.e., R2 values higher than 0.99) in the range 10–500 μg kg−1, repeatability (i.e., CV values lower than 9.2%), and limits of detection (LOD) values of 3, 2 and 0.7 μg kg−1 for Pb, Fe and Cu, respectively. None of the analytes displayed amounts over the upper limit permitted by law, and recovery values of all analytes evaluated in the different samples using external standard calibration were close to 100%, which excludes significant matrix effects. Finally, AGREEprep metric has been used to evaluate the method greenness (final score of 0.47) and it has been compared successfully with previous publications for the same type of analytes and matrices.

Do You Know What You Drink? Comparative Research on the Contents of Radioisotopes and Heavy Metals in Different Types of Tea from Various Parts of the World.

The aim of this study was to assess the potential health risks of radioactive elements and heavy metals ingested through the consumption of various types of tea imported to the Polish market (black, green, red, oolong and white). The concentrations [Bq/kg] of radionuclides (40K, 137Cs, 226Ra, 210Pb and 228Th) in tea leaves before and after brewing were measured using γ-ray spectrometry with high-purity germanium (HPGe). The concentrations [mg/kg] of the studied elements (Fe, Cr, Cu, Mo, Al, Mn, Ni, P, V, Cd and Pb) were determined using a microwave-induced plasma optical emission spectrometer (MIP-OES). The results presented here will help to expand the database of heavy metals and radioactivity in teas. With regard to the potential health risk, the percentage of leaching of individual elements in different types of tea infusions was determined, and the assessment of the consumption risk was estimated. Since the calculated exposure factors, namely the HQ (Hazard Quotient) and THQ (Target Hazard Quotient), do not exceed critical levels, teas can still be considered health-beneficial products (most of the radionuclides as well as elements remain in the leaves (65-80%) after brewing).

Elemental Analysis of Dietary Supplements by Microwave-Induced Plasma–Optical Emission Spectrometry (MIP-OES) With Ultrasound-Assisted Extraction (UAE)

The purpose of this study was to demonstrate the feasibility of determining metals (Cr, Mn, Zn, Fe, and Cu) in commercial dietary supplements using microwave-induced plasma optical emission spectrometry (MIP OES) after fast ultrasound-assisted extraction. Various parameters affecting the extraction process, such as the nature and concentration of the extractant solution, sonication time, and sample mass, were evaluated. Under the optimal conditions, it was possible to quantitatively extract metals from the samples by sonicating 1.0 g of the supplement dispersed throughout 25 mL of a 1.0 mol L−1 HNO3 for only 5 min. The developed method was applied to determine the analytes in four dietary supplements available in the Brazilian market. The results obtained with the extraction method were compared with the values obtained when the samples were completely mineralized with concentrated HNO3 in a microwave oven. There were no statistical differences between the developed and reference methods when the paired Student’s t-test was applied with a 95% confidence level. The application of ultrasound-assisted extraction was demonstrated to be advantageous compared to total sample digestion. This approach allowed the use of a higher mass of the sample, thereby enhancing the analytical capability of the method. Furthermore, employing less severe conditions, such as lower energy and a diluted acid solution, simplified and reduced the cost of the procedure compared to mineralization.

Mechanochemically Assisted Microwave-Induced Plasma Synthesis of a N-Doped Graphitic Porous Carbon-Based Aqueous Symmetric Supercapacitor with Ultrahigh Volumetric Capacitance and Energy Density

Mechanochemically Assisted Microwave-Induced Plasma Synthesis of a N-Doped Graphitic Porous Carbon-Based Aqueous Symmetric Supercapacitor with Ultrahigh Volumetric Capacitance and Energy Density

Low pressure closed system applied to sample preparation of instant soups for elemental determination by MIP OES

The increased consumption of ultra-processed foods has made the assessment of the presence of essential and/or potentially toxic elements more relevant. This work proposes the application and evaluation of a closed low pressure system for the acidic decomposition of instant soup samples and determination of Ba, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Pb and Zn by microwave-induced plasma optical emission spectrometry (MIP OES). The accuracy of the standard method was verified using certified reference materials and the values obtained were consistent with the certified values according to Student's t-test at 95% confidence. Addition and recovery tests were also performed, and the results varied from 86 to 119%. The concentrations varied of the 1.29 to 3.78 mg kg−1 for Ba; 414 to 6221 mg kg−1 for Ca; 0.40 to 1.13 mg kg−1 for Cr; < 0.006 to 4.16 mg kg−1 for Cu; 5.56 to 115 mg kg−1 for Fe; 48 to 444 mg kg−1 for K; 185 to 654 mg kg−1 for Mg; 0.11 to 8.39 mg kg−1 for Mn; 0.94 to 7.48 mg kg−1 for Pb and 3.01 to 42.7 mg kg−1 for Zn. For the Cd and Hg analytes, the concentration results were below their detection limits. The potentially toxic elements in this study showed concentrations below the established limit of daily intake, not offering risks to the consumer's health. As for the essential elements for the body, the concentrations were lower than those recommended for daily intake.

High conversion of H2S to H2 and S via a robust microwave-induced discharge plasma

Direct conversion of H2S could achieve the co-production of hydrogen and sulfur, avoiding hydrogen waste in the traditional Claus process. Herein, we propose a robust SiC-mediated microwave-induced discharge plasma, achieving H2S conversion of 98.8% to H2 and S with the inlet H2S of 2% (volume concentration) at 600 W. We realize efficient excitation and stable maintenance of microwave plasma in the multimode cavity via optimizing large SiC particles at the waveguide port. In addition, the introduction of tungsten sheets enhances discharge plasma. The H2S conversion of 52.8% was realized for the high inlet H2S concentration (30%) at 600 W. In-situ optical emission spectroscopy reveals that atomic S and H are the key reactive intermediates in the overall H2S decomposition. Direct electron-H2S collision coupling excited Ar atom-H2S collision contributes to H2S direct conversion. This work paves a path to hydrogen production toward sustainable energy applications from the direct conversion and utilization of H2S.

Fluorination of antimonene hexagons.

Fluorination of two-dimensional (2D) antimonene hexagons synthesized through a colloidal bottom-up approach has been explored using microwave-induced plasma and reactive ion etching fluorination strategies through the generation of CF4. The stability of the fluorine bond has been corroborated through DFT calculations. This work paves the way for further halogen-derivative modifications of heavy 2D pnictogens.

Evaluation of Total Concentrations and Bioaccessible Fractions of Essential and Toxic Elements in Amaranth, Quinoa and Chia by MIP OES

The total concentrations and the bioaccessible fractions of Al, B, Ba, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, V and Zn were evaluated in 10 samples of pseudocereals, being 3 of amaranth, 3 of quinoa and 4 of chia. The samples were decomposed in a digester block with a reflux system under conditions optimized and the analyses were performed by microwave-induced plasma optical emission spectrometry. In all grains investigated, the highest total concentrations were found for the macroelements K, Mg and Ca, as well as the microelements Fe, Mn, and Zn. When the bioaccessible fraction was evaluated, negative correlations were observed between the content of total phenolic compounds and the bioaccessibility for most elements, in all samples. Among the elements considered essential in our diet, K (99%) and Cu (59%) presented the highest percentages of bioaccessible fraction. Among those elements considered potentially toxic, Ba did not exceed 15% bioaccessible fraction and Al presented concentrations lower than the limit of detection in all samples.

Modified surfatron device to improve microwave-plasma-assisted generation of RONS and methylene blue degradation in water

Microwave-induced plasmas generated at atmospheric pressure are very attractive for a great variety of applications since they have a relatively high electron density and can generate large amounts of reactive species. Argon plasmas can be sustained inside dielectric tubes but are radially contracted and exhibit filamentation effects when the diameter of the tube is not narrow enough (over 1.5 mm). In this work, we describe a new approach for creating microwave (2.45 GHz) plasmas under atmospheric pressure conditions by using a surfatron device and power from 10 W. This modified design of the reactor enables the sustenance of non-filamented argon plasmas. These new plasmas have a higher gas temperature and electron density than the plasma generated in the original surfatron configuration. The new design also allows for the maintenance of plasmas with relatively high proportions of water, resulting in the generation of larger quantities of excited hydroxyl radicals (·OH*). Thus, this novel configuration extends the applicability of microwave-induced plasmas by enabling operation under new conditions. Finally, the degradation of methylene blue (MB) in aqueous solutions has been assessed under different initial dye concentrations and argon flow conditions. The new plasma produces a substantial increase in hydrogen peroxide and nitrate concentrations in water and leads to a noteworthy enhancement in MB degradation efficiency. The introduction of water into the plasma produces a minor additional improvement.

Experimental study on microwave-induced puffing, micro-explosion, and combustion characteristics of ammonium dinitramide-based liquid propellant droplets

Microwave ignition technology has the advantages of high ignition energy, stable ignition, and spatial multi-point ignition. These advantages make this technology promising for future application in green single-component propellants. In this paper, the ignition characteristics of ammonium dinitramide (ADN)-based liquid propellant droplets under the influence of microwaves at room temperature are investigated using experimental methods. The effects of microwave power on puffing, micro-explosion, and combustion behavior of ADN-based liquid propellant droplets were studied. The droplet and flame diameters were statistically related to time, and the microwave-assisted droplet ignition mechanism was analyzed. A new rectangular waveguide resonant cavity was designed in which the droplet is placed at the maximum electric field strength of the device. The droplet morphology and flame profile inside the resonant cavity were photographed with a high-speed camera. The experimental results showed that the microwave positively influenced the puffing, micro-explosion, and combustion behavior of droplets. When the microwave power was increased from 200 to 280 W, the total droplet evaporation time and ignition delay time were reduced by 56.5% and 35.2%, respectively. The positive effects of microwaves on combustion have been summarized as the thermal effect of microwaves on polar molecules and the promotion of fuel oxidation reactions by microwave-induced plasma. The plasma was found to control the development of the initial flame propagation front and to influence the temperature during the combustion reaction process. In this paper, we propose the mode of droplet combustion under microwave induction as a plasma discharge and several stages of the droplet combustion process. This research provides novel insight into the study of the microwave ignition mechanism of liquid fuels.

Should we think about green or white analytical chemistry? Case study: Accelerated sample preparation using an ultrasonic bath for the simultaneous determination of Mn and Fe in beef

Green Analytical Chemistry (GAC) metrics include a variety of criteria, such as the regent amounts and toxicity, energy consumption, generated waste, among others. The analytical greenness metric (AGREE) and its variant for sample preparation (AGREEprep) cover different aspects that contribute to the environmental sustainability of sample preparation. White Analytical Chemistry (WAC) considers not only environmental aspects but also analytical and practical aspects with a holistic vision based on a Red-Green-Blue color model.A case study is presented to assess the green and white profile of a method based on ultrasound-assisted extraction and determination of Mn and Fe in beef using microwave-induced plasma atomic emission spectroscopy (MP AES). The method was validated and resulted simple, fast without external heating using diluted acids.It was concluded that we should think in green sample preparation with the AGREEprep tool, as well as in white holistic assessments (WAC) as both constitute complementary tools.

Studying the Physicochemical Properties of Water Activated by Microwave-Induced Plasma Jet for Biological and Medical Applications

Studying the Physicochemical Properties of Water Activated by Microwave-Induced Plasma Jet for Biological and Medical Applications

Formation of structured silica layers from Dodecaphenyl POSS thin films via microwave-induced oxygen plasma treatment

The study investigated the effect of microwave-induced oxygen plasma on Dodecaphenyl-POSS (Ph12T12) thin films that were obtained by Physical Vapor Deposition (PVD) in an Ultra-High Vacuum (UHV) system. Due to its ability to self-assemble and its relatively low cost, Ph12T12 is a promising material as a precursor for the fabrication of silica thin films. The study found that the treatment of the Ph12T12 thin film with oxygen plasma results in the formation of a new material with a cage-like structure preserved. The thin films were examined using X-ray Reflectivity (XRR), Raman spectroscopy, and Atomic Force Microscopy (AFM). The results showed significant changes in the microstructure, chemical composition, and topography of the annealed POSS films. Thermal and plasma treatment improved the thermal resistance of the surface layer, increasing the evaporation temperature by over 80 °C. XRR modeling of the films' spectra enabled the determination of the composition of each interphase. Additionally, Bragg reflections (00l) remained visible on the spectra after annealing, indicating the presence of a preserved POSS cage-like structure.