Modeling of H2 and H2/CH4 Moderate-Pressure Microwave Plasma Used for Diamond Deposition

One-dimensional transport models of moderate-pressure H ₂ and H ₂ /CH ₄ plasmas obtained in a diamond deposition microwave reactor are presented. These models describe the plasma as a thermochemically nonequilibrium flow with three different energy modes. The solution of the one-dimensional plasma transport equations enabled the estimation of plasma species concentrations and temperatures on the axis of the reactor. As far as pure H ₂ plasmas are concerned, results showed that the model predictions of gas and vibration temperatures are in good agreement with experimental measurements. The model also yields a relatively good qualitative prediction of the variations of H-atom mole fraction with the power density absorbed by the plasma. The results obtained for H ₂ /CH ₄ discharges showed that the model prediction on the variations of H-atom mole fraction with methane percentage in the discharge is in good qualitative agreement with experimental results. They also showed that methane is rapidly converted to acetylene before reaching the discharge zone. The concentrations of neutral hydrocarbon species in the reactor are mainly governed by thermal chemistry. The addition of methane strongly affects the ionization kinetics of the plasma. Three major ions are generally obtained in H ₂ /CH ₄ plasmas: C ₂ H ₂ ⁺ , C ₂ H ₃ ⁺ , and C ₂ H ₅ ⁺ . The relative predominance of these ions depends on the considered plasma region and on the discharge conditions. The ionic species concentrations are also mainly governed by chemistry, except very near the substrate surface. Finally the use of this transport model along with the surface chemistry model of Goodwin ⁽¹⁾ enabled us to estimate the diamond growth rate for several discharge conditions.     

Zinc-catalyzed Williamson ether synthesis in the absence of base

Zinc powder was found to be a highly efficient catalyst for the synthesis of aromatic ethers using microwave heating in the presence of N,N-dimethylformamide as well as under stirring in an oil-bath using tetrahydrofuran as solvent without any inorganic base. This method can be used for selective mono-, di- or tri-O-alkylations.     

Immunochemical determination of dioxins in sediment and serum samples

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are considered highly toxic contaminants and the environmental and biological monitoring of these compounds is of great concern. Immunoassays may be used as screening methods to satisfy the growing demand for rapid and low cost analysis. In this work, we describe the application of an immunoassay that uses 2,3,7-trichloro-8-methyldibenzo-p-dioxin (TMDD) as a surrogate standard for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to sediment and human serum samples. Sample extraction and preparation methods were developed with the aim to establish the simplest, cost-effective and efficient removal of the matrix interferences in the enzyme-linked immunosorbent assay (ELISA). The overall method for sediments is based on a hexane extraction; clean up by a multilayered silica gel column and an activated carbon column; an organic solvent exchange with DMSO–Triton X-100 and ELISA measurement. The gas chromatography–high resolution mass spectrometry (GC–HRMS) validation studies (n = 13) revealed that the method is suitable for the toxic equivalents (TEQ) screening of dioxin in sediments with a method detection limit of about 100 pg g⁻¹ dry sediment with a precision of 13–33% R.S.D. The analysis of a large number of samples originating from different sources would be required to establish more precisely the screening level, as well as the number of false positives and negatives of dioxin TEQ by the immunoassay for sediments. The immunoassay method for sediment analysis offers improvement in speed, sample throughput, and cost in comparison to GC–HRMS. Dioxins were determined in serum samples after a simple liquid–liquid extraction and solvent exchange into DMSO–Triton X-100 without further dilution. The current method (approximate method LOQ of 200 pg ml⁻¹ serum) is not sufficiently sensitive for the determination of dioxins in serum to measure acceptable exposure limit.     

Microwave-promoted cross-coupling of acid chlorides with arylboronic acids: a convenient method for preparing aromatic ketones

Simple catalytic systems for cross-coupling reactions of acyl chlorides with arylboronic acids under microwave conditions were tested. Microwave irradiation facilitated the reaction course. Mild reaction conditions afford the symmetrical and unsymmetrical aryl ketones in reasonable to high yields within a short time. A wide range of substrates bearing an electron-donating or an electron-withdrawing substituent on aryl ring of acid chloride as well as on boronic acid were examined and high yields of ketones were produced.     

SPE – Microwave‐assisted extraction coupled system for the extraction of pesticides from water samples

SPE is a commonly applied technique for preconcentration of pesticides from water samples. Microwave‐assisted extraction (MAE) technique is the extraction applied for preconcentration of different compounds from solid samples. SPE coupled with MAE is capable of preconcentrating these compounds from water samples too. This investigation was aimed at improving the efficiency of atrazine, alachlor, and α‐cypermethrin pesticide extraction from the spiked water samples applying SPE followed by MAE. In this way, MAE served for elution of pesticides from C₁₈‐extraction disks with solvent heated by microwave energy. Various elution conditions were tested for their effects on the extraction efficiency of the SPE–MAE combined technique. Several parameters, such as elution solvent volume (mL), elution temperature (°C), and duration of elution (min), affect the extraction efficiency of the SPE–MAE coupled system and need to be optimized for the selected pesticides. In order to develop a mathematical model, 15 experiments were performed in the central composite design. The equation was then used to predict recoveries of the pesticides under specific experimental conditions. Optimization of microwave extraction was accomplished using the genetic algorithm approach. Best results were achieved using 20 mL of ethanol at 60°C. Optimal hold time was 5 min and 24 s. The SPE–MAE combination was also compared with the conventional SPE extraction technique with elution of a nonpolar or a moderately polar compound with nonpolar solvents.     

Monodisperse thermosensitive particles prepared by emulsifier-free emulsion polymerization with microwave irradiation

The emulsifier-free emulsion polymerization of styrene (St) and N-isopropylacrylamide (NIPAAm) was successfully carried out with microwave irradiation, and the monodisperse thermoresponsive poly(styrene-co-N-isopropylacrylamide) (poly(St-co-NIPAAm)) particles with diameters in the range 100–130 nm were prepared. The morphology, size and size distribution of the poly(St-co-NIPAAm) particles were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and photon correlation spectroscopy (PCS), respectively. The results showed that poly(St-co-NIPAAm) particles had spherical morphology, and the poly(St-co-NIPAAm) particles prepared by emulsifier-free emulsion polymerization with microwave irradiation were smaller, more uniform than those obtained with conventional heating. The hydrodynamic diameters of poly(St-co-NIPAAm) particles were decreased as the temperature increased from 25 °C to 40 °C, and poly(St-co-NIPAAm) particles collapsed remarkably at 32 °C, which is the lower critical solution temperature of the poly(N-isopropylacrylamide). The morphology of the assembled poly(St-co–NIPAAm) particles was observed by SEM, it was found that monodisperse poly(St-co-NIPAAm) particles could assemble to form the two-dimensional order structures.     

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene

has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r_g(S---C₂) = 1.719(2) Å, r_g(C₂=C₃) = 1.370(3) Å, r_g(C₃---C₆) = 1.497(6) Å, r_g(C₂---H) = 1.101(5) Å, CSC = 91.6(2)°, SC₂C₃ = 113.3(5)°, SC₅C₄ = 111.3(3)°, C₂C₃C₆ = 123.2(11)° and C₃C₆H = 112(2)°. The values of r(S---C₂) − r(S---C₅) and r(C₂=C₃) − r(C₄=C₅) were fixed at the 3–21G* value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.     

Molecular structure of 3-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

The molecular structure of 3-methylthiophene has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: r_{g(S---C2) = 1.719(2) Å}, r_{g(C2=C3) = 1.370(3) Å}, r_{g(C3---C6) = 1.497(6) Å}, r_{g(C2---H) = 1.101(5) Å}, CSC = 91.6(2)°, SC₂C₃ = 113.3(5)°, SC₅C₄ = 111.3(3)°, C₂C₃C₆ = 123.2(11)° and C₃C₆H = 112(2)°. The values of r(S---C₂) - r(S=C₅) and r(C₂=C₃)-r(C₄ =C₅) were fixed at the 3–21G* value of 0.002 Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit.     

微波等离子体炬发射光谱法去溶系统性能的研究

用微波等离子体矩（MPT）作激发光源，等离子体的工作气体为氩气，研究了气动雾化进样去溶系统的工作参数对分析性能的影响，探讨了水冷凝与浓硫酸吸收二者协同去溶的相关性，结果表明，OH （Q1带，带头谱线为308.520nm）的发射强度即可判别样品去溶效果。