Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces

CaBi₄Ti₄O₁₅ thin films were deposited by the polymeric precursor method and crystallized in a domestic microwave oven and conventional furnace. The films obtained for microwave energy are well-adhered, homogeneous and with good specularity when treated at 700 ^°C for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. When microwave oven is employed, the films presented bigger grains with mean grain size around 80 nm. For comparison, films were also prepared by the conventional furnace at 700 °C for 2 h.     

Recycling of poly(ethylene terephthalate) waste through methanolic pyrolysis in a microwave reactor

In this study, the methanolic pyrolysis (methanolysis) of poly(ethylene terephthalate) (PET) taken from waste soft-drink bottles, under microwave irradiation, is proposed as a recycling method with substantial energy saving. The reaction was carried out with methanol with and without the use of zinc acetate as catalyst in a sealed microwave reactor in which the pressure and temperature were controlled and recorded. Experiments under constant temperature or microwave power were carried out at several time intervals. The main product dimethyl-terephthalate was analyzed and identified by FTIR and DSC measurements. It was found that PET depolymerization, is favored by increasing temperature, time and microwave power. High degrees of depolymerization were measured at temperatures near 180 °C and at microwave power higher than 150 W. Most of the degradation was found to occur during the initial 5–10 min. Compared to conventional pyrolysis methods, microwave irradiation during methanolic pyrolysis of PET certainly results in shorter reaction times supporting thus the conclusion that this method is a very beneficial one for the recycling of PET wastes.     

Microwave-assisted photo-Fenton decomposition of chlorfenvinphos and cypermethrin in residual water

The coupling of microwave radiation with photo-Fenton reaction for wastewater treatment was evaluated. This strategy was performed in a focused microwave digestion oven with open vessels. Ultraviolet radiation was obtained from microwave lamps (MWL) activated by microwave radiation. The operational conditions were established considering the extent of degradation of chlorfenviphos and cypermethrin used for bovine ticks (Boophilus michoplus) control. The results were based on residual carbon content, always comparing the procedures in the presence or absence of UV radiation. The combination of MWL and Fenton reaction degraded pesticide residues efficiently (>98%) in about 4 min.     

Green extraction process of tannins obtained from Moroccan Acacia mollissima barks by microwave: Modeling and optimization of the process using the response surface methodology RSM

The effect of extraction conditions on polyphenols contents and condensed tannins by microwave-assisted extraction (MAE) was studied for the first time to our knowledge. Moroccan barks of Acacia mollissima was used to extract phenolic compounds. The variables studied are the following: power extraction, time extraction and solvent nature. Five powers extraction were tested: 150 W, 250 W, 300 W, 450 W and 600 W. A significant effect of power extraction on the extractable nature was proved by ANOVA and Student test. The yields were also affected by time extraction. Different solvent (water, ethanol, methanol and ethyl acetate) were tested to evaluate the best extraction solvent according to the extractable nature. Highest polyphenols contents were obtained with methanol. The proportion of this solvent, time extraction and power extraction were optimized using the response surface methodology (RSM). A face-centered composite design (FCCD) was applied to evaluate the effects of these variables on the polyphenols and condensed tannins contents. For each experiment, the extraction yield, the total polyphenolic contents and the condensed tannins contents were quantified using colorimetric essays. The extracts were characterized by their reactivity to formaldehyde and reverse phase high pressure liquid chromatography (RP-HPLC). The highest polyphenols content was obtained at 156 W using 80% of methanol during 5 min. For condensed tannins, the highest content of cyanidin was obtained at 182 W using 20% of methanol during 3.66 min. RSM applied in MAE, permitted to develop green extraction process of polyphenols and tannins extracted, using lower microwave power and methanol proportion with a shortest time extraction and in the same time improve the quantity of extractables obtained from renewable natural resource.     

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s²) to He (1s¹2p¹). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m³, and an energy balance of about −4×10⁵ kJ/mol H₂ compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H₂.     

Microwave-assisted organic synthesis versus conventional heating. A comparative study for Fisher glycosidation of monosaccharides

The Fisher glycosidation of monosaccharides (d-glucose and d-mannose) with fatty alcohols was studied under microwave irradiation and conventional heating with strict internal temperature control using a fiber optic sensor. Surfactants were obtained in only 3 minutes under microwave at maximum power of 5 W to avoid overshoot and products decomposition. In contrast with the typical reported glycosidation methods, the reaction under conventional heating can be carried out at the same time and temperature with high conversion.     

Efficient microwave-assisted synthesis of 1-aryl-4-dimethylamino methyleno-pyrrolidine-2,3,5-triones

A microwave-assisted synthesis of a series of 1-aryl-4-dimethylaminomethylene pyrrolidine-2,3,5-triones from the cyclocondensation reaction of ethyl 5,5,5-trichloro-3-dimethylamino methylene-2,4-dioxopentanoate with aniline, 3- or 4-substituted anilines [where the substituents = 3-Me, 3-OMe, 3-OH, 4-Me, 4-F, 4-Cl, 4-Br, 4-NO₂, and 4-COMe] is reported. This process is an efficient alternative to the conventional thermal heating and furnishes the products in a short reaction time (ca. 13 min), under mild conditions and in moderate to good yields (50–76%).     

Synthesis and photovoltaic property of polymer semiconductor with phthalimide derivative as a promising electron withdrawing material

Donor–acceptor type (DA-type) polymeric photovoltaic material with a dicarboxylic imide-substituted benzene (phthalimide) derivative as electron-withdrawing units, poly[4,4′-didodecyl-2,2′-bithiophene-co-5,5′-(3,6-bis(thieno-2-yl)-N-octyl-phthalimide] (PDBTTPT), was synthesized by a Stille coupling reaction. It had an optical band gap of 1.96 V and a relatively low HOMO energy level of ?5.34 eV in spite of it being a thiophene-based polymer. Photovoltaic devices with PDBTTPT/PC₇₁BM active layers were fabricated under a variety of conditions for optimizing device performance. PDBTTPT exhibited the best power conversion efficiency (PCE) of 1.5% in the device where 80 wt.% of the PC₇₁BM was contained in the active layer (PDBTTPT:PC₇₁BM = 1:4, w/w) and which was pre-annealed at 120 °C for 10 min. In addition, a device which was pre-annealed at 140 °C for 10 min and a device which was post-annealed at 120 °C for 10 min showed analogous PCE values of 1.5% as well, although small differences were exhibited between various parameters, such as V_OC, J_SC, and FF.     

Evaluation of a flow-photochemistry platform for the synthesis of compact modules

A custom-made meso-scale continuous flow-photochemistry platform was evaluated with the aim to enable the synthesis of synthetically relevant amounts (>5 g, with the option of 10–100 g) of novel compact modules, whose synthesis is based upon a photochemical transformation. The flow-photochemistry concept relies on the irradiation of thin-layers (20–90 μm) of reactant dissolved in a suitable solvent that is pumped through the single-pass photoreactor. The commercially available Ehrfeld Photoreactor XL system was equipped with standard UV lamps (emission maximum at 254 nm) which are cheap, durable and low in power consumption (8 W). The flow photochemistry system was evaluated using a known intramolecular [2+2] cycloaddition reaction investigating influence of flow rate (irradiation time), layer-thickness and reactant concentration. After a short initial optimisation phase, the system delivered in a first run 6 g of tricycle 4 which was further successfully up-scaled to 48 g, demonstrating the robustness and reliability of this flow photoreactor-platform.     

Carbazole-modified blue light-emitting copolymers with the backbones integrated by diphenyloxadiazole,fluorene, and triphenylamine

Two new blue light-emitting polymers, poly{[2,5-bis(4-phenylene)-1,3,4-oxadiazole]-[9,9-dihexylfluorene-2,7-diyl]-[N-(4-(9H-carbazol-9-yl)phenyl)-N,N-bis(p-phenylene)aniline]} (POFPA) and poly{[2,5-bis(4-phenylene)-1,3,4-oxadiazole]-[9,9-dihexylfluorene-2,7-diyl]-[4-(3,6-(di-9H-carbazol-9-yl)-9H-carbazol-9-yl)-N,N-bis(p-phenylene)-aniline]} (POFCPA), were synthesized by Suzuki coupling reactions. By GPC analysis against a linear polystyrene standard POFPA and POFCPA were found to have M_n of 1.68 × 10⁴ and 3.70 × 10³, respectively. In contrast to POFPA, the main absorption peak of POFCPA in dilute toluene solution was blue-shifted by Δλ = 26 nm owing to its backbone of relatively shorter π-conjugation length and more carbazole units in side chain. The absolute fluorescence quantum yield (Φ_f) of POFCPA in dilute toluene solution was determined as 73%, much higher than that of POFPA (Φ_f ≈ 58.9%) measured under the same conditions. An electroluminescence device based on POFCPA displays a stable blue emission having color coordinates of (0.15, 0.20), a maximum brightness of 4762 cd/m², and a maximum current efficiency of 1.79 cd/A. By using this polymer as the host material doped with 1 wt.% 4,4′-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl, the achieved highest brightness, maximum current efficiency and maximum power efficiency are 13,613 cd/m², 3.38 cd/A, and1.84 lm/W, respectively.     

Optical emission spectroscopy for quantification of ultraviolet radiations and biocide active species in microwave argon plasma jet at atmospheric pressure

This work deals with absorption and mainly emission spectrometry of a microwave induced surfatron plasma jet launched in ambient air and using an Argon flow carrier gas. The Ar flow rate varies between 1 and 3 L/min and the microwave power between 40 and 60 W. The analysis of the various spectra has led to the determination of the ozone and atomic oxygen concentrations, ultraviolet (UV) irradiance separating UVA, UVB and UVC, gas temperature, plasma electron density and excitation temperature. Most of these diagnostics are spatially resolved along the plasma jet axis. It is shown more particularly that rotational temperature obtained from OH(A-X) spectra ranges between 800 K to 1000 K while the apparent temperature of the plasma jet remains lower than about 325 K which is compatible with biocide treatment without significant thermal effect. The electron density reaches 1.2 × 10¹⁴ cm^− 3, the excitation temperature is about 4000 K, the UVC radiation represents only 5% of the UV radiations emitted by the device, the ozone concentration is found to reach 88 ± 27 ppm in the downstream part of the plasma jet at a distance of 30 mm away from the quartz tube outlet of the surfatron and the atomic oxygen concentration lies between 10 and 80 ppm up to a distance of 20 mm away from the quartz tube outlet. Ozone is identified as the main germicidal active species produced by the device since its concentration is in accordance with bacteria inactivation durations usually reported using such plasma devices. Human health hazard assessment is carried out all along this study since simple solutions are reminded to respect safety standards for exposures to ozone and microwave leakage. In this study, an air extraction unit is used and a Faraday cage is set around the quartz tube of the surfatron and the plasma jet. These solutions should be adopted by users of microwave induced plasma in open air conditions because according to the literature, this is not often the case.     

Synthesis of new calix[4]arene based chiral ligands bearing β-amino alcohol groups and their application in asymmetric transfer hydrogenation

A new series of chiral calix[4]arenes bearing β-amino alcohol groups have been synthesised. The crucial steps consist of the binding of glycidyl groups on the lower rim of the calix[4]arenas, followed by their regioselective opening with amines. These ligands were successfully tested in an asymmetric transfer hydrogenation. The best results (conversion max = 97% and ee max = 87%) were obtained using calix[4]arene mono-functionalised ligands. These results are the best ones obtained using calixarene based ligands in asymmetric catalysis.     

Comparison of two digestion procedures for the determination of lead in lichens by electrothermal atomic absorption spectrometry

The efficiency of two procedures for the digestion of lichen was investigated using a heating block and a microwave oven. In the open vessels, concentrated nitric acid was added to the samples, left for 1 h, and the addition of 30% (v / v) hydrogen peroxide completed the digestion. In the closed system, the complete digestion was performed using concentrated nitric acid and hydrogen peroxide, reducing the amount of chemicals, time and contamination risk. Both digestion methods gave comparable results, and recoveries were statistically not different. For a lichen sample spiked with 10 μg Pb, the recovery was 111% and 110% using microwave and heating block digestion, respectively, while it was 100% and 103% for a 100 μg Pb spike. For the determination by electrothermal atomic absorption spectrometry samples were diluted 20 times with water and a volume of 20 μL was injected into the graphite furnace without chemical modifier. Pyrolysis and atomization temperatures of 700 °C and 1500 °C, respectively, were used. The characteristic mass was 8.4 ± 0.6 pg for aqueous calibration solutions and 8.9 ± 0.8 pg for samples. Calibration was against matrix matched standards. The recovery test showed some contamination problem with the lowest concentrations in both procedures. The detection limits were 4.4 μg L^− 1 with microwave oven and 5.4 μg L^− 1 with the heating block in the undiluted blank.     

Asymmetric addition of diethylzinc to aldehydes catalyzed by a camphor-derived β-amino alcohol

The asymmetric addition of diethylzinc to aromatic and aliphatic aldehydes, including linear aliphatic ones, catalyzed by 2 mol % of β-amino alcohol (1S, 2R)-7,7-dimethyl-1-morpholin-4-yl-bicyclo[2.2.1]heptan-2-ol 10 gave the corresponding secondary alcohols in high yields and with up to 94% ee at ambient temperature after 15 min.     

Enhanced electrochemical capacitance of nitrogen-doped carbon gels synthesized by microwave-assisted polymerization of resorcinol and formaldehyde

Nitrogen-doped carbon gels were synthesized by ammonia-assisted carbonization of resorcinol–formaldehyde (RF) polymers obtained under microwave irradiation without any basic catalyst. Compared with the RF polymer synthesized by the conventional hydrothermal method, microwave polymerization produced spherical beads with a higher surface area (1710 m²/g vs. 1080 m²/g), and smaller (∼700 nm vs. ∼5 μm) but more uniform bead sizes. The majority of their pores were micropores. As a result, the electrochemical capacitance of microwave-assisted nitrogen-doped carbons was significantly higher than that of materials prepared by the conventional hydrothermal method. Thus microwave-assisted polymerization followed by ammonia-assisted carbonization is a useful method to synthesize nitrogen-doped carbon gels for electrochemical double layer capacitors.     

Studies on atmospheric plasma abatement of PFCs

Microwave plasma at 2.45 GHz frequency operating at atmospheric pressure in synthetic gas mixtures containing N₂, CF₄, C₂F₆, CHF₃, and SF₆ were investigated experimentally for various gas mixture constituents and operating conditions, with respect to their ability to destroy perfluorocompounds. It was found that the destruction and removal efficiency (DRE) of the process is highly dependent on the total gas flow. DREs of up to 99.9% have been achieved using 1.8 kW of microwave power at 20 l/min total flow rate.     

Expedient one-pot organometallics-free synthesis of tris(2-pyridyl)phosphine from 2-bromopyridine and elemental phosphorus

2-Bromopyridine reacts with elemental phosphorus (red or white) in a superbasic KOH/DMSO(H₂O) suspension at 100 °C (for red phosphorus) and 75 °C (for white phosphorus) over 3 h to afford tris(2-pyridyl)phosphine in a 62% yield (from red phosphorus) and a 50% yield (from white phosphorus). Under microwave assistance, the reaction with red phosphorus takes just 20 min to produce tris(2-pyridyl)phosphine in 53% yield. A hitherto unknown complex, [Pd(PPy₃)₂Cl₂]·CH₂Cl₂, synthesized from tris(2-pyridyl)phosphine and PdCl₂, has the cis-configuration; this is unusual for bis(phosphino)palladium dichloride complexes.     

Effect of ionic liquid 1-methylimidazolium chloride on the vapour liquid equilibrium of water,methanol, ethanol,and {water + ethanol} mixture

Measurements of vapour pressure data were conducted using a quasi-static ebulliometer for systems containing water, methanol, ethanol, and a mixture of {water + ethanol} in the presence of an ionic liquid (IL), namely, 1-methylimidazolium chloride ([MIm]Cl), wherein the IL-content ranged from w₂ = (0.10 to 0.50). The vapour pressure data of IL-containing binary systems were correlated by the NRTL model with an overall average absolute relative deviation (AARD) of 0.0103, and the resulting binary parameters were used to predict the vapour pressures of a ternary system {water + ethanol + [MIm]Cl} with an AARD less than 0.0077. Further, the isobaric vapour liquid equilibria (VLE) for the ternary system {water + ethanol + IL} with IL-content of w₃ = (0.10, 0.30, and 0.50) for [MIm]Cl and x₃ = 0.15 for [MIm]Cl, [C₄MIm]Cl, and [C₆MIm]Cl were predicted at 101.3 kPa, respectively. It is indicated that [MIm]Cl presents the strongest ability to enhance the relative volatility of ethanol to water in the mixture of {water + ethanol} than that of [C₄MIm]Cl and [C₆MIm]Cl, which is consistent with the cationic sizes and hence the ionic hydration ability. Therefore, distillation separation of the azeotrope of {water + ethanol} can be sufficiently facilitated by the addition of [MIm]Cl at a specified content.     

Sc(OTf)3/TsOH: a highly efficient catalytic system for the synthesis of 2,6-dioxabicyclo[3,2,1]octane derivatives

A variety of aldehydes undergo a tandem acetalization and intramolecular Prins cyclization with pent-4-ene-1,2-diol in the presence of 5 mol % scandium triflate and 15 mol % p-toluenesulfonic acid (TsOH) in dichloroethane at 80 °C to produce the corresponding bicyclic ethers, that is, 2,6-dioxabicyclo[3,2,1]octane derivatives in good yields and with high selectivity. The salient features of this methodology are higher yields, lower catalyst loadings, and faster reaction times. The combination of Sc(OTf)₃ and TsOH (1:3) was found to be more effective than either Sc(OTf)₃ or TsOH alone.     

Thermodynamic quantities for the different steps involved in the mechanism of osmium(VIII) catalysed oxidation of l-lysine by a new oxidant,diperiodatoargentate(III) (stopped flow technique)

The kinetics of Os(VIII) catalysed oxidation of l-lysine by diperiodatoargentate(III) (DPA) in alkaline medium at T = 298 K and a constant ionic strength of 0.50 mol · dm^?3 was studied spectrophotometrically. The oxidation products are aldehyde (5-aminopentanal) and Ag(I). The stoichiometry is i.e. [l-lysine]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)] and [DPA] and is less than unit order in both [l-lys] and [alkali]. Addition of periodate has no effect on the reaction. Effect of added products, ionic strength, and dielectric constant of the reaction medium have been investigated. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)-l-lysine complex, which further reacts with one molecule of deprotonated DPA in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated at different temperatures. The catalytic constant (K_C) was also calculated at different temperatures. From the plots of lg K_C versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.