Use Of Microwave Irradiation Research Articles

Microwave technology of thermal insulation materials based on liquid glass as an alternative to foam glass

An energy-saving and environmentally friendly microwave technology is proposed for producing composite thermal insulation materials based on liquid glass, which are not inferior to foam glass in terms of their properties. It is shown that the use of microwave radiation allows fabricating volumetrically grouted materials by simultaneous porization of the granules and the binder. In such a way, a monolithic structure of products is formed, where the space between the granules is filled with the swollen binder limited by a denser surface layer. It has been proven that the use of microwave radiation allows achieving heating and softening of the entire mass of the liquid-glass composition due to the internal acceleration of the movement of water molecules, their friction, and release of thermal energy, and not due to high temperature from the outside. This has made it possible to carry out swelling at a lower temperature and during a much shorter heat treatment time than at the traditional convective heating, because the sample layer is heated almost instantly under microwave exposure and the liquid glass composition reaches a pyroplastic state in a few seconds. It has been determined that a part of the energy of electromagnetic radiation is transformed into heat, which contributes to intensive porization with the volumetric expansion of the liquid-glass composition. The other part of the energy is directed to structural changes in the material leading to the improvement of its properties, which is associated with the "non-thermal" microwave radiation action.

Synthesis of Multifunctional Oligomethylsilsesquioxanes by Catalyst-Free Hydrolytic Polycondensation of Methyltrimethoxysilane under Microwave Radiation

The catalyst-free hydrolytic polycondensation of methyltrimethoxysilane under microwave radiation has been studied. The effect of molar ratios of the reagents (MTMS/H2O = 1/0.5-1/9), radiation power (20-300 W), temperature (30-50 °C) and duration of exposure (2.5-90 min) on the course of the process is considered. It has been shown that the use of microwave radiation promotes the activation of the process, and almost complete conversion of the monomer can be achieved in 5 min at 30 °C, 20 W and an MTMS/H2O ratio of 1/3. The optimal radiation power for the maximum conversion of the monomer and MeO-groups is in the range from 20 to 100 W. An increase in the water amount, the duration and temperature of the process contribute to an increase in the monomer conversion, a decrease in the content of residual MeO-groups and the yield of non-volatile oligomethylsilsesquioxanes. The limits of this approach using to the synthesis of multifunctional branched polyorganosilsesquioxanes are determined. Depending on the process conditions, homogeneous water-alcohol solutions of oligomethylsilsesquioxane with a concentration of 20 to 50 wt.% can be obtained. The OH-group content and the molecular weight of the obtained oligomers vary from 10 to 30 wt.% and from 1000 to 600 Da, respectively.

Recent developments on microwave-assisted organic synthesis of nitrogen- and oxygen-containing preferred heterocyclic scaffolds.

In recent decades, the utilization of microwave energy has experienced an extraordinary surge, leading to the introduction of innovative and revolutionary applications across various fields of chemistry such as medicinal chemistry, materials science, organic synthesis and heterocyclic chemistry. Herein, we provide a comprehensive literature review on the microwave-assisted organic synthesis of selected heterocycles. We highlight the use of microwave irradiation as an effective method for constructing a diverse range of molecules with high yield and selectivity. We also emphasize the impact of microwave irradiation on the efficient synthesis of N- and O-containing heterocycles that possess bioactive properties, such as anti-cancer, anti-proliferative, and anti-tumor activities. Specific attention is given to the efficient synthesis of pyrazolopyrimidines-, coumarin-, quinoline-, and isatin-based scaffolds, which have been extensively studied for their potential in drug discovery. The article provides valuable insights into the recent synthetic protocols and trends for the development of new drugs using heterocyclic molecules.

Microwave synthesis of cationic ABAB di-imidazolyl fluorinated porphyrins and manganese complexes

ABAB porphyrins are promising platforms for potential use in several applications, particularly in medical imaging. Herein, the synthetic optimization studies for preparing such porphyrins via the statistical condensation of 4-trifluoromethylphenyl and 1-methylimidazol-2-yl aldehydes with pyrrole, are described, with emphasis on the use of microwave irradiation as heating source, against conventional heating. Then, the preparation of the corresponding Mn(III) complex and cationization of the imidazole groups, using microwave irradiation, were also carried out and the photophysical, photochemical, and electrochemical properties were further assessed. The compounds revealed interesting features, including adequate log P, singlet oxygen yield, redox potentials, and excellent photostability, which pave the way for potential use as imaging probes in MRI or PET, or as photosensitizing molecules.

Advantages and Limitations of Anaerobic Wastewater Treatment—Technological Basics, Development Directions, and Technological Innovations

Anaerobic wastewater treatment is still a dynamically developing technology ensuring the effective degradation of organic compounds and biogas production. As evidenced in the large scale-up, this technological solution surpasses aerobic methods in many aspects. Its advantages stem from the feasibility of operation at a high organic load rate, the smaller production of difficult-to-manage sewage sludge, the smaller space and cubature required, and the high-methane biogas ultimately produced. The exploitation of anaerobic reactors is in line with the assumption of a circular economy, material recycling by reduced CO2 emissions and energy consumption, and the production of renewable energy. Despite their unquestionable advantages, there is still a need to seek novel approaches and improve the currently exploited installations. The key avenues of research entail improvements in the stability of bioreactor operations and the enhancement of bioreactor adaptability to changing and unfavorable process parameters. The versatility of such systems would also be greatly improved by increasing nitrogen and phosphorus removal rates. Attempts have been made to achieve these goals by setting up separate zones within bioreactors for the individual steps of methane fermentation, incorporating active fillings to promote nutrient removal, and introducing chemical and physical treatments. An interesting solution is also the use of microwave radiation to stimulate temperature conditions and induce non-thermal phenomena, such as enhancing the enzymatic activity of methanogenic microflora. Another prospective approach is to integrate digesters into microalgal biomass production systems. The aim of this review paper is to present the thus-far technological knowledge about anaerobic wastewater treatment, including standard solutions and innovative ones, the effectiveness of which has been corroborated in pilot-scale installations.

Microwave‐Assisted Synthesis of Bioactive Pyridine‐Functionalized N‐Alkyl‐Substituted (Benz)Imidazolium Salts

AbstractImidazolium salts have always been well recognized as the precursors to ionic liquids. Various studies have been extended to their biological properties, in which many have discovered interesting results. In this study, a series of pyridine‐functionalized (benz)imidazolium salts were synthesized using the conventional synthetic method, and microwave irradiation. The products were tested biologically against a list of microorganisms via broth microdilution assay and cancer cell lines using a standard MTT assay. Lead compound 4 e exhibited great antimicrobial properties with lowest MIC value of 3.91 μg/mL against Bacillus cereus, Bacillus subtilis, Staphylococcus aureus and Enterococcus faecalis. Remarkable anticancer properties of 3 f were shown with IC50 value as low as 0.71 μM against human colon cancer (HCT116). From our study, the MIC of 4 e and IC50 values of 3 f surpassed the potency of positive controls such as chloramphenicol (8.08–16.2 μg/mL) and cisplatin (10.78 μM) respectively. Additionally, the use of microwave irradiation has significantly reduced the reaction time from 5 days in a conventional setup, to a 3‐hour synthetic reaction in a microwave synthesizer.

Synthesis of Mixed Actinide Oxides Using Microwave Radiation

A method has been developed for producing mixed actinide oxides suitable for fabricating mixed nitride uranium plutonium fuel for fast neutron reactors. The method is based on the use of microwave radiation for the direct denitration of actinide nitrate solutions. The possibility of producing uranium, plutonium, and neptunium-mixed oxides was shown. A pilot installation for preparing actinide oxides by microwave denitration was designed and tested. Mixed oxides of uranium and cerium (for plutonium imitation) were successfully used to synthesize uranium cerium nitrides and produce fuel pellets. Compared with the precipitation (ammonia) method of producing mixed oxides, microwave denitration reduces the generation of secondary liquid radioactive waste by more than six times.

Fuel Oil Conversion in the Plasma Catalytic Mode, Stimulated by Microwave Radiation in the Presence of Nanosized Iron-Containing Systems

Conversion of mixtures of fuel oil with iron-containing substrates (carbon adsorbent and lignin, both modified with 0.5 wt % Fe) to hydrocarbon products and hydrogen was studied. The use of microwave radiation in the presence of the above-indicated iron-containing substrates capable of its absorption with the generation of breakdown phenomena and plasma is a promising approach to rapid processing of stable organic compounds of petroleum and natural origin into hydrocarbon products used in organic synthesis and for production of fuel components.

Microwave-Assisted Synthesis: Can Transition Metal Complexes Take Advantage of This "Green" Method?

Microwave-assisted synthesis is considered environmental-friendly and, therefore, in agreement with the principles of green chemistry. This form of energy has been employed extensively and successfully in organic synthesis also in the case of metal-catalyzed synthetic procedures. However, it has been less widely exploited in the synthesis of metal complexes. As microwave irradiation has been proving its utility as both a time-saving procedure and an alternative way to carry on tricky transformations, its use can help inorganic chemists, too. This review focuses on the use of microwave irradiation in the preparation of transition metal complexes and organometallic compounds and also includes new, unpublished results. The syntheses of the compounds are described following the group of the periodic table to which the contained metal belongs. A general overview of the results from over 150 papers points out that microwaves can be a useful synthetic tool for inorganic chemists, reducing dramatically the reaction times with respect to traditional heating. This is often accompanied by a more limited risk of decomposition of reagents or products by an increase in yield, purity, and (sometimes) selectivity. In any case, thermal control is operative, whereas nonthermal or specific microwave effects seem to be absent.

The use of microwave irradiation for preparation and fast-acting regeneration of magnetic biochars

The application of microwave irradiation for rapid synthesis of magnetic biochar from agricultural waste with the subsequent modification of carbon matrix by magnetic nanoparticles was performed. The magnetic biochar was characterized by 57Fe Mössbauer spectroscopy, X-ray diffraction, a low-temperature nitrogen adsorption method, and electron microscopy. Except of magnetic properties, modification of biochar brings surface texture increase (SBET = 21.1 m2/g for char precursor versus 139.1 m2/g for magnetic biochar), and therefore better adsorption properties. The magnetic biochar was tested as an adsorbent of As5+ oxyanion and methylene blue (MB) to study the sorption mechanism and regeneration process. Magnetic biochar is the excellent adsorbent of arsenic (Qm = 24.9 mg/g; pH = 3.8). In the regeneration procedure, fast-acting microwave irradiation (10 s) significantly increases the value of the As5+ desorption rate constant as well as the initial desorption rate. The adsorption of MB on the magnetic biochar (Qm = 55.0 mg/g; pH = 10.2) was realized to study microwave-induced thermal regeneration. After short microwave treatment (30 s), a degradation of MB was observed (no absorption in the UV/VIS spectrum), whereas six degradation products were detected (HPLC/ESI-MS) and proposed formulas were revealed. Longer irradiation (60 s) caused total degradation of MB.

Microwave assisted green synthesis of Fe@Au core–shell NPs magnetic to enhance olive oil efficiency on eradication of helicobacter pylori (life preserver)

• Gold coated iron (Fe@Au) nanoparticles were synthesized. • The synthesized nanoparticles were then characterized and Magnetic hysteresis loops. • Effect of microwave irradiations,during the synthetic process of nanoparticles. • The biosynthesized Fe@AuNPs showed significant biomedical properties. Eco friendly and green synthetic approach for the synthesis of metallic nanoparticles gained much importance in the recent era. In the present study, an environmental friendly and plant mediated synthetic approach was used for the synthesis of gold coated iron (Fe@Au) nanoparticles using extract solution of olive oil, licorice root (Glycyrrhiza glabra) and coconut oil (OLC). These extracts were acted as a reducing agent during the formation of core–shell nanoparticles that provides long-time stability, lower toxicity and higher permeability to specific target cells. In order to achieve the small sized, regular spherical shaped, and homogeneous nanoparticles optimum conditions were ensured. In fact, the use of microwave irradiation was offered higher reaction rate and better product. The Fe@AuNPs have been characterized by UV–Visible spectroscopy, Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), High resolution Transmission electron microscope (HR-TEM), Fourier Transform Infrared Spectroscopy (FT-IR), high-performance liquid chromatography (HPLC), High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), Particle-Size Distribution (PSD), and Magnetic hysteresis loops. The synthesized gold coated iron nanoparticles showed significant antioxidant potential with maximum inhibition rates, the biosynthesized nanoparticles were also found effective against Helicobacter pylori ( H. pylori ) and ulcer.

Microwave-Assisted Synthesis and Characterization of Zeolite Prepared From South Africa Coal Fly Ash

In industry, synthetic zeolites are commonly used as ion-exchange materials, catalyst supports, and adsorbents. As a result, a more energy-efficient alternative for its synthesis from low-cost and accessible raw materials is needed. This study, presents the possibility of using class F South African coal fly ash (SACFA) from Lethaba thermal-power station as a precursor to produce zeolites via a microwave (MW) assisted synthesis route. The mineral content of synthetic materials was determined using X-ray florescence (XRF). Morphology was determined using a Scanning electron microscopy (SEM), elemental composition by energy dispersive spectrometer (EDS). X-ray diffractometry (XRD) was used to get structural characterization. Microwave (MW) irradiation time and intensity enhance the crystallization of the zeolite phase as a result of sufficient energy required to enable the solubility of alumina and silica from coal fly ash. The use of MW irradiation provides a green alternative to zeolite synthesis from fly ash (FA) than traditional thermal and fusion techniques, which uses a great deal of energy consumption and a longer reaction time.

Microwave Sol-gel Synthesis of Co, Ni, Cu, Mn Ferrites and the Investigation of Their Activity in the Oxidation Reaction of Carbon Monoxide

Background: The study effect of microwave radiation on the catalytic properties of transition metal ferrites synthesized by ceramic and sol-gel methods in the oxidation reaction of carbon monoxide into dioxide. Objective: This work aims to study the effect of microwave radiation on the production of cobalt, copper, nickel, and manganese ferrites by sol-gel combustion technology using various organic reagents and to study their catalytic activity in the oxidative conversion of carbon monoxide into dioxide. Methods: Microwave treatment was carried out on a setup based on an EM-G5593V microwave oven (Panasonic) with a magnetron power varying from 300 to 800 W with an operating frequency of 2450 MHz. X-ray phase analysis of the products was carried out on a Bruker D 2Phazer automatic diffractometer. The measurement of the specific surface area of the samples was determined by low-temperature nitrogen adsorption by the multipoint BET method on a SORBI-MS instrument (ZAO META, Russia). IR spectra were recorded using FT-IR LUMOS Bruker spectrometers. The micrographs of samples were analyzed on the Sigma VP (Carl Zeiss Jena) equipment. Results: It was determined that the most active catalysts for the oxidation of carbon monoxide to dioxide are ferrites obtained by the sol-gel combustion method using microwave radiation to "ignite" the gel. Conclusion: The use of microwave radiation in the preparation of ferrites by the sol-gel method with combustion can initiate a self-propagating exothermic combustion reaction in the entire volume of the sample in a very short time, measured in seconds. The catalytic activity in the oxidative conversion of carbon monoxide obtained by this method of ferrites is comparable to the activity of ferrites obtained by the sol-gel method with traditional combustion.

Green synthesis of silver nanoparticles from Alpinia galanga extract with microwave irradiation and antibacterial activity against Escherichia coli

Background: This study deals with the rapid green synthesis of silver nanoparticles (Ag NPs) by microwave irradiation using water extract of Alpinia galanga as a reducing agent. Methods: The effect of concentrations of water extract and silver nitrate aqueous solution (1 mM) on the synthesis was investigated using the ratios 1:1, 1:5, 1:10, and 1:20. The formation of Ag NPs was observed after being microwaved for 30, 60, 90, 120, 150, and 180 seconds. Results: The best Ag NPs were produced from the ratio of 1:10 after 180 s irradiation, confirmed by the optimum absorbance at 450 nm using a UV-visible spectrophotometer. Transmission electron microscopy analysis showed that the size of the Ag NPs was 50 nm. Their antibacterial activity was determined using Resazurin microtiter assay against Escherichia coli, and the results showed that it inhibited 94.4% of E. coli. It was significantly different (p < 0.05) with the inhibition of extract and Amoxsan, which inhibited 71.1% and 85.8% of E. coli, respectively. Conclusion: The use of microwave irradiation on the synthesis of silver nanoparticles using Alpinia galanga extract as a reducing agent appears to be rapid and eco-friendly.

Synthesis and Chemistry of Diazo Compounds under Microwave Irradiation: A Review

AbstractDiazo compounds such as α‐diazocarbonyls, diazoalkanes, and diazoarenes are well known compounds in organic chemistry. Their synthetic utility is of paramount importance. They are commonly used as precursors of reactive intermediates like ketenes and carbenoids. Their reactions have been traditionally carried out under thermal or photochemical conditions in inert atmosphere. The synthesis and chemistry of such compounds under microwave irradiation have seen steady growth. The present article critically reviews the application of microwave irradiation in synthesis and chemistry of diazoalkanes and α‐diazocarbonyls. The microwave‐assisted reactions via ketenes and carbenes with alcohols, thiols, phenols, amines, imines, alkenes, alkynes, and three‐membered heterocyclic compounds, etc. are described. These reactions furnish synthetically useful building blocks and also biologically relevant heterocyclic compounds. Most reactions are accelerated by the use of microwave irradiation. There are also some reports revealing that the reactions did not occur by conventional heating but yielded products on irradiation with microwaves. The mechanisms of the reactions where necessary and synthetic and biological relevance of the products are highlighted.

Multistep Microwave-Assisted Synthesis of Avobenzone

Multistep synthesis is a key capstone experience in organic laboratory instruction. Here, a four-step synthesis of avobenzone, an active component in sunscreens, has been developed that can be completed in two 4 h laboratory periods. This synthesis incorporates green principles and includes an aldol condensation, electrophilic addition of bromine to an alkene, an E2 dehalogenation of a dibromide, and hydration of an alkyne. Highlights of this synthesis include the use of coupling constants to identify alkene configuration, NMR analysis to determine preferred tautomeric form, the use of microwave irradiation to reduce reaction times, a solvent-free synthesis of a chalcone, and a three-step reaction that can be completed in a single lab period.

A Valuable Method for the Synthesis of 2‐Benzylchromones: A Comparative Evaluation of Both Conventional and Microwave‐Assisted Synthesis

AbstractChromones (4H‐chromen‐4‐ones) contemplate a naturally occurring class of compounds widely distributed in Nature, particularly in plants. This singular ring system has emerged as a privileged scaffold in medicinal chemistry, mainly due to its unique structural features, diverse biological activities, and pharmacological properties. Throughout the past few years, our efforts have been focused on synthesizing a series of 2‐benzylchromones through a Claisen condensation, using 2’‐hydroxyacetophenones and ethyl 2‐phenylacetates. However, the extended periods of reaction necessary for the synthesis of 2‐benzylchromones led to the search for an alternative. Thus, microwave irradiation emerged as a suitable approach to obtain these chromones in shorter reaction times and with similar or even improved synthetic yields. Our work demonstrates that it is possible to synthesize 2‐benzylchromones through both conventional and microwave‐assisted synthesis, favoring the use of microwave irradiation.

SYNTHESIS OF THIOESTERS AND THIOAMIDES USING POTASSIUM THIOCYANATE UNDER MICROWAVE IRRADIATION

Microwave-assisted synthesis provides more time for chemists to expand their creativeness, develop new processes and new theories. Recent developments in chemical sciences created microwave energy a new proficient way of heating the reaction.1 Microwave energy bids abundant benefits for the execution of synthesis comprising enhanced reaction rates, improved yield and cleaner chemistries. Using this technique, reactions can be performed in minutes, instead of spending hours to days in a conventional manner. The difficulty accompanying effluent disposal is overcome by executing the reactions without the use of solvent under microwave irradiation. Microwave irradiation reaction under solvent-free conditions, mineralsupported catalyzed reactions etc. provides better chemical methods with higher reaction rate, improved yield, good selectivity.2 Chemical reactions that took an hour to days the completion can be performed in minutes. The microwave region is positioned between IR and radio waves in the electromagnetic spectrum. The wavelength of microwave radiation is 1 mm-1 m with the frequencies 0.3-300 GHz. Dielectric heating in microwaves utilizes the capability of various solids and liquids to convert electromagnetic energy into heat to progress the reactions. The microwave technique has been applied in various research technologies like drug release/targeting,3 polymer technology,4 waste treatment,5 ceramics,6 alkane decomposition,7 etc. Consequently, microwave technology entertains as a potential method in green chemistry.8 This technology unlocks new openings as a new heating technique which is very difficult by the regular heating method.9 Organosulfur compounds are versatile intermediates in synthetic chemistry, possess many imperative biological properties.10 The applications and choice of organo-sulfur compounds have augmented enormously as sulfur comprising groups continue to function as an imperative supplementary function in synthetic arrangements.11 Thiocarbonyl comprising compounds are useful synthetic intermediates, that find numerous uses in the preparation of natural products.12 Although various reagents are accessible for the preparation of thioesters or thioamides, there are some drawbacks. Some of the important reagents used for thionation comprises lawessons reagent,13 H2S,14 phosphorous pentasulfide,15 hexamethyldisilathine,16 R3OBF4/NaSH,17 R2PSX,18 (Et2Al)2S,19 bis(tricyclcohexylstannyl) sulfide/BCl3, 20 thiourea,21 etc. Many of these reagents involve high temperatures, prolonged reaction times, or harsh conditions for reaction execution and frequently require problematic column chromatography to separate and remove the unwanted products. Batool A. et al. described a green procedure for the synthesis of thieranes from oxiranes by using ammonium thiocyanate.22 Encouraged by this, and in persistence to our work on the development of biologically active heterocycles,23-26 we thought of using simple and commercially available reagent potassium thiocyanate for the transformation of esters into thioesters by making use of microwave irradiation.

Synthesis of Transition Metal Ferrites (Co, Cu, Ni, Mn) by the Sol-Gel Method with Combustion and the Use of Microwave Processing

This review considers recent work on the synthesis of transition metal ferrites (Co, Cu, Ni, Mn) by sol-gel method with combustion, as well as the effect of microwave radiation. Ferrites are interesting not only for magnetic and optical properties, but also for their catalytic ones. In recent years, there has been an increasing amount of literature, which investigates the catalytic properties of transition metal ferrites in various reac-tions, including oxidative reactions. Given the fact that various organic components are used as complexing agents and as a fuel in the sol-gel method with combustion, the review considers the influence of the organic reagent nature, its ratio to precursors, the pH of the medium, the power and time of microwave exposure to the process of ferrite formation as factors influencing the size of formed particles and their textural character-istics, which are of great importance in the catalysis. Recently, the attention of chemists working in the field of catalysis has been attracted by studies of the effect of physical fields, to which the microwave field be-longs, on various chemical processes, including the nanocatalysts synthesis. The use of microwave radiation in sol-gel synthesis of ferrite allows obtaining nanoferrites with high specific surface area. From this point of view, this paper considers the works of recent years devoted to the study of microwave sol-gel synthesis of ferrite.

Effect of Microwave Pretreatment on Leaching of Tetrahedrite

In mineral processing, the use of microwave radiation is important especially in pre-treatment processes. At present, there is an acceleration of processes as well as an increase in the efficiency of metal recovery. One of the main problems in copper recovery from complex sulphide ores is the removal of impurities such as antimony, arsenic, mercury. In the hydrometallurgical processing scheme, the key step is the leaching. The extraction process can be influenced by the selection of suitable leaching reagents or by suitable pre-treatment of the ore. The article describes the effect of microwave radiation on the leaching Sb, As and Hg of tetrahedrite and tetrahedrite concentrate. The samples were irradiated at the power 900 W for 30 seconds. The leaching of irradiated and non-irradiated samples was realized in an alkaline sodium sulphide. The positive effect of microwave radiation was confirmed by an increase in the recovery of Sb and As already after 15 min of extraction. After microwave leaching of irradiated tetrahedrite samples, the yield of Sb was 43.2 %, in irradiated tetrahedrite concentrate, the yield of Sb was 81.3 %.