Microwave Irradiation Research Articles

Oxidation regularities of the electroexplosive metal nanopowders during heating in air after microwave irradiation

Oxidation regularities of the electroexplosive metal nanopowders during heating in air after microwave irradiation

Effects of Microwave Treatment on Alkyd-Varnished Wood Exposed to Outdoor Conditions

In this study, it was planned to investigate the effects of microwave irradiation (MW) prior to varnish applications on the pine wood samples, which are subjected to three months of outdoor exposure. The samples of 180W15s, 270W15s, 360W5s, and 360W15s showed lower water sorption properties than the control, while the rest of the samples showed higher sorption properties than the control sample. The lowest water sorption value was 12.50% (-3.85% lower than the control). It was found that post-microwave treated samples provide a 1–3 degree increases in resistance against selected cold liquids of distilled water, fruit juice, milk and coke under similar conditions. After three months of outdoor exposure of the samples, the surface scratch resistance of the samples was found to be 1 to 4 degrees softer than the control sample (HB to 3B pencil hardness properties). However, the cross-cut properties of the samples showed almost similar level of adhesion properties, mostly between 2 and 3 (control sample: 3), which was assumed to be not notable different from control, regardless of treatment conditions. It was found to have various discoloration properties of the samples which subjected to weathering procedure of post-microwave treated and alkyd-varnish aplied samples. But the larger-sized samples (A-type) have a higher and wider range for b* (yellowness) and a* (redness) values, while smaller-sized samples (a-type) showed a wider range and higher brightness (L*) properties. Moreover, A-type samples had higher total color difference values than a-types at similar treatment conditions. It is important to note that all measured samples show an ΔE >1.0 (metric) value, which means the discoloration after three months of outdoor exposure could be realizable when carefully examined by the human eye. The results clearly indicated that the post-microwave radiation before alkyd-varnish application on pine wood samples were some level influences regarding the selected properties. The resistance of selected household cold liquids and surface cross-cut properties were prominent for some samples. In spite of wide properties measured, no any clear trend was found between MW radiation and selected properties.

Synthesis of Diphenhydramine Using Microwave Irradiation and Phase-Transfer Catalysis

Synthesis of Diphenhydramine Using Microwave Irradiation and Phase-Transfer Catalysis

Stereoselective Synthesis of trans-1,2,4-Trihydrobenzo[d][1,2]azaphosphinine 3-Oxides from In Situ Formed Phosphenes and Formaldimines.

Various trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides are synthesized highly stereoselectively from in situ generated phosphenes and formaldimines under microwave irradiation. Aryl(diazo)methyl(diaryl)phosphine oxides first undergo the Wolff rearrangement to generate phosphenes. Imines, in situ generated from 1,3,5-triazinanes or paraformaldehyde and primary amines, nucleophilically attack the phosphenes followed by a tandem stereoelectronic effect-controlled intramolecular nucleophilic addition and aromatization to give final trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides, exhibiting completely different annuloselectivity from linear nonformaldimines.

Multicomponent Synthesis of C(8)-Substituted Purine Building Blocks of Peptide Nucleic Acids from Prebiotic Compounds.

We have explored the reaction of a three-components mixture of aminomalononitrile, urea and α-amino acid methyl esters for the multicomponent synthesis substituted purines resembling PNA's building blocks. 2,6-diamino-purines, 6-amino-3,9-dihydro-2H-purin-2-one (iso-guanines), and 3,9-dihydro-6H-purin-6-one derivatives, selectively decorated at C(8)-position of the purine ring with different amino acid residues, were obtained from acceptable to good yields. The regio-selectivity of the transformation was controlled by the use of urea in the ternary mixture and by the annulation agent involved in the ring-closure of amino-imidazole carbonitrile intermediates. Solvent free conditions, microwave irradiation and simple one-carbon containing reagents further satisfied the major requirement of atom economy and sustainable chemistry. Due to the prebiotic nature of the three-components mixture and of annulation agents, it also embodies the possibility for the synthesis of novel PNAs bearing purine nucleobases decorated at C(8)-position of the imidazole ring as alternative RNA analogues in molecular evolution.

A Bacterial Capturing, Neural Network-Like Carbon Nanotubes/Prussian Blue/Puerarin Nanocomposite for Microwave Treatment of Staphylococcus Aureus-Infected Osteomyelitis.

Staphylococcus aureus (S. aureus)-infected osteomyelitis is a deep tissue infection that cannot be effectively treated with antibiotics. Microwave (MW) thermal therapy (MTT) and MW dynamic therapy (MDT) based on MW-responsive materials are promising for the therapy of bacteria-infected osteomyelitis occurring in deep tissues that cannot be effectively treated with antibiotics. In this work, the MW-responsive system of carbon nanotubes (CNTs)/Prussian blue (PB)/puerarin (Pue) with stable network-like structures is constructed. The PB is grown in situ on the CNTs, and its introduction not only reduces the aggregation of the network-like structures of the CNTs, but the large specific surface area and mesoporous structure can also provide many active sites for the adsorption of oxygen and polar molecules. Pue is a natural anti-inflammatory material that reduces inflammation at the infection site. The composite of the CNTs and PB avoids the skin effect and thus can improve dielectric and reflection losses. The MW thermal response of CNTs/PB/Pue is mainly due to the occurrence of reflection loss, dielectric loss, multiple reflections and scattering, interface polarization, and dipole polarization. In addition, under MW irradiation, the CNTs/PB/Pue can produce reactive oxygen species (ROS), such as singlet oxygen (1O2), hydroxyl radical (·OH).

The effects of microwave and microwave + infrared drying treatments of Pinus brutia and Picea orientalis on water absorption and physical properties

The goal of this study was to find a way to shorten wood drying time by using microwave and combined infrared + microwave drying methods and to analyze color and gloss changes. Wood samples prepared in three groups with dimensions of 20×20×30 mm were used in moisture tests and 75×5×150 mm were used in color change and gloss measurements, obtained from Red pine (Pinus brutia) and Eastern spruce (Picea orientalis) woods. The samples were oven dried, dried by microwave, or dried by infrared + microwave drying method. The wood samples all reached the target moisture. Their weight and volume were calculated in accordance with the principles of TS ISO 13061-1. Color change values were determined before and after drying with a portable color reader (Konica Minolta CR-10) device, and gloss measurements were taken with the Gardner brand gloss meter. By microwave drying for 15 min, 4% moisture content was reached in the wood samples, so both time and energy were saved. The moisture content values decreased compared to the whole drying methods. Most color change was observed in the drying methods using infrared for both red pine and eastern spruce.

Elucidating the Fate of the Organochlorine Pesticide Chlordecone under Abiotic Reductive and Oxidative Processes: Kinetics, Transformation Products, and C vs Cl Isotope Fractionation.

Pollution of French West Indies (FWI) soils by the organochlorine pesticide chlordecone poses environmental and societal concerns due to its long-term persistence. Assessing chlordecone degradation remains challenging due to analytical constraints to identify transformation products. Here, multielement compound-specific isotope analysis (ME-CSIA) was used to identify changes in stable isotope signatures of chlordecone produced during abiotic transformation reactions under reducing and oxidative conditions. Effective chlordecone transformation was shown in reactions with zerovalent iron (ZVI), vitamin B12 and sodium sulfide (VSS), alkaline ascorbic acid (AA), and sodium persulfate activated by microwave irradiation (MWPS). Significant enrichment of 13C and 37Cl was observed in all abiotic reactions, with εC,bulk and εCl,bulk values ranging from -4.3 ± 0.4‰ to -2.3 ± 0.2‰ and from -2.6 ± 0.4‰ to -1.3 ± 0.3‰, respectively. Distinct mechanisms were evidenced in dual isotope plots, resulting in Λ values of 1.17 ± 0.28 for ZVI, 1.26 ± 0.50 for VSS, 2.06 ± 0.30 for AA, and 2.90 ± 0.50 for MWPS. Two major products were formed, 10-monohydrochlordecone and 8-monohydrochlordecone. Cl-CSIA data suggested that the first Cl substitution at the C10-position likely produced secondary Cl isotope effects (via nucleophilic substitution). Overall, results suggest that ME-CSIA can help quantify in situ chlordecone degradation, distinguishing between different ongoing degradation mechanisms and fingerprinting pollutant sources from chlordecone formulations (Curlone).

One-pot synthesis of fused isoxazolo[4′,5′:4,5]thiopyrano[2,3-d]pyrimidines as potent EGFR targeting anti-lung cancer agents

The requirement for scaffolds has prompted synthetic chemists to devise simple and effective methods for optimal synthesis, which are critical in the medical industry. Under comparatively optimized conditions, a click followed by a CC bond coupling reaction between iodoalkyne (4) and substituted nitrile oxide was utilized to explore the synthesis of fused isoxazoles containing thiopyrano[2,3-d]pyrimidine under microwave irradiation. The synthesized compounds were tested for their anticancer activity against EGFR wild-type human non-small cell lung cancer cells (NCI-H460 and A549). The compounds 6i and 6l have shown more potent activity against both cancer cell lines as compared to standard drugs doxorubicin and erlotinib. And also compounds 6e, 6j, and 6k have shown more potent activity as compared to Doxorubicin and moderate activity compared to erlotinib. Later, in vitro EGFR results of more potent compounds revealed that compounds 6l and 6k have shown potent EGFR activity compared to standard erlotinib. To evaluate the molecular interactions of more potent compounds with the human epidermal growth factor receptor. It was observed that all the potent compounds exhibited greater binding energies in comparison to the standard drug erlotinib.

Ultra-sensitive liquefied petroleum gas (LPG) sensor based on monometallic Ag nanospheres synthesized via microwave-assisted facile approach

We present the synthesis, analysis, and utility of polyvinylpyrrolidone (PVP) stabilized monometallic silver nanospheres for liquefied petroleum gas sensing at room temperature. We have synthesised silver nanospheres (Ag-NSs) in the diameter range of 13–21 nm using a microwave assisted method, which is both easy and fast, because microwave irradiation only takes 30 s. A solution of 0.1 M silver nitrate (AgNO3) in an ethanolic medium was microwave-irradiated to produce Ag-NSs. PVP was used as a stabilising agent throughout the process. Spin coating method was used to produce thin films of synthesised monometallic Ag-NSs. X-ray diffraction (XRD), scanning electron microscopy (SEM), acoustic particle sizer (APS), UV–visible absorption (UV–visible) and Fourier Transform Infrared (FT-IR) spectroscopy were used for characterising Ag-NSs. Based on the acoustic attenuation of the prepared sample, the acoustic particle sizer estimated the diameter of Ag-NSs to be around 17 nm. The deposited films were examined for LPG leakage detection at ambient temperature. This is the first report on monometallic Ag-NSs for leakage detection of LPG at room temperature operation below its lower explosive limit (LEL). The significant finding of the developed sensor is that it prompts the quick response (∼16 s) and recovery (∼64 s) as Ag enhances the reaction rate between the sensing film surface and adsorbed LPG, thereby, augments the sensitivity of sensor even below LEL. Moreover, the fabricated LPG sensor shows noteworthy reproducibility (measured up to six cycles) and stability up to 06 months after fabrication.

Physicochemical properties, structure and biological activity of ginger polysaccharide: Effect of microwave infrared dual-field coupled drying

Ginger was dried by microwave infrared dual-field coupled drying (MIDFCD). The composition, structure, physicochemical properties and biological activity of ginger polysaccharides at various stages of MIDFCD were investigated. The MIDFCD significantly impacted the chemical composition, molecular weight (Mw), microstructure, and physicochemical properties of ginger polysaccharides. However, there were no notable differences in functional group composition. The Mw and chemical composition were notably influenced by microwave-infrared exposure and prolonged drying time. The degradation of polysaccharides due to high temperatures in the later stage resulted in further decreases in Mw and alterations in monosaccharide composition. These changes in chemical composition and Mw affected thermal properties, crystallization properties, particle size, rheological properties, antioxidant capacity, and hypoglycemic activity. These findings suggest that MIDFCD enhances the quality and bioactivity of natural polysaccharides. This study offers theoretical support for MIDFCD processing and the value-added utilization of ginger.

Microwave Assisted Williamson Synthesis: A Green Approach towards the Preparation of Ethers

Introduction: Microwave-assisted reactions align with the principles of green chemistry by significantly reducing synthesis time, avoiding high temperatures, and typically yielding high product quantities. Method: A catalyst was synthesized from waste banana peels, ensuring both availability and lowcost production. Ethers were synthesized using microwave irradiation at 300W, employing two different alkyl halide variants with both substituted and unsubstituted phenols. Results: The reaction proceeded efficiently without the need for corrosive bases such as caustic soda or caustic potash. Microwave irradiation facilitated reduced reaction times for ether formation. Additionally, the supported catalyst demonstrated the advantage of reusability. Conclusion: This protocol offers several benefits, including the use of a green solvent and the exclusion of phase transfer catalysts and harsh conditions. Consequently, an efficient and green synthesis of ethers has been achieved.

Enhancing photosynthesis of microalgae via photoluminescent g-C3N4 accelerated photoelectrons transfer in photosystem

Using photoluminescent (PL) graphitic carbon nitride (g-C3N4) to convert ultraviolet (UV) light into chloroplast absorbed blue or near infrared (NR) is an attractive methodology to facilitate sunlight energy storage and carbon sequestration by microalgae. However, most researches focus on inhibiting water bloom by g-C3N4, applying PL g-C3N4 to promote growth of microalgae is rarely reported. Accordingly, PL g-C3N4 is synthesized by a microwave heating method and co–cultured with Chlorella vulgaris (C. vulgaris) with concentration of 0, 50, and 250 mg/L, named as C. vulgaris-0, C. vulgaris-50, and C. vulgaris-250, respectively, to study effect of PL g-C3N4 on growth of C. vulgaris. Results indicate that there is no significant effect of microwave synthesized g-C3N4 on morphology of microalgae cells, while cell viability and growth rate of C. vulgaris-50 is obviously enhanced. Further analysis indicates that, on the one hand, PL fluorescence at 615 nm enlarges light absorption of microalgae; on the other hand, photogenerated electrons by g-C3N4 accelerate electron transfer in photosystem, subsequently enhancing formation of NADPH and ATP, which is favorable to growth of microalgae. Metabolism analysis illustrates that glucose, fructose, and galactose, involved in glycolysis and photosynthesis, are all up-regulated in C. vulgaris-50 group. This work reveals low concentration of PL g-C3N4 facilitates protein synthesis and energy metabolism through enhancing light absorption and electron transfers, providing a biochemical strategy to enhance carbon sequestration.

Turning Waste into Wealth: Optimization of Microwave/Ultrasound-Assisted Extraction for Maximum Recovery of Quercetin and Total Flavonoids from Red Onion (Allium cepa L.) Skin Waste

This study optimized the extraction conditions to maximize the recovery yields of quercetin and total flavonoids from red onion skin waste using sequential microwave/ultrasound-assisted extraction. Five effective factors of quercetin extraction yield were investigated using response surface methodology. The method was successfully performed under optimal 60 s microwave irradiation conditions followed by 15 min sonication at 70 °C with 70% (v/v, water) ethanol with a solvent-to-solid ratio of 30 mL/g. The variance analysis of the model for both quercetin (Y1) and total flavonoid (Y2) recovery from DOS demonstrated that ultrasound temperature (X2) was the most highly significant and influential factor, with a p-value of <0.0001 for both responses. Additionally, three key interaction terms—X1X2, X2X4, and X2X5—were identified as highly significant, further underscoring the critical role of ultrasound temperature in optimizing the extraction process for both quercetin and total flavonoids. The maximum recovery yields of quercetin and total flavonoids from red onion skin were 10.32% and 12.52%, respectively. The predicted values for quercetin (10.05%) and total flavonoids (12.72%) were very close to the experimental results. The recovery yields obtained from different extraction methods under the identical experimental conditions mentioned earlier were ultrasound/microwave-assisted extraction (7.66% quercetin and 10.18% total flavonoids), ultrasound-assisted extraction (5.36% quercetin and 8.34% total flavonoids), and microwave-assisted extraction (5.03% quercetin and 7.91% total flavonoids). The ANOVA confirmed highly significant regression models (p-values < 0.0001), with an insignificant lack of fit (p = 0.0515 for quercetin, p = 0.1276 for total flavonoids), demonstrating the robustness and reliability of the optimization. This study provides valuable insights for improving the extraction of bioactive compounds, which is critical for developing effective cancer treatments and advancing medical research. Additionally, the model shows potential for scaling up food processing applications to recover valuable products from red onion skin waste.

Luminescent carbon nanoparticles obtained by microwave assisted hydrolysis from dextrin

Carbon nanoparticles (CNPs) were synthesized by acid hydrolysis from dextrin by the microwave-assisted method. The effect of temperature and synthesis time on morphology, size, UV–Vis absorption, and photoluminescence properties was studied. An increase in temperature from 135 to 180 °C decreases the CNPs diameter from 17.8 to 9.7 nm. Similarly, an increase in synthesis time from 2 to 5 min promotes a decrease in sizes from 13.1 to 6.7 nm. UV–Vis absorption spectroscopy and photoluminescence studies indicated that the nanoparticles have a maximum absorbance around 300 nm and when the CNPs are excited with λ close to 400 nm, λ emission occurs in the range of 500–650 nm. CNPs were synthesized maintaining synthesis conditions of 150 °C, for 5 min, varying the type of acid (H2SO4 and CH3COOH) and pH before subjecting the solution to microwave irradiation. It was observed that, when CH3COOH is used as a hydrolysis agent instead of H2SO4, the intensity of the emission increases. Regarding pH, it was observed that CNPs synthesized at alkaline pH have greater photoluminescence than those synthesized at acid pH.

Mechanical and fracture characteristics of weak microwave-absorbing sandstone under microwave irradiation: influence of pore water

Microwave radiation is an effective method to weaken the strength of hard rock, but this weakening effect is not obvious enough for weak microwave-absorbing rocks. This work focuses on the role of water in amplifying the effect of microwaves on weak microwave-absorbing rocks, by examining the bursting characteristics of the rocks as well as their physical and mechanical properties before blasting. The experimental results show that when subjected to microwave irradiation, and the time taken for this bursting decreases with higher microwave power. In addition, the surface temperature of saturated sandstone gradually rises with increased irradiation power and duration. Under high microwave power, the uniaxial compressive strength (UCS) of heated saturated sandstone notably decreases within the same irradiation duration. When the microwave power is low, the UCS of saturated sandstone remains relatively unchanged over time. The UCS of dry sandstone exhibits no significant alteration under identical irradiation power and duration. In conclusion, sandstone shows no significant change in its physical and mechanical properties during brief exposure to low-power microwave irradiation in its dry state. As water within the sandstone undergoes a phase transition from liquid to gas due to microwave irradiation, the resulting steam pressure causes the sandstone to rupture.

Microwave-assisted continuous flow synthesis of propofol

Herein, we present a breakthrough microwave-assisted continuous flow synthesis method for Propofol, an essential anesthetic recognized by the World Health Organization (WHO). This innovative approach exploits the synergistic potential of two cutting-edge technologies in organic synthesis: microwave irradiation and continuous flow. Using this powerful combination, we have developed an enhanced synthesis process for Propofol. Our method achieves Propofol synthesis in only two steps: Friedel-Crafts isopropylation followed by decarboxylation, with a remarkably short total residence time of 21.25 min and an impressive overall yield of 80% over both steps. Of particular note is the decarboxylation step, which is performed in an environmentally friendly solvent, glycerol, and requires a residence time of only 1.25 min. This step yields an impressive 94% with a throughput of 7.07 g h−1, demonstrating the efficiency and sustainability of our approach.

Preparation of magnetic chitosan/polyaniline nanocomposite for efficient remediation of nitrate and phosphate from water

A gel comprising of N-(2-hydroxyethyl)acrylamide (HEAAm), N,N’-methylenebis(acrylamide) (MBA), chitosan (CS), and polyaniline (PANI) made through microwave irradiation was evaluated for effective removal of nitrate and phosphate from water. The material was transformed into a nanocomposite by incorporation of magnetite (Fe3O4) nanoparticles. The nitrate and phosphate removal capacity of the nanocomposite was also evaluated in order to understand the effect of the presence of Fe3O4 on the adsorption efficiency of the gel. The nanocomposite exhibited enhanced adsorption capacity of 55.24 mg g−1 towards nitrate when compared to the value of 44.5 mg g−1 for the neat gel without nanoparticles. Also, the phosphate removal was enhanced from 51.4 to 60.60 mg g−1 due to the presence of Fe3O4 nanoparticles. The enhanced adsorption capacity of the nanocomposite is attributed to the increased surface area of the adsorbent (32.53 m2 g−1) arising from the contribution of the Fe3O4 nanoparticles embedded in the polymer matrix; as evidenced by surface area measurements. The superparamagnetic nature of the nanocomposite arising due to the presence of magnetite nanoparticles facilitates easy removal of the adsorbent after use during purification process. The mechanism of adsorption is confirmed to be the electrostatic interaction between the active sites on the nanocomposite and the adsorbate anions as indicated by XPS studies. The extent of adsorption and desorption as indicated by % desorption data and adsorption capacity values remained unchanged for about 5 cycles indicating the reusability potential of the material.

Microwave‐Assisted, Multicomponent Synthesis of Pyrazolo [3, 4‐b] Pyridines Under Green Conditions

AbstractDeveloping novel and environmentally friendly green methodologies are critical in synthetic organic chemistry. Here, we investigated the one‐pot, efficient green synthesis of pyrazolo[3,4‐b]pyridine derivatives via a multicomponent approach. The reactions were operated in an aqueous medium by using microwave irradiation and conventional protocols. The green protocol offered high yields of desired product in swift reaction time, and good tolerance under reaction conditions.

Microwave-Assisted Synthesis of CdS-MOF MIL-101 (Fe) Composite: Characterization and Photocatalytic Performance.

The present study outlines the synthesis of cadmium sulfide-metal-organic framework (CdS-MOF) MIL-101 (Fe) heterojunctions achieved via fast microwave-assisted reactions. Thus, different CdS-MOF MIL-101 (Fe) ratios were prepared to study their effectiveness as photocatalysts. These compounds were employed in the photocatalytic degradation of methylene blue (MB) under UV and visible irradiation. Structural, morphological, textural, compositional, and optical properties of the synthesized compounds determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were utilized to characterize the structural, morphological, textural, compositional, and optical properties. Electrochemical impedance spectroscopy (EIS) was also employed to determine photovoltage and photocurrent densities. The resulting valence band offset (Vfb) and band gap energy values were utilized to construct an energy band scheme. Our research revealed that the CdS-MOF MIL-101 (Fe) heterojunction enhances the efficiency of electron-hole pair separation, thereby mitigating charge carrier recombination effects. Moreover, the type I electronic band structure established an efficient reaction mechanism, effectively suppressing the recombination of photogenerated electron-hole pairs. The photocatalytic system demonstrated exceptional behavior, achieving complete MB removal within 30 min of reaction time and exhibiting outstanding stability and reusability after four reaction cycles. These findings highlight the potential of the synthesized compounds in the field of wastewater treatment for organic pollutants, offering a promising alternative to current environmental issues.