Microwave Irradiation Research Articles

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

ABSTRACT 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.

Microwave-assisted synthesis of solketal from glycerol and acetone in the presence of SAPO-34 and SAPO-5

Solketal is one of the most promising additives improving the properties of motor fuels. Investigations related to process intensification of synthesis of solketal from glycerol and acetone is gaining importance. The present work illustrates the use of the microwave mode for intensification of this process in the presence of silicoaluminophosphates (SAPO) as catalysts. The main focus of the study was placed on tuning the textural, acidic, and catalytic properties of SAPO-34 and SAPO-5 via variation of the synthesis parameters, such as the nature of Al and Si sources and the structure-directing agent. The catalytic properties of SAPO materials were investigated in the synthesis of solketal from glycerol and acetone under microwave assistance at the acetone/glycerol molar ratio of 2.4 in a methanol solution (glycerol/methanol: 1 g/1 mL) and 56 °C. It was demonstrated that the selectivity towards solketal was 91.1–98.6 % in the presence of the studied materials. The activities of mesoporous SAPO-34 and SAPO-5 prepared in the presence of triethylamine were higher as compared with microporous SAPO-34 prepared in the presence of tetraethylammonium hydroxide due to the high mesoporosity and a larger content of acid sites. The 90.4 % conversion of glycerol and 98.6 % selectivity towards solketal were observed in the presence of mesoporous 7.6%SAPO-34 for 90 min. The advantage of using microwave technology is shown. The solketal yield in the reaction under microwave irradiation was 3 times higher than that in the process performed under thermal heating conditions.

Pt-decorated binary transition metal oxides (MnO-NiO, MnO-TiO2) for enhanced electrocatalysis of oxygen reduction and borohydride oxidation

Integrating transition metal oxides with precious metals is a strategic approach to designing cost-effective electrocatalysts with enhanced stability. Herein, platinum (Pt) nanoparticles (NPs) were prepared by microwave irradiation and anchored onto MnO and two binary metal oxides, MnO-NiO and MnO-TiO2, obtained by solid-state dispersion. Voltammetric and electrochemical impedance spectroscopy techniques evaluated their performance for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) in alkaline media. Tafel slope and the number of exchanged electrons, n, were determined to compare the three electrocatalysts’ performance for fuel cell applications. Pt/MnO-NiO revealed a Tafel slope of 177 mV dec–1 for ORR and an n value of ca. 4 and 3 e- for ORR and BOR, respectively. These findings demonstrate that Pt NPs supported on binary metal oxide supports, particularly Pt/MnO-NiO, are promising electrocatalysts for ORR and BOR in alkaline media, thus recommending their use in direct borohydride fuel cells.

Microwave Irradiation as a Powerful Tool for Isolating Isoflavones from Soybean Flour

The use of microwave irradiation energy for isolating bioactive compounds from plant materials has gained popularity due to its ability to penetrate cells and facilitate extraction of intracellular materials, with the added benefits of minimal or no use of organic solvents. This is particularly significant due to the possibility of using extracts in the food and pharmaceutical industries. The aim of this work is to examine the effect of microwave irradiation on the extraction of three of the most important isoflavones from soybean flour, glycitin, genistin, and daidzin, as well as their aglycones, glycitein, genistein, and daidzein. By varying the extraction time, temperature, and microwave power, we have established the optimal parameters (irradiation power of 75 W for 5 min) for the most efficient extraction of individual isoflavones. Compared to conventional maceration and ultrasound-assisted extraction, the total phenol content of the extracts increased from 3.66 to 9.16 mg GAE/g dw and from 4.67 to 9.16 mg GAE/g dw, respectively. The total flavonoid content increased from 0.38 to 0.83 mg CE/g dw and from 0.48 to 0.83 mg CE/g dw, and the antioxidant activity increased from 96.54 to 185.04 µmol TE/g dw and from 158.57 to 185.04 µmol TE/g dw, but also from 21.97 to 37.16 µmol Fe2+/g dw and from 30.13 to 37.16 µmol Fe2+/g dw. The positive correlation between microwave extraction and increased levels of total phenols, flavonoids, and antioxidant activity demonstrates the method’s effectiveness in producing bioactive compounds. Considering the growing recognition of glycitein’s potential role in medical and pharmaceutical applications, microwave-assisted extraction under optimized conditions has proven highly efficient.

Synthesis of coumarin dimers by a microwave-assisted double multicomponent reaction

A synthesis of coumarin dimers highly functionalized was developed using a double enol-Ugi reaction. The use of microwave irradiation permits the construction of this complex coumarin derivatives in only 5 min.This is the first report of a double enol-Ugi condensation using dialdehydes and diamines affording peptidomimetic coumarin dimers with different linkers and substituents. This methodology permits to obtain molecular diversity and complexity by a multicomponent protocol under microwave activation. The described double enol-Ugi reactions demonstrate excellent atom economy and favourable waste prevention metrics.

Enhanced microwave-catalytic performance for CO2 oxidative propane dehydrogenation by acidified and Bi-doped ZnO-based microwave catalysts

The oxidative dehydrogenation of propane by carbon dioxide (CO2-ODHP) has great potential in producing propylene. Resource utilization of CO2 will be the dominant trend in the future to mitigate environmental problems and cope with the growth in energy demand. However, simultaneously achieving high propane conversion, high propylene selectivity, and high CO2 conversion at low temperatures remains challenging. Herein, we report a novel efficient microwave catalyst (1.0-Zn4Bi1/Silicalite-1+SiC) by doping Bi on ZnO/Silicalite-1 and then acid treatment. The (1.0)-Zn4Bi1/Silicalite-1+SiC microwave catalyst exhibited 92 % C3H8 conversion, 84 % C3H6 selectivity, and 45 % CO2 conversion under microwave mode, significantly better than under the thermocatalysis (without microwave: 27 % C3H8 conversion, 92 % C3H6 selectivity, and 14 % CO2 conversion). The CO2 capture capacity was improved by adding Bi to ZnO/Silicalite-1. In addition, acid modification increased the propane and CO2 conversion by 1.9 and 1.3 times, respectively. Notably, acid treatment enriched the pore structure of the catalysts, altered surface acidity and alkalinity, and promoted C3H8 and CO2 activation and C3H6 desorption. In particular, the acid treatment enriches the state of the presence of Zn species in the catalyst. Microwave irradiation reduces the apparent activation energy of the catalytic system and accelerates the removal of coke from the catalyst surface. Microwave catalysis can activate CO2 and propane at lower temperatures than thermocatalysis.

Effects of Microwave, Infrared and Laser Beams on Physicochemical and Functional Characteristics of Cornstarch

Effects of Microwave, Infrared and Laser Beams on Physicochemical and Functional Characteristics of Cornstarch

One-Pot Synthesis of Sustainable Fluorescent Nanomaterials via Microwave Irradiation as a Probe for the Determination of Metformin in Pure and Pharmaceutical Dosage Forms: Greenness and Whiteness Metrics.

A rapid, green and sensitive technique for the determination of metformin determination was developed based on the direct fluorescence enhancement of carbon dots (CDs) induced by the cited drug. The water-soluble CDs were prepared via a one-pot synthesis from avocado peels using domestic microwave. The prepared CDs exhibited strong fluorescence at 405 nm after excitation at 320 nm with a quantum yield of 51%. The fluorescence of CDs was enhanced linearly by increasing the concentration of metformin within the range 0.5-25 μg/mL with limit of detection 0.087 μg/mL and limit of quantification 0.263 μg/mL. The designed probe was proved to be selective toward metformin in the presence of other drugs such as vildagliptin and alogliptin and also in the presence of excipients in the pharmaceutical dosage form. The suggested and reported methods were compared with the help of the whiteness and greenness tools, specifically the white analytical chemistry and analytical greenness metric tools, for assessing hazardous solvents and reagents used.

Green Synthesis of Silver Nanoparticles Using <i>Citrus sinensis</i> Peels Assisted by Microwave Irradiation as a Contrast Agents for Computed Tomography Imaging

Contrast agents are extensively used to enhance the quality of images in computed tomography (CT) scans for brain exams, vascular imaging, and full-body imaging. Recent data indicate that iodine-based contrast agents have brief durations of blood circulation and may lead to harmful toxicity effects. This study aims to produce silver nanoparticles using environmentally friendly synthesis techniques facilitated by microwaves. The characteristics of nanoparticles have been studied using UV-vis, FTIR, XRD, and TEM techniques. The TEM analysis reveals that the silver nanoparticle has an average diameter of 9 nm and exhibits a spherical shape. The contrast-to-noise ratio (CNR) values of silver nanoparticles at 100, 150, and 200 mg/L concentrations are 35.79, 48.16, and 74.66, respectively. In comparison, iodine exhibits CNR values of 28.57, 34.69, and 48.56 at the same concentrations. The CNR values for tube currents of 140, 160, and 180 mA are 37.83, 44.98, and 48.26, respectively. In contrast, the CNR values in silver nanoparticles are 63.64, 75.32, and 81.67. The results obtained from the different concentrations and tube currents clearly demonstrate that silver nanoparticles have a higher CNR than iopamidol. Hence, silver nanoparticles have significant potential as contrast agents.

Microwave-assisted dehydration of strontium hydroxide octahydrate: Experimental study and kinetic modeling analysis

In this context, the present study proposes the use of microwave irradiation to improve the dehydration rate and efficiency of strontium hydroxide octahydrate (Sr(OH)2·8H2O) without introducing contaminants. This study revealed that the use of microwave irradiation to dehydrate Sr(OH)2·8H2O is feasible and surprisingly efficient. The effects of this approach on important parameters were investigated using response surface methodology (RSM). The results revealed that the microwave dehydration process follows a linear polynomial model. In addition, compared with the heating time and material thickness, the microwave-assisted dehydration of Sr(OH)2·8H2O is sensitive to the microwave power and not to the material mass. The relative dehydration percentage reached 99.99% when heated in a microwave oven at 950 W for just 3 min. In contrast, a relative dehydration percentage of 94.6% was reached when heated in an electric furnace at 180 °C for 120 min. The XRD spectra also revealed that most of the Sr(OH)2·8H2O transformed into Sr(OH)2 after dehydration via microwave irradiation, whereas a significant portion of the Sr(OH)2·H2O remained after conventional electric dehydration. The experimental data were fitted and analyzed via the thin-layer drying dynamics model, and the results indicated that the dehydrating behavior of Sr(OH)2·8H2O could be well described by the Page model.

Influence of localized thermal effect of microwave heating on the carbothermic reduction process of ZnFe2O4

As an environmentally efficient method, microwave heating has been proposed to recover Zn from electric arc furnace dust (EAFD) recently. During the process, microwave irradiation has been shown to promote the reaction by lowering the reaction temperature and activation energy, in addition to providing efficient heat. However, the mechanism by which microwave heating promotes the zinc removal reaction of EAFD remains unclear. Thus, this study focused on ZnFe2O4, the primary component of EAFD, and developed an electromagnetic-thermal-chemical reaction coupling model to investigate the factors influencing the carbothermic reduction process of ZnFe2O4 and analyze the promoting mechanism of the microwave on the reaction. The main results indicate that the localized thermal effect, determined by the microwave distribution, exacerbates temperature differences and leads to non-uniform reaction behavior inside the sample. Increasing microwave power and graphite addition enhances the localized thermal effect, worsening field uniformity. In the simulation, the localized thermal effect of microwave heating reduced the activation energy of the zinc removal reaction to 252.97 kJ/mol, with an R2 reaction model. The assistance of the non-thermal effect in enhancing ion diffusion leads to a significant decrease in the activation energy observed in the actual microwave heating experiments.

Influence of Sulfur Addition on The Physical and Photocatalytic Properties Biosynthesized Se-doped ZnO Nanoparticles

Abstract The objective of this study was to investigate the influence of Sulfur (S) addition to selenium-doped zinc oxide (Se-ZnO) nanoparticles on their physical properties and photocatalytic activity. S,Se-ZnO sample was prepared by adding 1wt% sulfur onto 4%Se-ZnO nanoparticles. In the synthesis procedure, microwave irradiation was used as heating power and matoa leaf extract was used as a bioreductor. The nanoparticles were characterized using UV-Vis Spectroscopy, X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). The calculated band gap energies of Se-ZnO and 1% S,Se-ZnO are 2.38 eV and 2.62 eV, respectively. Both samples exhibit a hexagonal wurtzite structure. FESEM image of addition S reveals flower petal flake formations and decrease particle size of 187 nm. The photocatalytic activity of nanoparticles was evaluated through 4-nitrophenol (4-NP) degradation under UV-C irradiation. 1% S,Se-ZnO exhibits high photocatalytic efficiency compared to Se-ZnO, with a degradation percentage of 85.09% after 60 min and a reaction rate of -0.0315 min−1. Based on these results, the addition of S on Se-ZnO biosynthesized shows improve physical properties and efficient photocatalytic materials for pollutant removal.