Microwave Irradiation Research Articles

Facile Green Production of Chitin Nanomaterials from Shrimp Shell Chitin Using Recyclable Maleic Acid and Microwave Irradiation

Facile Green Production of Chitin Nanomaterials from Shrimp Shell Chitin Using Recyclable Maleic Acid and Microwave Irradiation

Effect of Perilla Seeds Pretreatment on the Volatile Profile and Flavor Characteristics of Perilla Oil: Comparison of Oven, Infrared, and Microwave Heating

ABSTRACTThe effects of microwave (MW), infrared (IF), and oven heating (OH) on the volatile profile and flavor of perilla oil were investigated in this study. Physicochemical properties and Maillard reaction products of perilla oil were measured to investigate the potential pathway of flavor formation. Sensory evaluation, combined with headspace‐solid‐phase microextraction‐gas chromatography‐mass spectrometry (HS‐SPME‐GC‐MS) and electronic nose (E‐nose) techniques, was employed to determine the categories and contents of volatile compounds in perilla oil. Three heating treatments all effectively increased the content of odor‐active volatile compounds in perilla oil. Samples treated by MW contained higher concentration of heterocyclics, while samples treated using IF and OH contained more aldehydes. The content of (E,E)‐2,4‐heptadienal were highly correlated to P‐AV. The contents of pyrazines and furans were positively correlated with A420nm, particularly 2,5‐dimethyl‐pyrazine, trimethyl‐pyrazine, and 2‐pentylfuran. The content of hexanal and (E)‐2‐hexenal showed a negative correlation with the content of heterocyclic compounds. Consequently, the volatile compounds in perilla oils were generated through three potential mechanisms: lipid oxidation, the Maillard reaction, and their synergistic effect.

One-pot green synthesis, biological evaluation, and in silico study of pyrazole derivatives obtained from chalcones

Abstract Several chalcones and their pyrazole derivatives have been synthesized using traditional methods under microwave (MW) and ultrasonic (US) irradiation. The latter were synthesized using US-assisted and MW-assisted one-pot techniques. The use of this technology led to a reduction in reaction time and energy consumption, as well as an increase in the yield of the final products, which means more efficient synthesis. An in silico study was conducted and the plant growth-stimulating effects of the synthesized compounds were revealed. To study the growth-regulating activity of the synthesized compounds, a study of aqueous suspensions at a concentration of 50 and 25 mg·L−1 was carried out on the viability, germination, and growth of seeds.

Effect of Microwave–Vacuum Drying and Pea Protein Fortification on Pasta Characteristics

The widespread popularity of pasta has driven innovations in formulations and production technologies to enhance its versatility. Techniques such as alternative drying methods and fortification of wheat pasta seek to improve the nutritional value and functional properties of pasta products, thereby increasing their attractiveness to consumers. This study aimed to evaluate the effects of microwave–vacuum drying versus conventional drying on the characteristics of durum wheat semolina pasta, including moisture content, water activity, microstructure, colour, texture, weight gain factor, and cooking loss. Three types of pea protein concentrates (80, 84, and 88% dry matter) were used at levels of 3, 6, and 9% (g/100 g flour). Results indicated that microwave–vacuum drying had a significant impact on the physical properties and cooking quality of pasta. Microwave–vacuum drying caused material puffing, resulting in microstructure with high open porosity (64.1%) and minimal closed porosity (0.1%). This has likely contributed to the short rehydration time (2 min in boiling water) of produced pasta, effectively transforming it into an instant food product. All pasta samples had low water content (<9%) and water activity (<0.4), which ensure food safety. The microwave–vacuum-dried pasta weight gain factor (2.2) was lower than in the conventionally dried pasta (2.8). The firmness of microwave–vacuum-dried pasta was significantly higher (135 g) than that of conventional pasta (16 g). Fortification with pea protein enhanced porosity but did not affect pasta’s culinary parameters, such as weight gain or cooking loss, although it resulted in darker pasta (p = 0.001), especially notable with a 9% pea protein addition.

Carbon dots nanoparticles derived from showy Asian grapes (Medinilla speciosa) for free radical scavenger

Carbon dot nanoparticles (CNPs) were synthesized from the peels of showy Asian grapes (Medinilla speciosa) using microwave irradiation for free radical scavenging. The optimal emission and absorption intensities were achieved with a 50-min irradiation duration, at wavelengths of 430 nm and 267 nm, respectively. XRD analysis revealed characteristic peaks at angles of 26.37° and 29.63°. FTIR analysis indicated that antioxidant potential is attributed to hydroxyl and carboxyl groups on the CNPs’ surface. TEM images showed diameters ranging from 2 nm to 8 nm. The CNPs exhibited 73.82% antioxidant activity at 5 mg/mL, with an IC50 value of 6.89 ppm, indicating strong antioxidant activity. Additionally, the CNPs demonstrated good storage stability, suggesting potential applications in food supplements and biomedical materials.

Rapid Synthesis of Non-Toxic, Water-Stable Carbon Dots Using Microwave Irradiation

Carbon dots (C-Dots) have garnered significant attention in various fields, including biomedical applications, photocatalysis, sensing, and optoelectronics, due to their high luminescence, biocompatibility, and ease of functionalization. However, concerns regarding their potential toxicity persist. Conventional synthesis methods for C-Dots often require long reaction times, high pressures, expensive equipment, extreme temperatures, and toxic reagents. In contrast, microwave irradiation provides a rapid, cost-effective, and scalable alternative for the synthesis of high-quality C-Dots. In this study, we report the single-step, 3-min synthesis of water-stable carbon dots at 100 °C, 120 °C, and 140 °C using microwave irradiation. Particle stability was achieved through polyethyleneimine (PEI) functionalization. The toxicity of the synthesized carbon dots was evaluated in marine crustaceans, revealing that C-Dots with an estimated size below 10 nm did not exhibit toxicity after 24 and 48 h of exposure. These findings demonstrate the potential of microwave-synthesized carbon dots as non-toxic, water-stable nanomaterials for environmental and biomedical applications.

Micro-fracture mechanism of microwave induced fracturing of basalt based on a novel Electromagnetic–Thermal–Mechanical coupling model

Microwave-assisted rock fracturing is recognized for its efficiency, energy savings, and environmental benefits. Investigating microscopic mechanisms of microwave-induced rock fracturing is essential for predicting the weakening effect on rock. A coupled Electromagnetic–Thermal–Mechanical model based on FEM–DEM was established to describe the response of rock under microwave irradiation. This model employs interpolation algorithms and mineral lattices randomization algorithms to establish a 2D cross-sectional representation of rock. A discrete element calculation method is proposed to synchronize computational time with the experimental time. The model can simulate the multi-physical field response of different rocks under various conditions, making it an effective tool for studying microwave-induced rock fracturing. The effectiveness of the numerical model was validated through open-end microwave-induced fracturing experiments on basalt. Additionally, the study elucidates the micro-fracture mechanism of basalt under microwave irradiation. The results indicate that the direction of crack propagation is influenced by microwave power and boundary effects. The patterns of fracture development between minerals are summarized as follows: Initial fractures primarily result from the rapid heating of microwave-absorbing minerals like enstatite,creating a significant temperature gradient. With increased heating time, heat transfers to highly expansive minerals such as olivine, causing fractures due to localized thermal expansion.

Dynamic Nuclear Polarization with P1 Centers in Diamond.

Substitutional nitrogen impurities within the diamond lattice, known as P1 centers, have unpaired electrons that can mediate microwave driven dynamic nuclear polarization (DNP). In this paper we explore DNP of the bulk 13C spins in micrometer-sized P1 diamond particles and demonstrate a 550-fold DNP enhancement of the bulk 13C spins at room temperature in a 9 T magnetic field or 250 GHz for g ≈ 2 electrons. We study the DNP mechanisms, exploring their dependence on sample spinning frequency and microwave irradiation frequency using both continuous wave and frequency swept microwave irradiation, and discuss the results alongside recent DNP studies in the literature. Even with a modest microwave irradiation power of 160 mW from our frequency swept solid-state microwave source, we achieve a significant 13C signal enhancement, ε = 270 at room temperature. The enhancements were found to increase with the magic angle spinning (MAS) frequency, ωr/2π, and the results provide mechanistic insights into how different electron populations contribute to the observed DNP efficiency. These findings are inherently interesting and of practical importance in view of the recently reported diamond rotors fabricated from P1 high-pressure, high-temperature (HPHT) diamond.

In Situ Synthesis of NPC-Cu2O/CuO/rGO Composite via Dealloying and Microwave-Assisted Hydrothermal Technique

The nanoporous copper (NPC)-copper oxides (Cu2O/CuO)/reduced graphene oxide (rGO) composite structure was synthesized by combining the dealloying process of Cu48Zr47Al5 amorphous ribbons with a microwave-assisted hydrothermal technique at a temperature of 200 °C. The main advantage of the microwave-assisted hydrothermal process is the oxidation of nanoporous copper together with the in situ reduction of graphene oxide to form rGO. The integration of rGO with NPC improves electrical conductivity and streamlines the process of electron transfer. This composite exhibit considerable potential in electrochemical catalysis application, due to the combined catalytic activity of NPC and the chemical reactivity of rGO. Our study relates the transition to n-type rGO in microwave-assisted hydrothermal reactions, and also the development of an electrode material suitable for electrochemical applications based on the p-p-n junction NPC-Cu2O/CuO/rGO heterostructure. To confirm the formation of the composite structure, structural, morphological, and optical techniques as XRD, SEM/EDX, UV-Vis and Raman spectroscopy were used. The composite’s electrochemical properties were measured by EIS and Mott-Schottky analyses, showing a charge transfer resistance (Rp) of 250 Ω and indicating the type of the semiconductor properties. The calculated carrier densities of 4.2 × 1018 cm−3 confirms n-type semiconductor characteristic for rGO, and 7.22 × 1018 cm−3 for Cu2O/CuO indicating p-type characteristic.

Microwave-induced enhancements in the structural, optical, dielectric, and magnetic properties of Er2O3/MgO nanocomposites

Erbium-trioxide (Er2O3) and magnesium oxide (MgO) nanocomposite were effectively synthesized in the form of crystalline powder using a microwave irradiation approach. Various techniques were employed for identifying crystalline structure, FTIR fingerprint region, fluorescence emission behaviors, and surface morphology, dielectric, and magnetic properties using PXRD, FTIR spectroscopy technique, fluorescence spectroscopic technique, SEM analysis, frequency vs. dielectric constant, and MH curve analysis, respectively. Confirmation of the metal-oxygen bond such as Er2O3, and MgO was established through the analysis of stretching frequencies in the FTIR spectrum. The PXRD results using Rietveld refinement confirmed the crystalline nature of the synthesized nanoparticles, consisting of Er2O3, and MgO with unit cell compositions ~ 94.12 and ~ 5.88%, respectively. SEM imaging provided insights into the morphology of the particles, revealing a spherical shape with noticeable agglomeration. The elemental compositions such as Erbium (Er) and Oxygen (O), were validated by the EDS spectrum, confirming the successful achievement of Er2O3, and MgO nanoparticle in the synthesized composite. In addition, the vibrating sample magnetometer (VSM) graph illustrated the paramagnetic behavior of the doped Er2O3/MgO composite at room temperature. The thorough examination of the synthesized Er-MgO NPs, covering structural, morphological, and magnetic characteristics, contributes to a comprehensive understanding of their properties.

NHC‐Catalyzed, Microwave‐Assisted and Base‐Dependent Reactions of Substituted Cinnamaldehydes Towards γ‐Lactones or Saturated Esters

N‐Heterocyclic carbenes (NHCs) generated from imidazolium, imidazopyridinium and imidazoquinolinium hydrochlorides in situ using base and microwave irradiation were employed as organocatalysts to yield homoenolates from cinnamaldehyde and its aryl‐substituted analogs. Depending on the catalytic base either γ‐lactones were prepared when the strong base tBuOK was used or the corresponding saturated ethyl 3‐aryl propionates were synthesized with the milder DIPEA base. Novel imidazopyridinium and imidazoquinolinium hydrochlorides were synthesized and were compared to commercially available NHCs IMes and IDip for their catalytic activity. The optimum reaction conditions were established using IMes and the broad scope of both reactions was investigated using the 4 most efficient NHCs.

Copper-Catalyzed Radical Sulfonylation: Divergent Construction of C(sp3)-Sulfonyl Bonds with Sulfonylhydrazones.

Sulfonylhydrazones have been proven to be versatile synthetic intermediates in a panel of transformations. However, radical sulfonylation with sulfonylhydrazone as sulfonyl radical source is relatively rare. Here, we found that sulfonylhydrazone can serve as a new sulfonyl radical precursor to couple various partners such as arylacetic acids, ene-yne-ketones, and para-quinone methides under copper catalysis and microwave irradiation. The reactions of sulfonyl radicals have been successively developed to enable the divergent synthesis of C(sp3)-sulfonyl bonds. In addition, when alkynes and alkenes are used as radical receptors, this method can also promote the formation of C(sp2)-sulfonyl bonds. This finding suggests that sulfonylhydrazone could be regarded as a potentially useful sulfonyl radical in sulfone synthesis.

Green Synthesis of 2-Mercapto 5,6-Dihydro-4H-1,3-Thiazines via Sequential C–S Couplings

The six-membered N,S-heterocyclic 1,3-thiazines and their derivatives are widely acknowledged as pharmaceutical molecules with a wide range of biological activities. In this study, we developed a unique thiol-involved cascade reaction that enables the efficient construction of the 5,6-dihydro-4H-1,3-thiazine scaffold through consecutive intermolecular thiol-isothiocyanate and intramolecular thiol-halogen click reactions. Structurally diverse 2-mercapto dihydrothiazines including three antitumour candidates of bis-dihydrothiazines were readily obtained in high yields from the readily available thiols and 3-chloroisothiocyanate in the green solvent EtOH/H2O (1:1) using K2CO3 (0.6 equiv.) as the base. Between the two synthesis procedures investigated, the microwave-assisted reaction generally behaved more efficiently than that under routine heating conditions. Furthermore, DFT calculation confirmed the sequential addition–substitution mechanism. This cascade C–S coupling reaction methodology offers several advantages, including rapid completion, high reliability, easy purification, and benign conditions.

Utilization of poly(methacrylic acid)‐rice straw graft copolymers for Pb2+ ions removal from wastewater: Synthesis, characterization, and adsorption studies

AbstractRice straw bio waste was converted into a high‐performance adsorbent for Pb2+ ions removal by grafting it with methacrylic acid using microwave irradiation. For this purpose, six levels of poly(MAA)‐rice straw graft copolymers having different graft yields % with increasing order and designated as (PMAARSGC‐I to PMAARSGC‐VI) were prepared and characterized using FTIR, SEM, XRD, TGA, zeta potential and BET analysis. Different factors affecting the Pb2+ removal expressed as adsorption capacity such as pH, extent of grafting, treatment time, and lead ions concentrations were studied in detail. Various kinetics models (pseudo‐first‐order, pseudo‐second‐order, Elovich, and intraparticle diffusion), isothermal (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich) and thermodynamic studies have been applied. The results demonstrated that (a) FT‐IR, SEM, XRD, TGA, zeta potential, and BET analysis confirmed the formation of carboxyl groups onto the graft copolymer, (b) the adsorption capacity increased with increasing the Pb2+ concentration and extent of grafting within the range studied; pH from 1 to 6; and the adsorption time up to 60 min then leveled off afterward, (c) maximum adsorption capacity of poly(MAA)‐rice straw graft copolymer was found to be 118 mg/g at pH 6, 200 mg/L lead ions concentration, adsorption time, 60 min, and 0.1 g adsorbent, (d) the kinetic and isothermal studies revealed that the privilege of Elovich model and pseudo‐second‐order rate equation as well the Langmuir model with more R2 value. The calculated thermodynamic parameters indicated that the adsorption process was achievable, spontaneous, and exothermic at 298–318 K. Finally, the preliminary adsorption mechanism representing the interaction between the adsorbent and adsorbate has been projected.

Multi-stage evolution of pore structure of microwave-treated sandstone: Insights from nuclear magnetic resonance

Microwave fracturing has great potential in improving the efficiency of hard rock breaking. However, the pore evolution, which can be regarded as the damage accumulation and progressive failure of the rock subjected to microwave irradiation, remains unclear. In this study, nuclear magnetic resonance (NMR) is employed to investigate the pore evolution and fracture mechanism of the sandstone under different microwave power levels. The results show that the pore evolution of the specimens, including distribution of pore size, the weight in volume of various-sized pore, and porosity, exhibits different changing trends under various microwave power levels. The pore evolution of the specimens under microwave irradiation can be categorized into four phases: overall pore expansion, localized pore closure in the internal region, micro-cracks propagation induced by thermal stress, and macro-cracking (or melting). Moreover, pore evolution also plays a crucial role in the decomposition and evaporation of bound water, particularly when the specimens experience fractures triggered by thermal stress induced by the microwave treatment (TSIMT). The employing of NMR imaging (NMRI) description also provides an auxiliary and effective illustration on the pore evolution of the specimens under microwave irradiation. Finally, the mechanism of microwave-assisted rock breaking under different power levels is comprehensively discussed based on the NMR results from a microscopic perspective. It is anticipated that the findings of this study can provide valuable insights for enhancing the efficiency of microwave-assisted rock breaking.

High volumetric-energy-density flexible supercapacitors based on PEDOT:PSS incorporated with carbon quantum dots hybrid electrodes

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a highly successful conductive polymer utilized as an electrode material in energy storage units for portable and wearable electronic devices. Nevertheless, employing PEDOT:PSS in supercapacitors (SC) in its pristine state presents challenges due to its suboptimal electrochemical performance and operational instability. To surmount these limitations, PEDOT:PSS has been integrated with carbon-based materials to form flexible electrodes, which exhibit physical and chemical stability during SC operation. We developed a streamlined fabrication process for high-performance SC electrodes composed of PEDOT:PSS and carbon quantum dots (CQDs). The CQDs were synthesized under microwave irradiation, yielding green- and red-light emissions. Through optimizing the ratios of CQDs to PEDOT:PSS, the SC electrodes were prepared using a spray-coating technique, marking a significant improvement in device performance with a high volumetric capacitance (104.10 F cm−3), impressive energy density (19.68 Wh cm−3), and excellent cyclic stability, retaining ∼85% of its original volumetric capacitance after 15,000 repeated GCD cycles. Moreover, the SCs, when utilized as a flexible substrate, demonstrated the ability to maintain up to ∼85% of their electrochemical performance even after 3,000 bending cycles (at a bending angle of 60°). These attributes render this hybrid composite an ideal candidate for a lightweight smart energy storage component in portable and wearable electronic technologies.

Exploration of microwave absorptivity and catalysis of CMF@Co-MoS2 for microwave-initiated depolymerization of lignin

Obtaining key platform chemicals from lignin is a sustainable refining concept of the non-petroleum route. Rapid pyrolysis is a potential refining technology, and microwave-assisted catalytic depolymerization with low energy consumption is preferred. Herein, we reported the strategy of microwave-initiated depolymerization using a self-designed dynamic vapor flow reaction system with a facilely prepared CMF@Co-MoS2-0.18 catalyst, achieving efficient conversion of lignin (Dealkalize) to monophenol. Under constant microwave irradiation (2.45 GHz), the CMF@Co-MoS2-0.18 catalyst had excellent dielectric properties (Dielectric loss factor: 0.56) and microwave heating properties (∼140 s rise to ∼ 600℃). Therefore, microwave-initiated depolymerization of lignin showed that the CMF@Co-MoS2-0.18 catalyst can improve the monophenol content (54.72 %) and phenol selectivity (35.84 %) under the synergistic effect of microwave absorptivity and catalysis. The reaction of the lignin model and kinetics analysis show that the CMF@Co-MoS2-0.18 catalyst increases the yield of monophenol by reducing depolymerization activation energy and selectively breaking the β-O-4 bond. The finite element analysis pointed out that under microwave irradiation, CMF@Co-MoS2-0.18 continuously conducted heat to lignin and the lignin vapor would have sufficient energy to collide with the catalyst active site at a high frequency, which led to an increase in the pre-exponential factor and initiated catalytic depolymerization lignin. In summary, we provide a potential pathway for the rapid conversion of lignin into key platform chemicals.

A selective resonance Rayleigh scattering method for determination of iodine by graphene oxide surface molecularly imprinted polyacrylamide probe

A new graphene oxide nanosurface molecularly imprinted polymer (GO@MIP) probe was synthesized by microwave irradiation, using graphene oxide (GO) as the carrier, iodine as the template molecule, acrylamide as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinking agent, azodiisobutyronitrile (AIBN) as the initiator, and acetonitrile as the pore forming agent. The nanoprobe recognizes the iodine, and exhibits significant resonance Rayleigh scattering energy transfer (RRS-ET) effect between iodine as the acceptor and the nanoprobe as donor. When iodine concentration was in the linear range of 0.02–0.5 mmol/L, the decreased RRS intensity was linear to the concentration. And it was used for the determination of iodine in water samples and iodate ions in salt samples.

Identification of imidazo[1,2-a]pyridines-pyrazole-pyran hybrids as potent glucose-6-phosphate dehydrogenase (G6PD) inhibitors: Synthesis, molecular docking, DFT studies and ADME prediction

In this study, we aimed to identify new anticancer agents by synthesizing a series of Imidazo[1,2-a]pyridines fused with pyrazole-pyran scaffolds 7a–g in good yields (75–85 %) under microwave irradiation. The synthesis was performed through a one-pot, three-component cyclocondensation reaction of 2-(p-substituted)imidazo[1,2-a]pyridine-3-carbaldehyde 4a-g, malononitrile 5, and 5-methyl-2,4-dihydro-3H-pyrazol-3-one 6 in the presence of triethylamine as a catalyst in acetonitrile. The characterization of all synthesized compounds was accomplished through various spectroscopic techniques. All the synthesized compounds were investigated for their anticancer potential in vitro, using an MTT-based assay against A549 lung cancer cell lines. Compounds 7b, 7e, and 7c demonstrated notable anti-proliferative activity against the A549 cell line, while compound 7e showed a significantly lower fluorescence generation (24-fold less) in the G6PD inhibition assay compared to the other compounds.

Effect of Hierarchical Architecture of Nickel Modified Mesoporous Catalysts on the Knoevenagel Condensation Reaction

AbstractA series of ordered mesoporous silicas (MCM‐41, SBA‐15 and KIT‐6) were successfully synthesized and modified with nickel by incipient wetness impregnation method. The supports and catalysts were characterized by N2 adsorption‐desorption, XRD, TEM, H2‐TPR, UV vis‐DR, XPS, ICP and Py FT‐IR techniques. All the materials were evaluated in the Knoevenagel condensation reaction between vanillin and malononitrile under microwave irradiation. The catalytic results show the key role that the chosen porous structure plays in the deposition of the active phase and its catalytic behaviour. Thus, by designing a suitable mesoporous catalyst it was possible to carry out such Knoevenagel condensation to obtain 2‐(4‐hydroxy‐3‐methoxybenzylidene) malononitrile through a highly efficient and environmentally friendly process, without solvents and reducing reaction times by employing microwave heating.