Microwave Irradiation Research Articles

Tetrabutylammonium Hydrogen Sulfate (TBAHS) Catalyzed Microwave-Assisted Synthesis of 3,4,5,6,7,9-Hexahydro-1H-xanthene-1,8-(2H)-dione Derivatives and its Biological Study

In this study, a facile and eco-friendly synthesis of novel 3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione derivatives using tetrabutylammonium hydrogen sulfate (TBAHS) as a catalyst in the microwave reactor is presented. The reaction involved the condensation of aromatic aldehydes with 1,3-cyclohexanedione in ethanol as solvent, offering significant advantages in terms of reaction rate, yield and purity. The use of TBAHS as catalyst in conjunction with microwave irradiation facilitated the formation of the target xanthene derivatives in remarkably short reaction times. Moreover, Monowave 50 microwave reactor provided precise control over reaction parameters, enabling rapid optimization of reaction conditions. Further these synthesized compounds were systematically evaluated for their antibacterial, antituberculosis and antioxidant activities.

Synthesis of exocyclic enaminone-based thiohydantoins as potent antifungal agents

A highly efficient and stereoselective synthesis of (E)-5-(dimethylamino)methylene thiohydantoins is herein reported. It was carried out through a one-pot, two-step reaction between methyl N-arylglycinates, isothiocyanates, and DMFDMA under microwave irradiation. The thermal and catalyst-free reaction of the (dimethylamino)methylene thiohydantoins with anilines led to the stereoselective formation of (E)-(anilinomethylene) thiohydantoins. The antifungal activity of the products was evaluated with a series of five Candida spp., finding a potent effect, even against a fluconazole-resistant C. glabrata strain. The docking studies suggest that this inhibitory effect is due to the binding of the compounds to the active site of fungal HMGR.

Single Step Synthesis of Cu2ZnSnS4 by Microwave Combustion Method

We report a novel single step process to synthesize Cu2ZnSnS4 nanopowder. Our novel approach is based on combustion method assisted with microwave irradiation. The obtained results showed that the precursors can be quickly decomposed in the microwave field to form Cu2ZnSnS4 nanopowder. The effects of fuel and microwave power on structures and properties of the nanopowder were investigated thoroughly by Raman spectroscopy. This synthesis process is promising for large scale fabrication of light absorbing materials for photovoltaic devices because it is facile, low cost, non-vacuum, single step and time saving.

Evaluating microwave energy impact on 3G snacks: A study on dielectric properties and expansion

Third-generation (3G) snacks, a food type of widespread interest in the industry, have a longer shelf life than second-generation (2G) snacks. The primary regeneration process for these snacks involves frying and microwaving. However, only a few studies have detailed the effects of microwave irradiation on these products. This study aims to analyse the influence of the type of material, compression, and microwave power on the expansion capabilities of the pellets. Four raw materials (rice flour, rice semolina, corn semolina, and wheat starch) were combined with water to achieve uniform moisture content and extruded into pellets with different compression ratios (1:1, 2:1, and 3:1). The elaborated samples were processed at different microwave powers (heating rates of 2 and 10 °C/s) using an instrument capable of accurately delivering microwave energy to food samples while monitoring key process parameters, including dielectric properties. Samples with high starch content, low protein content, and low fibre content, in conjunction with higher compression ratios exhibited a more pronounced expansion.

Effects of high-intensity microwave (HIMW) treatment on mechanical properties and bending failure mechanisms of radiata pine (Pinus radiata D. Don)

Effects of high-intensity microwave (HIMW) treatment on mechanical properties and bending failure mechanisms of radiata pine (Pinus radiata D. Don)

Mechanical properties and damage constitutive relationship of microwave irradiation of granite under uniaxial compression

Microwaves have great potential to increase the efficiency of hard rock breakage during mechanical excavation in engineering. This study conducted uniaxial compression tests on granite specimens after microwave irradiation at 4.85 kW. The results demonstrated a linear decrease in uniaxial compressive strength and elastic modulus correlating with increasing irradiation durations. Acoustic emission data indicated increased normalized crack closure stress and decreased normalized crack initiation and damage stress, suggesting complex crack propagation and evolution patterns under microwave influence. 3D Digital Image Correlation revealed that as heating time increased, the macrocrack leading to specimen failure shifted from being load-dominated to involving both load and microwave-induced thermal cracks. A simple four-parameter damage constitutive model for granite (a 1, r 1 , a 2, and r 2) effectively described the damage evolution under the coupling effect of microwave and uniaxial load. The model accurately characterized the complete stress–strain curves, including both microcrack compaction and post-peak stages, revealing that initial damage escalates with longer heating, though the progression rate decreases.

Green Synthesis of Magnetic Fe2O3 Nanoparticle with Chenopodium glaucum L. as Recyclable Heterogeneous Catalyst for One-Pot Reactions and Heavy Metal Adsorption.

The growth of the environment depends upon developing greener and ecological methods for managing pollutants and contamination from industrial wastewater, which causes significant effects on human health. The removal of these pollutants from wastewater using nanomaterials covers an ecological method that is free from expensive and secondary pollution. In this report, we developed magnetic iron nanoparticles from Chenopodium glaucum (CG), which showed excellent adsorption capacity at pH 5 for selective Hg2+ and Pb2+ metal ions among various heavy metal ions, with maximum adsorption capacities of 96.9 and 94.1%, respectively. These metals' adsorption process conforms to the Langmuir model, which suggests that monolayer adsorption transpires on CG-Fe2O3 nanoparticles. CG-Fe2O3 nanoparticles also act as an efficient and recyclable heterogeneous catalyst for one-pot synthesis of xanthene derivatives, yielding products with high yields (up to 97%) and excellent purity (crystalline form) within a short timeframe (6 min) using microwave irradiations (at 120 W).

Microwave-Assisted Enzymatic Reactions toward Medicinally Active Heterocycles

Microwave-Assisted Enzymatic Reactions toward Medicinally Active Heterocycles

PH-RESPONSIVE INTERPENETRATING POLYMER NETWORK HYDROGEL MICROBEADS OF POLYACRYLAMIDE-G-GUM KONDAGOGU AND SODIUM ALGINATE FOR GASTROPROTECTIVE DRUG DELIVERY: IN VITRO-IN VIVO CHARACTERIZATIONS

The present work aims to design interpenetrating polymer network (IPN) mediated hydrogel microbeads of hydrolyzed polyacrylamide-g-gum kondagogu (H-pAAm-g-GK) and sodium alginate (SA) for pH-sensitive gastroprotective drug delivery of diclofenac sodium (DS). In brief, the pAAm-g-GK was prepared using microwave irradiation, followed by conversion into a pH-sensitive polymer (H-pAAm-g-GK) using alkaline hydrolysis. Then, DS-loaded IPN microbeads were made utilizing an ionotropic gelation method using Ca+2 ions and glutaraldehyde (GA) as a crosslinking agent. After this, different characterizations, such as FT-IR, DSC, PXRD, swelling analysis, drug entrapment, drug release study, in vivo anti-inflammatory activity, etc., were performed. The amorphous state of DS in the microbeads was validated by thermograms and diffractograms, whereas SEM analysis confirmed the spherical shape of the obtained DS-loaded H-pAAm-g-GK@SA mediated microbeads. The pulsatile swelling analysis assured the H-pAAm-g-GK@SA mediated microbeads showed significantly increased swelling as the pH switched from 1.2 to 7.4. Additionally, the microbeads exhibit a 15% DS release in a pH 1.2 buffer medium, while a substantial 94% of the drug was released in a pH 7.4 buffer. It assured the DS release was drastically augmented as the pH of the surrounding medium was switched from acidic to alkaline. Principally, the COOH- groups of hydrogels offer ionization at higher pH levels, wherein the osmotic pressure within the microbeads rises, resulting in more swelling and higher drug release. Finally, the in vivo anti-inflammatory activity assured pH-sensitive sustained release of DS. In conclusion, the H-pAAm-g-GK@SA mediated pH-sensitive IPN hydrogel microbeads show potential in the design of gastroprotective oral delivery systems for DS. In the future, H-pAAm-g-GK can be used for the design of pH-sensitive IPN hydrogel microbeads for targeted delivery.

Microwave-Assisted Synthesis of Bis-(Hydroxybenzylidene)-Cycloalkanones via Acid Catalyzed Claisen-Schmidt Condensation

In the present study, bis-(hydroxybenzylidene)cycloalkanone derivatives were synthesized by Claisen-Schmidt condensation using cycloalkanones and arylaldehydes in the presence of HCl as an acid catalyst. The synthetic reaction was carried out under microwave irradiation. The structure of the synthesized compounds was determined by UV, IR, 1H NMR spectroscopic methods. The obtained reaction yields were not optimal due to the self-polymerization of p-hydroxybenzaldehyde in an acid solution.

Facile microwave synthesis of various-shaped magnetite/ reduced graphene oxide heterostructures and their magnetization properties

Heterostructures of magnetite (Fe3O4) nanoparticles and reduced graphene oxide (RGO) sheets are very common composite materials for different applications such as catalysis, energy storage, and biomedicine. Developing methods for the facile control of the size and shape of both freestanding Fe3O4 nanoparticles and those anchored onto RGO sheets is in demand. Herein, we report on the rapid and facile microwave synthesis (MWS) of Fe3O4 nanoparticles and Fe3O4/RGO with various sizes and shapes using the oleylamine (OAm)/oleic acid (OAc) ligand pair. The solvothermal synthesis using microwave irradiation (MWI) resulted in the concurrent conversion of graphene oxide (GO) into RGO and the in-situ formation of various-shaped Fe3O4 on RGO sheets. Freestanding Fe3O4 nanoparticles of various shapes were prepared using MWS for comparison. The morphological, structural, and surface properties of the samples were studied using different characterization techniques. The magnetization properties of the prepared samples were determined using a vibrating sample magnetometer. Various-shaped standalone and RGO-supported Fe3O4 nanoparticles including nanospheres, nanocubes, and nanotriangles were synthesized via MWI at 1000 W for 20 min by changing the ratios of the iron precursor and the OAm/OAc ligand pair. Interestingly, the MWI using OAm/OAc ligand pair of a molar ratio of 3:4 resulted in the in-situ formation of large hexagonal Fe3O4/RGO. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results confirm the crystallinity and spinel structure of the prepared Fe3O4 samples and prove the concurrent conversion of GO into RGO with assemblies of Fe3O4 nanoparticles. The magnetization measurements further emphasized the role of size and shape in affecting the magnetic properties of Fe3O4 and Fe3O4/RGO heterostructures. The results identify the qualities of the prepared samples and prove the MWS as a facile one-pot method for the preparation of Fe3O4 and Fe3O4/RGO heterostructures.

Selective synthesis of oxygenated fuel derivative from microwave assisted acetalization of glycerol: Optimization and mechanistic investigations

Glycerol contains 52 wt% oxygen content, therefore unable to be directly used as fuel due to its poor combustion ability. Thus, the catalytic conversion of glycerol into various oxygen-containing fuel additives is grabbing more attention nowadays. This work provides a novel, sustainable, and eco-friendly method for synthesizing heterogeneous acid carbon catalysts from pearl millet cob (PMC) waste. The hydrothermal carbonization process was carried out at different temperatures to fabricate the series of sulfonated pearl millet cob (SPMC) catalysts. XRD, FT-IR, SEM-EDS, XPS, BET, TGA, and CHNSO analyses were performed to characterize fabricated catalysts. The synthesized catalyst, SPMC-70 (catalyst synthesized at 70 °C temperature), possesses OH, COOH, and SO3H functional groups and a significant total acid density (2.03 mmol/g) with 37 m2/g surface area. The SPMC catalysts were employed for the microwave-assisted acetalization reaction of glycerol with acetone for solketal production. The optimization process was carried out using various reaction parameters, including catalyst dosage (2–6 wt.%), reaction temperature (30–60 °C), glycerol to acetone (GL to AC) molar ratio (1:3–1:9), and reaction time (4–13 min). The SPMC-70 catalyst showed the highest catalytic activity among all the synthesized catalysts and provided 99.11 ± 0.3 % GL conversion with 100 % selectivity of solketal under optimal reaction conditions. Additionally, the recyclability test was performed, and it found that the best catalyst was reusable for up to five reaction cycles. These results showed the effectiveness of carbon-based heterogeneous acid catalysts in deriving a fuel additive, solketal.

Underlying mechanism of the microwave non-thermal effect as additional microbial inactivation on Clostridium sporogenes at pasteurization temperature level

Microwave processing can induce non-thermal effects that can inactivate additional levels of microorganisms at pasteurization temperature level (80–100 °C). The objective of this study was to investigate the mechanism behind the non-thermal effects of microwaves on vegetative cells of Clostridium sporogenes. Cell membrane damage were assessed through nuclear fluorescent dyes and by measuring nuclear acid and protein leakage. The results showed that microwave non-thermal effects and conventional water bath treatment resulted in similar nuclear acid leakage. However, microwave non-thermal effects inflicted more severe damage to the cell membranes of Clostridium sporogenes, resulting in increased protein leakage from both the inner of the cell and the cell membrane (A260 = 0.25 vs. 0.18). Consequently, it can be inferred that the inactivation of additional Clostridium sporogenes by microwave non-thermal effects is primarily attributed to the disruption of cell membranes induced by alternating electromagnetic fields, and this phenomenon is further potentiated at elevated temperatures.

Investigation of Micro-Scale Damage and Weakening Mechanisms in Rocks Induced by Microwave Radiation and Their Associated Strength Reduction Patterns: Employing Meta-Heuristic Optimization Algorithms and Extreme Gradient Boosting Models

Microwave-assisted mechanical rock breaking represents an innovative technology in the realm of mining excavation. The intricate and variable characteristics of geological formations necessitate a comprehensive understanding of the interplay between microwave-induced rock damage and the subsequent deterioration in rock strength. This study conducted microwave irradiation damage assessments on 78 distinct rock samples, encompassing granite, sandstone, and marble. A total of ten critical parameters were identified: Microwave Irradiation Time (MIT), Microwave Irradiation Power (MIP), Longitudinal Wave Velocity prior to Microwave Treatment (LWVB), Longitudinal Wave Velocity post-Microwave Treatment (LWVA), Percentage Decrease in Longitudinal Wave Velocity (LWVP), Porosity before Microwave Treatment (PB), Porosity after Microwave Treatment (PA), Percentage Increase in Porosity (PP), and Uniaxial Compressive Strength following Microwave Treatment (UCSA). Utilizing the Pied Kingfisher Optimizer (PKO) alongside Extreme Gradient Boosting (XGBoost), we developed a PKO-XGBoost machine learning model to elucidate the relationship between UCSA and the nine additional parameters. This model was benchmarked against other prevalent machine learning frameworks, with Shapley additive explanatory methods employed to assess each parameter’s influence on UCSA. The findings reveal that the PKO-XGBoost model provides superior accuracy in delineating relationships among rock physical properties, microwave irradiation variables, microscopic attributes of rocks, and UCSA. Notably, PA emerged as having the most significant effect on UCSA, indicating that microwave-induced microscopic damage is a primary contributor to reductions in rock strength. Additionally, MR exhibited substantial influence; under identical microwave irradiation conditions, rocks with lower density demonstrated greater susceptibility to strength degradation. Furthermore, during microwave-assisted rock breaking operations, it is imperative to establish optimal MIT and MIP values to effectively diminish UCSA while facilitating mechanical cutting processes. The insights derived from this research offer a more rapid, cost-efficient approach for accurately assessing correlations between microwave irradiation parameters and resultant rock damage—providing essential data support for enhancing mechanical rock-breaking efficiency.

Tensile and Elastocaloric Properties of Natural/Devulcanized Waste Rubber Blends.

The need for eco-friendly cooling materials and material recycling are two urgent challenges to address. In this paper, the role of the ground tyre rubber treatment (cryo-grinding and devulcanization) is investigated on the tensile and elastocaloric properties of Natural rubber (NR)/ ground tyre rubber (GTR). The GTR particles that are sieved (<63µm) and devulcanized by microwave irradiation (1 min at 800Watts) exhibit a low network chain density (0.53 × 10-4mol.cm-3) resulting from crosslinks breakage and rubber chains scission, as supported by FTIR showing a decrease of S─S, C─S, and C─C bonds. The NR/GTR blends show a high elastocaloric effect as compared to the pristine NR, which can be ascribed to the high content of carbon black in the GTR (52wt.%) and also the high level of devulcanization of the GTR. NR/GTR blends reach a heating of +8°C and a cooling of >-6°C, resulting in a material's coefficient of performance COPmat = 2.8-3 compared to 2.6 for the pristine NR. The concomitant effect of cryogrinding and microwave devulcanization is proposed as a way to improve the tensile and elastocaloric properties of natural rubber/waste rubber blends for their possible integration into elastocaloric devices for heating/cooling applications.

Redistribution of radiative recombination centers in the SiC/por-SiC/Dy2O3 structure under the influence of athermal microwave irradiation

In this work, the authors have considered the effect of short-term nonthermal action of microwave radiation on the distribution of radiative recombination centers in SiC/por-SiC/Dy2O3 structures. The analysis of photoluminescence spectra of these structures excited by the radiation with an energy lower than the band gap in the 4H-SiC crystalline substrate has shown that the short-term action of microwave radiation leads to the migration of dislocations and, as a consequence, to redistribution of radiative recombination centers and local symmetry change.

A novel propiolate-enabled deaminative hiyama coupling of aryl silanes and propargylamines

The development of general approaches for the regioselective construction of propargylic derivatives from propargylic electrophiles remains a formidable challenge in synthetic chemistry. Enabled by the newly developed propiolate-enabled C−N activation, we disclosed an efficient palladium-catalyzed deaminative Hiyama coupling of propargylamines with aryl silanes under microwave irradiation. Various structurally diverse propargyl derivatives are produced in good to excellent yields, utilizing propargylamines as propargylic electrophiles in which C−N bond was activated by in situ formed propargylic ammonium salts. The salient features of this protocol include readily or easily available feedstock, broad substrate scope, single-step preparation, and high regioselectivity.

An insight in to microwave induced defects and its impact on nonlinear process in NiO nanostructures under femtosecond and continuous wave laser excitation.

This work demonstrates the impact of microwave (MW) irradiation on third-order nonlinear optical (NLO) processes in chemically deposited NiO nanostructure films. The optical nonlinearity of the NiO nanostructure films was studied using third-harmonic generation (THG) measurements in the pulsed femtosecond laser regime and the Z-scan technique in the continuous wave laser regime. In the ultrafast pulsed regime, THG measurements revealed a significant increase in the THG signal of MW-irradiated NiO nanostructures due to photoexcitation and relaxation processes, resulting from an enhancement in defect concentration. This increase in defect density upon MW irradiation was quantified by PL and XPS studies. Under continuous wave laser irradiation, the Z-scan technique showed an enhanced absorption coefficient of ∼10-1 m W-1 and a nonlinear refractive index of ∼10-7 m2 W-1. The high NLO values in both pulsed and continuous laser regimes indicate that MW-irradiated NiO nanostructure films hold promise for optoelectronic device applications.

Mechanism analysis of enhanced desulfurization of pulverized coal through high-gradient magnetic separation with microwave radiation

Dry high gradient magnetic separation technology is a low-carbon green technology. It can be embedded in a power plant to remove coal pyrite with a high-efficiency magnetic separator and remarkable magnetic properties difference between coal pyrite and coal matrix. This study selected the microwave radiation method to improve the magnetic properties difference and carried out a desulfurization experiment with a self-developed high-gradient permanent magnetic separator using the tapered iron auxiliary magnetic pole. The results demonstrate that the pyrite content and specific magnetic susceptibility increase with the decrease in particle size. The desulfurization rate did not change significantly at 25 °C. The coal sample began to appear in the thermal reaction at 450 °C, and the pyrite can become a strong magnetic property pyrrhotite. The desulfurization rate can achieve 58.70 % at 700 °C, and is equivalent to the wet washing index, due to the supply of high magnetic field force. The dynamic characteristic response of magnetic particles becomes more obvious with short time adsorption, and the probability of carrying non-magnetic particles is reduced. This study demonstrates that the high-gradient magnetic separation technology of pulverized coal enhanced by microwave irradiation is feasible.

Effects of low-temperature plasma, microwave and 60Co γ-irradiation treatments on the flavor characteristics of lychee whole fruit powder

Powdering whole lychee fruit is one of the most effective methods for improving the comprehensive utilization rate of lychees. In this study, lychee whole fruit powder (LWFP) was prepared and treated with low-temperature plasma, microwave, and 60Co γ-irradiation treatments to enhance its quality. Volatile organic compounds (VOCs) were analyzed using Headspace Solid Phase Micro-extraction Gas Chromatography-mass Spectrometry (HS-SPME-GC-MS), Headspace Gas Chromatography Ion Mobility Spectrometry (HS-GC-IMS), and electronic nose (E-nose) techniques. Electronic tongue (E-tongue) analysis revealed that both sweetness and bitterness were significant taste indicators of LWFP. GC-MS analysis revealed that the predominant volatile compounds in LWFP were terpenoids and alcohols, specifically nerol, geraniol, ɑ-pinene, hexylbenzene, ɑ-caryophyllene, caryophyllene oxide, and isoamylenol. GC-IMS identified small-molecule aldehydes such as 2-methyl propanal, hexanal, propanal, and 2-methylbutanal as significant contributors to the aroma profile. Moreover, key aromatic contributors include dimethyl sulfide, 1-penten-3-one, and acetic acid. Notably, microwave treatment exerted the most significant effect on the aroma profile of lychee. In contrast, low-temperature plasma and irradiation treatments exhibited similar and consistent changes. Specifically, microwave treatment primarily increased the concentration of larger terpenoid molecules such as nerol, 1-phenylhexane, and caryophyllene oxide, whereas low-temperature plasma and irradiation had a greater impact on smaller aldehyde molecules such as hexanal and 2-methylbutanal. All treatments enriched the sweet fruity, brilliant woody, and cabbage scents of LWFP.