Min Of Microwave Irradiation Research Articles

Cyclic Voltammetry Study and Solar Light Assisted Photocatalytic Activity of the CeFeO3/CeO2/Fe2O3 Composite.

The semiconducting nature of CeFeO3/CeO2/Fe2O3 nanocomposite has permitted the degradation of the organic toxic dye methylene blue under the irradiation of ultraviolet and visible light portions of solar radiation. Fullprof-assisted Rietveld refinement analysis, performed using the Match software, has revealed the orthorhombic nature of CeFeO3. In addition, in the synthesized material, the cubic phase byproduct CeO2 was found due to the highly oxidizing nature of the cerium element. This occurred due to 6 min microwave irradiation because the microwave-assisted technique offered random distribution of heating during the supply of 800-W power for 30 s, followed by 12 cycles. Additionally, the presence of Fe2O3 was also confirmed through Match software-assisted Rietveld refinement analysis through phase matching. During the synthesis, a certain portion of the synthesized CeFeO3 experienced overheating, leading to phase transformation from CeFeO3 into Fe2O3 and CeO2. The unit cell compositions of CeFeO3, CeO2, and Fe2O3 were found in the sample material with 35.54%, 52.43%, and 12.03%, respectively. The appearance of a fingerprint absorption region in the FTIR spectrum around 577.36 and 535.38 cm-1 further confirmed the similarity of these values (577.36 and 535.38 cm-1) to those obtained from the calculated values obtained by substituting Rietveld refined bond length parameters. The fourth step process in the thermal analysis curve (TGA) revealed the oxidation process, which led to the destruction of the CeFeO3 phase, causing the transformation of CeFeO3 into two byproducts (CeO2 and Fe2O3). This oxidation process permitted in an observable weight gain, which is observed in the thermal analysis curve (TGA). A cyclic voltammetry study (the experimentally measured current-voltage characteristic curve) revealed slightly distorted semirectangular CV curves, confirming the pseudo-capacitive behavior of the synthesized composite.

Vaccinium myrtillus L. Leaf Waste as a Source of Biologically Potent Compounds: Optimization of Polyphenol Extractions, Chemical Profile, and Biological Properties of the Extracts.

The aims of the present research include (1) optimization of extraction from Vaccinium myrtillus leaf waste via investigation of plant material:medium ratio, extraction medium, and extraction period, employing extractions at room and high temperatures, or using ultrasound and microwaves (M, HAE, UAE, and MAE, respectively), (2) physicochemical characterization, and (3) investigation of extract biological potential. The statistical analysis revealed that optimal levels of parameters for the greatest polyphenolic yield were a proportion of 1:30 g/mL, ethyl alcohol 50% (v/v) during 2 min of microwave irradiation. By LC-MS analysis, 29 phenolic components were detected; HAE showed the highest richness of almost all determined polyphenols, while chlorogenic acid and quercetin 3-O-glucuronide were dominant. All extracts showed a high inhibition of Staphylococcus aureus growth. The effect of different parameters on extracts' antioxidant capacity depended on the used tests. The extracts also showed a stimulative influence on keratinocyte viability and anti-inflammatory activity (proven in cell-based ELISA and erythrocyte stabilization assays). The extraction procedure significantly affected the extraction yield (MAE ≥ maceration ≥ UAE ≥ HAE), whereas conductivity, density, surface tension, and viscosity varied in a narrow range. The presented research provides evidence on the optimal extraction conditions and technique, chemical composition, and antioxidant, antimicrobial, anti-inflammatory, and keratinocyte viability properties of bilberry extracts for potential applications in pharmacy and cosmetics.

Microwave responsive copper-ferrite (CuFe2O4) encapsulated in molybdenum-disulfide (MoS2) nanoflower catalyst for antibiotic removal via persulfate oxidation

Microwave (MW) responsive copper-ferrite/molybdenum-disulfide (CuFe2O4/MoS2) nanoflower catalyst was implemented for rapid antibiotic metronidazole (MNZ) degradation via persulfate oxidation under MW irradiation. The catalyst was synthesized via co-precipitation followed by hydrothermal methods, and characterized by XRD, FTIR, SEM, TEM, VSM, XPS, and UV-DRS. As a first step, MW induced MNZ removal was studied at different initial mass of CuFe2O4/MoS2 (2.5–20%), where 5% CuFe2O4 in the nanocomposite performed the best. Within 5 min of MW irradiation, 100% MNZ removal was observed (Kobs ∼ 1.063 min−1) under the optimal reaction conditions (i.e., CuFe2O4/MoS2 dose ∼ 0.4 g/L; PS dose ∼ 100 mg/L; temperature ∼ 90 °C; and MW power ∼ 350 W). The MNZ removal was independent of solution pH 3–11, and the removal was by SO4•−and •OH radicals alongside the limited contribution from O2•−. PS and H2O were thermally decomposed to produce SO4•−and •OH radicals, whereas intrinsic semiconductor CFO/MS with a narrow bandgap of 1.53 eV allowed electrons to jump into conduction band from valance band to create SO4•− and O2•−. However, the performance of MW system was inhibited by the presence of anions in the order of Cl−< NO3− <CO32− <H2PO4−. Robustness of the CuFe2O4/MoS2 was proved via recyclability experiments, and MNZ removal was found to be dropped ∼ 4.89% at the end of 5th cycle. It was proposed that the absorbed MW energy was dissipated through various losses to generate ‘hotspots’ (>1200 °C) for MNZ removal. Synergistically, redox couples of transitional metals contributed to MNZ degradation.

Agricultural waste-based microporous catalysts for oxidative desulfurization of highly sour heavy gas oil

In recent years, the use of abundant and low-cost biomaterials such as agricultural wastes in the preparation of activated carbon has been receiving a lot of attention. Besides, the conventional middle and heavy fuel cuts require a substantial and cost-effective sweetening process because sulfur in transportation fuel was found as one of the main causes of air pollution. The present work explored the preparation and characterization of microporous activated carbon (AC) catalysts prepared from olive stone by tubular furnace (Fe/AC1) and microwave (Fe/AC2) heating methods using H3PO4 (85 wt%) as chemical activating agents. The kinetics of the oxidative desulfurization process (ODS) of a highly sour diesel fuel (sulfur content = 7361 ppm) was determined. The effect of the heating method on the texture and morphological structure, surface area, and surface chemistry of the carbons produced was investigated. Fe/AC1 was prepared in a horizontal tabular furnace at 650 °C calcination temperature and 90 min residence time under a nitrogen atmosphere, while Fe/AC2 was performed in a microwave reactor with 565 W and 7 min microwave power and irradiation time respectively. The catalysts were characterized by N2- adsorption-desorption, SEM-EDX, FTIR, XRD, XRF, TGA, PSD, and elemental analysis. It was found that the use of a tubular furnace for heating the olive seeds resulted in a higher surface area and yield. Also, the characterizations of the Fe/AC1 catalyst showed that it has a large surface area of 1175 m2/g and micropore volume of 0.6954 cm3/g whereas Fe/AC2 had a surface area of 854 m2/g and micropore volume of 0.6936 cm3/g. Moreover, SEM-EDX results indicated that Fe/AC1 was dispersed uniformly better than Fe/AC2. Also, TGA/DTA results revealed better results for Fe/AC1 than Fe/AC2 making it favorable in ODS experiments. The difference in texture and chemical properties is caused by the heating methods. The desulfurization removal was investigated under different temperatures (80, 90, 100, 110 °C) and reaction time (30–90 min). The kinetics of the ODS were conducted over the efficient Fe/AC1 catalyst prepared. It was shown that the ODS reaction followed pseudo-first-order kinetics with a fairly low activation energy over the catalyst was 40.71 kJ/mol.

Ultrasonic-Assisted and Microwave-Assisted Extraction of Phenolics and Terpenoids from Abelmoschus sagittifolius (Kurz) Merr Roots Using Natural Deep Eutectic Solvents.

This research extracted phenolics and terpenoids from Abelmoschus sagittifolius (Kurz) Merr roots using natural deep eutectic solvent-based novel extraction techniques. Twelve natural deep eutectic solvents (NADESs) were produced for recovering phenolics and terpenoids. Citric acid/glucose and lactic acid/glucose, with a molar ratio of 2:1, were determined as the most appropriate NADESs for extracting phenolics and terpenoids, respectively. Afterward, the proper conditions for NADES-based ultrasonic-assisted and microwave-assisted extraction were investigated. Then, the time and liquid-to-solid ratios of ultrasonic- and microwave-combined extraction methods and the sequence of ultrasound and microwave treatments were examined. The conditions of ultrasonic-assisted extraction were 40 mL/g liquid-to-solid ratio, 40% water content, 30°C, 5 min, and 600 W ultrasonic power for the highest terpenoid recovery at 69 ± 2 mg UA/g dw, while 150 W ultrasonic power was suitable for phenolic recovery at 9.56 ± 0.17 mg GAE/g dw. The conditions of microwave-assisted extraction were 50 mL/g liquid-to-solid ratio, 20% water content, 400 W microwave power, and 2 min to acquire the highest phenolics and terpenoids at 22.13 ± 0.75 mg GAE/g dw and 90 ± 1 mg UA/g dw, respectively. Under appropriate conditions, the biological activities, phenolic content, and terpenoid content of obtained extracts from four extraction methods, including ultrasonic-assisted, microwave-assisted, ultrasonic-microwave-assisted, and microwave-ultrasonic-assisted extraction, were compared to select the most proper method. The conditions of ultrasonic-microwave-assisted extraction were 40 mL/g liquid-to-solid ratio, 5 min sonication, and 1 min microwave irradiation to obtain the highest phenolic and terpenoid contents (27.07 ± 0.27 mg GAE/g dw and 111 ± 3 mg UA/g dw, respectively). Ultrasonic-microwave-assisted extraction showed the highest phenolic content, terpenoid content, and biological activities among the four extraction techniques. The changes in the surface morphology were determined using scanning electron microscopy. This study demonstrated that ultrasonic-microwave-assisted extraction was an effective and sustainable method in food and pharmaceutical industries for recovering phenolics and terpenoids from Abelmoschus sagittifolius (Kurz) Merr.

Enhancing Microwave Dynamic Effects via Surface States of Ultrasmall 2D MOF Triggered by Interface Confinement for Antibiotics-Free Therapy.

Microwave (MV)-trigged dynamic therapy based on MV-responsive materials is promising for treating deep infection diseases that cannot be effectively treated by antibiotics, like life-threatening osteomyelitis. Surface states of materials affect the generation of free charges under the excitation source with energy less than the band gap, consequently influencing the MV dynamic effects. Herein, an MV responsive system with interface confined 2D metal-organic framework (2D MOF) on oxidized carbon nanotube (CNT) is prepared, in which the ultrasmall Cu-based 2D MOF possesses sufficient surface/interface defects, endowing the system a large number of surface states. Under MV irradiation, the synthesized CNT-2D MOF not only efficiently absorbs and converts the microwave into heat for microwaveocaloric therapy (MCT) via enhanced hetero-interfacial polarization, but also generates excited electrons via surface state for microwave dynamic therapy (MDT). This biocompatible CNT-2D MOF exhibits highly effective broad-spectrum antimicrobial activity against seven pathogenic bacteria, including Gram-negative and Gram-positive pathogens, under 7min MV irradiation. And this system is proven to efficiently eradicate Staphylococcus aureus infected rabbit tibia osteomyelitis. Significantly, MV-excited MCT and MDT of CNT-CuHHTP developed in this study makes a major step forward in antibiotic-free MV therapy in deep tissue bacterial infection diseases.

Fast Microwave-Assisted Green Synthesis of Silver Nanoparticles Using Low Concentration of Seminyak (&lt;i&gt;Champeria&lt;/i&gt; sp.) Leaf Extract

Silver nanoparticles (AgNPs) are fascinating materials for biomedical applications thanks to their strong antibacterial activity and biocompatibility. This study applied the green synthesis method using 0.5 wt.% Seminyak leaf extract and assisted with one min microwave irradiation to enhance AgNPs formation. Extremely small sizes AgNPs with an average particle size of 9.1 ± 4.1 nm and spherical shapes were obtained. The synthesized AgNPs displayed potent antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria with a zone of inhibition of 12.3 ± 0.1 and 13.7 ± 0.7 mm, respectively. The MTT assay results demonstrated that the cells’ viability of the obtained AgNPs was 88.5 ± 7.0 %, implying biocompatibility for biomedical applications.

Microwave-assisted alkali pre-treatment medium for fractionation of rice straw and catalytic conversion to value-added 5-hydroxymethyl furfural and lignin production

In the current study, the use of microwave-assisted sodium hydroxide medium (MWSH) for pre-treatment and saccharification of rice straw to obtain sugar syrup for the production of 5-hydroxymethyl furfural (5-HMF) was investigated. The optimization of the MWSH pre-treatment was carried out using central composite methodology, resulting in a maximum reducing sugar yield of 350 mg/g of treated rice straw (TRS) and a glucose yield of 255 mg/g of TRS under the conditions of a microwave power of 681 W, a NaOH concentration of 0.54 M, and a pre-treatment time of 3 min. Additionally, the microwave assisted transformation of sugar syrup with titanium magnetic silica nanoparticle as catalyst, producing 41.1 % yield of 5-HMF from the sugar syrup after 30 min microwave irradiation at 120 °C with catalyst loading of 2.0:200 (w/v)). The structural characterization of the lignin was analysed using 1H NMR techniques, and the surface carbon (C1s spectra) and oxygen (O1s spectra) composition changes of the rice straw during pre-treatment were analysed using X-ray photoelectron spectroscopy. The rice straw based bio-refinery process which contains MWSH pretreatment followed by dehydration of sugars achieved high efficiency of 5-HMF production.

An efficient method to obtain essential oil from Asarum heterotropoides via homogenate-microwave-assisted hydrodistillation and evaluation of Fusarium species inhibition activity in vitro compared to its main components

An improved method was investigated to obtain the essential oil from the roots and rhizomes of Asarum heterotropoides (RRAH) via homogenate-microwave-assisted hydrodistillation compare to conventional grinding process and the RRAH essential oil, methyleugenol, 3,4,5-trimethoxytoluene, and 3,5-dimethoxytoluene all had inhibitory effects on Fusarium species, with methyleugenol exhibiting the greatest inhibitory effect on them. We systematically explored some of the parameters that may affect the yield of essential oils. The maximum yield of the RRAH essential oil was 27.98 ± 1.4 mL/kg under the optimized conditions (22000 r/min homogenization speed, 3 min homogenization time, 460 W microwave irradiation power, 23 min microwave irradiation time and 23 mL/g liquidsolid ratio). Methyleugenol was the main component of RRAH essential oil (41.13%) analysed by GCMS. Studies on antifungal activity suggest that methyleugenol has potential and broad application prospects in the direction of preservative-related fields such as slow-release microencapsulation in the future.

A novel insight into the microwave induced catalytic reduction mechanism in aqueous Cr(VI) removal over ZnFe2O4 catalyst.

Aqueous Cr(VI) pollution is an emerging environmental issue. Herein, a sphere-like ZnFe2O4 catalyst with a size of ∼430nm was prepared by a solvothermal method, by which the aqueous Cr(VI) in a 50mL solution with concentration of 50mg/L was completely removed after 10min-microwave (MW) irradiation. "Surface temperature visualization" tests and COMSOL simulations showed that the surface temperature of the as-prepared ZnFe2O4 catalysts could be as high as >1000°C only after 300sMW irradiation, and the work function calculations and scavenging experiments demonstrated that the excited electrons derived by the "hot spots" effect of the ZnFe2O4 catalysts reduced the Cr(VI) to Cr(III). Kinetic reaction process of the reduction of *Cr2O72- to *CrO3H3 over the ZnFe2O4 catalysts was clarified by using DFT calculation, and the results indicated that *Cr2O72- adsorbed on the Fe atoms was more easily to be reduced, and that Fe atoms played more significant roles than the Zn and O atoms in ZnFe2O4 catalysts. The present study not only proves that the MW induced ZnFe2O4 catalytic reduction was promising for ultrafast remediation of toxic Cr(VI), but also provides a new insight into the corresponding mechanism.

Co nanoparticles/N-doped carbon nanotubes hybrids as highly efficient catalysts for microwave-induced catalytic degradation of tetracycline

Large-scale magnetic Co nanoparticles/N-doped carbon nanotubes (Co@NCNTs) hybrids have been designed by pyrolyzing the mixture of cobalt nitrate and melamine for microwave (MW)-induced tetracycline (TC) degradation. The results demonstrated that Co@NCNTs-5, annealed from cobalt nitrate and melamine (mole ratio: 1:5), possessed a good MW absorption ability, resulting in excellent degradation performance towards TC. Specifically, 99.5 % TC (20 mg/L, natural pH) could be removed after 6 min of MW irradiation (520 W) in the presence of Co@NCNTs-5. Meanwhile, Co@NCNTs-5 exhibited competitive degradation efficiency over TC at various concentrations (20–100 mg/L) and pH values (3−8). Results of reusability experiments identified the magnetic recovery ability and stability of Co@NCNTs-5. Based on free radical experiments and electron paramagnetic resonance (EPR) results, HO• and O2−• radicals participated in the catalytic degradation process. The degradation pathway of TC was proposed with the assistance of ultrahigh-performance liquid chromatography-mass spectrometry (UPLC-MS). This work develops a facile, low-cost and large-scale method to synthesize Co@NCNTs, which demonstrates great potential in MW-induced catalytic treatment of antibiotic pollutants as high-efficient catalysts.

A binary oxide-biochar composite for adsorption of arsenic from aqueous solutions: Combined microwave pyrolysis and electrochemical modification

Biochar composites are promising and cost-effective materials that can be applied in wastewater treatment. In the current study, a novel biochar composite impregnated with Zn and Al oxides (AlZnBC) was synthesized utilizing a non-conventional microwave pyrolysis combined with an electrochemical modification. The temperature distribution inside the sample was modeled using COMSOL Multiphysics (USA) to identify the level of temperature non-uniformity, and a pathway was proposed for the deposition of Al(OH)3 on the composite surface. A temperature gradient of 399 to 741 °C from the reactor surface to the center of the sample was found after 9 min of microwave irradiation. Maximum arsenite and arsenate adsorption capacities of 10,728 and 11,786 µg/g were attained by AlZnBC which were markedly higher than Zn oxide impregnated biochar capacities (ZnBC) of 6,030 µg/g and 7,783 µg/g, respectively. Studying the effect of co-existing ions selenite (SeO32−), selenate (SeO42−), phosphate (PO43−), nitrate (NO3−), and chloride (Cl−) on the biochar arsenic adsorption capacities indicated an interfering effect of the SeO32− and PO43− ions with inner-sphere complexation proposed as the main adsorption mechanism. X-ray absorption near edge structure spectroscopy (XANES) demonstrated that about 24% of the added arsenite was oxidized to arsenate, while no reduction was detected in arsenate adsorption experiments. Overall, both the ZnBC and AlZnBC exhibit promising potential for use in treating arsenic contaminated waters.

Microwave biochars produced with activated carbon catalyst: Characterization and sorption of volatile organic compounds (VOCs)

A series of microwave biochars derived from wheat straw in the presence of a granulated activated carbon (GAC) catalyst, using a range of microwave conditions, were produced, characterized and tested as sorbents of three benzene series volatile organic compounds (VOCs). The microwave biochar with the greatest specific surface area (SSA), total pore volume (TPV), and micropore volume (312.62 m2 g−1, 0.2218 cm3 g−1, and 0.1380 cm3 g−1, respectively), were produced with 1:3 biomass:GAC catalyst mass ratio, 10 min microwave irradiation time, and at 500 W power level (WB500). Maximum adsorption capacities of WB500 to benzene, toluene and o-xylene were 53.9 mg g−1, 75.8 mg g−1 and 63.0 mg g−1, respectively, and were directly correlated to microwave biochar properties such as SSA, TPV or micropore volume, but were also influenced by VOC properties such as molecular polarity and boiling point. Kinetic modeling suggested that adsorption was governed by both physical partitioning and chemisorption mechanisms. In addition, microwave biochars maintained 79% to 92% of their initial adsorption capacity after ten adsorption/desorption cycles. These results suggest that microwave biochars produced with an GAC catalyst have excellent potential for efficient use in the removal of VOCs from waste gas.

Myrica Rubra-like MnFe2O4 Microsphere: A high efficiency microwave reduction catalyst for Cr(VI) removal from water

Aqueous hexavalent chromium (Cr(VI)) is easy to enter the biological system, causing serious threat to human and aquatic environment health. In this paper, a myrica rubra-like MnFe2O4 catalyst with average diameter of 200–300 nm were prepared by a simple solvothermal method. Benefiting from the knobby surface and the considerable microwave absorption ability, the as-prepared MnFe2O4 microsphere exhibited excellent microwave catalytic reduction ability for Cr(VI) in water, and the catalysts dosage, initial Cr(VI) concentration, solution pH value and temperature showed crucial effect on the catalytic reduction process. When the pH value of the solution was 2, the amount of catalysts was 2 g/L, and the temperature was 100 ℃, the myrica rubra-like MnFe2O4 catalysts could remove as high as 96% of Cr(VI) from a 50 mg/L aqueous solution only after 10 min microwave irradiation, which is much higher than the commercial one. The enhanced catalysis performance could be ascribed to the surface “knob” with a size of ∼ 17 nm, which accelerated the generation of e– under microwave irradiation, finally promoted the catalytic reduction performance. The microwave catalytic reduction strategy is a hopeful alternative for ultrafast reduction of Cr(VI) in sewage with high efficiency.

Removal of Impurities from Shungite Via a Combination of Physical and Chemical Treatments

This study investigated the removal of sulfur and iron from shungite rocks through different methods after fine grinding: flotation, magnetic separation, microwave treatment, and chemical leaching. In this work, first, a mineralogical study of shungite was conducted. The carbon, silica, iron, and sulfur compositions in the as-received shungite were 45.4%, 38.3%, 4.6%, and 2.4%, respectively. In flotation, a sulfur grade of 1.4% was obtained. In the wet high-gradient magnetic separation at a magnetic flux density of 1 tesla, the iron and sulfur grades in the nonmagnetic fraction were 2.8% and 1.9%, respectively. Furthermore, the sulfur reduced to 0.2% by the 9 min microwave irradiation. In addition, chemical leaching using chelating reagents and inorganic acids was utilized to remove iron and sulfur. Nitrilotriacetic acid (NTA) could reduce the iron and sulfur grades to 2.0% and 0.9%, respectively. For leaching using reverse aqua regia, the iron and sulfur grades were reduced to 0.9% and 0.23%, respectively. For leaching using a 6N HCl with H2O2 aqueous solution, the iron and sulfur grades were reduced to 0.8% and 0.34%, respectively. Overall, chemical leaching using HCl with H2O2 was the most effective for iron and sulfur removal from shungite.

Immediate and sensitive detection of sporulated Bacillus subtilis by microwave release and tandem mass spectrometry of dipicolinic acid.

Spore lysis of Bacillus species is achieved by brief (1 min) microwave irradiation while tandem mass spectrometry (MS/MS) allows identification of the characteristic spore marker, dipicolinic acid. This rapid measurement, made on 105-108 spores, has significant implications for biothreat recognition.

Evaluation of Structurally Different Ionic Liquid-Based Surfactants in a Green Microwave-Assisted Extraction for the Flavonoids Profile Determination of Mangifera sp. and Passiflora sp. Leaves from Canary Islands.

Aqueous solutions of ionic liquids (ILs) with surface active properties were used as extraction solvents, taking advantage of their impressive solvation properties, in a green microwave-assisted solid-liquid extraction method (IL-MA-SLE) for the extraction of flavonoids from passion fruit and mango leaves. The extraction method was combined with high-performance liquid chromatography and photodiode-array detection (HPLC-PDA) and optimized by response surface methodology using the Box-Behnken experimental design. Under optimum conditions, the extraction efficiency of six structurally different IL-based surfactants was evaluated. Thus, imidazolium-, guanidinium- and pyridinium-type ILs with different tailorable characteristics, such as side chain length and multicationic core, were assessed. The decylguanidinium chloride ([C10Gu+][Cl–]) IL-based surfactant was selected as key material given its superior performance and its low cytotoxicity, for the determination of flavonoids of several samples of Passiflora sp. and Mangifera sp. leaves from the Canary Islands, and using as target analytes: rutin, quercetin and apigenin. The analysis of 50 mg of plant material only required 525 µL of the low cytotoxic IL-based surfactant solution at 930 mM, 10.5 min of microwave irradiation at 30 °C and 50 W, which involves a simpler, faster, more efficient and greener method in comparison with other strategies reported in the literature for obtaining bioactive compounds profiles from plants.

A Facile Synthesis of Self-Catalytic Hydrogel Films and Their Application as a Wound Dressing Material Coupled with Natural Active Compounds.

A simple and economical method for polyvinyl alcohol/polyvinylpyrrolidone/citric acid (PVA/PVP/CA) hydrogel preparation using microwave-assisted irradiation was presented. The synthesized hydrogels embedded with berberine or chlorogenic acid were investigated as a wound dressing agent. This study showed that the optimum condition for the hydrogel synthesis based on gel fraction and a degree of swelling values was 6:6:3% (w/v) of PVA/PVP/CA under 600 W at 120 °C for 3 min of microwave irradiation. Herbal active compounds, berberine and chlorogenic acid, were loaded onto the hydrogel (4% (w/v)), and both were able to inhibit the growth of Staphylococcus aureus. Additionally, the anti-inflammatory study revealed that 700 μg/mL berberine and 2500 μg/mL chlorogenic acid could inhibit protein degradation equivalent to a 200 μg/mL aspirin solution. The drug release study demonstrated that both compounds showed a more sustained release into PBS than water. The mechanism for the three-dimensional network formation based on esterification and the hydrogen-bonding interaction was also proposed. The ionic liquid-like structure of PVP-CA possibly played an important role in the cross-linking process. In addition, sodium bicarbonate applied to the synthesized hydrogel also had a significant effect in enhancing gel formation. The proposed approach showed a potential of the loaded hydrogels to protect wounds from infection and enhance the healing process.

A new microwave approach for the synthesis of green emitting Mn2+-doped ZnAl2O4: A detailed study on its structural and optical properties

A simple recipe for synthesizing green emitting Mn2+-doped ZnAl2O4 phosphor has been developed. Metal-organic complexes, with their unique properties, were employed as precursors to obtain phase-pure, nanocrystalline material in the as-prepared form within just 5 min of microwave irradiation. The Mn2+ doping concentration that showed the highest photoluminescence (PL) intensity was optimized and a comprehensive investigation of the structural and optical properties were made for various annealing temperatures. Rietveld refinement of the samples annealed at 1200 °C and 1400 °C, showed that the cationic inversion in the spinel decreased from 3.4 to 2.1% and this change was validated by the X-ray photoelectron spectroscopy results. XPS confirmed that the inversion for Zn2+, Al3+, and Mn2+ cations decreased with annealing temperature, despite of which, inversion remained at 20%, 10%, and 15%, respectively for the sample annealed at 1400 °C, emphasizing the fact that synthesis plays an important role in controlling the amount of inversion in an otherwise normal spinel. Electron paramagnetic resonance spectra of the as-prepared and the samples annealed at high temperatures confirmed that the Mn2+ hyperfine spectrum was not just a function of the crystal field environment but also strongly depends on the doping concentration. The PL spectrum taken at different annealing temperatures, comprised of the characteristic 4T1 (G) → 6A1 (S) spin-forbidden Mn2+ transitions, showed that the emission intensity depends on the material crystallinity. The sample annealed at 1400 °C displayed a significantly higher PL intensity compared to those annealed at lower temperatures. The variation of PL spectrum of this sample was investigated between 9 K and 300 K to determine the origins of the asymmetry at room temperature and the vibrational sidebands at lower temperatures. The energy levels of the Mn2+ dopant, calculated theoretically and verified experimentally, were used to determine the spectroscopic parameters such as the Racah B and C values and the crystal field energy, Dq. These values showed that the Mn2+ was in a weak tetrahedral field. This work demonstrates a technologically important, green, and swift technique in synthesizing phosphors for various applications in displays, bioimaging, solid state lighting, etc.

A novel microwave-assisted steam distillation approach for separation of essential oil from tree peony (Paeonia suffruticosa Andrews) petals: Optimization, kinetic, chemical composition and antioxidant activity

Microwave-assisted steam distillation (MSD) was developed as an efficient technique for the separation of essential oil (EO) from tree peony (Paeonia suffruticosa Andrews) petals, on the basis of ensuring the extraction of flavonoids. During MSD process, the raw material was separated from water to keep it in a relatively dry state, thus contributing to the subsequent extraction of flavonoids. In this work, the optimization of MSD process was conducted to obtain the optimum conditions (1.7 mL/g water ratio for soaking, 1 h soaking time, 540 W microwave irradiation power and 30 min microwave irradiation time) and high yield of EO (0.66 ± 0.03 mg/g). The MSD technique was compared with other reference methods in terms of kinetic model fitting, economic value, environmental impact, EO composition and antioxidant activity. The result pointed out that the MSD method could be reasonably fitted by first-order kinetic model, was environmentally friendly and economically sustainable, provided higher separation efficiency, required lower energy consumption, and had certain advantages in the separation of EO with higher proportion of oxygenated components and better antioxidant activity. Furthermore, microwave-assisted extraction (MAE) of flavonoids from the petal residues obtained after MSD showed better result than that obtained after microwave hydrodistillation, and the result was comparable with MAE and heat reflux extraction. Overall, MSD is a potential and powerful alternative to traditional methods for the efficient distillation of EO, on the premise of reducing the loss of flavonoids etc. non-volatile components.