Min Of Microwave Irradiation Research Articles

A facile synthesis of Fe3O4@SiO2@ZnO with superior photocatalytic performance of 4-nitrophenol

Nitrophenols in wastewater have posed a serious threat to ecosystem and human health, hence it is very important to remove them from wastewater using an environmental-friendly and effective method. In this study, Fe3O4@SiO2@ZnO magnetic nanoparticles (ZnO MNPs) were synthesized via a moderate and rapid route using microwave irradiation and diethylene glycol (DEG) as solvent. The facile synthesis conditions of ZnO nanoparticles coating on Fe3O4@SiO2 were confirmed owing to lower reaction temperature (160°C) and quick reaction time (15min microwave irradiation). In addition, the synthesized ZnO MNPs demonstrated the comparable or even better photocatalytic activity for 4-nitrophenol (4-NP) as compared with TiO2 with respect to small catalyst dosage, quick degradation rate and broad pH range. Moreover, ZnO MNPs exhibited good stability and reusability after eight times successive degradation experiments of 4-NP. The mechanism of the enhanced photocatalytic activity of ZnO MNPs was mainly related to the stronger adsorption ability for 4-NP, the improved light absorption ability and the retarding recombination of hole–electron pairs. In summary, ZnO MNPs is a promising candidate for 4-NP photocatalytic degradation from wastewater.

A novel approach for distillation of paeonol and simultaneous extraction of paeoniflorin by microwave irradiation using an ionic liquid solution as the reaction medium

Abstract In the present work, a simple and efficient method for steam distillation of paeonol and simultaneous extraction of paeoniflorin from the root bark of Paeonia suffruticosa Andr. (Cortex Moutan) was developed using an ionic liquid as the reaction medium and microwave irradiation. A series of 1-alkyl-3-methylimidazolium ionic liquids with different anions and alkyl chain lengths were evaluated for this method. The optimum conditions were 1.25 M 1-butyl-3-methylimidazolium bromine as the extraction solvent, 20 mL/g liquid–solid ratio, 25 min microwave irradiation time, 700 W microwave irradiation power, and 60–80 mesh particle size. Under these conditions, satisfactory yields of paeoniflorin (80.49 ± 2.58 mg/g) and paeonol (10.52 ± 0.36 mg/g) were obtained. The initial purity of paeonol was 84.95%, and this increased to >99% with simple recrystallization. The ionic liquid extraction solution, either with or without trace paeonol, was passed through HPD100B macroporous resin for enrichment and separation of paeoniflorin and recycling of the ionic liquid used. Recycling and reuse of the ionic liquid were achieved successfully, which could reduce ionic liquid requirements and the process cost. The method was validated using stability, recovery, and repeatability experiments. The proposed method is very promising for separation of natural compounds, especially for small molecules that can be isolated by steam distillation.

Microwave assisted synthesis of perovskite structured BaTiO3 nanospheres via peroxo route for photocatalytic applications

A novel perovskite structured barium titanate (BaTiO3) nanopowder was successfully synthesized at low temperature by a facile and an inexpensive microwave method. The synthesized nanosphere shaped BaTiO3 was analyzed using advanced characterization techniques such as X-ray diffraction analysis, Fourier transform infrared, Micro Raman, Scanning electron microscope with energy dispersive analysis and ultraviolet-visible diffuse reflectance spectroscopic techniques. Photocatalytic dye degradation study was carried out using newly synthesized BaTiO3 catalyst. The synthesized sphere shaped barium titanate nanopowders effectively degrade the various dyes such as Methylene Blue (MB), Malachite Green (MG) and Alizarin Red S (ARS) under UV light irradiation. The band gap energy of synthesized BaTiO3 was calculated by UV-DRS spectra using kubelka-Munk equation. The higher dye decomposition efficiency of nearly 100% was successfully achieved by BaTiO3 (BT10) nanosphere which was prepared using 10min microwave irradiation.

Sequential ultrasound-microwave assisted acid extraction (UMAE) of pectin from pomelo peels

This study aims to optimize sequential ultrasound-microwave assisted extraction (UMAE) on pomelo peel using citric acid. The effects of pH, sonication time, microwave power and irradiation time on the yield and the degree of esterification (DE) of pectin were investigated. Under optimized conditions of pH 1.80, 27.52min sonication followed by 6.40min microwave irradiation at 643.44W, the yield and the DE value of pectin obtained was respectively at 38.00% and 56.88%. Based upon optimized UMAE condition, the pectin from microwave-ultrasound assisted extraction (MUAE), ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE) were studied. The yield of pectin adopting the UMAE was higher than all other techniques in the order of UMAE>MUAE>MAE>UAE. The pectin’s galacturonic acid content obtained from combined extraction technique is higher than that obtained from sole extraction technique and the pectin gel produced from various techniques exhibited a pseudoplastic behaviour. The morphological structures of pectin extracted from MUAE and MAE closely resemble each other. The extracted pectin from UMAE with smaller and more regular surface differs greatly from that of UAE. This has substantiated the highest pectin yield of 36.33% from UMAE and further signified their compatibility and potentiality in pectin extraction.

Influence of ionic liquid-modified LDH on microwave-assisted polymerization of ε-caprolactone

The study reported herein describes multifunctional effect of layered double hydroxide (LDH) modified with phosphonium-based ionic liquids (IL) containing phosphinate, carboxylate and phosphate anions on progress of ring-opening polymerization of ε-caprolactone under microwave irradiation. The extent of IL-modification had a crucial effect on the exfoliation of LDH. The non-modified LDH was able to catalyse the ring-opening polymerization of ε-caprolactone with polymer yield 89% but provided only micro-composite material. On the contrary, LDH with intercalated IL-anions promoted exfoliation of LDH after only 3 min of microwave irradiation. The developed process is fast, environmentally-friendly (solvent-free) and adaptable to various polymer matrices, since a broad variety of IL-anions might be applied.

Facile conversion of activated carbon to battery anode material using microwave graphitization

As the most commonly used anode material, graphite is crucial to the battery industry and other energy storage applications. Natural graphite is classified as a supply risk material, and the artificial graphitization process is extremely inefficient, so an alternative method of making graphite for use as an anode material is highly desired. In this work, activated carbon powder is graphitized by microwave irradiation with catalyst precursor impregnation. Further, the characteristics of microwave-graphitized activated carbon powder as an anode material in lithium ion batteries are investigated. After 5 min of microwave irradiation, a graphite (002) peak develops at 26.46° in the X-ray diffraction pattern (the corresponding d002 was 3.3664 Å), and the IG/ID ratio in Raman spectra increases from 1.07 to 1.89. As an anode material, graphitized active carbon exhibits stable charge–discharge processes typical of graphite (plateau around 0.2 V). These results indicate that microwave irradiation is an effective way to produce graphitic carbon from low-crystalline activated carbon for use as an anode material. We believe they pave the way to research toward a stable supply of anode material.

Yellow–red luminescence in ZnO nanoparticles synthesized from zinc acetylacetonate phenanthroline

ZnO powders/thin films/coatings when excited by a suitable excitation source, usually yield green luminescence in the visible wavelength range along with characteristic ultra-violet emission. We report yellow–red emission from ZnO nanoparticles synthesized within 5min of microwave irradiation by using zinc acetylacetonate phenanthroline as the starting precursor material. The emission is strongly dependent on the typical structure of the starting precursor for ZnO synthesis, where one phenanthroline moiety is attached with zinc acetylacetonate hydrate complex. These ZnO nanoparticles could be potentially suitable phosphor for white light generation when excited by a blue laser. In contrast, the ZnO nanoparticles obtained from zinc acetylacetonate by similar method yield weak green emission.

Wettability modification of graphene oxide by removal of carboxyl functional groups using non-thermal effects of microwave

We study the non-thermal effects of microwave on the wettability of graphene oxide. It is shown that removal of carboxyl compound by using the non-thermal microwave effects decrease the wettability of graphene oxide. X-ray photoelectron spectroscopy (C1s and O1s peaks) and Fourier transform infrared spectroscopy show that carboxyl compound decreases dramatically due to microwave irradiation while other functional groups were gradually reduced. Consequently, after 20min microwave irradiation, carboxyl functional groups are removed. Wettability tests of carboxyl-reduced graphene oxide show that water uptake capability decreases to half and contact angle of water droplets increases from ~29.7° to ~69.9°.

Self-assembled ZnO nanoparticles on ZnO microsheet: ultrafast synthesis and tunable photoluminescence properties

We report on the tunable photoluminescence characteristics of porous ZnO microsheets fabricated within 1–5 min of microwave irradiation in the presence of a capping agent such as citric acid, and mixture of citric acid with polyvinylpyrrolidone (PVP). The UV emission intensity reduces to 60% and visible emission increases tenfold when the molar concentration of citric acid is doubled. Further diminution of the intensity of UV emission (25%) is observed when PVP is mixed with citric acid. The addition of nitrogen donor ligands to the parent precursor leads to a red shift in the visible luminescence. The deep level emission covers the entire visible spectrum and gives an impression of white light emission from these ZnO samples. The detailed luminescence mechanism of our ZnO samples is described with the help of a band diagram constructed by using the theoretical models that describe the formation energy of the defect energy levels within the energy band structure. Oxygen vacancies play the key role in the variation of the green luminescence in the ZnO microsheets. Our research findings provide an insight that it is possible to retain the microstructure and simultaneously introduce defects into ZnO. The growth of the ZnO microsheets may be due to the self assembly of the fine sheets formed during the initial stage of nucleation.

Microwave Assisted Energy Efficient Biodiesel Production from Crude Pongamia pinnata (L.) Oil Using Homogeneous Catalyst

Abstract Microwave assisted biodiesel production from crude Pongamia pinnata oil using homogeneous base catalyst (KOH) was unsuccessful because of considerable soap formation. Therefore, a two step process of biodiesel production from high free fatty acid (FFA) oil was investigated. In first step, crude P. pinnata oil was acid catalyzed using H 2 SO 4 and acid value of oil was reduced to less than 4 mg KOH/g. Effect of sulfuric acid concentration, alcohol-oil molar ratio and microwave irradiation time on acid value of oil was studied. Result suggested that 1.5% H 2 SO 4 (w/w), 6：1 methanol oil molar ratio and 3 min microwave irradiation time was sufficient to reduce the acid value of oil from 12 and 22 mg KOH/g to 2.9 and 3.9 mg/KOH/g, respectively. Oil obtained after pretreatment was subsequently used for microwave assisted alkali catalyzed transesterification. A higher biodiesel yield (99.0%) was achieved by adopting two step processes. Microwave energy efficiency during alkali catalyzed transesterification was also investigated. The results suggested a significant energy saving because of reduced reaction time under microwave heating.Key Words: microwave, pongamia pinnata, biodiesel, acid value, energy efficiency

Magnetic nano-sized cadmium ferrite as an efficient catalyst for the degradation of Congo red in the presence of microwave irradiation

A highly active nano-sized CdFe2O4 catalyst was prepared by a hydrothermal process and characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), BET specific surface area method, and vibrating sample magnetometer (VSM) at room temperature. Application of the microwave-induced catalytic degradation method in the abatement of Congo red (CR) using the magnetic catalyst was studied. The degradation ratio of CR with CdFe2O4 reached 94.4% with 10 min microwave irradiation (MW), proving CdFe2O4 to be an excellent microwave catalyst. The intermediate products from CR degradation were investigated by UV-Vis, HPLC and ion chromatography. The reaction kinetics, effects of different ion species (SO42−, NO3−, HCO3−, and CH3COO−), pH of the solution, dye initial concentration, dosage of catalyst, as well as degradation mechanism were comprehensively studied. Radical trapping studies and the fluorescence technique revealed the holes (h+) and hydroxyl radicals (˙OH) were involved as the main active species in the reaction. The band structure of CdFe2O4 was analyzed by UV-Vis diffuse reflectance spectroscopy and Mott–Schottky measurements. The mechanism of the degradation was discussed in detail. This work can provide an effective technology for dye wastewater treatment.

A rapid protein sample preparation method based on organic-aqueous microwave irradiation technique

Fast and efficient sample preparation methods are a prerequisite for protein identification in bottom-up proteomics. Here, an innovative microwave irradiation sample preparation method was developed based on an optimized organic-aqueous solvent system for protein identification. Specifically, protein solutions containing high-concentration acetonitrile were subjected to 5 min microwave irradiation. After cooling down, trypsin was added and the digestion was performed with 30 s microwave irradiation, and the resulting peptides were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A shortened processing time of only 5.5 min is needed with this method (more than 12 h is necessary in the traditional overnight protein sample preparation). Moreover, due to the absence of urea and other chaotropic reagents, the digests can be readily identified by MALDI-TOF MS. When an assessment of this method was performed by digesting a model protein BSA, 69% ± 3% sequence coverage corresponding to 47 ± 3 peptides was obtained, which shows better protein identification than that from the standard overnight protein sample preparation method (51% ± 2% sequence coverage and 23 ± 1 peptides). Another model protein a-casein was used for the analysis of protein phosphorylation with the newly developed method that yielded 4 phosphopeptides with 8 phosphorylation sites, whereas 3 phosphopeptides with 2 phosphorylation sites were obtained from the traditional overnight approach. Moreover, the organic-aqueous microwave irradiation method provides effective digestion for proteins down to fmol.

Peptic hydrolysis of bovine beta‐lactoglobulin under microwave treatment reduces its allergenicity in an ex vivo murine allergy model

SummaryIn this study, the in vivo allergenicity of bovine beta‐lactoglobulin (BLG) in peptic whey protein hydrolysates generated during microwave and conventional heating treatments was assessed. The allergenicity of the hydrolysates was explored by studying the reaction of the murine jejunum from previously immunised Balb/c mice to treated BLG in an Ussing chamber. Intestinal anaphylactic reactions after stimulation of the gut‐associated immune system are a good indicator of potential in vivo allergenicity of whey hydrolysates. Fifty‐two per cent of BLG was hydrolysed by pepsin after only 3 min of microwave irradiation at 200 watts (W), yet it remained intact under conventional heating. Far‐ and near‐UV circular dichroism spectra indicated significant changes in BLG secondary and tertiary structures with microwave irradiation at 200 W. Pepsin whey protein hydrolysates obtained with microwave irradiation at 200 W for 3 min did not stimulate secretion of chloride in the Ussing chamber, as shown by the intensity of the short current values recorded (27.86 μA cm−2), compared to the conventional pepsin hydrolysates (68.21 μA cm−2). This demonstrates the low allergenicity of whey protein hydrolysates generated in this manner. These results confirm that microwave treatment combined with peptic hydrolysis could be applied to produce low allergenicity milk peptides.

Microwave-induced combustion of crude oil for further rare earth elements determination by USN–ICP-MS

A procedure for light and heavy crude oils digestion by microwave-induced combustion (MIC) is proposed for the first time for further rare earth elements (REE) determination by inductively coupled plasma mass spectrometry (ICP-MS) equipped with an ultrasonic nebulizer (USN). Samples of crude oil (API density of 10.8–23.5, up to 250mg) were inserted in polycarbonate capsules and combusted using 20bar of oxygen and 50μL of 6molL−1 ammonium nitrate as igniter. Nitric acid solutions (1–14.4molL−1) were evaluated for analyte absorption and a reflux step was applied after combustion (5min of microwave irradiation at 1400W) in order to achieve better analyte recoveries. Accuracy was evaluated using a spiked sample and also by comparison of results obtained by microwave-assisted digestion combined to ultraviolet radiation (MW–UV) and by neutron activation analysis (NAA). Using 3molL−1 HNO3, quantitative recoveries (better than 97%) were obtained for all analytes. Blank values were always negligible. Agreement was higher than 96% for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y by comparison of results with those obtained by MW–UV and by NAA (only for La, Ce, Nd, Sm, and Yb). Residual carbon content in digests using MIC was always below 1%. As an advantage over conventional procedures for crude oil digestion, using MIC, it was possible to use diluted acid as absorbing solution, obtaining better limits of detection and avoiding interferences in REE determination by USN–ICP-MS.

Investigation on microwave absorbing properties of loaded MnFe2O4 and degradation of Reactive Brilliant Red X-3B

Four nanocomposite catalysts namely MnFe2O4, MnFe2O4-SiC, MnFe2O4-TiO2 and MnFe2O4-diatomite, were synthesized and characterized by X-ray diffraction (XRD) and N2 adsorption (BET specific surface area). Measurements of the catalysts’ complex permittivity and permeability in the microwave (MW) frequency range of 0.5–18GHz showed MnFe2O4-SiC composites to be the best MW absorbers. The surface temperature of MnFe2O4-SiC (1450°C) under MW was higher compared to those of the other three catalysts, indicating that silicon carbide (SiC) was an effective support. MW-assisted experiments demonstrated that the degradation of RBR X-3B with MnFe2O4-SiC reached 92%, achieved 70% of TOC removal and exhibited lower toxicity with 5min MW irradiation, proving MnFe2O4-SiC to be an excellent microwave catalyst. These findings are important regarding the development of efficient sorbents that are effective microwave absorbers as well as catalysts of rapid degradation of pollutants.

Ionic liquid-based vacuum microwave-assisted extraction followed by macroporous resin enrichment for the separation of the three glycosides salicin, hyperin and rutin from Populus bark.

An effective ionic liquid vacuum microwave-assisted method was developed for extraction of the thermo- and oxygen-sensitive glycosides salicin, hyperin and rutin from Populus bark due to the strong solvating effects of ionic liquids on plant cell walls. In this study, [C4mim]BF4 solution was selected as the extracting solution for extraction of the target analytes. After optimization by single factor experiments and response surface methodology, the optimum condition parameters were achieved, which included 1.0 M [C4mim]BF4, 2 h soaking time, −0.08 MPa vacuum, 20 min microwave irradiation time, 400 W microwave irradiation power and 25 mL/g liquid/solid ratio. Under the optimum conditions, higher extraction yields of salicin (35.53 mg/g), hyperin (1.32 mg/g) and rutin (2.40 mg/g) were obtained. Compared with other extraction methods, the developed method provided higher yields of the three target components after a relatively shorter extraction time (20 min). No obvious degradation of the target analytes was observed under the optimum conditions in performed stability studies and the proposed method had a high reproducibility. Meanwhile, after adsorption and desorption on macroporous D101 resin, the target analytes can be effectively separated from the [C4mim]BF4 ionic liquid extraction solution and the yields of salicin, hyperin and rutin were 89%, 82% and 84%, respectively. The recovered [C4mim]BF4 ionic liquid presented a good extraction effect on the three analytes after recycling five times.

Mechanism and process of methylene blue degradation by manganese oxides under microwave irradiation

Numerous studies have been conducted on the removal of dyes from wastewater, although fewer were focused on the reactions under the influence of microwave irradiation (MI). In this paper, degradation of methylene blue (MB) in simulated wastewater by manganese oxides (MOs) under MI was investigated. A significant increase in MB removal efficiency by akhtenskite or birnessite was observed in the presence of MI. After 30min MI, the MB removal by birnessite was 230mg/g, in comparison to only 27mg/g in the absence of MI. The kinetics of MB removal by MOs under MI followed the pseudo-first-order kinetic model well with rate constants of 0.005 and 0.04min−1 for akhtenskite and birnessite, respectively. In contrast, the rate constants were only 0.0006 and 0.0007min−1 for MB removal by akhtenskite and birnessite in the absence of MI. Results of XPS and LC–MS showed cyclic redox processes responsible for the step-wise degradation from MB to C14H13N2OS, C13H11N2OS, C12H8NO2S, C12H9N2OS, and eventually to smaller molecules. As akhtenskite and birnessite had no electric dipole moment in their crystal structure, it was deduced that stronger MI effect on MB removal by birnessite could be attributed to the larger spin dipole moment of the central manganese ion in octahedra.

Effects of compound treatment of exogenous feed enzymes and microwave irradiation on in vitro ruminal fermentation and intestinal digestion of guar meal

Effects of compound treatments of microwave irradiation (900 W) for 0, 2 and 4 min and exogenous feed enzymes at the application rate of 0, 250 and 500 g/ton on fermentation kinetics and digestibility of guar meal were evaluated by in vitro gas production and 3-step in vitro digestion techniques. Cumulative gas production was recorded at 2, 4, 6, 8, 12, 16, 24, 36, 48, 72 and 96 h of incubation and its kinetic was estimated using model: GP = A[1 - e-(t-L)]. To investigate ruminal and post ruminal digestion, the in situ and Ankom daisy-II incubation techniques were performed. Although enzyme supplementation levels had no significant effects on gas production, quadratic response to enzyme levels was observed after 12 h post-incubation and continued up to 96 h post-incubation. Microwave irradiation did not show significant impact on cumulative gas production. Interaction of enzyme and microwave irradiation was also not significant. While, there was no significant difference in potential gas production parameter (A) due to the effects of exogenous enzyme levels, microwave irradiation times or their interactions, gas production rate (c) was higher than control for all enzyme treatments. Significant effect of feed enzyme and microwave irradiation interaction was observed on guar dry matter (DM) digestibility. Post-ruminal digestibility of CP in compound treatment of no enzyme and 2 min microwave irradiation has the lowest digestibility (905.4 g/ kg). Moreover, interaction between enzyme and microwave irradiation on guar meal post-ruminal CP digestibility was significant. It was concluded that heat processing of high protein oil seed meals followed by exogenous feed enzyme supplementation might lessen the possible Maillard reaction effects of heat processing. In conclusion, according to present study such order of compound treatments might shift protein digestion from rumen to post- ruminal sites. Consequently, this will improve protein and amino acids profile of followed digesta to small intestine, which is crucial in animal productivity performance.

Impact of Irradiation Time on the Hydrolysis of Waste Activated Sludge by the Dielectric Heating of Microwave

The effects of initial solid concentration and microwave irradiation (MWI) time on the hydrolysis of waste activated sludge (WAS) were investigated. MWI time strongly influenced WAS hydrolysis for all initial solid concentrations of 8.20, 31.51, and 52.88 g VSS/L. For all WAS, the volatile suspended solids (VSS) solubilization degree ranged from 35.6% to 38.4% during a total MWI time of 10 min. Soluble chemical oxygen demand (SCOD) concentration increased at a rate proportional to the decrease of VSS during the MWI. However, the clearly different VSS solubilization patterns that were observed during the MWI were explained by the 2-step hydrolysis of WAS, consisting of the initial disintegration of the easily degradable part of the sludge, followed by the subsequent disintegration of the hardly degradable part of the sludge. WAS hydrolysis rates for 3 to 6 min of MWI were significantly lower than those for less than 3 min, or more than 6 min. From these results, 3 min MWI time and WAS of 31.51 g VSS/L (centrifugal thickener WAS) showed the most efficient hydrolysis of WAS at 36.0%. The profiles of total nitrogen (T-N) concentrations corresponded well to the SCOD increases in terms of the empirical formula of bacterial cell mass (C5H7O2N). The negligible T-N increase and pH decrease during WAS hydrolysis by MWI will allow the application of this process to subsequent biological processes, such as anaerobic digestion.

Rapid microwave-assisted synthesis of silver decorated-reduced graphene oxide nanoparticles with enhanced photocatalytic activity under visible light

A facile, fast, and scalable microwave irradiation (MWI) method for the synthesis of Ag nanoparticles (Ag NPs) dispersed on graphene sheets has been developed. The reduction of graphene oxide takes place in ethanol solution within 2min of MWI without any additional reducing agent or complicated treatment. The morphology and microstructure of the as-prepared hybrid were characterized by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images. The result showed the Ag NPs with an average size of 5–10nm decorated on the rGO sheets. X-ray powder diffraction (XRD) determined that the crystallographic structure of Ag is face-centered cubic and there was a strong interaction between Ag NPs and rGO sheets. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed that GO had been reduced to rGO in our hybrid. Moreover, visible photocatalytic activity of the rGO–Ag nanocomposites was tested using Rhodamine B (RhB) as the model contaminant. This result indicates that rGO–Ag nanocomposites display distinctly enhanced photocatalytic activities. The investigation gave a promise to the development of original yet highly efficient graphene-based photocatalysts that utilize visible light as an energy source.