Fast Microwave-assisted Method Research Articles

Microwave-Assisted ultrafast Synthesis of Bimetallic Nickel-Cobalt Metal-Organic Frameworks for Application in the Oxygen Evolution Reaction.

A series of monometallic Ni-, Co- and Zn-MOFs and bimetallic NiCo-, NiZn- and CoZn-MOFs M2(BDC)2DABCO and (M,M')2(BDC)2DABCO, respectively, with the same pillar and layer linkers 4-diazabicyclo[2.2.2]octane (DABCO) and benzene-1,4-dicarboxylate (BDC) were prepared through a fast microwave-assisted thermal conversion synthesis method within only 12 min. In the bimetallic MOFs the ratio M:M' was 4:1. The mono- and bimetallic MOFs were selected to systematically explore the catalytic-activity of their derived metal oxide/hydroxides for the oxygen evolution reaction (OER). The NiCoMOF exhibits superior catalytic activity for the OER with the lowest overpotentials of 301 mV and Tafel slopes of 42 mV dec-1 on a glassy carbon electrode in 1 mol L-1 KOH electrolyte at a current density of 10 mA cm-2. In addition, NiCoMOF was in situ grown in just 25 min by the MW synthesis on the surface of nickel foam (NF) where overpotentials of 313 and 328 mV at current densities of 50 and 300 mA cm-2, respectively, were delivered and superior long-term stability for practical OER application. The low Tafel slope of 27 mV dec-1, as well as a low reaction resistance from electrochemical impedance spectroscopy measurement (Rfar = 2 Ω), confirm the excellent OER performance of this NiCoMOF/NF composite.

Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions.

The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal-organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m-3·day-1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m-3·day-1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.

Optimizing microwave-assisted synthesis of akermanite nanoparticles using citric acid as a chelating agent: A combined machine learning and experimental approach

This study aims to synthesize akermanite (Ca2MgSi2O7) using an eco-friendly and fast microwave-assisted method and understand the effect of using citric acid (CA) as a chelating agent to optimize the calcination temperature for synthesizing pure akermanite nanoparticles (along with a trace amount of merwinite) at low calcination temperatures. This study developed a new predictive model by machine learning-assisted modeling to advance the understanding of relationship between synthesis parameters and the resulting purity and particle size of akermanite. To evaluate the reliability of the developed model in predicting the purity and characteristics of the resultant Ak powder, the crystallization behavior and phase formation sequence of citric acid-containing samples and those without citric acid were experimentally investigated by differential thermal analysis (DTA) and X-ray diffraction (XRD) techniques. Following validation and training, the developed model indicates promising effects of citric acid on reducing crystallization temperature, enhancing purity, and decreasing particle size. The synthesized powders were further characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) analyses. For the first time, our results addressed the microwave-assisted synthesis as an effective method via experimental evidence and machine learning-assisted modeling that allows for the production of akermanite containing a trace amount of merwinite with the aid of citric acid at a relatively low calcination temperature of 950 °C. In vitro bioactivity evaluation supported the potential suitability of Ak powders for bone tissue engineering applications.

Microwave-assisted rapid synthesis of bismuth molybdate with enhanced oxidative desulfurization activity

In this work, six different bismuth molybdate catalysts were synthesized by a fast microwave-assisted hydrothermal method. By adjusting the pH in the preparation process, the morphology and structure of the synthesized catalysts can be modified, and the transition of Bi2MoO6 crystals to Bi3.2Mo0.8O7.5 crystals can be selectively achieved. The sample prepared at pH 1, BMO-1, exhibited excellent activity for oxidizing sulfur compounds in fuel oil at 60 °C with a molar hydrogen peroxide to sulfur ratio of four, achieving removal rates of dibenzothiophene, 4,6-dimethyldibenzothiophene, and benzothiophene of 99.71%, 99.68%, and 77.95%, respectively. When recycling the catalyst seven times, the removal rate of dibenzothiophene still reached 98.07%. A probable mechanism for the oxidative desulfurization process was proposed. This work not only offers a high-efficiency, method for the rapid preparation of bismuth molybdate catalysts but also extends the application of this catalyst in the field of deep oxidative desulfurization.

Two-dimensional NiO nanosheets for efficient Congo red adsorption removal

Strategies for developing new adsorbents are necessary for more efficient processes to remove contaminants from wastewater. Thus, it is essential to adjust the synthesis parameters of the adsorbent nanomaterial to control the surface area and morphology and, therefore, enhance the adsorption performance. Herein, α-Ni(OH)2 nanosheets were synthesized via a simple and fast microwave-assisted solvothermal method and converted to NiO nanostructures by calcination in air. The effect of different calcination temperatures (range of 300–600 °C) on the morphology, crystal structure, and adsorption performance of Congo red (CR) was evaluated. The calcination of α-Ni(OH)2 at 300 °C resulted in 2D NiO nanosheets, which showed the best performance to remove CR dye due to the increased surface area and porosity provided by the 2D morphology. The nanosheet-like structure is lost with increasing the calcination temperature and the nanoparticles become bigger, consequently, the CR adsorption capacities are significantly reduced. The 2D NiO nanosheets can adsorb a significant amount of CR quickly, reaching equilibrium after only 120 min, indicating a high affinity between the adsorbate species and the surface of the adsorbent. Additionally, the adsorption isotherm was compatible with the Langmuir model, which provides a maximum calculated adsorption capacity of 259.74 mg g−1. Thus, our findings showed how to adequate the synthesis parameters to obtain NiO nanosheets and improve the adsorption parameters to CR, which can be extended to the fabrication of new materials to promote advances in sustainable technologies.

Study on Adsorption Kinetics of Methylene Blue by Modified Sago Frond Waste

The modified sago frond waste (PSM) using the Fast Microwave-Assisted Acid method, which has several characteristic changes, was tested to determine its adsorption ability to a cationic textile dye. PSM samples as adsorbents have variations in the modification of oxalic acid addition at 0; 1,5; 3,0 and 4,5% (w/v) were used for the adsorption of Methylene Blue (MB) dye on several parameters. This study was conducted to determine the adsorption kinetics through the effect of the ratio of the adsorbent and the contact time and the acid variation of the adsorbent as additional variables. Optimum MB absorption was obtained at a ratio of 0,6 g/L and a contact time of 120 minutes. The data results were analyzed using four general kinetic models: pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich equation. Adsorption followed the pseudo-second-order reaction rate with a coefficient of determination (R2) 0.9996-0.9999 in all variations of PSM. The theoretical adsorption capacity was 25.58 to 27.32 mg/g, and the effect of increasing acid on PSM increased the adsorption and absorption capacity of MB. Keywords: sago frond waste, adsorption, kinetic models, methylene blue.

Highly stable UiO-66-NH2 by the microwave-assisted synthesis for solar photocatalytic water treatment

This work introduces the novel use of a highly stable UiO-66-NH2 in water with a linker release less than 0.2‰ (per-mile) in a wide pH range. The MOF was prepared by a fast microwave-assisted method comparing for the first time the effect of two Zr precursors: Zr oxychloride and organic Zr alkoxide; with synthesis temperatures 120–180 ºC. The use of oxychloride as Zr precursor led to a MOF with bigger particle and crystal size than the Zr alkoxide. The sample prepared with ZrOCl2 at 140 ºC resulted in the best crystallinity, highest textural definition (area 875 m2 g−1, pore volume 0.39 cm3 g−1), good optical properties for solar radiation absorption (bandgap 2.88 eV), and the highest photoactivity to remove sulfamethoxazole in water. The activity of the optimum UiO-66-NH2 sample was assessed in a continuous flow experiment, testing the ability of the simultaneous degradation of a six pharmaceutical mixture fed at a more realistic environmental scenario (500 μg L−1 each). The MOF showed an outstanding stability over 20 h with no detectable release of linker and high removal efficiency.

Microwave hydrothermal synthesis and electrochemical characterization of NiMoO4 nanosheets/SnO2 nanospheres/rGO nanocomposite as high-performance anode for lithium-ion batteries

Hybrid ultrathin NiMoO4 nanosheets/SnO2 nanospheres/rGO sheets nanocomposite developed via a versatile fast microwave-assisted hydrothermal method was investigated as feasible anode material for lithium-ion batteries. Synthesized NiMoO4/SnO2/rGO phase pure nanocomposite was confirmed by XRD, Raman, FESEM-EDX, XPS and TEM analysis. Lithium ion batteries fabricated using the newly developed hybrid ultrathin NiMoO4/SnO2/rGO nanocomposite as an anode material exhibit a high initial discharge capacity of 2128 mAh g−1 and at the 100th cycle is 620 mAh g−1 at a current density of 500 mA g−1. Further, NiMoO4/SnO2/rGO nanocomposite exhibits excellent rate capability and much better capacity of 498 mAh g−1 after the 500th cycle at a higher current density of 1000 mA g−1 with a coulombic efficiency of ∼100%. The NiMoO4/SnO2/rGO nanocomposite shows better electrochemical performance than pure NiMoO4 nanosheets and NiMoO4/SnO2 nanocomposite and it is attributed to the synergetic effect of NiMoO4 nanosheets and SnO2 nanospheres dispersed on rGO sheets, which improves the surface area, electronic conductivity, low particle size and maintains structural integrity.

TiO2 derived from NTU-9 metal-organic framework as highly efficient photocatalyst

Herein we report the use of a titanium metal-organic framework (NTU-9) prepared by an easy and fast microwave-assisted method as precursor to prepare porous titanium dioxide by a one-step pyrolysis (TiO2-NTU-9). The as-synthesized TiO2-NTU-9 material was characterized by XRD, SEM, TEM, N2 adsorption–desorption isotherms and UV–Vis diffuse reflectance spectroscopy. The results showed that the TiO2-NTU-9 was a C-doped mesoporous material with mixed anatase/rutile phase structure. Its performance for the photocatalytic degradation of methylene blue dye under batch conditions by visible light was evaluated, showing an excellent degradation performance. For practical applications, the obtained porous TiO2-NTU-9 was used to fabricate a magnetic stirrer using an easy coating procedure with PVDF. The prepared stirrer (TiO2-NTU-9-S) was characterized and applied for dye degradation from water, and its recyclability was also evaluated.

Microwave-assisted synthesis of nanoscale VO2 structures

Nanoscaled VO2 structures were made using a fast microwave-assisted synthesis method in acetophenone as solvent, starting from vanadium pentoxide V2O5. Insights in the reaction and purification process were elaborated by attenuated total reflection infrared and nuclear magnetic resonance spectroscopy, which validated the choice of oleyl amine as ligand and acetophenone as solvent. A straightforward heat treatment in inert atmosphere was used to convert the mixture of VOx (M) and VOOH phases to thermochromically active monoclinic VO2 (M) nanomaterials. This conversion process was monitored via in-situ X-ray diffraction and gave insight in the influence of ethanol and tert-butyl hydroperoxide on the crystal structure and morphology, monitored via bright-field transmission electron microscopy. The thermochromic switching was investigated with differential scanning calorimetry showing a latent heat up to 43.34 ​J/g.

Controlled microwave-assisted and pH-affected growth of ZnO structures and their photocatalytic performance

A fast microwave-assisted method was used to grow zinc oxide. The synthesis was carried out under three different pH conditions (8, 10 and 12) with the precipitation agent triethylamine. The obtained materials were comprehensively characterised using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), low-temperature N2 sorption (BET model), and analysis of electrokinetic potential and thermal stability (TGA). It was established that the pH value had a significant impact on the crystallinity, morphology and thermal stability of the final products. The primary purpose of this study was to use the synthesised materials in a process of photodegradation (in the UV light range) of the model organic pollutant – 4-chlorophenol (20 mg/dm3). The photo-oxidation tests showed that the obtained zinc oxide materials exhibit good photodegradation and mineralisation efficiency. Moreover, the kinetics of the photocatalytic degradation of 4-chlorophenol were determined based on the pseudo-first-order model, assuming the Langmuir–Hinshelwood mechanism.

Growth of ZnFe2O4 nanosheets on reduced graphene oxide with enhanced ethanol sensing properties

The design and synthesis of materials with unique hierarchical structure has important scientific and practical significance in improving their sensing properties. Herein, ZnFe2O4 nanoparticles assembled nanosheets (ZnFe2O4NSs) grown on reduced graphene oxide (RGO) was creatively constructed via a simple and fast microwave-assisted solvothermal method. RGO played the role as ground for the growth of ZnFe2O4NSs, and the growing process was investigated by a series of irradiation time dependent experiments. Finally, the gas sensing properties for the as-prepared ZnFe2O4NSs/RGO composites were evaluated. The integration of RGO was found to increase the selectivity of ZnFe2O4 to ethanol. It was found that the ZnFe2O4NSs/RGO composite with an irradiation time of 4 h (ZnFe2O4NSs/RGO 4 h) based sensor showed better ethanol sensing performance than that of sensors based on ZnFe2O4NSs assembled sphere without RGO, ZnFe2O4 nanoparticles and ZnFe2O4NSs/RGO composites with other irradiation time, respectively. ZnFe2O4NSs/RGO 4 h based sensors showed good stability and satisfied response to ethanol ranging from 0.1 ppm to 100 ppm at 210℃. The high response was attributed to its unique architecture, the integration of RGO and the formation of heterojunction between RGO and ZnFe2O4.

Alumina-K3PO4 Solid Supported Microwave Synthesis of 1, 3-diaryl-2- propene-1-one Derivatives as a Prominent Antioxidant Scavenger

Background: The various industrial processes have a diverse effect on the environment through pollution. In view of these observations, some environmentally benign synthetically protocols have developed under green chemistry. For rapid and sustainable synthesis, the microwave irradiation (MI) has gained popularity as a powerful tool compared to conventional synthesis. The present study describes the synthesis of novel substituted 1, 3-diaryl-2-propene-1-one derivative using alumina supported K3PO4-MWI combination. Objective: Chalcones are important compounds which are widely spread in nature like in fruits, vegetables, tea, spices, etc. The 2’-hydroxy derivative of chalcones plays an important role in the synthesis of bioactive compounds. The present communication deals with a convenient and rapid synthesis of 1, 3-diaryl-2-propene-1-one under the support of alumina-tripotassium phosphate and microwave irradiation. Our efforts are focused on the introduction of typical and easier route for the synthesis of title compounds using a microwave. All synthesized chalcones have been screened and evaluated for the antioxidant activity by DPPH and nitric oxide radical scavenging. Some of these compounds are found to be more potent scavengers and may lead to the development of a new class of antioxidants. Methods: The α, β-unsaturated carbonyl functionality contains two electrophilic centers allowing them to undergo addition and cyclization reactions with different nucleophiles. In the literature survey, we found that Chalcones were synthesized using tripotassium phosphate catalyst under refluxing by a conventional method. A novel method for the synthesis of 1, 3-diaryl-2-propene-1-one via Claisen Schmidt has been introduced by reacting substituted 2’- hydroxyl acetonaphthones with substituted aromatic aldehydes under the support of basic alumina –tripotassium phosphate via microwave radiations. Formation of corresponding Chalcones was confirmed by spectral studies followed by their screening for antioxidant activity. The scavenging activity is expressed in terms of % inhibition and IC50 value (μg/ml). Results: The structures of newly synthesized Chalcones were confirmed and in good agreement with obtained spectral analysis such as IR, NMR, Mass and elemental analysis. Commercially available basic alumina and tripotassium phosphate in combination of microwave were utilized and found to be effective, convenient route for the synthesis of 1, 3-diaryl-2-propene-1-one derivatives with desirable yields in short reaction time (5-12 min). The results of antioxidant activity revealed that the IC50 value for compounds 3a, 3d, 3e, 3f, 3g, 3h, 3j, 3l and 3n are lower than that of standard ascorbic acid to scavenge DPPH radical. This indicates that these compounds are more significant scavengers in comparison with standard drug. On the other hand, compounds 3a, 3b, 3c, 3d, 3g, 3l and 3n are more potent scavengers for NO free radical. Conclusion: We have introduced an efficient, ecofriendly, simple and fast microwave assisted method using basic alumina-tripotassium phosphate for the synthesis of 1, 3-diaryl-2-propene-1- one derivatives. Microwave irradiation provides an effective way for the preparation of Chalcones in terms of several advantages as a simple procedure, short reaction time, milder reaction condition, cleaner reaction and excellent yield. The scavenging activity of chalcones against DPPH and NO free radicals showed excellent properties of antioxidants.

Microwave-Assisted Growth of Silver Nanoparticle Films with Tunable Plasmon Properties and Asymmetrical Particle Geometry for Applications as Radiation Sensors

We report a simple and fast microwave-assisted method to grow silver nanoparticle films with tunable plasmon resonance band. Microwaving time controls nucleation and growth as well as particle agglomeration, cluster formation, particle morphology, and the plasmonic properties. Films produced with times shorter than 30 s presented a single well-defined plasmon resonance band (~ 400 nm), whereas films produced with times longer than 40 s presented higher wavelength resonances modes (> 500 nm). Plasmon band position and intensity can be easily tuned by controlling microwaving time and power. SEM and AFM images suggested the growth of asymmetrical silver nanoparticles. Simulated extinction spectra considering particles as spheres, hemispheres, and spherical caps were performed. The films were employed to enhance the sensitivity of ionizing radiation detectors assessed by optically stimulated luminescence (OSL) via plasmon-enhanced luminescence. By tuning the plasmon resonance band to overlap with the OSL stimulation (530 nm), luminescence enhancements of greater than 100-fold were obtained, demonstrating the importance of tuning the plasmon resonance band to maximize the OSL intensity and detector sensitivity. This versatile method to produce silver nanoparticle films with tunable plasmonic properties is a promising platform for developing small-sized radiation detectors and advanced sensing technologies.

Microwave-Assisted Extraction of Ricinine from Ricinus communis Leaves.

The alkaloid ricinine (3-cyano-4-methoxy-N-methyl-2-pyridone) is found in different parts of the Ricinus communis plant and is known to possess several bioactive properties, including strong antioxidant activity. In this study, a new microwave-assisted extraction (MAE) method was developed for the recovery of ricinine from R. communis leaves. The extraction variables studied were extraction temperature (between 125 °C and 175 °C), microwave power (between 500 W and 1000 W), extraction time (between 5 min and 15 min), extraction solvent (between 10% and 90% of EtOAc in MeOH), and solvent-to-sample ratio (between 25:1 mL and 50:1 mL of solvent per gram of the sample). On studying the effects of extraction variables, both solvent and liquid-to-solid ratio were found to exhibit the highest effects on ricinine recovery. A fast (15 min) microwave-assisted extraction method was developed (high temperatures can be applied because the stability of ricinine is proven in the literature), allowing for the recovery of ricinine from R. communis leaves. The study revealed that R. communis leaves had almost 1.5 mg g−1 (dried weight) of ricinine.

Construction of flourinated-TiO2 nanosheets with exposed {001} facets/CdSe-DETA nanojunction for enhancing visible-light-driven photocatalytic H2 evolution

Although much significant efforts have been devoted to design highly efficient photocatalysts for addressing energy crisis and environmental issues, it remains challenging to construct a promising and efficient heterostructure among semiconductors for photocatalytic hydrogen (H2) production under visible-light excitation. Herein, the novel structure with 2D fluorinated-TiO2 nanosheets (F–TiO2 NSs) decorated CdSe-diethylenetriamine nanoflowers (CdSe-DETA NFs) was designed and fabricated by a simple and fast microwave-assisted hydrothermal method. The F–TiO2/CdSe-DETA heterojunction displays enhanced photocatalytic activity in splitting water to produce H2. Among them, 20%F–TiO2/CdSe-DETA exhibited the highest H2 evolution rate (12381 μmmol g−1 h−1), which is 2.92 and 6.44 times greater than that of pristine CdSe-DETA and CdSe, respectively. Meanwhile, 20%F–TiO2/CdSe-DETA composite shows a good stability in the cyclic runs for photocatalytic H2 evolution. The enhanced activity and reusability are primarily attributed to rapid separation of charge carriers, enrich catalytic active sites as well as strong light absorption capability. Besides, the in-situ growth of a certain amount F–TiO2 NSs with exposed {0 0 1} high-energy facets on surface of inorganic-organic CdSe-DETA NFs greatly helps to strengthen intimate interfacial contact. These results may furnish a reference to fabricate the heterostructures on the basis of CdSe that is extremely insightful for conversion of solar power to H2 energy.

Microwave-assisted integration of transition metal oxide nanocoatings on manganese oxide nanoarray monoliths for low temperature CO oxidation

Manganese oxide (OMS-2), a promising exhaust treatment catalyst, has been successfully integrated onto the channel wall surfaces of cordierite honeycombs in the form of a nanoarray forest. To further improve their catalytic carbon monoxide (CO) oxidation activity, a series of different metal oxide nanocoatings were uniformly grown on the surface of OMS-2 nanoarrays by utilizing a facile and fast microwave-assisted synthesis method. The manganese-cobalt oxide core-shell nanoarray based monolithic catalysts exhibit the highest catalytic performance with a 100% CO conversion at 150 °C, in a sharp contrast with 325 °C for the bare OMS-2 nanoarrays. Different growth mechanisms of the layered Co(OH)2 and spinel Co3O4 induced by different cobalt precursors are used to explain the morphology evolution of the manganese-cobalt oxide core-shell nanoarrays. The Co3+ distributed on the surface of the nanoarrays acts as the active sites for CO oxidation. The small grain size, abundant surface-adsorbed oxygen, and interfacial effects between MnO2 and Co3O4 were found to favor the observed high catalytic activity. A thermal annealing study showed that high temperature induces the sintering of the nanoarray catalyst, which further affects the CO oxidation activity. This fast, cost-effective, and scalable method will provide a new route for synthesizing efficient core-shell nanoarray monolithic catalysts for low temperature catalysis.

Temperature-dependent preparation of bismuth pyrostannate Bi2Sn2O7 and its photocatalytic characterization

Bi2Sn2O7 nanoparticles were successfully synthesized via a fast microwave-assisted method and high temperature treatment. The obtained nanoparticles were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), UV-Vis diffuse reectance spectroscopy (DRS), photoluminescence spectroscopy (PL), total organic carbon (TOC) measurement and Raman spectroscopy. We found that there is an optimal thermal treatment temperature for Bi2Sn2O7 for the highest photocatalytic activity in the decomposition of rhodamine B (RhB) under visible light irradiation. We observed an improvement in activity when the thermal treatment temperature increases from room temperature to 500∘C, but the activity decreases when the sintering temperature is increased further. The reason behind the enhanced photocatalytic efficiency is a better separation of the charge carriers which is competitive with the specific surface area, crystallinity and crystal size.

Microwave-assisted solution synthesis, microwave sintering and magnetic properties of cobalt ferrite

A simple, soft, and fast microwave-assisted hydrothermal method was used for the preparation of nanocrystalline cobalt ferrite powders from commercially-available Fe(NO3)3∙9H2O, Co(NO3)2∙6H2O, ammonium hydroxide, and tetrapropylammonium hydroxide (TPAH). The synthesis was conducted in a sealed-vessel microwave reactor specifically designed for synthetic applications, and the resulting products were characterized by XRD, FE-SEM, TEM, and HR-TEM. After a systematic study of the influence of the microwave variables (temperature, reaction time and nature of the bases), highly crystalline CoFe2O4 nanoparticles with a high uniformity in morphology and size, were directly obtained by heating at 130 °C for 20 min using the base TPAH. Dense ceramics of cobalt ferrite were prepared by non-conventional, microwave sintering of synthesized nanopowders at temperatures of 850–900 °C. The magnetic properties of both the nanopowders and the sintered specimens were determined in order to establish their feasibility as a permanent magnet.

Efficient and Environmentally Friendly Microwave-Assisted Synthesis of Catalytically Active Magnetic Metallic Ni Nanoparticles

Pure magnetic metallic nickel was synthesized by a simple and fast microwave-assisted method using a monomode microwave reactor. Nickel chloride was employed as metal precursor, while an environmental-friendly mixture of ethylene glycol and ethanol was simultaneously used as solvent and reducing agent. The parameters combination, for the occurrence of the reaction, of the mixture molar fraction and the metal precursor concentration was developed. The influence of the temperature and the time of the irradiation was investigated. The best performance (71% yield) was achieved at 250°C in 5 minutes of microwave irradiation. The phase and the morphology of the metal were analyzed by X-ray diffraction (XRD), scanning emission microscopy (SEM) and transmission electron microscopy (TEM) while the surface area was determined by nitrogen physisorption. The material exhibited a strong magnetic behavior. The metallic Nickel showed high catalytic activity for the hydrogenolysis of benzyl phenyl ether, a lignin model c...