Microwave-assisted Solvothermal Synthesis Research Articles

Ultrafast, low temperature microwave-assisted solvothermal synthesis of nanostructured lithium iron phosphate optimized by a chemometric approach

Nanostructured LiFePO4/C composites having ordered olivine structure are prepared by a newly elaborated low temperature microwave-assisted solvothermal synthesis in the presence of a cationic surfactant. The microwave-assisted approach is simple and cost effective: it significantly decreases reaction times compared to the conventional hydrothermal/solvothermal processes. A study on the influence of the synthesis parameters on both the morphology and the electrochemical behavior of the samples is performed by means of X-ray powder diffraction, N2 physisorption at 77K, scanning electron microscopy, cyclic voltammetry and constant current charge/discharge cycling. Moreover, a chemometric approach through design of experiments (DoE) is here successfully demonstrated for the first time for the optimization and fine tuning of the experimental conditions, including synthetic procedure and electrochemical characteristics of the materials. As a result, we show a nanostructured LiFePO4/C with high rate capability and delivering a very stable cycling behavior for more than thousand cycles with excellent Coulombic efficiency and exceptional capacity retention at 1C.

Microwave-assisted solvothermal synthesis of Bi4O5I2 hierarchical architectures with high photocatalytic performance

TiO2 usually exhibits good photocatalytic activity and stability, but requires UV irradiation (smaller than 387nm) for effective photocatalytic reactions, thus greatly limiting its application range. It is highly desirable to develop visible-light driven photocatalysts with high photocatalytic performance under sunlight or daylight lamp irradiation. Herein, Bi4O5I2 hierarchical architectures with high visible-light photocatalytic activity were fabricated by a microwave-assisted solvothermal method. Oil bath synthesis and direct hydrolysis were also applied to prepare bismuth oxyiodides for comparison. The Bi4O5I2 hierarchical architectures obtained by microwave treatment exhibited the highest photocatalytic activity toward phenol degradation under visible-light irradiation. This is attributed to its more surface active sites and strongest internal electric field, originating from the highest specific surface area and thinnest nanosheet morphology, respectively. The prepared Bi4O5I2 hierarchical architectured photocatalysts may find potential application in catalysis, separation technology, solar cell, biomedical engineering, and nanotechnology. This work will provide some new insight into the design and fabrication of visible-light photocatalysts.

Microwave-Assisted Solvothermal Synthesis of Three Polymorphs of LiCoPO4 and Their Electrochemical Properties

Many investigations have been conducted on polyanion cathodes for lithium-ion batteries, specifically LiMPO4 (M = Fe, Mn, Co, Ni), but a majority were restricted to the olivine polymorph with the Pnma space group. This study presents the synthesis and characterization of three orthorhombic polymorphs of LiCoPO4 belonging to the space groups Pnma, Pn21a, and Cmcm. The three polymorphs were synthesized with a microwave-assisted solvothermal (MW-ST) synthesis method at a relatively low temperature of 260 °C. The properties and morphology of the materials were characterized with X-ray diffraction, inductively coupled plasma–optical omissions spectroscopy, Raman and infrared spectroscopy, scanning electron microscopy, thermogravometric analysis, galvanostatic charge/discharge, and cyclic voltammetry. The electrochemical properties of the Cmcm polymorph and nanosized Pn21a polymorph are reported for the first time.

Zinc oxide nanoparticles with surface modified by degradation of capping polymers in situ during microwave synthesis

Surface modified zinc oxide nanoparticles with variable lipophilicity were prepared by the help of microwave-assisted solvothermal synthesis from mechano-chemically prepared precursor. Sodium carbonate and zinc acetate dihydrate were used as starting materials, diethylene glycol was used as a solvent, poly(ethylene glycol) and polyvinyl alcohol were used as surface capping agents. The zinc oxide was obtained during the first three minutes of reaction and its surface was further modified with prolonged time of the reaction due to degradation of polymers used as capping and stabilising agents. Scanning Electron Microscopy was employed for powder morphology evaluation. Inorganic phase structure development was characterized by means of X-ray diffraction. Nanostructured composite materials with crystallite size below 10nm were obtained with specific surface area varying from 35 to 86m2g−1 according to Brunauer–Emmett–Teller analysis. The progress of degradation of adsorbed polymer moieties was manifested by the powder colour change. Optical properties as well as the structure of materials were further analysed by Diffuse Reflectance Ultraviolet–visible Spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy and correlated with Thermogravimetric observations and Lipophilicity degree analysis.

Microwave-Assisted Solvothermal Synthesis of Pd-MnO2 Hybrid at Onion-like Carbons: Electrocatalytic Oxidation of Alcohols in Alkaline Media

The use of less toxic glycerol, (a non-flammable, volatile, and little-valued residue of biodiesel production), ethanol as well as ethylene glycol (EG) as fuel may be an interesting alternatives to methanol for Direct Alcohol Fuel Cell (DAFC) technology. The volumetric energy densities of glycerol, ethanol and EG are 5.80, 6.31 and 5.97 kW h L-1 compared to 5.81 kW h L-1for methanol makes them good fuel cell candidates [1-2]. The secret to the efficient electrocatalysis of alcohols is the use of efficient nanocatalyst. Palladium-based catalysts have emerged as the most viable electrocatalysts for alcohol in alkaline electrolytes. To harness the great catalytic potential offered by Pd, and to reduce cost, Pd-based alloys supported on different carbon supports are constantly used in direct alcohol fuel cells (DAFCs). In this work, palladium-manganese oxide nanoparticles supported on carbon nano onions (Pd-MnO2/OLC) were synthesized using the microwave-assisted solvothermal technique. Palladium-manganese oxide nanoparticles supported on Vulcan carbon (Pd@MnO2/XC–72) were also synthesized using the same technique for comparison. The catalysts were characterized using XRD, XPS, FESEM and HRTEM techniques. Electroxidation of the alcohols was performed in 0.5 M alcohol / 0.5 M KOH via cyclic and linear sweep voltammetry, chronoamperometric and elelctrochemical impedance spectroscopy. Results obtained show that the catalyst supported on OLC exhibited the highest current density and least charge transfer resistance relative to the catalyst supported on XC–72. Pd-MnO2/OLC gave the best result amongst the catalyst synthesized with respect to the current density, and electrochemical stability as well as exhibited the least charge transfer resistance in all the alcohols studied. For instance, the onset oxidation potential and current density of the glycerol oxidation process were -0.5386 V and 5.58mAcm-2, respectively. The implications of these results relative to methanol oxidation using the best catalyst system synthesized are discussed.

The formation mechanism of iron oxide nanoparticles within the microwave-assisted solvothermal synthesis and its correlation with the structural and magnetic properties.

Magnetic nanoparticles based on Fe3O4 were prepared by a facile and rapid one-pot solvothermal synthesis using FeCl3·6H2O as a source of iron ions, ethylene glycol as a solvent and NH4Ac, (NH4)2CO3, NH4HCO3 or aqueous NH3 as precipitating and nucleating agents. In contrast to previous reports we reduce the synthesis time to 30 minutes using a pressurized microwave reactor without the requirement of further post-treatments such as calcination. Dramatically reduced synthesis time prevents particle growth via Ostwald ripening thus the obtained particles have dimensions in the range of 20 to 130 nm, they are uniform in shape and exhibit magnetic properties with saturation magnetization ranging from 8 to 76 emu g(-1). The suggested method allows simple particle size and crystallinity tuning resulting in improved magnetic properties by changing the synthesis parameters, i.e. temperature and nucleating agents. Moreover, efficiency of conversion of raw material into the product is almost 100%.

The microwave-assisted solvothermal synthesis of a crystalline two-dimensional covalent organic framework with high CO2 capacity

We report the synthesis of a two-dimensional enamine-linked covalent organic framework (COF) using a rapid microwave-assisted solvothermal method in significantly less time and high yield under a relatively low temperature. This COF was found to have a high crystallinity, high stability, high BET surface area, and a high CO2 capacity and adsorption selectivity of CO2/N2.

Microwave-assisted solvothermal synthesis of sulfur-doped graphene for electrochemical sensing

Heteroatom doping is an effective way to modulate the electronic structure and properties of graphene. Despite a growing interest in sulfur (S)-doped graphene (SG), synthesis of high-quality SG at low cost remains a great challenge. In this study, we developed a rapid, efficient and cost-effective microwave-assisted solvothermal (MAS) method for the preparation of SG. It was found that a short MAS time of 6min could generate few-layer SG (0.5μm in lateral size) having effective oxygen reduction, high level of S-doping, sole thiophene-S bonding configuration, and high electrical conductivity. Furthermore, the resulting SG could serve as an effective electrocatalyst for H2O2 reduction, showing improved electrocatalytic activity over its undoped counterpart and good sensing performances for highly sensitive and selective detection of H2O2, indicating that SG may be a promising candidate for electrochemical sensor applications.

Microwave-assisted solvothermal synthesis and upconversion luminescence of CaF2:Yb3+/Er3+ nanocrystals

Water-dispersible CaF2 and Yb3+/Er3+ codoped CaF2 (CaF2:Yb3+/Er3+) nanocrystals with different sizes and different Yb3+ and Er3+ dopant concentrations were synthesized using ionic liquid 1-n-butyl-3-methyl imidazolium tetrafluoroborate as a fluorine source by the rapid microwave-assisted solvothermal method. It was found that the morphology, size and crystallinity of CaF2:Yb3+/Er3+ nanocrystals could be adjusted by using adenosine 5′-triphosphate disodium salt (ATP). Yb3+ and Er3+ ions were doped into CaF2 nanocrystals to enable upconversion luminescence emission, and the as-prepared CaF2:Yb3+/Er3+ samples exhibited upconversion luminescence upon excitation at 980nm. Confocal laser scanning microscopy images showed that the CaF2:Yb3+/Er3+ nanocrystals could be used for efficient labeling of human gastric carcinoma cells. Moreover, in vitro cytotoxicity experiments indicated that the as-prepared CaF2:Yb3+/Er3+ nanocrystals had essentially little cytotoxicity. These results indicate that the as-prepared CaF2:Yb3+/Er3+ nanocrystals are promising for the application as a luminescent label material in biological imaging.

Microwave-assisted solvothermal synthesis of nickel molybdate nanosheets as a potential catalytic platform for NADH and ethanol sensing

Novel β-nickel molybdate (β-NiMoO4) nanosheets were synthesized by a microwave-assisted solvothermal method, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution TEM (HRTEM), and energy dispersive spectrum (EDS). The as-prepared NiMoO4 nanosheets exhibited strong absorption property for electroactive ferricyanide ion (Fe(CN)63−) and graphite, allowing their easy and stable modification on carbon paste electrode (CPE), which was demonstrated good electrocatalytic activity toward the oxidation of β-nicotinamide adenine dinucleotide (NADH). In addition, a nonenzymatic ethanol sensor based on NiMoO4 nanosheets was also first presented in this work.

Microwave-assisted solvothermal synthesis of spinel AV2O4 (M = Mg, Mn, Fe, and Co).

Lower-valent vanadium oxide spinels AV2O4 (A = Mg, Mn, Fe, and Co) consisting of A(2+) and V(3+) ions have been synthesized by a low-temperature microwave-assisted solvothermal (MW-ST) synthesis process in a tetraethylene glycol (TEG) medium. The oxides are formed within a short reaction time of 30 min at 300 °C. Subsequent postheat treatment of the oxides at elevated temperatures in inert or reducing atmospheres results in an instability of the spinel phase, especially CoV2O4 due to the ease of formation of metallic Co, demonstrating the advantage of the low-temperature MW-ST process in accessing these oxides. This MW-ST synthesis approach is attractive for synthesizing other lower-valent transition-metal oxides that are otherwise difficult to obtain by conventional synthesis methods and for subsequent study of their unique physical and chemical properties.

Battery Division Research Award: From Insertion-compound Electrodes to Conversion-reaction Electrodes for Energy Storage

The current lithium-ion technology is based on insertion-compound cathodes and anodes. Layered and spinel oxides and olivine phosphates are the leading insertion-cathode hosts while graphite is the sole insertion-anode host at the present time. Each of the three cathode systems in play offers advantages and disadvantages while exhibiting rich but complex structural/chemical behaviors, and their adoption in practical cells is determined largely by the type of application. This presentation will focus on the challenges and prospects of transitioning from insertion-compound electrodes to next-generation, high-capacity, conversion-reaction electrodes.First, an overview of how low-temperature synthesis and processing (e.g., chemical lithium extraction and microwave-assisted solvothermal synthesis) approaches have assisted to develop a fundamental understanding of some of the complex behaviors of the three classes of cathodes. For example, with the use of low-temperature synthesis processes, the roles of the position of the transtion-metal:3d energy relative to the top of the oxygen:2p band, degree of metal-oxygen covalence, morphology and surface crystal planes, surface compositions, isovalent and aliovalent cationic and anionic doping on the electrochemical performances (e.g., capacity, irreversible capacity loss in the first cycle, rate capability, and cycle life) will be pointed out with representative examples. Second, the potential of alternative, conversion-reaction, nanocomposite alloy anodes to overcome the safety issues of the graphite anode will be presented. Specifically, the use of facile mechanochemical reactions to realize nanoengineered alloy anodes both for lithium-ion and sodium-ion batteries will be discussed.Third, novel electrode architectures as well as innovative cell designs to overcome the persistent problems of the conversion-reaction sulfur cathode will be presented. Specifically, approaches to enhance the electrochemical utilization of sulfur and suppress the migration of dissolved polysulfide ions to the anode will be discussed both with lithium-sulfur and ambient-temperature sodium-sulfur cells. Also, approaches to stabilize the lithium-metal anode surface in a polysulfide-rich environment will be outlined.Fourth, to overcome the formidable challenges of aprotic lithium-air cells, the possibility of hybrid lithium-air cells in which a solid electrolyte separates the lithium-metal anode in an aprotic electrolyte from the air electrode in an aqueous catholyte will be briefly presented. Specifically, the design and development of inexpensive, efficient catalysts for the oxygen reduction reaction and oxygen evolution reaction will be discussed.

Evaluation of structural transformation in 2D metal–organic frameworks based on a 4,4′-sulfonyldibenzoate linker: microwave-assisted solvothermal synthesis, characterization and applications

Structural transformation has been observed in 2D MOFs.

Microwave-Assisted Solvothermal Synthesis of In-Si Co-Modified TiO<sub>2</sub> Photocatalysts with Enhanced Photocatalytic Activity

Microwave-Assisted Solvothermal Synthesis of In-Si Co-Modified TiO<sub>2</sub> Photocatalysts with Enhanced Photocatalytic Activity

Microwave-Assisted Solvothermal Synthesis and Optical Properties of Tagged MIL-140A Metal–Organic Frameworks

A series of tagged MIL-140A-R frameworks have been synthesized using a microwave-assisted solvothermal method. Compared with their UiO-66-R polymorphs, the absorption energies in the MIL-140A-R series (R = NH2, NO2, Br, Cl, and F) are extended toward the visible region because of the spatial arrangement of the linkers.

Solution-based synthesis of BaZrO3 nanoparticles: conventional versus microwave synthesis

In this paper, we report on the synthesis of BaZrO3 nanostructures by novel bottom-up synthesis methods. Nanocrystals with diameters ranging from 5 to 10 nm are prepared from aqueous or multiple phase precursor solutions. In order to transform the precursor solutions into nanocrystal containing suspensions, both conventional and microwave-assisted solvothermal treatments are used. An additional heat treatment was necessary to obtain crystalline particles starting from the aqueous precursor, while crystalline particles are directly obtained after solvothermal treatment of the multiple phase precursor. The crystallinity and size of the obtained nanoparticles are investigated by means of dynamic light scattering, X-ray diffraction and transmission electron microscopy. We found that the nature of the bases used in the multiple phase precursor have an effect on the particle morphology. In general, the microwave-assisted solvothermal synthesis renders the best prospects towards small particle sizes between 3 and 5 nm in diameter with a narrow size distribution. In addition, the process exhibits higher energy efficiency, resulting in lower reaction times (5 min–2 h) in comparison with the conventional solvothermal treatment (4–24 h).

Microwave-assisted solvothermal synthesis of flower-like Ag/AgBr/BiOBr microspheres and their high efficient photocatalytic degradation for p-nitrophenol

Flower-like Ag/AgBr/BiOBr microspheres were successfully fabricated by the approach of microwave-assisted solvothermal and in situ photo-assisted reduction. A reactive ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) was employed as Br source in the presence of surfactant polyvinylpyrrolidone (PVP). The photocatalytic activity of Ag/AgBr/BiOBr towards the decomposition of p-nitrophenol under visible light irradiation was evaluated. The results indicated that Ag/AgBr/BiOBr showed enhanced photocatalytic activity towards p-nitrophenol, comparing with P25, BiOBr and Ag/AgBr. More than 96% of p-nitrophenol was decomposed in 3.5 h under visible-light irradation. The excellent photocatalytic activity of flower-like Ag/AgBr/BiOBr microspheres can be attributed to the large specific surface area, strong visible-light absorption, suitable energy band structure and surface plasmon resonance effect of Ag nanoparticles. The possible photocatalytic mechanism was proposed based on the active species test and band gap structure analysis.

Microwave-assisted solvothermal synthesis of 3D carnation-like SnS2 nanostructures with high visible light photocatalytic activity

Novel 3D carnation-flowerlike hexagonal SnS2 hierarchical structures have been successfully synthesized through a simple microwave-assisted solvothermal process. The as-prepared products were characterized by power X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron micrographs (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activity of the sample under visible-light irradiation (λ>420nm) was evaluated by the degradation of two different organic pollutants, rhodamine B (RhB) and phenol. The results reveal that the carnation-flowerlike SnS2 architectures show much higher photocatalytic activity than the SnS2 nanoparticles. The high catalytic performance of the SnS2 architectures comes from their hierarchical mesoporous structures, high BET surface area, high surface-to-volume ratios, and increased light absorbance. In addition, the SnS2 hierarchical architectures are stable during the photocatalytic reaction and can be used repeatedly.

Synthesis and characterization of zinc borophosphates with ANA-zeotype framework by the microwave method

Abstract Zinc borophosphate (NH 4 ) 16 [Zn 16 B 8 P 24 O 96 ] (denoted as ZnBP-ANA) with ANA-zeotype structure has been synthesized by employing microwave-assisted solvothermal synthesis in the reaction system ZnCl 2 ∙6H 2 O-(NH 4 ) 2 HPO 4 –H 3 BO 3 using ethylene glycol as a co-solvent. The influences of various experimental parameters, such as reaction temperature, solvent ratio, zinc precursors and reactive power, have been systematically investigated. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA), and so on. Small and homogeneous ZnBP-ANA single crystal with regular cube morphology are crystallized by using microwave solvothermal synthesis method within a shorter time, and its grain size decreases with power.

Microwave-Assisted Solvothermal Synthesis and Characterization of Barium Orthovanadate Nanoparticles

Microwave-Assisted Solvothermal Synthesis and Characterization of Barium Orthovanadate Nanoparticles