Microwave-solvothermal Method Research Articles

Surface modification of hierarchical Li1.2Mn0.56Ni0.16Co0.08O2 with melting impregnation method for lithium-ion batteries

Layered Li-rich oxide material Li1.2Mn0.56Ni0.16Co0.08O2 (LRM) has been studied intensively by virtue of its high discharge capacity. Nevertheless, the inferior cycle stability and rate capability issues hinder its application for electrified vehicles (EVs). Here, the CeO2-modified LRM was synthesized via an ultrafast microwave solvothermal method following by a low temperature melting impregnation method. It is not only convenient and fast, but also reducing the surface eroding which is caused by larger amount of water in traditional coating processes. The modified LRM shows an improved cycling performance that the specific discharge capacity is 168.2 mA h g−1 with the capacity retention of 86.7% at 200 mA g−1 after 100 cycles. Even current up to 5 A g−1, it also displays a high discharge capacity of 66.4 mA h g−1 with a superior capacity retention of 85.9% (based on the reversible capacity of the fifth cycle) after 300 cycles. This work demonstrates that the low temperature melting impregnation method is less surface destructive and promising to obtain surface modified LRM as cathode material for the high-energy LIBs.

Photocatalytic defluorination of perfluorooctanoic acid by surface defective BiOCl: Fast microwave solvothermal synthesis and photocatalytic mechanisms

There is an urgent need for developing cost-effective methods for the treatment of perfluorooctanoic acid (PFOA) due to its global emergence and potential risks. In this study, taking surface-defective BiOCl as an example, a strategy of surface oxygen vacancy modulation was used to promote the photocatalytic defluorination efficiency of PFOA under simulated sunlight irradiation. The defective BiOCl was fabricated by a fast microwave solvothermal method, which was found to induce more surface oxygen vacancies than conventional solvothermal and precipitation methods. As a result, the as-prepared BiOCl showed significantly enhanced defluorination efficiency, which was 2.7 and 33.8 times higher than that of BiOCl fabricated by conventional solvothermal and precipitation methods, respectively. Mechanistic studies indicated that the defluorination of PFOA follows a direct hole (h+) oxidation pathway with the aid of •OH, while the oxygen vacancies not only promote charge separation but also facilitate the intimate contact between the photocatalyst surface and PFOA by coordinating with its terminal carboxylate group in a bidentate or bridging mode. This work will provide a general strategy of oxygen vacancy modulation by microwave-assisted methods for efficient photocatalytic defluorination of PFOA in the environment using sunlight as the energy source.

Influence of operational parameters on the photocatalytic performance of DE-NOx process Via MIL-101(Fe)

Metal organic framework (MOF) has been paid great attention as a potential candidate for various applications in the field of energy and environment, particularly in air purification. Among various MOFs, MIL-101(Fe) represents an interesting material possessing many advantages, including the ease of fabrication, high porosity, high specific surface area with open metal sites, making it a promising material in the field of harmful gas treatment. Taking these advantages, MIL-101(Fe) was synthesized by facile microwave-solvothermal method and applied as a photocatalyst for the degradation of NOx. The de-NOx efficiency of the synthesized powder was evaluated with respect to various operating parameters including substrates, sample doses, light spectrum and light intensity, initial NO concentration, and relative humidity. The results have shown that the efficiency of NOx photocatalytic degradation reaches to 77% under solar irradiation via 0.1 g of MIL-101(Fe) with optimum condition of reaction, (alumina substrate, 350 ppb of initial NO concentration, 40–50% of relative humidity). Then this work provides the optimum condition for the efficient photocatalytic degradation of NOx.

Transverse magnetoresistance peculiarities of thermoelectric Lu-doped Bi2Te3 compound due to strong electrical disorder

The n-type thermoelectric Bi1.9Lu0.1Te3 was prepared by microwave-solvothermal method and spark plasma sintering. The magnetic field and temperature dependences of transverse magnetoresistance measured within temperature 2–200 K interval allow finding the peculiarities characteristic for strongly disordered and inhomogeneous semiconductors. The first peculiarity is due to appearance of linear-in-magnetic field contribution to the total magnetoresistance reflected in a crossover from quadratic magnetoresistance at low magnetic fields to linear magnetoresistance at high magnetic fields. The linear magnetoresistance can result from the Hall resistance picked up from macroscopically distorted current paths due to local variations in stoichiometry of the compound studied. The second peculiarity is that both linear magnetoresistance magnitude and crossover field are functions of carrier mobility which is in agreement with the Parish and Littlewood model developed for disordered and inhomogeneous semiconductors. An increase in the mobility due to a decrease in temperature is accompanied by an increase in the magnetoresistance magnitude and a decrease in the crossover field. Finally, the third peculiarity is related to the remarkable deviation of the total magnetoresistance measured at various temperatures from the Kohler's rule. Presence of strong inhomogeneity and disorder in the Bi1.9Lu0.1Te3 structure concluded from the magnetoresistance peculiarities can be responsible for the remarkable reduction in the total thermal conductivity of this compound.

Synthesis of Cu2(Zn1−xCox)SnS4 nanocrystals and formation of polycrystalline thin films from their aqueous dispersions

Cu2(Zn1−xCox)SnS4 nanocrystals were synthesized using a microwave solvothermal method. The influence of Co incorporation in the annealed thin films formation was analyzed.

Mechanisms of thermoelectric efficiency enhancement in Lu-doped Bi2Te3

The LuxBi2−xTe3 thermoelectrics with x = 0, 0.05, 0.1 and 0.2 have been prepared by microwave-solvothermal method and spark plasma sintering. All the compositions are semiconductors of n-type conductivity. It was found that electron concentration increases and electron mobility decreases with x increasing. The Lu doping results in remarkable increase of the thermoelectric figure-of-merit from ∼0.4 for undoped Bi2Te3 up to ∼0.9 for Bi1.9Lu0.1Te3. Enhancing the thermoelectric efficiency at the doping is originated from: (i) increase of the electron concentration since the Lu atoms behave as donors in the Bi2Te3 lattice that decreases the specific electrical resistance, (ii) increase of the Seebeck coefficient via increase of the density-of-states effective mass for conduction band, (iii) decrease of the total thermal conductivity via forming the point defects like antisite defects and Lu atoms substituting for the Bi sites. Formation of narrow non-parabolic impurity band lying near the Fermi energy with sharp density of states is believed to be responsible for increasing the density-of-states effective mass and decreasing the electron contribution to the total thermal conductivity.

Microwave Solvothermal Fabrication of Zirconia Hollow Microspheres with Different Morphologies Using Pollen Templates and Their Dye Adsorption Removal

Both porous and scale-like wall zirconia (ZrO2) hollow microspheres were successfully prepared through a facile and mild microwave solvothermal method using the rape pollen as biotemplates. The formation mechanisms were discussed for both ZrO2 hollow microspheres fabricated using pollen biotemplate with different pollen treatments. The porous ZrO2 hollow microspheres had a specific surface area of 40.92 m2·g–1, significantly higher than scale-like wall ZrO2 hollow microspheres (24.79 m2·g–1) and ZrO2 particles (27.99 m2·g–1). The adsorption test results showed that porous ZrO2 hollow microspheres had a higher adsorption capability (96.98 g·mg–1) than scale-like wall ZrO2 hollow microspheres (38.55 g·mg–1) and ZrO2 particles (32.03 g·mg–1) for Congo red. The adsorption followed pseudo-second-order kinetics, and the adsorption process was homogeneous adsorption of monolayer.

Enhancement of thermoelectric efficiency in Bi2Te3 via rare earth element doping

The Bi2Te3, Bi1.9Lu0.1Te3 and Bi1.9Tm0.1Te3 thermoelectrics of n-type conductivity were prepared by microwave-solvothermal method and spark plasma sintering. At the Lu and Tm doping, the Seebeck coefficient increases, while the specific electrical conductivity and total thermal conductivity decreases resulting in thermoelectric efficiency enhancement of Bi2Te3. It is believed that the thermoelectric efficiency can enhance mainly due to formation of narrow impurity Lu or Tm band with high and sharp density of states near the Fermi level. Both increase of the density-of-states effective mass of electrons and decrease of electronic contribution to the total thermal conductivity take place in this case.

Effects of Lu and Tm Doping on Thermoelectric Properties of Bi2Te3 Compound

The Bi2Te3, Bi1.9Lu0.1Te3 and Bi1.9Tm0.1Te3 thermoelectrics of n-type conductivity have been prepared by the microwave-solvothermal method and spark plasma sintering. These compounds behave as degenerate semiconductors from room temperature up to temperature T d ≈ 470 K. Within this temperature range the temperature behavior of the specific electrical resistivity is due to the temperature changes of electron mobility determined by acoustic and optical phonon scattering. Above T d, an onset of intrinsic conductivity takes place when electrons and holes are present. At the Lu and Tm doping, the Seebeck coefficient increases, while the specific electrical resistivity and total thermal conductivity decrease within the temperature 290–630 K range. The increase of the electrical resistivity is related to the increase of electron concentration since the Tm and Lu atoms are donor centres in the Bi2Te3 lattice. The increase of the density-of-state effective mass for conduction band can be responsible for the increase of the Seebeck coefficient. The decrease of the total thermal conductivity in doped Bi2Te3 is attributed to point defects like the antisite defects and Lu or Tm atoms substituting for the Bi sites. In addition, reducing the electron thermal conductivity due to forming a narrow impurity (Lu or Tm) band having high and sharp density-of-states near the Fermi level can effectively decrease the total thermal conductivity. The thermoelectric figure-of-merit is enhanced from ∼ 0.4 for undoped Bi2Te3 up to ∼ 0.7 for Bi1.9Tm0.1Te3 and ∼ 0.9 for Bi1.9Lu0.1Te3.

Optimization of microwave-solvothermal synthesis of Fe3O4 nanoparticles. Coating, modification, and characterization

In this research, magnetite nanoparticles were synthetized by the microwave-solvothermal method. The parameters related to this method were evaluated with: 1) the Plackett-Burman design, in order to evaluate the influence of the holding time [th] and the gradient time [tg] (reaction times) in the synthesis percent yield; and 2) the Box-Behnken design (BBD), selected in order to reduce the number of experimental experiences. In this last, the ammonium acetate amount (mmol) [th], and the microwave system temperature were optimized in order to achieve the smallest magnetite nanoparticles. Microwave assisted coating and modification with TMSPT/AMT were performed to the synthetized nanoparticles, in order to avoid degradation. The response variable considered for optimization of the synthesis was the nanoparticle's size, which was estimated by X-ray diffraction. Temperature and th resulted to be the most important parameters affecting the nanoparticle's size. The BBD allowed to obtain nanoparticle sizes between 10 and 32 nm. Polynomial validation was performed with confirmatory experiments considering the following conditions: T = 255 °C, th = 10 min, tg=7 min, ammonium acetate amount = 4.55 mmol, Fe(III) = 2 mmol, sodium citrate amount = 1.55 mmol and ethylene glycol = 6 mL. The obtained nanoparticles, with a size of 14 nm, were characterized by FT-IR, X-RD, SEM, and STEM.

Microwave-assisted solvothermal synthesis and performances of LiMn0.7Fe0.3PO4 nanoplates

ABSTRACTLiFexMn1-xPO4 (x = 0 ~ 1) cathode materials were widely studied in the past few years. The results show that this olivine-structured material would present higher energy density that can be achieved at higher Mn content. However, the specific capacity and rate capability of the LiFexMn1-xPO4 would decrease with decrease of x from results of various studies. Here, we chose the optimal x value of 0.3 and successfully synthesized the pure LiMn0.7Fe0.3PO4 via microwave-solvothermal method at 200°C with a short reaction time of 10 min. In spite of the low synthesis temperature, the as-synthesized powders with thinner thickness along [010] direction are highly crystalline. Sample exhibited excellent rate capability and showed good cyclic performance. The short reaction times of just 10 min show the basis for an efficient and time-saving synthesis of nanosized LiMn0.7Fe0.3PO4.

Facile synthesis of fusiform layered oxides assisted by microwave as cathode material for lithium-ion batteries

A facile microwave solvothermal reaction is performed to synthesize novel LiMn0.25Ni0.5Co0.25O2 ternary layered oxide with 1 D fusiform morphology. Scanning electron microscopy (SEM) images show that material synthesized at 800°C well keeps the fusiform morphology of the precursor with a particle size of 100–300nm. All the three elements are perfectly dispersed and a well-formed layered structure is obtained. Thus, good electrochemical performances with high initial discharge capacity of 183mAhg−1 is reached. Furthermore, high discharge capacity of 154mAhg−1 is remained with a capacity retention of 84.2% after 100 cycles at 20mAg−1. Excellent rate capability is also obtained with high discharge capacity of 99mAhg−1 at 2000mAg−1. It seems such facile microwave solvothermal method is one of the most promising candidates for preparing ternary layered oxides with excellent electrochemical properties as cathode material for lithium ion batteries.

High performance of LiMn1-x Fe x PO4/C (0 ≤ x ≤ 0.5) nanoparticles synthesized by microwave-assisted solvothermal method

High specific energy olivine LiMn1-x Fe x PO4/C (0 ≤ x ≤ 0.5) nanoparticles have been synthesized in 20 min at extremely low temperature 160 °C by microwave-solvothermal method. The obtained cathode materials are orthorhombic solid solutions with size of 30–100 nm. Electrochemical test shows that Fe substitution could significantly increase the initial specific capacity and specific energy, as well as cycling performance and rate capability. LiMn0.8Fe0.2PO4/C exhibits the best reversible specific discharge capacity of 165.9 mA h g−1 and specific discharge energy of 643.1 W h kg−1 at 0.1 C. Its discharge capacity remains 95.7% of its initial value of 129.0 mA h g−1 after 50 cycles at 0.5 C. According to the electrochemical impedance spectroscopic analysis, the performance improvement is mainly attributed to the enhancement of Li+ diffusion coefficient (D Li) by Fe substitution. D Li is 4.43 × 10−14 and 1.34 × 10−12 cm2 s−1 for LiMnPO4/C and LiMn0.5Fe0.5PO4/C, respectively.

Microstructure and thermoelectric properties of Bi1.9Lu0.1Te3 compound

Effect of fabrication conditions on microstructure and thermoelectric properties of the Bi1.9Lu0.1Te3 compound was studied. Starting nanopowder with mean nanoparticle size of ~37 nm was synthesized by a microwave–solvothermal method. In order to prepare samples with various micro-grained structures, the synthesized nanopowder was compacted by two methods. The first method is cold isostatic pressing with further high-temperature annealing, while the second method is spark plasma sintering at various temperatures of process (653 and 683 K). It is found that mean grain size is equal to ~290, ~730 and ~1160 nm for cold isostatically pressed and spark plasma sintered at 653 and 683 K samples, respectively. The micro-grained sample with maximum mean grain size shows the best thermoelectric properties. This sample is structurally inhomogeneous and has the lowest thermal conductivity and the specific electrical resistivity. Maximum dimensionless figure of merit for this sample is equal to ~0.9 for temperature range of 450–500 K.

Microwave-Assisted Rapid Synthesis of Self-Assembled T-Nb2 O5 Nanowires for High-Energy Hybrid Supercapacitors.

Recently ion-intercalation hybrid supercapacitors, with high energy density at high power density, have been widely investigated to meet ever-increasing practical demands. Here, a unique hybrid supercapacitor has been designed and fabricated using self-assembled orthorhombic-phase niobium oxide@carbon (T-Nb2 O5 @C) nanowires as an anode and commercially available activated carbon as a cathode. The 3D-interconnected T-Nb2 O5 @C nanowires have been synthesized through a highly efficient microwave-solvothermal method, combined with subsequent thermal treatment. The experimental parameters (e.g., time and temperature) can be easily programmed, and the synthesis time can be significantly shortened, thus enabling the buildup of abundant recipes for the engineering of scaled-up production. The Li-ion intercalation pseudocapacitance electrode, made from the as-formed self-assembled T-Nb2 O5 @C nanowires, shows excellent charge storage and transfer capability. When assembled into a hybrid supercapacitor with a cathode of activated carbon, a high energy density of 60.6 Wh kg-1 and a high power density of 8.5 kW kg-1 with outstanding stability are achieved. In virtue of easy optimization and programmability of the synthetic strategy, and the remarkable electrochemical performance, the self-assembled T-Nb2 O5 @C nanowires offer a promising anode for asymmetric hybrid supercapacitors.

Controlling Cu2ZnSnS4 (CZTS) phase in microwave solvothermal synthesis

The crystalline phase of Cu2ZnSnS4 can be controlled between kesterite and wurtzite by varying the initial oxidation state of Cu and Sn ions, and the source of the sulfur excess in a microwave solvothermal method.

Metal nanofoams via a facile microwave-assisted solvothermal process.

A novel, facile, non-hazardous, low temperature/pressure microwave solvothermal method of producing pure copper, silver, and nickel metal nanofoams is presented. The nanofoams have been produced using inexpensive metal acetates and polyglycol solvent. The nanofoam formation proceeds in two steps within a single-pot synthesis: formation of metal nanoparticles, followed by the sintering of nanoparticles into nanofoams. The nanofoams have many potential uses in clean energy applications, particularly lithium-ion batteries.

Clean and flexible synthesis of TiO2 nanocrystallites for dye-sensitized and perovskite solar cells

A clean and flexible synthesis of TiO2 nanocrystallites for dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) was proposed. Anatase nanocrystallites with different morphologies and sizes ranging from 5nm to 30nm were synthesized in one pot via the microwave solvothermal method using different types of alcohol solvents, namely, n-propanol (NPA), isopropanol (IPA), and octanol (OCT). No ionic additive was added during the synthesis. The influences of crystallite size and morphology on the photovoltaic performances of the DSSCs and PSCs were investigated. Results showed that using OCT (5–7nm) as a photoanode offered the highest power conversion efficiency (PCE), which gave rise to the apparent high dye loading capability and long electron recombination lifetime of OCT. The best PCE of the OCT-based DSSC device reached 9.58%, with the film thickness being only 10.6μm where no scattering layer was needed. By contrast, the IPA (20–30nm)-based photoanode showed good adaptability to PSC applications because of its homogeneity and large mean pore size that facilitated the infiltration of the perovskite sensitizer. The IPA-based PSC device attained the highest PCE of 15.3%, with Jsc being 21.55mA/cm2 and VOC being 1.07V.

Sustainable, Rapid Synthesis of Bright-Luminescent CuInS2-ZnS Alloyed Nanocrystals: Multistage Nano-xenotoxicity Assessment and Intravital Fluorescence Bioimaging in Zebrafish-Embryos.

Near-infrared (NIR) luminescent CuInS2-ZnS alloyed nanocrystals (CIZS-NCs) for highly fluorescence bioimaging have received considerable interest in recent years. Owing, they became a desirable alternative to heavy-metal based-NCs and organic dyes with unique optical properties and low-toxicity for bioimaging and optoelectronic applications. In the present study, bright and robust CIZS-NCs have been synthesized within 5 min, as-high-as 230 °C without requiring any inert-gas atmosphere via microwave-solvothermal (MW-ST) method. Subsequently, the in vitro and in vivo nano-xenotoxicity and cellular uptake of the MUA-functionalized CIZS-NCs were investigated in L929, Vero, MCF7 cell lines and zebrafish-embryos. We observed minimal toxicity and acute teratogenic consequences upto 62.5 μg/ml of the CIZS-NCs in zebrafish-embryos. We also observed spontaneous uptake of the MUA-functionalized CIZS-NCs by 3 dpf older zebrafish-embryos that are evident through bright red fluorescence-emission at a low concentration of 7.8 μg/mL. Hence, we propose that the rapid, low-cost, large-scale “sustainable” MW-ST synthesis of CIZS-NCs, is an ideal bio-nanoprobe with good temporal and spatial resolution for rapid labeling, long-term in vivo tracking and intravital-fluorescence-bioimaging (IVBI).

Rapid microwave-assisted synthesis of mesoporous NiMoO4 nanorod/reduced graphene oxide composites for high-performance supercapacitors

Mesoporous NiMoO4 nanorods grown on the surface of reduced graphene oxide composites (NiMoO4-rGO) were synthesized via a simple, rapidly, and environment-friendly microwave-solvothermal method. The structure and morphology of the composites were characterized by X-ray diffraction, Raman spectra, scanning electron microscopy, and transmission electron microscopy. The NiMoO4-rGO composite exhibited high performance as an electrode material for supercapacitors. At a current density of 1Ag−1, the specific capacitance reached 1274Fg−1, which is higher than that of pure NiMoO4 (800Fg−1). NiMoO4-rGO can retain about 81.1% of its initial capacitance after 1000 charge/discharge cycles. Remarkably, NiMoO4-rGO composites can be applied in asymmetric supercapacitors with ultrahigh energy density of 30.3Whkg−1 at a power density of 187Wkg−1. The enhanced electrochemical performance of NiMoO4-rGO is mainly ascribed to the mesoporous-NiMoO4 nanorods with large specific surface area, as well as high coupling with conductive rGO.