Microwave Hydrothermal Method Research Articles

The effect of honeycomb pore size on the electromagnetic interference shielding performance of multifunctional 3D honeycomb-like Ag/Ti3C2Tx hybrid structures

To solve pollution problems caused by electromagnetic waves, advanced three-dimensional (3D) honeycomb Ag/Ti3C2Tx hybrid materials were produced by a microwave hydrothermal method. The Ag/Ti3C2Tx hybrid materials retained their hollow sphere structure after the polymethyl methacrylate (PMMA) template was removed by annealing. The hybrid materials changed from hydrophilic to hydrophobic and exhibited cross-surface heat insulation and reflection-dominant electromagnetic interference shielding (EMIS) performance owing to their special honeycomb structure. This study innovatively explored the influence of different particle sizes of honeycomb holes on EMIS performance. In particular, the Ag/Ti3C2Tx 5 μm hybrid materials had an excellent average EMIS performance of 51.15 dB in the X-band and 56.64 dB in the Ku-band. The superior performance was due to conduction loss, interface polarization, multi-reflection, and scattering caused by the 3D porous structure of the Ag/Ti3C2Tx hybrid materials. In general, Ag/Ti3C2Tx hybrid materials with honeycomb structures retained the advantages of lightweight, hydrophobicity, and EMIS performance, illustrating the great application prospects of these materials in high-end electronic equipment.

Synthesis and Photocatalytic Application of Mn<sub>3</sub>O<sub>4</sub>/CdS Composite

In this work, CdS nanosheets were synthesized by microwave hydrothermal method. We used a simple synthesis method to prepare Mn3O4/CdS composites. The crystal phase, surface chemical component and optical properties of Mn3O4/CdS, Mn3O4 and CdS were analyzed based on the characterizations such as XRD, FT-IR, DRS and PL. Mn3O4/Cd composites showed obvious broadened visible-light adsorption at wavelength over 460 nm. When the mass ratio of Mn3O4 and CdS was 1.0%, Mn3O4/CdS displayed the best RhB degradation efficiency which was 22.39% higher than the pure CdS. The improved photocatalytic efficiency should be attributed to the lower photo-induced electron–hole pair recombination rate and accelerated transfer rate of photogenerated electrons based on heterojunction structure. The achievements provided new way to exploring novel CdS-based heterojunctions for decomposing organic pollutants.

Energy-Saving Synthesis of Functional CoS2/rGO Interlayer With Enhanced Conversion Kinetics for High-Performance Lithium-Sulfur Batteries.

Lithium sulfur (Li-S) battery has exhibited great application potential in next-generation high-density secondary battery systems due to their excellent energy density and high specific capacity. However, the practical industrialization of Li-S battery is still affected by the low conductivity of sulfur and its discharge product (Li2S2/Li2S), the shuttle effect of lithium polysulfide (Li2Sn, 4 ≤ n ≤ 8) during charging/discharging process and so on. Here, cobalt disulfide/reduced graphene oxide (CoS2/rGO) composites were easily and efficiently prepared through an energy-saving microwave-assisted hydrothermal method and employed as functional interlayer on commercial polypropylene separator to enhance the electrochemical performance of Li-S battery. As a physical barrier and second current collector, the porous conductive rGO can relieve the shuttle effect of polysulfides and ensure fast electron/ion transfer. Polar CoS2 nanoparticles uniformly distributed on rGO provide strong chemical adsorption to capture polysulfides. Benefitting from the synergy of physical and chemical constraints on polysulfides, the Li-S battery with CoS2/rGO functional separator exhibits enhanced conversion kinetics and excellent electrochemical performance with a high cycling initial capacity of 1,122.3 mAh g−1 at 0.2 C, good rate capabilities with 583.9 mAh g−1 at 2 C, and long-term cycle stability (decay rate of 0.08% per cycle at 0.5 C). This work provides an efficient and energy/time-saving microwave hydrothermal method for the synthesis of functional materials in stable Li-S battery.

Effective microwave-hydrothermal reduction of graphene oxide for efficient energy storage

Reduced graphene oxide (rGO) is an important member of the family of graphene-based nanomaterials. Conventional strategies for preparing rGO include chemical, thermal, photo, laser, hydrothermal, and microwave reduction. Here we report on a rapid microwave-hydrothermal (MH) method for the effective production of pure rGO (denoted as M-rGO) without using any reducing agents. The MH process was optimized in terms of temperature and duration to tune the structure and composition of the formed M-rGO to attain high specific capacitance for energy storage. The M-rGO possessed a three-dimensional (3D) interconnected porous structure with the C/O ratio of 9:5. The 3D interconnected structure of M-rGO not only increased the active surface area and enhanced the electrical double layer capacitance, but also improved its stability. Retaining the appropriate proportion of active functional groups also made a notable contribution of pseudocapacitance. The synthesized M-rGO exhibited a much higher capacitance of 298 F g−1 (1 A g−1, 0.5 M H2SO4) for a three-electrode system and 263 F g−1 (0.5 A g−1, 20% H2SO4- PVA gel) for a two-electrode system, as well as much better capacitance retention and cyclability, in contrast to conventional chemically reduced graphene oxide (C-rGO) and thermally reduced graphene oxide (T-rGO). Moreover, the energy density of the M-rGO was very high (36.6 Wh kg−1) at a power density of 0.5 kW kg−1. This first-rate energy storage performance of the M-rGO can be attributed to its highly active surface area, appropriate carbon-oxygen ratio, porous structure, and interconnected 3D morphology.

Structural, magnetic and electromagnetic properties of microwave-hydrothermally synthesized Sr(Zr-Mn)2xFe12-2xO19 hexaferrites

The Sr(Zr-Mn)2xFe12-2xO19 (x = 0.0–1.0) were synthesized using microwave-hydrothermal method at 200 ⁰C/60 min. The Rietveld refined X-ray diffraction patterns show single-phase hexagonal structure. The lattice parameter a is increased from 5.886 Å (x = 0.0) to 5.930 Å (x = 1.0) and c from 23.063 Å to 23.339 Å with x. The percentage of increase in a is 0.74% and is less as compared to c (1.179%). The fourier transform infrared spectrum shows the two absorption bands, 452 and 604 cm−1. The agglomeration of grains increased with doping concentration and it is also observed that the grain distribution is non uniform. With x, the coercivity drastically decreased from 2384 (x = 0.0) to 126 Oe (x = 1.0) and exhibits soft magnetic nature. The minimum reflection loss of -27.68 dB is observed for x = 0.6 in the frequency bandwidth of 10.14–10.64 GHz.

Three-dimensional embroidered ball-like α-Fe2O3 synthesised by a microwave hydrothermal method as a sulfur immobilizer for high-performance Li–S batteries

The practical application of lithium–sulfur (Li–S) batteries is restrained by the sluggish conversion kinetics of lithium polysulfides (LiPSs) and the consequent shuttle effect.

Heterostructure Composites of Tio2 and Cdzns Nanoparticles Decorated on Ti3c2 Tx Nanosheets and Their Enhanced Photocatalytic Performance by Microwave Hydrothermal Method

Heterostructure Composites of Tio2 and Cdzns Nanoparticles Decorated on Ti3c2 Tx Nanosheets and Their Enhanced Photocatalytic Performance by Microwave Hydrothermal Method

Tunable Luminescence Properties and Elucidating the Electronic Structures of Single-Phase Spherical BaWO4: Dy3+, Tm3+, Eu3+ Phosphors for Warm-White-Lighting

A series of uniform single-phase spherical BaWO4: Dy3+, Tm3+, Eu3+ phosphors were prepared via a microwave hydrothermal method by using trisodium citrate dehydrate as surfactant. The phase structure, morphology and photoluminescence properties were measured by powder X-ray diffraction, scanning electron microscope and fluorescence spectrometer, respectively. The results show that uniform spherical microcrystals with diameters in the range of 2–4 μm are obtained. And the phase and morphology of samples are not significantly changed by doping rare earth (RE3+) ions. Under the excitation wavelength of 356 and 365 nm, the samples BaWO4: 0.03Dy3+, yTm3+ can emit cold white light. In order to lower the correlated color temperature (CCT) to get a warm white light, the Eu3+ ions were doped into BaWO4: 0.03Dy3+, 0.01Tm3+. Especially, under the excitation of 365 nm, BaWO4: 0.03Dy3+, 0.01Tm3+, 0.03Eu3+ phosphor shew a bright warm white light with color coordinate of (0.4013, 0.3629) and CCT of 3288 K. Moreover, in the BaWO4: Dy3+, Tm3+, Eu3+ phosphors, the energy transfer mechanism among Dy3+, Tm3+ and Eu3+ ions have been discussed and the change of electron structures have been calculated by first-principles calculations. The results shew that the uniform single-phase spherical BaWO4: Dy3+, Tm3+, Eu3+ phosphors could be favorable candidates in warm white LEDs.

Study on denitration performance of multi element modified MIL-101 (Fe) at low temperature

MIL-101 (Fe) was modified by amino group and doped by Cu and Co elements by microwave hydrothermal method. The effect of SCR denitrification at low temperature was investigated with high concentration of NOx as adsorption object. The results show that when the flue gas temperature is 200 °C and the NOx concentration is up to 1640 mg/m3, the removal efficiency of NOx can reach 86% under the optimal conditions, which is 1.5 times higher than that before modification. In addition, the characterization results indicated that the specific surface area of the modified catalyst increased, the thermal stability was good at low temperature, the selective adsorption capacity of NO was enhanced, and the doping played a synergistic catalytic role. It can be used for flue gas denitration in various industries.

Synthesis and characterization of rod-like amino acids/nanohydroxyapatite composites to inhibit osteosarcoma.

In this study, rod-like hydroxyapatite (HA) with uniform morphology and controllable particle size modified by doping with two different amino acids (alanine and threonine) was synthesized by a microwave hydrothermal method. The physical and chemical properties of the composites were tested by utilizing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), general thermogravimetric analysis (TG) and scanning electron microscopy (SEM). The SEM and XRD results show that the presence of amino acids (especially threonine) can significantly reduce the aspect ratio and crystallinity of hydroxyapatite. Pure hydroxyapatite and modified hydroxyapatite doped with two different proportions of amino acids were cultured with mouse osteoblasts (MC3T3-E1) for 1, 3 and 5 days, respectively, nanohydroxyapatite modified by threonine has better biocompatibility compared with pure hydroxyapatite. The amino acid-modified hydroxyapatite samples were co-cultured with osteosarcoma cells (MG63) for 1, 4 and 7 days, respectively, and showed better inhibitory effects on osteosarcoma cells. The nanohydroxyapatite doped with amino acids could be used as a potential drug that promotes bone repair and inhibits the growth of osteosarcoma cells.

Facile Treatment of Municipal Solid Waste Incineration Fly Ash by One-Step Microwave Hydrothermal Method: Hazards Detoxification and Tobermorite Synthesis

Facile Treatment of Municipal Solid Waste Incineration Fly Ash by One-Step Microwave Hydrothermal Method: Hazards Detoxification and Tobermorite Synthesis

Construction of SrTiO3-BiOCl composite catalyst via facial microwave hydrothermal for highly efficient photocatalytic activity towards organic compounds degradation

ABSTRACT This work mainly focuses on the preparation and performance study of SrTiO3-BiOCl composite photocatalysis. The SrTiO3-BiOCl photocatalysts are prepared via the facial microwave hydrothermal method. XRD, UV-vis DRS, SEM, TEM, XPS, N2 adsorption and desorption isothermal experiment, FT-IR, and PL are applied to characterize the prepared samples. The spherical particles of SrTiO3 grow on the flaky BiOCl, and the crystal size is uniform and evenly disperses on the BiOCl. The catalytic performance of the samples was evaluated over the degradation rates of methylene blue(MB). Typically, the clearance rates of MB reached to 99.65% over SrTiO3-BiOCl-50% under visible light, which was much higher than that of SrTiO3 and BiOCl (55.86%, 79.79%, respectively). The active species capturing experiments and ESR showed that the holes (h+) and ·OH are playing the main roles in the degradation process.

Microwave-assisted synthesis of oxygen vacancy associated TiO2 for efficient photocatalytic nitrate reduction

The solar-driven photocatalytic technology has shown great potential in nitrate (NO3−) pollutants reduction, however, it has been greatly hindered by the complex preparation and high cost of photocatalysts. Herein, a relatively low-cost photocatalyst, rutile and anatase mixed phase TiO2 was synthesized by a facile microwave-hydrothermal method. Meanwhile, oxygen vacancy is successfully generated, leading to an acidic surface for strong adsorption towards NO3−, which further improved the reduction activity. Compared with the commercial P25, a higher NO3− conversion of ca. 100% and nitrogen (N2) selectivity of 87% were achieved under UV (365 nm) irradiation within 2 h. This research provides a promising strategy for designing efficient noble metal free photocatalyst in the NO3− reduction.

Firmly-supported porous fabric fiber photocatalysts: TiO2/porous carbon fiber cloth composites and their photocatalytic activity

The use of a support may overcome the limitations of nano-photocatalysts (poor recyclability, secondary pollution, and agglomeration that decreases photocatalytic activity); however, supports such as fibers, fabrics, films, and foams, still exhibit many defects (low loadings, non-uniform particle loadings, and insufficient loading firmness). In this study, we fabricated TiO2/porous carbon fiber cloth through a microwave hydrothermal method and thermal reduction. The highly porous structure of fiber could provide abundant space to firmly-supported TiO2 nanoparticles. Therefore, the results showed that large amounts of TiO2 were uniformly and firmly loaded onto the porous carbon fiber cloth, and the obtained composite exhibited excellent photocatalytic activity. The initial loading rate reached 51 wt.%. Even after 10 photocatalytic cycles, the pollutant degradation rate exceeded 95%, and 55% of TiO2 was retained, showing its stability. This investigation provides a method to prepare supported photocatalysis, which can greatly promote their practical applications for wastewater treatment.

Effect of Dy3+ substitution on microwave behaviour of nanocrystalline Mn-Zn Ferrite

Microwave-hydrothermal (M-H) method had been employed to synthesize a series of Dy3+doped Mn-Zn ferrite Mn0.6Zn0.4Fe2–xDyxO4 (x=0, 0.01, 0.03, 0.05, 0.07, 0.09) nanopowders at 160°C/30 min. The prepared samples have been characterized by Fourier Transform Infrared Spectrometer. The grain size of sintered ferrites are in the range of 60-70 nm. Decrease in saturation magnetization and increase in coercivity were observed with an increase of Dy3+ concentration in Mn-Zn ferrites. The complex permeability and complex permittivity of the prepared samples were measured in the frequency range of 2–18 GHz using a using a vector network analyzer. It is observed that small variation of Dy3+ substitution in spinel ferrite tailored microwave absorbing parameters dramatically. The reflection loss (RL) increased with the Dy3+ content upto x ≤ 0.03. The sample with x=0.03 of thickness 2.3 mm showed minimum reflection loss of -20.5 dB with a bandwidth of 3.8 GHz. Thus the present materials exhibit good microwave absorption properties and hence can act as EMI suppressors. Copyright © 2018 VBRI Press.

B- and N-doped carbon dots by one-step microwave hydrothermal synthesis: tracking yeast status and imaging mechanism

BackgroundCarbon dots (CDs) are widely used in cell imaging due to their excellent optical properties, biocompatibility and low toxicity. At present, most of the research on CDs focuses on biomedical application, while there are few studies on the application of microbial imaging.ResultsIn this study, B- and N-doped carbon dots (BN-CDs) were prepared from citric acid, ethylenediamine, and boric acid by microwave hydrothermal method. Based on BN-CDs labeling yeast, the dead or living of yeast cell could be quickly identified, and their growth status could also be clearly observed. In order to further observe the morphology of yeast cell under different lethal methods, six methods were used to kill the cells and then used BN-CDs to label the cells for imaging. More remarkably, imaging of yeast cell with ultrasound and antibiotics was significantly different from other imaging due to the overflow of cell contents. In addition, the endocytosis mechanism of BN-CDs was investigated. The cellular uptake of BN-CDs is dose, time and partially energy-dependent along with the involvement of passive diffusion. The main mechanism of endocytosis is caveolae-mediated.ConclusionBN-CDs can be used for long-term stable imaging of yeast, and the study provides basic research for applying CDs to microbiol imaging.Graphical

Insight into a novel microwave-assisted W doped BiVO4 self-assembled sphere with rich oxygen vacancies oriented on rGO (W-BiVO4-x/rGO) photocatalyst for efficient contaminants removal

A novel W doped BiVO4 with rich oxygen vacancies (OVs) oriented on reduced graphene oxide (rGO) photocatalyst (W-BiVO4-x/rGO) was developed by a simple one-step microwave hydrothermal method for efficient removal of ciprofloxacin (CIP) and chlortetracycline (CTC) under visible light. The synergistic effect of W doping, BiVO4 with OVs, and rGO on the enhancement of photocatalytic activity was clarified from experimental and Density Functional Theory (DFT) calculations results. W doping significantly improved the density of photo-generated charge carriers. The introduction of rGO enlarged the specific surface area, expanded the light absorption range, and promoted the charge transfer of BiVO4. OVs both narrowed the band gap and enhanced the generation of O2−. W doping and OVs both enhanced the interactions between BiVO4 and rGO. The CIP degradation rate constant of W-BiVO4-x/rGO photocatalyst was 1.73, 5.32, 6.43, and 10.70 times higher than those of W-BiVO4/rGO, BiVO4/rGO, W-BiVO4, and BiVO4, respectively. Besides, W-BiVO4-x/rGO photocatalyst prepared by microwave hydrothermal method exhibited higher photocatalytic activity and better combination between materials. This study offers a new strategy to address the problem of antibiotic residues in wastewater.

Theoretical and experimental study of effects of Co2+ doping on structural and electronic properties of ZnO

In this study, we theoretically investigated the electronic structure of Zn1-xCoxO using different approaches for the exchange-correlation potential comprising GGA with the on-site Coulomb correlation interaction U to the Zn d orbital (GGA + UZn), GGA with modified Becke–Johnson exchange potential (GGA + mBJ), and (GGA + mBJ + UZn). To support the theoretical results, a Co2+-doped ZnO sample was obtained experimentally by using the microwave–hydrothermal method. Changes in the structural, vibrational, electronic, and magnetic properties induced by the insertion of the Co2+ impurities in the ZnO lattice were determined based on first principles calculations. The theoretical results showed that the 3d orbitals derived from Co2+ appear in the deep region of the band gap. These orbitals are responsible for the magnetic behavior of cobalt doped materials. The energy levels introduced by the Co2+ dopant ions reduced the theoretical band gap value, which was also observed experimentally. The addition of Co2+ ions weakened the Raman mode E2H intensity, which was attributed to the increasing distortion induced by doping. Photoluminescence spectroscopy results indicated a reduction in the visible emission region after adding Co2+ ions, thereby indicating the formation of alternative pathways for the recombination process.

Effect of Y2O3 on the corrosion resistance of two-step sintered Al5Y3O12-MgAl2O4 sidewalls in the aluminum electrolyte

Magnesium–aluminum spinel (MAS) precursor powder was synthesized through a microwave hydrothermal method. The synergistic effects of sintering process and sintering aids on the densification, hardness and corrosion resistance of MAS were revealed. X-ray diffraction analysis (XRD), Archimedes’ drainage method, fully automatic micro-Vickers hardness test and scanning electron microscopy (SEM) were performed to analyze the phase composition, bulk density, hardness microstructure and corrosion depth of the samples, respectively. Results revealed that the best two-step sintering condition is 1650 °C/3 min/1550 °C/20 h. The MAS products obtained under the best condition have clear grain boundaries, uniform particle size distribution, and few pores. When the amount of Y2O3 added is 4 wt.%, Y2O3 and Al2O3 form the second-phase solid solution Al5Y3O12, which activates the crystal lattice and benefits the sintering densification of MAS. Under these conditions, the relative density of the MAS composite ceramics prepared is relatively large (95.94 %), the grain size is relatively uniform, the hardness is relatively large (1264 HV), and the corrosion depth is relatively small (94.58 μm).

A comprehensive evaluation of Co, Ni, Cu and Zn doped manganese oxalate for lithium storage

Transition metal oxalates have attracted people's attention owing to their low cost, low lithium insertion potential and high theoretical reversible capacities. Disappointingly, high irreversible capacity thanks to the formation of SEI as well as the consumption and exfoliation of active materials during the process of cycling severely restrict its application of it. In this work, a comprehensive evaluation of Co, Ni, Cu and Zn doped manganese oxalate was made. All samples are synthesized via facile and time-saving microwave hydrothermal method. It is intriguing that merely 30 ​min is required to accomplish the entire process and all samples possess fine electrochemical performance. As far as the four bimetallic oxalates, the resulting Mn0·5Ni0·5C2O4 exhibits the optimum performance (746.2 ​mA ​h ​g−1 after 100 cycles at 0.2 ​A ​g−1 and 546.7 ​mA ​h ​g−1 at 1 ​A ​g−1 after 400 cycles), which can be attributed to one-dimensional rod-like morphology of Mn0·5Ni0·5C2O4 as well as the synergistic and catalytic effect of Mn and Ni, resulting in faster electrode kinetics. Mn0.5Ni0.5C2O4 displays incalculable potential and can be applied in the highly reversible lithium-ion batteries.