Microwave Hydrothermal Synthesis PZT of Nanometer Crystal

It was focused on the applications and developments of microwave hydrothermal synthesis piezoelectric ceramic powder. The microwave hydrothermal vessel was designed and manufactured. The microwave hydrothermal synthesis system was established and the PZT piezoelectric ceramic powder was synthesized. XRD and TEM have been used to characterize the products in detail. The diameter of the PZT powder particle is from 40 to 60 nm.

Microwave hydrothermal synthesis and characterization of rare-earth stannate nanoparticles

Rare-earth stannate（Ln_2Sn_2O_7（Ln = Y, La–Lu）） nanocrystals with an average diameter of 50 nm were prepared through a facile microwave hydrothermal method at 200°C within 60 min. The products were well characterized. The effect of reaction parameters such as temperature, reaction time, p H value, and alkali source on the preparation was investigated. The results revealed that the p H value plays an important role in the formation process of gadolinium stannate（Gd_2Sn_2O_7） nanoparticles. By contrast, the alkali source had no effect on the phase composition or morphology of the final product. Uniform and sphere-like nanoparticles with an average size of approximately 50 nm were obtained at the p H value of 11.5. A possible formation mechanism was briefly proposed. Gd_2Sn_2O_7：Eu^（3＋） nanoparticles displayed strong orange-red emission. Magnetic measurements revealed that Gd_2Sn_2O_7 nanoparticles were paramagnetic. The other rare-earth stannate Ln_2Sn_2O_7（Ln = Y, La–Lu） nanocrystals were prepared by similar approaches.

Preparation of Monodisperse Spherical SiO_2 by Microwave Hydrothermal Method and Kinetics of Dehydrated Hydroxyl

Monodisperse spherical SiO2 particles were successfully synthesized in 2-propanol-H2O-NH3 system by the microwave hydrothermal method using ammonia as catalyst. To investigate the influences on the size of spherical SiO2 particles, factors such as ammonia concentration, reaction temperature, stirring intensity and reactants mol ratio have been studied. The orthogonal experiments were carried out. The as-prepared SiO2 particles were characterized by X-ray diffraction （XRD）, transmission electron microscopy （TEM）, Fourier transform infrared spectroscopy （FTIR） and differential thermal analysis （DTA）. The results indicated that the size of SiO2 particles increased greatly with the increase in ammonia concentration, temperature and reactants mol ratio, but increased slightly with the increase in stirring intensity. Monodisperse spherical Si02 particles were amorphous with perfect sphere and uniform size. Hydroxyl was detected in SiO2. Kinetic parameters were calculated, and finally the reaction rate equation of dehydrated hydroxyl was obtained.

Microwave Hydrothermal Synthesis and Characterization of ZnO Nanostructures in Aqueous Solution

ZnO nanostructures were prepared in aqueous solution by microwave hydrothermal synthesis. X- ray diffraction （XRD） and field emission scanning electron microscopy （FESEM） were used to characterize ZnO nanostructures （ZNs）. The effects of pH, reaction temperature and reaction time on yield of ZnO were investigated. The yield of ZnO increased significantly with the increase of pH value, reaction temperature and reaction time. High yield and well crystallinity of ZNs could be obtained at 120~C for 60min by microwave hydrothermal synthesis. The spherical and rugby-like ZNs were obtained at 120 ℃ without triethanolamine （TEA） and with TEA （mass ratio, r = mzn2＋ ： mTEA = 1 ： 1）, respectively. The concentration of Zn（OH）2- ions in the reaction solution and TEA had an important effect on the nucleation and morphology of ZnO nanostructures. Mechanism for the formation of ZnO nanostructures was proposed.

Microwave-assisted Hydrothermal Synthesis of Carbon Materials with Tunable Microstructure

A facile microwave-assisted hydrothermal route has been developed for a synthesis of versatile carbon materials. The monosaccharide fructose aqueous solution was adopted as the starting material, and the p H of the solution was adjusted to be in acidic（pH 4）, neutral（pH 7） and basic（pH 10.5） conditions. The p H buffered fructose solutions were treated at different temperatures by a microwave-assisted hydrothermal technique. As-prepared carbon materials displayed p H and temperature dependent multi-morphologies（porous, spherical or core-shell）, which were determined by transmission and scanning electron microscopic analyses（TEM and SEM）. And the hypothesis of dehydration mechanism of hydrothermal synthesis was analyzed by ultraviolet extinction and Fourier transform infrared spectroscopy. It was found that as compared with normal hydrothermal synthesis, microwave assistance could efficiently increase the production yield and improve the spherical geometry of the carbon particles in neutral condition. By changing the p H of the system, acidic p H induces aggregation of the spheres, while basic p H produces more trends toward core-shell or sponge-like porous structure. The study opens a novel route to the production of polytropic carbon materials and suggests a potential niche market established from the green synthesis.

HYDROTHERMAL SYNTHESIS OF ZEOLITE NaA BY MICROWAVE RADIATION

In this paper,we report a novel application of microwave radiation for the synthesis of zeolite NaA in a fraction of the time required for conventional synthetic method under very mild condition.The pure product was obtained under the condition of microwave radiation in 10-20 minutes.

Two-Step Preparation of Hierarchical Porous Carbon Materials Derived from Tannin for Use as an Electrode Material for Supercapacitors

The development and utilization of biomass and agroforestry processing byproducts for high-value applications have been an important topic in the field of renewable materials research.Based on this,a two-step microwave hydrothermal pre-carbonization and KOH activation method was proposed to synthesize tannin-based activated carbons with a high specific surface area,hierarchical pore structure,and good electrochemical performance.The microstructure,texture properties,and physicochemical characteristics were investigated.The results show that the prepared tannin-based activated carbons presented a hierarchical pore structure(micro-and mesopores)with a specific surface area as high as 997.46 m^(3) g^(−1).The electrochemical analysis shows that the tannin-based activated carbons have good wettability and charge transfer rates.Under the three-electrode system with 6 M KOH as the electrolyte,the active material TAC_(600-4) had a maximum specific capacitance of 171 F g^(−1)at 0.5 A g^(−1).As the current density increases to 10 A g^(−1),the specific capacitance can still be maintained at 149 F g^(−1),indicating a good rate capability.Therefore,the specific surface area and pore size of tannin-based activated carbons can be effectively adjusted by the alkali/carbon ratio,making it a promising supercapacitor electrode material and providing a new method for the high-value development of tannins in the field of electrochemical energy storage.

Microstructure and thermoelectric properties of nanoparticled copper selenide alloys synthesized using a microwave-assisted hydrothermal method

With the fabrication of high-performance thermoelectric(TE)materials,developments are being made in enhanc-ing the figure of merit,zT,of TE materials.Liquid-like binary copper selenide(Cu_(2) Se)chalcogenides recently gained significant recognition because of their anomalous but fascinating electrical and thermal transport perfor-mances.In this study,a facile synthesis technique was adopted in fabricating Cu_(2) Se nanoparticles using a rapid microwave-assisted hydrothermal route at different reaction times.The results were compared with those of the Cu_(2) Se solid-state(SS)sample synthesized using the traditional melting and annealing technique.X-ray diffrac-tion patterns revealed successful synthesis of nanoparticles and a phase transition from orthorhombic𝛼-phase and cubic𝛽-phase to a single orthorhombic structure after hot-pressing.Scanning electron microscopic images revealed that although the grain sizes of the nanoparticle(NP)bulk samples increased with the reaction time of the microwave hydrothermal process,the grain sizes were significantly smaller than that of the SS sample.Additionally,NP bulk samples exhibited plenty of nano-grains and pores that are absent in the SS sample.The size and distribution of the grains and pores were measured to study their effects on the transport of carriers and phonons.The NP30 sample exhibited the highest power factor of 983.3μW K−2 m at 673 K among the NP samples,exhibiting intermediate values of resistivity and Seebeck coefficient that are close to those of the SS sample.Moreover,the NP samples exhibited appreciably lower thermal conductivity than the SS sample that is attributed to strengthened phonon scattering.The minimum thermal conductivity of the NP05 sample,0.78 WK−1 m−1 at 348 K,is 1.7 times lower than that of the SS sample.Finally,a maximum zT of 0.56 at 673 K,being approximately 1.3 times higher than that of the SS sample owing to the optimized thermal conductivity,was achieved for the NP30 sample.This value is comparable to or higher than that reported for Cu_(2) Se synthesized using the traditional SS method.Investigations revealed that the proposed microwave hydrothermal synthesis technique is a facile,rapid,and reliable method that results in Cu_(2) Se alloys with excellent TE performance.

Rapid synthesis of Ti-MCM-41 by microwave-assisted hydrothermal method towards photocatalytic degradation of oxytetracycline

This study employed microwave-assisted hydrothermal method to synthesize Ti-MCM-41,which are mesoporous materials with a high surface area and excellent photocatalytic ability. Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS）, transmission electron microscopy（TEM）, and ultraviolet–visible spectroscopy（UV–Vis） were employed. The XRD findings showed that Ti-MCM-41 exhibited a peak at 2θ of 2.2°, which was attributed to the hexagonal MCM-41 structure. The BET（Brunauer–Emmett–Teller） results agreed with the TEM findings that Ti-MCM-41 has a pore size of about 3–5 nm and a high surface area of 883 m-2/g. FTIR results illustrated the existence of Si–O–Si and Si–O–Ti bonds in Ti-MCM-41. The appearance of Ti2 p peaks in the XPS results confirmed the FTIR findings that the Ti was successfully doped into the MCM-41 structure. Zeta（ζ）-potential results indicated that the iso-electric point（IEP） of Ti-MCM-41 was at about pH 3.02. In this study, the photocatalytic degradation of oxytetracycline（OTC） at different pH was investigated under Hg lamp irradiation（wavelength 365 nm）. The rate constant（K′obs） for OTC degradation was 0.012 min-1at pH 3. Furthermore, TOC（total organic carbon） and high resolution LC–MS（liquid chromatography–mass spectrometry） analyses were conducted to elucidate the possible intermediate products and degradation pathway for OTC. The TOC removal efficiency of OTC degradation was 87.0%, 74.4% and 50.9% at pH 3, 7 and 10, respectively. LC–MS analysis results showed that the degradation products from OTC resulted from the removal of functional groups from the OTC ring.

Low-cost fabrication of highly dispersed atomically-thin MoS2 nanosheets with abundant active Mo-terminated edges

In this work,highly dispersed atomically-thin MoS2 nanosheets were fabricated at one thousandth of the commercial cost using sepiolite(SEP)mineral nanofibers as carriers via a microwave hydrothermal method.Atomresolved microscopy revealed the MoS2 nanosheets were only 1–4 atomic layers thick.The Mo atoms anchored on the mineral surface served as nucleation sites for the nanosheet growth.The MoS2 layers were in staggered stacking yielding abundant atomic steps at the nanosheets’edges,where catalytically active molybdenum terminations dominated instead of the inert sulfur atoms commonly reported.DFT calculations disclosed that the bonding of Mo(MoS2)and O(SEP)at the MoS2/sepiolite(MSEP)interface enabled SEP to be a unique support,superior to the other minerals for growing such highly-dispersed ultrathin MoS2 architecture.In a typical photocatalyisis application,the MSEP demonstrated a significantly improved photocatalytic performance for RhB degradation compared with the MoS2 nanosheets assembled microspheres.This work provides an important new strategy for low-cost batch preparation of high quality 2D materials via assembly on mineral materials.

Photocatalytic degradation of Rhodamine B by microwave-assisted hydrothermal synthesized N-doped titanate nanotubes

Microwave-induced nitrogen-doped titanate nanotubes（NTNTs） were characterized by transmission electron microscopy（TEM）, X-ray diffraction（XRD）, X-ray photoelectron spectroscopy（XPS）, Fourier transform infrared spectroscopy（FT-IR）, Zeta potential analysis,specific surface area（SBET）, and UV-Visible spectroscopy. TEM results indicate that NTNTs retain a tubular structure with a crystalline multiwall and have a length of several hundred nanometers after nitrogen doping. XRD findings demonstrate that the crystalline structure of NTNTs was dominated by anatase, which is favored for photocatalytic application. The Ti-O-N linkage observed in the XPS N 1s spectrum is mainly responsible for narrowing the band gap and eventually enhancing the visible light photoactivity. FT-IR results demonstrated the existence of H3O＋, which could be excited by photo-generated holes to form hydroxyl radicals and degrade environmental pollutants. After sintering at 350°C, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which indicates N atom doping into the nanotubes. Photocatalytic degradation of Rhodamine B（RhB） via NTNTs show good efficiency, with pseudo first-order kinetic model rate constants of 3.7 × 10-3, 2.4 × 10-3and 8.0 × 10-4sec-1at pH 3, 7, and 11, respectively.

Synthesis of Flower-Like Nanoparticles of Anatase Titania by Microwave Solvo-Hydrothermal Method

Anatase titania nanoparticles with an average size of about 14 nm were synthesized by microwave solvothermal method from TiCI4 and ethanol as a precursor and solvent respectively. The shapes of as prepared samples were modified by microwave hydrothermal treatment in strongly alkaline medium at 100℃ for 2 h, the agglomerate particles can be converted to the nanorods then to flower-like sphere. The structure, morphology and optical properties of as-prepared powders were investigated by X-ray diffraction, scanning electron microscopy and UV- vis absorption spectroscopy, the quality of the samples was examined by IR absorption spectroscopy and room temperature photoluminescence （PL）. The results showed that the synthesized Ti02 revealed the formation of the nanorods and the flower-like shape of titania after post treatment in 5 mol/L and 10 mol/L NaOH solution, respectively. IR absorption spectra showed that the as-prepared TiO2 nanocrystals were highly pure and strongly surface hydrated, The photoluminescence measurement showed that five main emission peaks appeared in UV, violet, blue and green regions.

Tunable Luminescence Properties and Elucidating the Electronic Structures of Single-Phase Spherical BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)Phosphors for Warm-White-Lighting

A series of uniform single-phase spherical BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)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 2–4μm are obtained.And the phase and morphology of samples are not significantly changed by doping rare earth(RE^(3+))ions.Under the excitation wavelength of 356 and 365 nm,the samples BaWO 4:0.03Dy^(3+),yTm^(3+)can emit cold white light.In order to lower the correlated color temperature(CCT)to get a warm white light,the Eu^(3+)ions were doped into BaWO 4:0.03Dy^(3+),0.01Tm^(3+).Especially,under the excitation of 365 nm,BaWO 4:0.03Dy^(3+),0.01Tm^(3+),0.03Eu^(3+)phosphor shew a bright warm white light with color coordi-nate of(0.4013,0.3629)and CCT of 3288 K.Moreover,in the BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)phosphors,the energy transfer mechanism among Dy^(3+),Tm^(3+)and Eu^(3+)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 BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)phosphors could be favorable candidates in warm white LEDs.

Microwave-assisted hydrothermal synthesis of Pt/SnO2 gas sensor for CO detection

In this paper,the Pt/SnO2 nanostructures were prepared via a facile one-step microwave assisted hydrothermal route.The structure of the introduced Pt/SnO2 and its gas-sensing properties toward CO were investigated.The results from the TEM test reveal that Pt grows on the SnO2 nanostructure,which was not found for bulk in this situ method,constructing Pt/SnO2.The results indicated that the sensor using 3.0 wt%Pt/SnO2 to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt%and 4.5 wt%Pt/SnO2 at 225℃.The response time of 3.0 wt%sensor is 16 s to 100 ppm CO at225℃.Such enhanced gas sensing performances could be attributed to the chemical and electrical factors.In view of chemical factors,the presence of Pt facilitates the surface reaction,which will improve the gas sensing properties.With respect to the electrical factors,the Pt/SnO2 plays roles in increasing the sensor’s response due to its characteristic configuration.In addition,the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.

High-pressure microwave-assisted synthesis of WS_(x)/Ni_(9)S_(8)/NF hetero-catalyst for efficient oxygen evolution reaction

Designing the specific crystal phase with better intrinsic activity and more active sites is a very promising strategy for earth-abundant electrocatalysts for oxygen evolution reaction(OER).Herein,a facile two-step method including the high-pressure microwave and the hydrothermal sulfurization is adopted to prepare the WS_(x)/Ni_(9)S_(8) hetero-catalyst on nickel foam(WS_(x)/Ni_(9)S_(8)/NF).Firstly,WO3 polyhedrons homogeneously cover the surface of NF through the high-pressure microwave hydrothermal process.Secondly,WS_(x)/Ni_(9)S_(8) nanoparticles on the surface of NF can be synthesized after a hydrothermal sulfurization,which has been confirmed by scanning electron microscopy(SEM) elemental mapping and high-resolution transmission electron microscopy(HRTEM).The amorphous WSx and Ni9 S8 phase may provide the dual active sites for OER.The electrochemical measurements show that WS_(x)/Ni_(9)S_(8)/NF has superior OER activity with a low overpotential of 320 mV at the current density of 100 mA·cm^(-2),better than those of other samples.The enhanced OER performance may be due to the synergistic catalysis from Ni9 S8 phase and high valence of W.Owing to the stable structure of Ni9 S8,the long-term stability of WS_(x)/Ni_(9)S_(8)/NF for at least 10 h can be obtained.This work may provide a new approach for the doped nickel sulfides crystal phase through high-pressure microwave hydrothermal assistance for OER.

Comparative study of Co_(3)O_(4)-ZSM-5 catalysts synthesized by different hydrothermal methods for the catalytic oxidation of dichloromethane

In this work,various Co_(3)O_(4)-ZSM-5 catalysts were prepared by the microwave hydrothermal method(MH-Co_(3)O_(4)@ZSM-5),dynamic hydrothermal method(DH-Co_(3)O_(4)@ZSM-5),and conventio nal hydrothermal method(CH-Co_(3)O_(4)/ZSM-5).Their catalytic oxidation of dichloromethane(DCM)was analyzed.Detailed characterizations such as X-ray diffractometer(XRD),scanning microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Brunauer-Emmett-Teller(BET),H2 temperature-programmed reduction(H2-TPR),temperature-programmed desorption of O_(2)(O_(2)-TPD),temperature-programmed desorption of NH_(3)(NH_(3)-TPD),diffuse reflectance infrared Fourier-transform spectra with NH_(3)molecules(NH_(3)-DRIFT),and temperature-programmed surface reaction(TPSR)were performed.Results showed that with the assistance of microwave,MH-Co_(3)O_(4)@ZSM-5 formed a uniform core-shell structure,while the other two samples did not.MH-Co_(3)O_(4)@ZSM-5 possessed rich surface adsorbed oxygen species,higher ratio of Co^(3+)/Co^(2+),strong acidity,high reducibility,and oxygen mobility among the three Co_(3)O_(4)-ZSM-5 catalysts,which was beneficial for the improvement of DCM oxidation.In the oxidation of dichloromethane,MH-Co_(3)O_(4)@ZSM-5 presented the best activity and mineralization,which was consistent with the characterizations results.Meanwhile,according to the TPSR test,HCl or Cl_(2)removal from the catalyst surface was also promoted in MH-Co_(3)O_(4)@ZSM-5 by their abundant Bronsted acid sites and the promotion of Deacon reaction by Co_(3)O_(4)or the synergistic effect of Co_(3)O_(4)and ZSM-5.According to the results of in situ DRIFT studies,a possible reaction pathway of DCM oxidation was proposed over the MH-Co_(3)O_(4)@ZSM-5 catalysts.