Thermal annealing of LaF3:Eu3+ nanocrystals synthesized by a solvothermal method and their luminescence properties

In this work, we used a low temperature solvothermal method to synthesize Eu³⁺-doped LaF₃ (LaF₃:Eu³⁺) nanocrystals. The effect of thermal annealing on their phase structures and luminescence properties was studied. Transformation from LaF₃ to LaOF was observed after the annealing, and the initial transformation process was studied using a rapid thermal annealing technique. It was found that a sufficiently high annealing temperature is required for the transformation of LaF₃ to LaOF. LaOF phase started to be formed after annealing at 500 °C for as short as 5 min, and higher annealing temperatures and longer annealing time led to a larger amount of LaOF formed. With the increase of the formation of LaOF, the luminescence was greatly enhanced. Strong O^2? → Eu³⁺ charge transfer band was present in these samples annealed at 500 °C and higher temperatures, and greatly enhanced ⁷F₀ → ⁵D₂ transition of Eu³⁺ was also observed.     

Thermal characterization of titania-modified alumina-supported palladium and catalytic properties for methane combustion

Thermal characterization of Pd/TiO₂-Al₂O₃ catalysts under oxygen or hydrogen atmosphere was investigated by means of thermogravimetry (TG), differential scanning calorimetry (DSC), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). Further, the effects of titania on the catalytic property of Pd/Al₂O₃ towards methane combustion were also examined. A TG-DSC studies revealed that the heat evolved during oxygen adsorption at 25 °C depended on the crystallite diameter. TPR and TPD studies of oxidized samples also demonstrated that the coating of Pd/Al₂O₃ catalysts with titania can weaken the strength of the PdO bonds. Apparently the effect of coating Pd/Al₂O₃ catalyst with TiO₂ is the improvement of the methane combustion at lower temperatures. This is probably due to the decrease of the strength of the PdO bonds.     

Selective self-propagating combustion synthesis of hexagonal and orthorhombic nanocrystalline yttrium iron oxide

Macroporous nanocrystalline YFeO₃ was prepared by a self-propagating combustion method using yttrium nitrate and iron nitrate as precursors and glycine as a fuel. The phase structure of the product can be selectively controlled to be hexagonal or orthorhombic by simply adjusting the ratio of glycine to nitrate. The samples were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, micro-Raman spectroscopy, Fourier transform infrared absorption spectroscopy (FT-IR), thermal analysis (TGA/DSC), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and magnetic property analysis. Photocatalytic activity for the degradation of methylene blue in water under visible light irradiation shows that the orthorhombic YFeO₃ is superior to the hexagonal form. More adsorbed oxygen and ferromagnetism of the orthorhombic sample may explain its high activity.     

Electrochemical performance of metal-organic framework synthesized by a solvothermal method for supercapacitors

A series of metal-organic frameworks (MOFs) based on isonicotinic acid and nickel nitrate were successfully synthesized by a solvothermal method as electrode materials for supercapacitor. The MOF were examined by X-ray diffraction (XRD) patterns and N₂ adsorption/desorption isotherms. Electrochemical properties of the materials were characterized by cyclic voltammetry (CV) in 6 M KOH aqueous solutions. The effect of solvothermal time, temperature and the mol ratio of isonicotinic acid and nickel nitrate on the electrochemical performance were also studied. The maximum specific capacitance is found to be 634 F g^?1 at 5 mV s^?1 and the stable cycling properties measurement showed the sample kept 84% after 2000 cycles at a 50 mV s^?1 scan rate.     

Ce1-xFexO2复合氧化物催化剂的制备及其对甲烷的催化燃烧性能

采用柠檬酸溶胶-凝胶法和微波技术制备了Ce1-x Fex O2复合氧化物,以甲烷催化燃烧为探针反应测定了催化剂的活性及XRD、DRS、BET和TPR进行了表征。结果表明,Ce1-x Fex O2复合氧化物为介孔材料,所制得的复合氧化物在x≤0．2时以单一立方萤石结构的Ce1-x Fex O2固溶体存在,x〉0．2时形成了立方萤石结构Ce1-x Fex O2固溶体和少量的CeFeO3混合相。Ce1-x Fex O2固溶体的甲烷催化燃烧活性高于单组分CeO2,且随着x的不同而变化,其中以Ce0.9 Fe0.1 O2固溶体的催化活性最高。     

Thermal stabilities of polynitroaromatic compounds and their derivatives

The thermal stabilities of 33 polynitroaromatic compounds and their derivatives were determined using non-isothermal differential thermal analysis (DTA). For twelve of these, the thermal stabilities of their mixtures with 1,3,5-trinitrobenzene was also determined. The results obtained are discussed from a molecular structural point of view.The results obtained from DTA measurements are compared with the published data which were derived from the results of the application of the manometric method to the study of the thermal reactivity of polynitroaromatic compounds. The differences which exist between the conclusions reached on basis of DTA application, on the one hand, and those obtained on the basis of the application of the manometric method, on the other hand, are discussed.Using the published relationship for the calculation of the temperature limit (T_max) for the use of polynitroaromatic compounds as secondary thermostable explosives, T_max values are calculated for the compounds being measured. A relationship is derived between T_max and T_D the initial exothermal decomposition temperature obtained from the DTA of the studied compounds.     

ZnSe colloidal nanoparticles synthesized by solvothermal method in the presence of ZrCl4

The nanocrystalline ZnSe was synthesized from precursors of zinc acetate and Se powder in a high boiling trioctylphosphine (TOP), oleic acid, and ZrCl(4) by solvothermal method. The produced ZnSe nanoparticles showed gradual absorption edge shifting towards blue wavelength region as well as transformation of crystal phase from cubic to hexagonal with increasing ZrCl(4) concentrations in precursor solutions. The particle size calculated from XRD measurements for ZnSe nanoparticles was decreased with increasing ZrCl(4) concentrations for a reaction time of 240 min, from 6.5 nm to 5.1 nm whereas from TEM measurements it was 7.0 to 6.1 nm at 0.0 and 22.5 mol% of ZrCl(4), respectively. No trace of zirconium was found in solid ZnSe nanoparticles by SEM-EDS analysis but the atomic percentage of Se with respective to Zn was decreased with increasing ZrCl(4). The absorption edge blue shifting was explained on the basis of decreased particle size. The crystal phase transformation may be due to the combined effect of small internal energy difference between the two phases and the decrease of crystallite size.     

In situ growth of Co3O4 nano-dodecahedeons on In2O3 hexagonal prisms for toluene catalytic combustion

In this paper, in situ growth of Co₃O₄ nano-dodecahedra on In₂O₃ hexagonal prisms were synthesized via pyrolysis of ZIF-67/MIL-68. Interestingly, the amount of Co₃O₄ dodecahedra on In₂O₃ hexagonal prisms was regularly regulated and controlled. In detail, four Co₃O₄/In₂O₃ catalysts with various Co/In molar ratio were prepared, including Co₄In₁ (Co/In molar ratio was 4:1), Co₂In₁ (Co/In molar ratio was 2:1), Co₁In₁ (Co/In molar ratio was 1:1), Co_0.5In₁ (Co/In molar ratio was 0.5:1). The catalytic performance of Co₃O₄/In₂O₃ catalysts was systematically investigated for toluene combustion. It could be noted that the Co₂In₁ sample exhibited the superior catalytic performance, and the temperatures for 90% toluene conversion (T₉₀) was 182 °C. Furthermore, the toluene conversion of Co₂In₁ sample had no significant decrease at 178 °C for 15 h, indicating that it presented superior stability for toluene oxidation reaction. Through various characterizations, it was verified that the Co/In molar ratio of Co₃O₄/In₂O₃ catalyst could obviously alter the surface atomic ratio of Co³⁺/(Co³⁺ + Co²⁺), BET surface area, the number of surface adsorbed oxygen, the interaction between In₂O₃ and Co₃O₄ of CoInO_x catalysts and so on. The lots of surface adsorbed oxygen, strong interaction between In₂O₃ and Co₃O₄ would promote the catalytic oxidation of toluene. Especially, we discovered that the catalytic activity of Co₃O₄/In₂O₃ was obviously improved with the increase of Co³⁺/(Co³⁺ + Co²⁺) surface atomic ratio.     

甲烷催化燃烧反应机理及催化剂研究进展

在煤矿开采及燃气轮机等工业应用或移动源领域存在甲烷大体量排放,且传统高温焚烧法会导致二次污染,因此,在低温下实现甲烷高效转化成为亟待解决的问题.从能源利用和环境保护角度,催化燃烧技术是实现甲烷废气高效净化的有效措施.本文综述了近年来催化机理和催化剂的研究进展.首先,在实验和理论基础上,总结概括了甲烷氧化机理,其中,重点...     

Novel Ni/CeO2-Al2O3 composite catalysts synthesized by one-step citric acid complex and their performance in catalytic partial oxidation of methane

A series of novel Ni/CeO2-Al2O3composite catalysts were synthesized by one-step citric acid complex method. The as-synthesized catalysts were characterized by N2physical adsorption/desorption, X-ray diffraction(XRD), Fourier transform infrared(FT-IR) spectroscopy, hydrogen temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS) and thermogravimetry analysis(TGA). The effects of nickel content, calcination and reaction temperatures, gas hourly space velocity(GHSV) and inert gas dilution of N2on their performance of catalytic partial oxidation of methane(CPOM) were investigated. Catalytic activity test results show that the highest methane conversion(85%), the best selectivities to carbon monoxide(87%) and to hydrogen(95%), the excellent stability and perfect H2/CO ratio(2.0) can be obtained over Ni/CeO2-Al2O3with 8 wt% Ni content calcined at 700 ℃ under the reaction condition of 750 ℃, CH4/O2ratio of 2 : 1 and gas hourly space velocity of 12000 mL h-1 g-1. Characterization results show that the good catalytic performance of this composite catalyst can be contributed to its large specific surface area(～108 m2 g-1), small crystallite size, easy reducibility and low coking rate.     

Novel Ni/CeO2-Al2O3 composite catalysts synthesized by one-step citric acid complex and their performance in catalytic partial oxidation of methane

A series of novel Ni/CeO2-Al2O3composite catalysts were synthesized by one-step citric acid complex method. The as-synthesized catalysts were characterized by N2physical adsorption/desorption, X-ray diffraction(XRD), Fourier transform infrared(FT-IR) spectroscopy, hydrogen temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS) and thermogravimetry analysis(TGA). The effects of nickel content, calcination and reaction temperatures, gas hourly space velocity(GHSV) and inert gas dilution of N2on their performance of catalytic partial oxidation of methane(CPOM) were investigated. Catalytic activity test results show that the highest methane conversion(85%), the best selectivities to carbon monoxide(87%) and to hydrogen(95%), the excellent stability and perfect H2/CO ratio(2.0) can be obtained over Ni/CeO2-Al2O3with 8 wt% Ni content calcined at 700 ℃ under the reaction condition of 750 ℃, CH4/O2ratio of 2 : 1 and gas hourly space velocity of 12000 mL h-1 g-1. Characterization results show that the good catalytic performance of this composite catalyst can be contributed to its large specific surface area(～108 m2 g-1), small crystallite size, easy reducibility and low coking rate.     

Enhanced electrochemical performance of LiFePO4 of cathode materials for lithium-ion batteries synthesized by surfactant-assisted solvothermal method

Lithium iron phosphate (LiFePO₄) cathode materials were synthesized by the solvothermal method with the assistance of different surfactants. The influences of polyethylene glycol 2000 (PEG 2000), polyvinylpyrrolidone (PVP), and cetyltrimethyl ammonium bromide (CTAB) on the microstructure and electrochemical performance of LiFePO₄ were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and charge/discharge measurements. The particle size of the LiFePO₄ synthesized with the assistance of PEG was uniform and showed a flat rhombohedron-like shape. The initial discharge specific capacity is up to 122.80 mAh/g with an initial coulombic efficiency of 95.50% at 0.1C. LiFePO₄ synthesized with PVP-assisted presents a porous structure with an initial discharge specific capacity of 91.01 mAh/g. LiFePO₄ synthesized with CTAB-assisted shows a flower-like morphology with an initial discharge specific capacity of 100.44 mAh/g. Though the initial discharge capacities of the LiFePO₄ materials prepared with the assistance of CTAB and PVP are lower than those of the LiFePO₄ prepared without the assistance of surfactant, the two materials exhibited excellent cyclic stability at 0.1C.

     

Characterization and catalytic properties of nickel-substituted hexagonal mesoporous silica prepared by microwave-hydrothermal method

The liquid phase of acetylation of 1,2-dimethoxybenzene with acetic anhydride has been investigated over a series of acid nickel-mesoporous materials (Ni-MCM-41) synthesized by the microwave irradiation method with different Si/Ni ratios (Si/Ni = 80, 50, 10) and characterized by several spectroscopic techniques such as: N₂ physical adsorption, ICP, XRD, TEM, FT-IR, and a temperature programmed desorption (TPD) of pyridine. In fact, the catalyst Ni-MCM-41 (10) showed better performance in the acid-catalyzed acetylation of 1,2-dimethoxybenzene employing acetic anhydride as an acylating agent. Furthermore, the kinetics of the acetylation of 1,2-dimethoxybenzene over these catalysts have also been investigated.     

Thermal and photolytic stabilities of perfluoroalkane sulfonic acids and their derivatives

The use of perfluoroalkanesulfonic acids and their derivatives in drastic conditions leads us to study their behaviour with respect to temperature and radiative factors.Such acids as CF₃SO₃H and C₂F₅SO₃H, used in a pure state as well as their related pure anhydride are stable until they reach a temperature of at least 180°C.On the other hand, the solutions of anhydride with its related acid, yield perfluorosulfonic esters and SO₂ at room temperature already:

This mechanism is discussed.These results involve a new and easy synthesis of symmetrical perfluorosulfonic esters R_FSO₃R_F with acids and P₂O₅.

Further more, it occurs no transformation of the anhydride under UV and visible irradiation. But under the same conditions, a small account of acids are deshydrated into anhydrides.A further experiment combining both effects of temperature and light leads to the esters.     

Preparation of LaFe0.95Pd0.05O3 perovskites and their catalytic performances in methane combustion

The physic-chemical properties of LaFe0.95Pd0.05O3 perovskites were strongly dependent on the temperature of calcination. Most of the organic substances and inorganic impurities were readily removed at 723 K but single-phase and well crystallized perovskite structure was formed at 873 K. With further raising the calcination temperature, the crystallite size of LaFe0.95Pd0.05O3 increased considerably. The LaFe0.95Pd0.05O3 sample that calcined at 1073 K showed only comparable activity as the reference LaFeO3 catalyst, in particular below 923 K, but pre-treatment with the reaction gas at 1223 K resulted in significantly enhanced activity due to the generation of active PdO species on the surface. The hysteresis feature upon heating-cooling cycle further confirmed the strong interaction between Pd and LaFeO3 in the perovskite structure.     

Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion

Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission elec-tron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.     

Plasma assisted preparation of cobalt catalysts by sol–gel method for methane combustion

Novel cobalt catalysts were prepared by sol–gel method, and enhanced by plasma treatment, for methane catalytic combustion. These samples were characterized using X-ray diffraction, X-ray photoelactron spectroscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetrical analysis, N₂ Adsorption–desorption, temperature-programmed reduction and hydrogen–oxygen titration technologies. The XPS characterizations suggested that plasma treatment was favorable for the enrichment of surface cobalt, with a value of surface cobalt from 2.2% to 8.5% in mole. The specific surface area of the glow plasma assised sample (Co-Plas-Solgel-2) increased to 320 m²/g comparing with 305 m²/g of the conventional sample (Co-Solgel-1). The ignition temperature (T_10%) of Co-Plas-Solgel-2 catalyst was about 50 °C lower than that of Co-Solgel-1, and its CH₄ conversion was two times higher than that of Co-Solgel-1 during the whole range of catalytic combustion activity test (340–520 °C). With a better dispersion and more active sites, the plasma assisted sample exhibited significant enhancement in catalytic performances.     

Photocatalytic properties of ZnO powders synthesized by conventional and microwave-assisted solution combustion method

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using conventional and microwave ignition routes. The effects of starting solution acidity on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. The chelated species in dried gels were predicted by theoretical calculations and confirmed by Fourier transform infrared spectroscopy. The combustion reaction rate increased with the increase of pH values. Single phase and well-crystalline ZnO powders were achieved by both of ignition methods regardless of pH values. The hexagonal particles (200–80?nm) formed by microwave ignition were larger than the spherical particles (60–40?nm) in conventional heating. Conventionally combusted ZnO powders exhibited higher photocatalytic activity under ultraviolet irradiation, due to their narrower band gap and smaller particle size.

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C/C0 vs. irradiation time for photodegradation of MB dye under ultraviolet light irradiation by the as-combusted ZnO powders (filled symbols present conventional combusted powders and open symbols are for the microwave combusted powders)

     

Thermal stabilities of copolymers of styrene and acrylic acid and their salts

The thermal stabilities of copolymers of styrene and acrylic acid and their alkali metal salts have studied.The thermal stability properties T_i and T_s, and the kinetic parametersn, E, S andZ were determined and the results are discussed. It was found that the thermal stabilities of the investigated copolymers of styrene and acrylic acid are somewhat lower than that of polystyrene and decrease with increase of the quantity of acrylic acid introduced into the copolymers.The thermal stabilities of the sodium salts of these copolymers are somewhat higher than those of the initial copolymers, and are almost equal to that of polystyrene.The thermal stabilities of the investigated ionomers depend on the nature of the alkali metal introduced into the copolymer.

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Zusammenfassung Es wurde die thermische Stabilität von Kopolymeren aus Styrol und Acrylsäure bzw. Acrylsäurealkalimetallsalzen untersucht. Die Werte T_i und T_s für die thermische Stabilität sowie die kinetischen Parametern, E,S undZ wurden bestimmt und die Ergebnisse diskutiert. Man fand, daß die thermische Stabilität der untersuchten Kopolymere aus Styrol und Acrylsäure etwas niedriger ist als die von Polystyrol und daß sie mit einer Zunahme des Anteiles an Acrylsäure an den Kopolymeren absinkt. Die thermische Stabilität der Natriumsalze dieser Kopolymere erwies sich als etwas höher als die die ursprünglichen Kopolymere, erreicht aber nur die von Polystyrol. Die thermische Stabilität der untersuchten Ionomere hängt von der Art der in die Kopolymere eingebrachten Alkalimetalle ab.

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. T _i ,T _s , E, n, S Z. , , . , , . , .

     

Thermal stabilities of copolymers of styrene and methacrylic acid and their salts

The thermal stabilities of copolymers of styrene and methacrylic acid and their sodium salts have been studied. The values of the thermal stability IDT,T _s and the kinetic parametersn, E, S andZ have been determined and the results are discussed. It has been found that the thermal stabilities of the investigated copolymers of styrene and methacrylic acid and their sodium salts are practically independent of the amount of methacrylic acid or sodium methacrylate introduced.