Synthesis and characterization of crystalline nanosized MgF2 powder via microemulsion route

Nanosized MgF₂ was synthesized by precipitation in microemulsions of water in cyclohexane stabilized by polyethylene glycol tert-octylphenyl ether. The synthesized MgF₂ powder was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET specific surface area, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results showed that the synthesized powder was a MgF₂ powder with a crystallite size in the range of 9-11 nm and a specific surface area of 190 m²/g.     

Corrosion resistance and cytotoxicity of a MgF2 coating on biomedical Mg–1Ca alloy via vacuum evaporation deposition method

To reduce the biocorrosion rate and enhance the biocompatibility by surface modification, MgF₂ coatings were prepared on Mg–1Ca alloy using vacuum evaporation deposition method. The average thickness of the coating was about 0.95 µm. The results of immersion test and electrochemical test indicated that the corrosion rate of Mg–1Ca alloy was effectively decreased after coating with MgF₂. The MgF₂ coating induced calcium phosphate deposition on Mg–1Ca alloy. After 72 h culture, MG63 cells and MC3T3‐E1 cells were well spread on the surface of the MgF₂‐coated Mg–1Ca alloy, while few cells were observed on uncoated Mg–1Ca alloy samples. In summary, MgF₂ coating showed beneficial effects on the corrosion resistance and thus improved cell response of the Mg–1Ca alloy effectively and should be a good surface modification method for other biomedical magnesium alloys. Copyright © 2013 John Wiley & Sons, Ltd.     

MgF2 as a non-conventional catalyst support

This review reports progress in the study of the surface structure of MgF₂ and its use as a support of catalytically active phases. Magnesium fluoride was applied first as a support in catalysis for systems containing individual oxides of transition metals (Mo, V, W, Cu, Cr) and then two different oxide phases (Cu-Cr, Cu-Mn), a metal phase (Ru, Pd) or heteropolyacids. Its use as a support enabled determination of the structure and surface properties of these catalysts. The MgF₂-supported catalysts are characterized by high activity and selectivity in such processes as: hydrodechlorination of chlorofluorocarbons (CFCs), hydrodesulfurization of organic compounds and purification of fuel combustion products from nitrogen oxides. Magnesium fluoride has been also used in MgF₂-doped chromium or aluminum fluoride catalysts for Cl/F exchange on hydrochlorocarbons.     

Synthesis and characterization of MgF2 and KMgF3 nanorods

MgF₂ nanorods with diameters of 60-100 nm were synthesized by a microemulsion method. Subsequent hydrothermal reaction of as-synthesized MgF₂ nanorods and KF at 240°C for 3 days or 140°C for 7 days resulted in KMgF₃ nanorods, which retained the rod-like morphology of the source material MgF₂ in the reaction process. The morphology of as-synthesized MgF₂ strongly depended on the molar ratio between water and the surfactant CTAB and the concentration of CTAB.     

The reaction of MgCl2·4H2O with CCl2F2

A new reaction of MgCl₂·4H₂O with CCl₂F₂ is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF₂ was obtained between 252 and 350 °C, Below the temperature, MgCl₂·4H₂O dehydrates and hydrolyzes to MgCl₂ and Mg(OH)Cl, which are the real reactants of the reaction with CCl₂F₂. The formation of MgF₂ is ascribed to the reaction of MgCl₂ and Mg(OH)Cl with HF, which forms by decomposition of CCl₂F₂ with the taking part in of H₂O released from dehydration of hydrated magnesium chloride on the surface of MgCl₂ and Mg(OH)Cl, which catalyzes the decomposition of CCl₂F₂ in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF₂ formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl₂F₂ (rather than release into the atmosphere). It is also a method for the preparation of MgF₂.     

Preparation and adsorption performance of a NiO/MgF2 composite adsorbent

Fluoride adsorbents have been applied for the purification of UF₆ product from fluorination process. A MgF₂-based adsorbent, NiO/MgF₂, was prepared using NiF₂ as doping agent. The specific surface area of NiO/MgF₂ was 5 times larger than that of MgF₂, its porosity was also larger than that of MgF₂. The saturated adsorption capacity of NiO/MgF₂ for MoF₆ was 21.4?±?1.9 mg g^?1. The desorption behavior was examined by thermogravimetric analysis (TG). The NiO/MgF₂ with adsorbed MoF₆ was investigated using extended X-ray absorption fine structure spectroscopy (EXAFS), which showed no bonding interactions between NiO and MoF₆, while the adsorption of MoF₆ on NiO/MgF₂ was chemisorption via a Mo–F–Mg bond.

     

Sol–gel doped TiO<Subscript>2</Subscript> nanomaterials: a comparative study

Among the great number of sol–gel prepared nanomaterials, TiO₂ has attracted significant interest due to its high photocatalytic activity, excellent functionality, thermal stability and non-toxicity. The photocatalytic degradation of pollutants using un-doped and doped TiO₂ nanopowders or thin films is very attractive for applications in environmental protection, as a possible solution for water purification. The present work describes a comparative structural and chemical study of un-doped TiO₂ and the corresponding S- and Ag-doped materials. The photocatalytic activity was established by testing the degradation of organic chloride compounds from aqueous solutions. Sol–gel Ag-doped TiO₂ coatings, prepared by co-gelation and sol–gel Ag-doped TiO₂ coatings obtained from nanopowders were also compared. Their structural evolution and crystallization behaviour (lattice parameters, crystallite sizes, internal strains) with thermal treatment were followed by thermal analysis, X-ray diffraction, transmission electron microscopy, atomic force microscopy and specific surface areas measurements. X-ray photoelectron spectroscopy analyses were performed to characterize the surface composition and S or Ag speciation, which was used to interpret the catalytic data.     

Investigations of MgF2 Optical Thin Films Prepared from Autoclaved Sol

MgF₂ thin films with ultra low refractive indices were obtained by sol–gel method using sols prepared from magnesium acetate and hydrofluoric acid. The sols were autoclaved in a Teflon cell at 100–180°C for 24 h and then coated on SiO₂ glass or CaF₂ crystal substrates by spin coating. Subsequently, the samples were heat treated at 150°C for 1 h. The optical properties of the thin films, such as refractive index and transmittance, were investigated in the UV region, especially in the deep UV (DUV, below 250 nm) region. Though the coatings consist of single layers, both samples exhibited high transmittance. In addition, they exhibit such antireflection effect over a very wide range of wavelength. Such a good antireflection effect was produced only by low refractive indices. It has also been confirmed that, even in the range of vacuum UV (VUV, 200–150 nm), CaF₂ samples with antireflection coatings could keep such a good antireflection effect.     

Fabrication and properties of MgF<Subscript>2</Subscript> composite film modified with carbon nanotubes

Carbon nanotubes (CNTs) were used to modify magnesium fluoride (MgF₂) film via the spin coating technique. Nanoparticles of MgF₂ were in situ synthesized on surfaces of CNTs resulted in the composites (MgF₂–CNTs) by means of sol–gel technique. The sizes of the MgF₂ nanoparticles in situ synthesized on CNTs surfaces could be modulated by processing the MgF₂ sol–gel in different ways. The MgF₂–CNTs as prepared was mixed with MgF₂ sol to fabricate composite films (MgF₂–CNTs/MgF₂). Instead of adding directly CNTs, adding MgF₂–CNTs, into MgF₂ sol could effectively improve the dispersion of CNTs, avoid emergence of carbon clusters in the compsite film, decrease surface roughness of the film, and enhance the interaction between the CNTs and MgF₂ matrix. In the paper, the MgF₂ nanoparticles were in situ synthesized on the surfaces of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) respectively to prepare MgF₂–SWCNTs/MgF₂ and MgF₂–MWCNTs/MgF₂ composite films. Experimental results showed that the transparency of the MgF₂–SWCNTs/MgF₂ composite film was higher than that of the MgF₂–MWCNTs/MgF₂ film in the range of ultraviolet, visible and near-infrared wavelengths. The results showed SWCNTS could be an ideal reinforcement of MgF₂ films to get good toughness, and retain its optical transmittance at the same time.     

Silica-Zirconia Sol–Gel Coatings Obtained by Different Synthesis Routes

Homogeneous xSiO₂-(1−x)ZrO₂ coatings have been prepared onto glass-slides, monocrystalline Si and stainless steel (AISI 304) using sols prepared via acid and basic catalysis. Zirconium tetrabutoxide (TBOZr), zirconium n-propoxide (TPZ), tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used as precursors of zirconia and silica, respectively. The different parameters involved in the synthesis procedure, as molar ratios H₂O/alkoxides, NaOH/alkoxides, and sintering temperature have been analysed, correlating the stability and rheological properties of the sols. The evolution and structure of the sols and coatings have been studied by FTIR. Coatings have been prepared by dipping from acid and basic sols. Electrophoretic Deposition (EPD) technique has also been used to prepare coatings onto stainless steel from basic particulate sols in order to increase the critical thickness. A maximum thickness of 0.5 μ m was reached by both dipping and EPD process for 75SiO₂: 25 ZrO₂ composition. The critical thickness decreases with ZrO₂ amount depending strongly of the drying conditions. Si–O–Zr bonds have been identified by FTIR, indicating the existence of mixed network Si–O–Zr in the coatings obtained by the different routes. Crystallisation of ZrO₂(t) was only observed at high sintering temperature (900^∘C) by FTIR and confirmed by DRX.     

具有双孔径分布的介孔C-Al2O3-TiO2纳米复合材料的合成及其红外发射率

以嵌段共聚物F127 (PEO₁₀₆PPO₇₀PEO₁₀₆, M_W=12600)为模板剂, 异丙醇铝和钛酸四丁酯为金属源, 低分子量的酚醛树脂为碳源, 通过溶胶-凝胶三元共组装法合成了具有双孔径分布的C-Al₂O₃-TiO₂纳米复合材料.用X射线衍射(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)及N₂吸附-脱附对该复合材料进行结构表征. 结果显示, 当铝钛原子的摩尔比为1:10 时, 对应的纳米复合材料具有较好的有序介孔结构, 其双孔径分别为3.9和6.5 nm, 比表面积可达259 m²·g^-1, 孔容0.37 cm³·g^-1. 以三元乙丙橡胶(EPDM)为粘结剂, 与介孔纳米复合材料混合制备涂层. 通过调节复合材料中铝钛摩尔比和涂层厚度, 红外发射率在0.450-0.617之间可调.     

Microwave-assisted synthesis of spherical monodispersed magnesium fluoride

Spherical monodispersed magnesium fluoride has been obtained using the microwave-assisted precipitation technique from magnesium nitrate and ammonium fluoride solutions. Studies aimed at optimizing synthesis conditions from the point of view of preparing spherical MgF₂ particles of possibly high monodispersity were performed. Spherical MgF₂ particles of 0.25-0.36 μm in diameter have been obtained with relative standard deviation from the average value ranging from 7 to 15%. It has been established that a certain optimal range of Mg(NO₃)₂ and NH₄F concentrations exists that enables a highly monodispersed MgF₂ to be prepared. The range is narrow (0.01-0.03 mol dm⁻³) for both precursors. Spherical MgF₂ particles have been characterized by SEM, XRD, DTG/DTA and FTIR techniques.     

Catalytic methanol decomposition to carbon monoxide and hydrogen over Pd/CeO2-ZrO2-La2O3 with different Ce/Zr molar ratios

The catalytic behaviors of Pd (1.4 wt%) catalysts supported on CeO₂-ZrO₂-La₂O₃ mixed oxides with different Ce/Zr molar ratios were investigated for methanol decomposition. Nitrogen adsorption-desorption (BET), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD) and Pd dispersion analysis were used for their characterization. Pd/Ce_0.76Zr_0.18 La_0.06O_1.97 catalyst showed the highest BET surface area, best Pd dispersion capability and strongest metal-support interaction. Moreover, XPS showed that there was lattice defect oxygen or mobile oxygen. According to the result of O 1s measurements the lattice defect oxygen or mobile oxygen helped to maintain Pd in a partly oxidized state and increased the activity for methanol decomposition. The Pd/Ce_0.76Zr_0.18La_0.06O_1.97 catalyst exhibited the best activity. A 100% conversion of methanol was achieved at around 260 °C, which was about 20-40 °C lower than other catalysts     

Preparation and characterization of nanotube Li-Ti-O by molten salt method

Nanotube Li-Ti-O compound with high surface (198.6 m²·g⁻¹) was prepared by a method involving the treatment of nanotube Na₂Ti₂O₅·H₂O in molten LiNO₃ and characterization by means of transmission electron microscopy (TEM), energy-dispersive spectra (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetry-differential thermal analysis (TG/DTG). Results show that the nanotube Li-Ti-O compound prepared by this method involves two crystal phases: spinel Li₂Ti₂O₄ and anatase Li_xTiO₂ (x < 0.1). Li⁺ exhibits different Li1s binding energy in the two crystal phases. In ambient air, the Li-Ti-O compound adsorbs water easily, and the chemically adsorbed water is difficult to remove below 400°C. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(12): 2135–2139 [译自: 无机化学学报]     

Optimization of the Sintering Process by DSC for the Preparation of High-Temperature Superconductors

The optimum calcination and sintering conditions for the preparation of the desired phases with the proper stoichiometry of the bulk high-temperature superconductors YBa₂Cu₃O_7-x (YBCO) and Bi₂Sr₂CaCu₂O_y> (BSCCO) were investigated by differential scanning calorimetry. DSC analysis on the corresponding superconducting coatings, electrophoretically deposited, indicated that the sintering and annealing procedure was suitable for the production of stable, strong and adherent coatings. X-ray diffraction analysis, Raman spectroscopy and magnetic measurements confirmed the improved properties of the superconducting powders and coatings obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal behaviour study of some sol-gel TiO2 based materials

Among the great number of sol-gel materials prepared, TiO₂ holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO₂ nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO₂ matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO₂ crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.     

Effects of aging time on V2O5 sol-gel coatings

Vanadium pentoxide (V₂O₅) sols have been used in conductive coatings and related applications [1, 2, 3]; however, the changes which may occur in the properties of these coatings with sols of different ages have not been carefully shown. Properties which may be dependent on the age of the sol (sol viscosity, film morphology and conductance) were measured in this work. The coating sols were prepared by ion-exchange of sodium metavanadate solutions.It was found that the coating thickness, sol viscosity, and surface morphology of the coatings were directly related to the age of the sol used. The dried coating thickness increased from 3 microns to 20 microns over a 30 day period. The sol viscosity increased from 1 centipoise to near 2 centipoise. The surface morphology of the coatings changed from that of a featureless surface at day 1 to a continual coverage of micron-sized fibers as the coating sols aged. The conductivity of the coatings, though, was unaffected by the age of the sol. The coating properties were correlated to the amount of polymerization of dissolved precursors in solution.     

扫帚状氧化铈制备及其对Pt基阳极催化剂催化性能的影响

采用水热合成法,合成了比表面积为175 m²·g^-1,孔径在2~4nm范围内的扫帚状CeO₂。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO₂/RGO催化剂,探究扫帚状CeO₂的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪（XRD）、扫描电镜（SEM）、N₂吸附-脱附、X射线光电子能谱（XPS）对所制备的CeO₂及催化剂进行表征。利用电化学工作站对催化剂进行电化学性能测试。结果表明,催化剂中CeO₂保持原有扫帚状,Pt纳米粒子均匀分布于石墨烯载体表面;当m_RGO∶m_CeO2=1∶2时,添加了扫帚状CeO₂的Pt-CeO₂/RGO催化剂的电催化性能最优,电化学活性表面积为102.83 m²·g^-1,对乙醇氧化的峰值电流密度为757.17 A·g^-1,1 000 s的稳态电流密度为108.17 A·g^-1,对乙醇催化氧化反应的电荷转移电阻最小,活化能最低。     

Blue Emission of ZnGa2O4 Nanoparticles Dispersed in Fluoride Thin Films via Sol-Gel Process

Nanocomposite thin films where ZnGa₂O₄ nanoparticles were dispersed in fluorides, MgF₂ or LaF₃, were prepared by a sol-gel method using metal acetates and nitrates as starting reagents and trifluoroacetatic acid as a fluorine source. ZnGa₂O₄ and the fluorides such as MgF₂ and LaF₃ were formed simultaneously after the heat treatment of the spin-coated gel films as evidenced by X-ray diffraction. The films were transparent in the visible region. With decreasing the ZnGa₂O₄ content, absorption edges showed blue-shift. All the films exhibited a broad-band blue emission around 430 nm by ultra-violet excitation at 254 nm. The intensity of the blue emission in the PL spectra increased with decreasing the ZnGa₂O₄ content. These phenomena were attributed to the quantum size effects (the increased band-gap) and the surface effects (the increased luminescent center) in the nano-sized ZnGa₂O₄. The mechanism of the emission was discussed in view of surface states in the oxide nanoparticles.     

Preparation of a highly active nanocrystalline TiO2 photocatalyst from titanium oxo cluster precursor

Nanocrystalline TiO₂ (sample S1) was prepared from a titanium oxo cluster (Ti₇O₄(OEt)₂₀) precursor via a sol-gel route. This photocatalyst showed a higher photocatalytic activity than the TiO₂ (sample S2) obtained from titanium tetraisopropoxide. The samples were characterized by thermal analysis (TGA/DSC), X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy, N₂ adsorption (BET surface area), infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy. The characterization results show that both samples are anatase nanocrystals with particle sizes of about 12 nm, but the more photocatalytically active sample S1 has more surface hydroxyl groups and larger surface area and pore volume than sample S2.