Pure Crystal Phase Research Articles

Morphological Control Synthesis and Characterization of Hydroxyapatite with Star-Shaped

The aim of the present work was to study the feasibility of wet synthesizing hydroxyapatite (HAP) with star-like and high specific surface area. HAP was synthesized by one-step self-assembly process in ionic liquid media under microwave irradiation, and treated at 300, 600, 900 , respectively. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis revealed that HAP was pure crystal phase. Nitrogen adsorption and desorption isotherms (NADI) with a characteristic hysteresis loop further confirmed the existence of uniform micropores or channels of HAP. The BET surface area, pore volume, and pore size distribution were calculated to be 324m2g-1, 0.39cm3g-1, and 3.28 nm, respectively. Scanning electron microscopy (SEM) results indicated that the HAP was of star-shaped morphology. The formation of HAP could be explained by functional ionic liquid as structure-directing template. Well-ordered mesostructure of HAP with star-like might be therefore used as a potential biomaterial for preparation of bone implant materials.

Preparation and photoelectrochemical properties of densely immobilized Cu2ZnSnS4 nanoparticle films

Colloidal Cu2ZnSnS4 (CZTS) nanoparticles with sizes of 5–6 nm that contain no highly toxic elements were successfully synthesized through thermal reactions of metal acetate and sulfur in high-temperature oleylamine solution. The reaction temperature was a key factor for the synthesis of CZTS nanoparticles: synthesis at temperatures higher than 240 °C gave a pure CZTS crystal phase, whereas a secondary phase of CuS was formed at reaction temperatures lower than 180 °C. Nanoparticles were successfully accumulated on ITO-coated or quartz glass substrates via layer-by-layer deposition using 1,2-ethanedithiol as a cross-linking agent. The resulting CZTS particle films exhibited a photoresponse similar to that of p-type semiconductor photoelectrodes in an aqueous solution containing Eu(NO3)3 as an electron scavenger. Potentials of the valence band edge and conduction band edge were determined from the onset potential of the cathodic photocurrent to be +0.3 and −1.2 V vs. Ag/AgCl, respectively.

Surfactant-free synthesis of pure anatase TiO2 nanorods suitable for dye-sensitized solar cells

A non-aqueous, solvothermal method was applied to the synthesis of TiO2 nanorods in pure anatase crystal phase using Ti(IV)-isopropoxide. The use of benzyl alcohol as both solvent and reactant was investigated in combination with the addition of acetic acid to the reaction mixture. Various values of the AcOH : Ti(OiPr)4 molar ratio were realized in the synthesis and tested in order to obtain a significant dimensional and morphological control over the resulting TiO2 nanostructures, as well as to devise a simple and scalable synthetic protocol. On the basis of the experimental results, a substantially modified version of the well-established “benzyl alcohol route” was then designed and developed. X-ray diffractometry and transmission electron microscopy revealed that monodisperse anatase nanorods having a length of about 13–17 nm and a diameter of 5 nm can be obtained when AcOH and Ti(OiPr)4 are reacted in comparable proportions. Investigation of the characteristic parameters of dye-sensitized solar cells fabricated using the synthesized nanorods as photoanode revealed a power conversion efficiency of about 7.5% corresponding to an improvement of 28% with respect to a commercial spheroidal nanotitania (P25) based reference device.

Effects of Hydrothermal Temperature on the Microstructures of BiVO4 and Its Photocatalytic O2 Evolution Activity under Visible Light

Microspheric and lamellar BiVO(4) powders were selectively prepared through a hydrothermal process by using cetyltrimethylammonium bromide (CTAB) as a template-directing reagent. The as-prepared BiVO(4) powders were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption-desorption experimentation, Fourier transform infrared spectrometry, and UV-vis diffuse reflectance spectroscopy. Experimental results indicate that microspheric BiVO(4) with particle sizes in the range of 7-12 microm can be derived from a relatively low hydrothermal temperature (<or=160 degrees C) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas lamellar BiVO(4) with a pure monoclinic phase can be obtained at a higher hydrothermal temperature (200 degrees C). Their photocatalytic activities for O(2) evolution were investigated by using Fe(NO(3))(3) as a sacrificial reagent under visible-light irradiation, and the lamellar BiVO(4) shows a better photoactivity than the microspheric product due to its pure monoclinic crystal phase. Moreover, the effects of CTAB content on the morphologies and crystal phases of the obtained products were also discussed. It was found that the addition of CTAB can adjust the morphologies of BiVO(4) and obstruct the crystal phase transformation from the mixed crystal to pure monoclinic BiVO(4) during the hydrothermal process.

INTEGRATION OF FERROELECTRIC BaTiO3 THIN FILMS DIRECTLY ON NI AND TI METALLIC TAPES FOR STRUCTURAL HEALTH MONITORING SYSTEMS AND ENERGY HARVEST APPLICATIONS

ABSTRACT Ferroelectric BaTiO3 thin films were fabricated directly on various metallic substrate materials such as Ni and Ti by using the pulsed laser for the development of structural health monitoring systems and energy harvest applications. Microstructure studies from x-ray diffraction and electron microscopy indicate that the as-grown BaTiO3 thin films have pure BaTiO3 crystal phase. The TEM studies indicate that the BaTiO3 films are composed of crystalline assemblage of nanopillars with average cross sections from 100 nm to 200 nm and can be directly integrated on the Ni tapes without the formation of NiO interlayer suggesting that this system can be developed for super-capacitor devices. The BaTiO3films have good interface structures and strong adhesion with respect to Ni and Ti substrates. Dielectric measurements have shown the hysteresis loop at room temperature in the film with a large remanent polarization, indicating that the ferroelectric domains have been created in the as-deposited BTO films. The successful integration of ferroelectric thin films directly on metallic materials has promised for the development of the structural health monitoring systems and energy harvest devices.

The effect of Zn contents on phase composition, chemical stability and cellular bioactivity in Zn–Ca–Si system ceramics

Ca-Si system ceramics, in particular CaSiO(3) ceramics, are regarded as potential bioactive bone repair/regeneration material. However, their high dissolution rate limits their biological applications. The aim of this study was to incorporate Zinc (Zn) into the Ca-Si system ceramics to produce part (at 10 and 20% Zn) or complete (at 50% Zn) new crystal phase (hardystonite: Ca(2)ZnSi(2)O(7)) with improved chemical stability and cellular activity. Zn-Ca-Si ceramics with four Zn contents (0, 10, 20, and 50%) were successfully prepared by sintering sol-gel-derived Zn-Ca-Si powder compacts. A new pure crystal phase Ca(2)ZnSi(2)O(7) was formed only when 50% Zn was added. The chemical stability of Zn-Ca-Si ceramics was evaluated by soaking in simulating body fluid (SBF), and the ion release from ceramics and the change in pH values of the SBF were measured. Their ability to form apatite in SBF was determined by analyzing the surface phase composition and morphology of the ceramics using X-ray diffraction and scanning electron microscopy (SEM). Results indicated that, with the increase of Zn contents, the chemical stability of ceramics increased while the apatite-formation ability decreased. The ability of Zn-Ca-Si ceramics to support attachment, proliferation, and differentiation of the human bone osteoblastic-like cells (HOB) was assessed using SEM, MTS, and alkaline phosphate activity assays, respectively. Zn-Ca-Si ceramics supported HOB attachment and their proliferation increased with the increase of Zn content. ALP activity of HOB on Zn-Ca-Si ceramics with 50% Zn (Ca(2)ZnSi(2)O(7)) was the highest among the levels obtained for the four ceramics tested. Taken together, Ca(2)ZnSi(2)O(7) ceramics possessed the best chemical stability and cellular bioactivity in Zn containing Ca-Si ceramics, indicating their potential application in skeletal tissue regeneration.

ZnO:Eu Thin‐Films: Sol—Gel Derivation and Strong Photoluminescence from 5D0 → 7F0 Transition of Eu3+ Ions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Crystal Structure, Thermal and Magnetic Behavior of Inorganic–Organic Hybrid [VIV 4O10 VV 2O4] (C6H14N2)·H2O Polymeric Framework

The inorganic–organic hybrid [VIV 4O10VV 2O4] (C6H14N2)·H2O polymeric framework was prepared under mild hydrothermal conditions from a mixture of DABCO and V2O5 in deionized water with a 1:1:450 mole ratio, at neutral pH. The reaction was carried out at 180 °C for 3 days under autogenous pressure yielding phase pure crystals product. The crystal structure was studied using both powder and single crystal X-ray crystallography, revealing the structure to be of the ({UuDd}:T*)α′ type in the SP+T class and Z-T subclass. The presence of the organic cation was confirmed by FT-IR spectrum and chemical composition analysis. The structure was thermally stable up to over 400 °C, and showed ferromagnetic character at room temperature with the maximum molar susceptibility of 8.26 × 10−3 emu/mol−1 at zero applied field.

ZnO:Eu thin-films: Sol–gel derivation and strong photoluminescence from 5D0→7F0 transition of Eu3+ ions

Abstract ZnO:Eu films on silicon wafers were prepared by a simple sol–gel route. It was found that in order to achieve pure ZnO crystal phase, the annealing temperature could not be higher than 850 °C. The pronounced peaks in the photoluminescence (PL) spectra of the ZnO:Eu films were originated from 5 D 0 → 7 F 0,1,2 transitions. It is somewhat unexpected that the PL emission from the 5 D 0 → 7 F 0 transition, which is principally believed to be forbidden, was remarkable. In order to explain this phenomenon, it is proposed that a majority of incorporated Eu 3+ ions in the films occupy the interstitial sites of ZnO host.

ReaxFFMgH Reactive Force Field for Magnesium Hydride Systems

We have developed a reactive force field (ReaxFF(MgH)) for magnesium and magnesium hydride systems. The parameters for this force field were derived from fitting to quantum chemical (QM) data on magnesium clusters and on the equations of states for condensed phases of magnesium metal and magnesium hydride crystal. The force field reproduces the QM-derived cell parameters, density, and the equations of state for various pure Mg and MgH(2) crystal phases as well as and bond dissociation, angle bending, charge distribution, and reaction energy data for small magnesium hydride clusters. To demonstrate one application of ReaxFF(MgH), we have carried out MD simulations on the hydrogen absorption/desorption process in magnesium hydrides, focusing particularly on the size effect of MgH(2) nanoparticles on H(2) desorption kinetics. Our results show a clear relationship between grain size and heat of formation of MgH(2); as the particle size decreases, the heat of formation increases. Between 0.6 and 2.0 nm, the heat of formation ranges from -16 to -19 kcal/Mg and diverges toward that of the bulk value (-20.00 kcal/Mg) as the particle diameter increases beyond 2 nm. Therefore, it is not surprising to find that Mg nanoparticles formed by ball milling (20-100 nm) do not exhibit any significant change in thermochemical properties.

Modification of NASICON Solid Electrolyte for NO x Measurements

The construction and sensing performance of solid-state potentiometric sensors using a natrium superionic conductor (NASICON) as solid electrolyte are reported. Dense ceramic pellets with a pure NASICON crystal phase were produced by a solid-state reaction method using a modified procedure. The NASICON surface on the Pt sensing electrode side was modified with a layer as an auxiliary phase using a melting-quenching method. By the same method, the other surface of the NASICON was modified with an AgCl layer and was connected with an Ag wire as a reference electrode. An air/Pt quasi-reference electrode was fabricated by exposing the Pt black attached NASICON surface to the ambient. Both sensor devices using air/Pt and Ag/AgCl reference electrodes were investigated for sensing. The two sensor designs exhibited Nernstian behavior, fast response, stability, and reproducibility. The Ag/AgCl reference electrode provides an all-solid-state design for the sensor device without the need for a reference gas with fixed composition or a hermetic seal separating the reference electrode from the sample gas. A sensing mechanism is discussed. © 2004 The Electrochemical Society. All rights reserved.

Solid-State 13C CPMAS NMR and Molecular Mechanics Study of Conformational Recognition in Mixed Crystals of Two Phenylalkyl Ketones

A detailed structural analysis of a dilute mixed crystal of 13C-Me-labeled 1,2-diphenylpropanone (1) in 2-methyl-l,2-diphenylpropanone (2) has been carried out with the help solid state 13C cross polarization and magic angle spinning (CPMAS) NMR, molecular mechanics calculations of mixed crystal models, and X-ray diffraction techniques. After characterization of the crystal phases of the pure components, mixed crystals prepared with 1-5% 1 (99.9% 13C-Me labeled) were investigated by solid-state NMR with the goal of addressing structural questions at the molecular level. In the mixed crystals, the NMR signals assigned to the host remained unperturbed, while signals of 1 were different from those observed in its pure crystal phases (racemic and enantiomorphous). Two different types of spectra were observed from samples obtained in different mixed crystallization experiments. We postulate that two groups of signals in one type arise from disorder of the guest in the crystal host when guest molecules crystallize in their two lowest energy conformers. In contrast, ordered mixed crystallization in the second type results in one signal assigned to the guest in its lowest energy conformer. These conclusions are supported by molecular mechanics calculations carried out for gas phase and model crystal systems.

The electronic spectrum of acenaphthylene

The electronic absorption spectrum of acenaphthylene has been measured in the vapor and pure crystal phases, and in single crystal matrices of acenaphthene, fluorene, naphthalene, and durene. Acenaphthylene preferentially occupies one of the two inequivalent types of sites in the acenaphthene lattice. The first three transitions are polarized, respectively, along the long, short, and long molecular axes. Intensity stealing by b 2 vibrations is observed in the first system. An X-ray investigation of the acenaphthylene crystal shows that the molecular C 2 and crystal b axes coincide.

Phase Equilibria in the System NaF‐ThF4‐UF4

Phase equilibria in the condensed system NaF‐ThF4‐UF4 were determined by cooling‐curve and thermal‐gradient quenching experiments from the liquidus to ∼450°C. A phase diagram of the ternary system was constructed, showing three singular points and eleven invariant points, including two eutectics, occurring in association with the primary phases of ten solid solutions and two pure solids. The eutectic mixture having the composition 75.5NaF‐10.5ThF4‐14UF4 (mole %) melts at 575°C, the lowest liquidus temperature in the system. Except for NaF, NaF‐ThF4, and ThF4‐UF4 solid solutions, phases crystallizing from molten NaF‐ThF4‐UF4 mixtures are solid solutions formed by interchange of U4+ and Th4+ ions in NaF‐ThF4 and NaF‐UF4 compounds. No ternary compounds were found. Phase diagrams of the systems NaF‐ThF4 and NaF‐UF4, revised in the course of this study to include the newly identified phases, 7NaF.2ThF4 and 7NaF.2UF4, are presented. X‐ray diffraction and optical data are given for the pure crystal phases, 4NaF.ThF4, 7NaF.2ThF4, 7NaF.2UF4, 3NaF.UF4, and for 3NaF.2ThF4‐5NaF.3UF4 solid solutions. The system is unique among the fluoride systems reported in containing so wide a variety of substitutional solid solutions and in containing a continuous solid solution formed of binary compound pairs 3NaF.2ThF4 and 5NaF.3UF4 which are isomorphous but of different stoichiometry.