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Hydrothermal Synthesis (hydrothermal + synthesis)
Selected AbstractsFirst Examples of Ternary Lanthanide 2,2,-Diphenyldicarboxylate Complexes: Hydrothermal Syntheses and Structures of Lanthanide Coordination Polymers of 2,2,-Diphenyldicarboxylic Acid and 1,10-PhenanthrolineEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2003Yibo Wang Abstract In the four new lanthanide coordination polymers {[La2(2,2,-dpdc)3(phen)(H2O)]·2H2O}n (1), [Eu2(2,2,-dpdc)3(phen)(H2O)2]n (2), {[Ln2(2,2,-dpdc)3(phen)2(H2O)2]·4H2O}n [Ln = Tb (3), Yb (4)] (2,2,-dpdc = 2,2,-diphenyldicarboxylate, phen = 1,10-phenanthroline), prepared by hydrothermal synthesis, the 2,2,-dpdc dianion affords tetradentate, pentadentate, and hexadentate coordination modes. Complex 1 is a two-dimensional network of infinite 1-D chains assembled through ,,, interactions, with nine- and ten-coordinate La3+, and arranged in wave-like layers. In 2, Eu3+ possesses nine- and ten-coordinate geometries bridged by 2,2,-dpdc ligands to give a 3-D structure. The isomorphous complexes 3 and 4, in which Tb3+ and Yb3+ ions are both nine-coordinate, have two-dimensional structures of 1-D zigzag chains stacked via hydrogen bonds and ,,, interactions of phen molecules. The high-resolution emission spectrum of 2 shows two Eu3+ ion sites, which is consistent with the results of the X-ray crystal structure analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Hydrothermal Syntheses of Gold Nanocrystals: From Icosahedral to Its Truncated Form,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2008J. Xu Abstract We have successfully controlled the shape of gold nanocrystals through a simple and low-cost hydrothermal method based on a modified polyol process. Well-defined gold nanocrystals of icosahedral shape were synthesized in high yields by the rapid reduction of gold precursors with ethylene glycol (EG) in the presence of poly(vinyl pyrrolidone) (PVP) under hydrothermal conditions for 1 h. Truncated icosahedra (football-shaped) have been prepared for the first time by prolonging the reaction time to 4 h. Both nanocrystal shapes were obtained quantitatively. Addition of citric acid inhibits the shape-change process (from icosahedron to truncated icosahedron) by blocking oxidative etching, while addition of Fe(III) facilitates the shape-change process by enhancing oxidative etching. We propose that growth of truncated icosahedra can be induced and maintained through interplay of the following processes: generation of multiple twinned seeds, shape- and size-focusing by Ostwald ripening, and oxidative etching and preferential growth on the {100} face. [source] ChemInform Abstract: Hydrothermal Syntheses and Crystal Structures of Two Hybrid Materials Constructed from Polyoxometalate Clusters and Metal,Dipyridine Complexes.CHEMINFORM, Issue 25 2008Guangzhe Li Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Lone-Pair Self-Containment in Tellurite Tubes: Hydrothermal Syntheses and Structures of BaTe3O7 and BaTe4O9.CHEMINFORM, Issue 28 2002Magnus G. Johnston Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Hydrothermal Syntheses, Structures, and Properties of the New Uranyl Selenites Ag2(UO2)(SeO3)2, M[(UO2)(HSeO3)(SeO3)] (M: K, Rb, Cs, TI), and Pb(UO2)(SeO3)2.CHEMINFORM, Issue 19 2002Philip M. Almond Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: The First Organically Templated Open-Framework Niobium Silicate and Germanate Phases: Low-Temperature Hydrothermal Syntheses of [(C4N2H11)Nb3SiO10] (NSH-1) and [(C4N2H11)Nb3GeO10] (NGH-1).CHEMINFORM, Issue 46 2001Robin J. Francis Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydrothermal Syntheses, Crystal Structure and Thermal Behavior of [(CH3)2NH2]2[B5O6(OH)4]2·[HCON(CH3)2] and [NH3CH2CH2NH3]2[B14O20(OH)6]CHINESE JOURNAL OF CHEMISTRY, Issue 11 2009Ping Li Abstract Two novel organic base templated nonmetal borates [(CH3)2NH2]2[B5O6(OH)4]2·[HCON(CH3)2] (?) and [NH3CH2CH2NH3]2[B14O20(OH)6] (II) have been synthesized under hydrothermal conditions, and characterized by elemental analyses, FT-IR spectroscopy, X-ray diffraction, and TG-DTA. Their crystal structures were determined from single crystal X-ray diffraction. The crystal structure of compound I is characterized by forming a 3D supramolecular structure with large channels along axes b and c through OH···O hydrogen-bonding among the [B5O6(OH)4], anions. The crystal structure of compound II is characterized by forming a 3D supramolecular structure with large channels along axis a and direction [111] through OH···O hydrogen-bonding among the [B14O20(OH)6]4, anions. The templating organic amine cations in I and II are both obtained through in situ hydrothermal reactions, and are both located in the channels of the 3D supramolecular structure, respectively. Their thermal behavior has been also investigated. [source] Hydrothermal Synthesis and Structural Characterization of the High-Valent Ruthenium-Containing Polyoxoanion [{PW11O39}2{(HO)RuIV,O,RuIV(OH)}]10,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2008Su-Wen Chen Abstract The high-valent ruthenium-containing [{PW11O39}2{(HO)RuIV,O,RuIV(OH)}]10, anion (1) has been synthesized by hydrothermal reaction and characterized by X-ray diffraction, IR, multinuclear (31P and 183W) NMR spectroscopy andelectrochemistry. Single-crystal analysis was carried outon Rb10[{PW11O39}2{(HO)RuIV,O,RuIV(OH)}]·21H2O, which crystallizes in the monoclinic system, space group P21/n, with a = 11.1912(14), b = 21.9257(12), c = 38.7310(96) Å, , = 94.682(19)°, V = 9472(3) Å3, Z = 4. Polyanion 1 consists of two lacunary [,-PW11O39]7, anions connected by a linear {(HO)Ru,O,Ru(OH)}4+ unit. Each ruthenium ion achieves six-coordination through interaction with two terminal oxo ligands from the lacuna of each [PW11O39]7, anion.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Microwave-Assisted Hydrothermal Synthesis of Structurally and Morphologically Controlled Sodium Niobates by Using Niobic Acid as a PrecursorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Amauri J. Paula Abstract There are many advantages to using a microwave as a source of heat in hydrothermal reactions. Because it is a quick and homogeneous way to crystallize ceramic powders, it was used in this work for the production of antiferroelectric sodium niobate (NaNbO3) in a cubic-like form and its intermediary phase, disodium diniobate hydrate (Na2Nb2O6.H2O), with a fiber morphology. The syntheses were carried out by treating niobic acid (Nb2O5·nH2O) with NaOH. By changing the reaction time and the concentration of the reactants, particles with different structures and different morphologies could be obtained. The structural evolution of the products of this reaction was elucidated on the basis of the arrangement of the NbO6 octahedral units. Conclusive results were obtained with morphological and structural characterizations through XRD, TEM, MEV, and NMR and Raman spectroscopy. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Three Novel Functional CdII Dicarboxylates with Nanometer Channels: Hydrothermal Synthesis, Crystal Structures, and Luminescence PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2007Yu-Peng Tian Abstract Three novel functional transition-metal complexes with H2A (H2A = 9-ethylcarbazole-3,6-dicarboxylic acid), Cd(HA)2(H2O)2 (1), [Cd(A)(phen)]·1.5H2O (2) (phen = 1,10-phenanthroline), and Cd(HA)2(bipy) (3) (bipy = 4,4,-bipyridine), have been successfully synthesized by a hydrothermal synthetic method and characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence. The results show that all of the complexes contain nanometer channels, while the coordination modes were changed by the addition of the mixed ligands. The 2D supramolecular open-framework 1 is constructed through hydrogen-bond and aromatic ,,, interactions. 2D coordination polymer 2 is constructed by ,,, interactions between adjacent metal-organic polymeric coordination chains. Interestingly, the 3D supramolecular architecture of 3 first formed 2D grid layers from 1D chains by intermolecular hydrogen bonds and then extended into a 3D structure through aromatic ,,, interactions. Furthermore, strong emissions from these complexes were also changed by the coordination modes in the solid state. However, complexes 1,3 show high thermal stability.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Hydrothermal Synthesis, Structure and Magnetic Properties of a One-Dimensional Iron Arsenate, 1,[NH3(CH2)2NH(CH2)2NH3][Fe2F4(HAsO4)2]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004Sandip Chakrabarti Abstract A novel one-dimensional iron arsenate, 1,[NH3(CH2)2NH(CH2)2NH3][Fe2F4(HAsO4)2], built up exclusively from SBU-4 units (two octahedral units sharing an edge and connected through two tetrahedra) with Fe3+ ions in the high-spin state has been synthesized by hydrothermal methods. Structure elucidation reveals that the compound is a two-leg ladder with very weak antiferromagnetic exchanges along the chains. The magnetic susceptibility data show activated behaviour at T = 14 K, suggesting a finite spin gap between the nonmagnetic ground state and the excited triplet state. We have estimated the exchange parameters theoretically based on the S = 5/2 Majumdar,Ghosh model with frustrations and dimerisations. Although the magnetic gap is quite small, this is the first example, to the best of our knowledge, where the rungs with two S = 5/2 spins form strong singlet dimers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Hydrothermal Synthesis and Characterization of a Novel Sinusoidal Layer Structure Constructed From Polyoxometalates and Coordination Complex FragmentsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2004Xiao-Bing Cui Abstract A novel polyoxometalate compound, [As8V14O42(SO4)][Ni(en)2]3·4.5H2O (1), has been synthesized by a hydrothermal method and characterized by X-ray crystallography, showing that the compound 1 is the first example of a sinusoidal layer structure constructed from polyoxometalates and coordination complex fragments. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Tris(8-hydroxyquinoline-5-sulfonate)aluminum Intercalated Mg,Al Layered Double Hydroxide with Blue Luminescence by Hydrothermal SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Shuangde Li Abstract Blue luminescent hybrid materials (DDS,AQS(x%)/LDH) are successfully prepared by co-intercalating tris(8-hydroxyquinoline-5-sulfonate)aluminum anions (AQS3,) and dodecyl sulfonate (DDS,) with different molar ratios into Mg,Al layered double hydroxides (LDHs) by the hydrothermal and solution co-precipitation methods. A film of the material on a quartz substrate is obtained by the solvent evaporation method. The results show the blue luminescence is remarkably different from the pristine Na3AQS, which has cyan luminescence (ca. 450,470 nm vs. 495 nm). Furthermore, the hydrothermal product of DDS,AQS(66.67%)/LDH exhibits optimal luminous intensity and a significantly enhanced fluorescence lifetime. Nuclear magnetic resonance and Fourier-transform infrared spectroscopy indicate that the cyan,blue luminescence transition is due to the isomerization of meridianal to facial AQS via ligand flip caused by a host,guest electrostatic interaction, in combination with the dispersion and pre-intercalation effect of DDS. The hydrothermal conditions can promote a more ordered alignment of the intercalated fac -AQS compared with alignment in the solution state, and the rigid LDHs environment can confine the internal mobility of AQS to keep the facial configuration stable. This stability allows a facile preparation of large amounts of blue luminous powder/film, which is a new type of inorganic,organic hybrid photofunctional material. [source] Hydrothermal Synthesis of Structure- and Shape-Controlled Manganese Oxide Octahedral Molecular Sieve NanomaterialsADVANCED FUNCTIONAL MATERIALS, Issue 9 2006W.-N. Li Abstract Highly uniform single-crystal Na-OMS-2 (OMS: octahedral molecular sieve), pyrolusite, and ,-MnO2 nanostructures with an interesting 3D urchinlike morphology have been successfully prepared using a hydrothermal method based on a mild and direct reaction between sodium dichromate and manganese sulfate. The crystal phases, shapes, and tunnel sizes of the manganese dioxide nanostructures can be tailored. Reaction temperature, concentrations of the reactants, and acidity of the solution play important roles in controlling the synthesis of these manganese dioxides. Field-emission scanning electron microscopy and transmission electron microscopy (TEM) studies show that the nanomaterials obtained are constructed of self-assembled nanorods. X-ray diffraction and TEM results indicate that the constituent manganese dioxide particles are single-crystalline materials. Energy dispersive X-ray analysis and magnetic studies imply that chromium cations may be incorporated into the framework and/or tunnels of the manganese dioxides. A mechanism for the growth of manganese dioxides with urchinlike architectures is proposed. [source] Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2003Y.-P. Fang Abstract In this paper, Tb(OH)3 and Y(OH)3 single-crystalline nanotubes with outer diameters of 30,260,nm, inner diameters of 15,120,nm, and lengths of up to several micrometers were synthesized on a large scale by hydrothermal treatment of the corresponding oxides in the presence of alkali. In addition, Tb4O7 and Y2O3 nanotubes can be obtained by calcination of Tb(OH)3 and Y(OH)3 nanotubes at 450,°C. X-ray diffraction (XRD), field-emission scanning electron microscopy, transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry, and differential scanning calorimetry (DSC) have been employed to characterize these nanotube materials. The growth mechanism of rare earth hydroxide nanotubes can be explained well by the highly anisotropic crystal structure of rare earth hydroxides. These new types of rare earth compound nanotubes with open ends have uses in a variety of promising applications such as luminescent devices, magnets, catalysts, and other functional materials. Advantages of this method for easily realizing large-scale production include that it is a simple and unique one-pot synthetic process without the need for a catalysts or template, is low cost, has high yield, and the raw materials are readily available. The present study has enlarged the family of nanotubes available, and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials. [source] Hydrothermal Synthesis and Characterization of KxNa(1,x)NbO3 PowdersINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 6 2007Jun-Hai Lv NaNbO3, KNbO3, and KxNa(1,x)NbO3 powders were successfully prepared by the hydrothermal method. The phase of the products was identified to be orthorhombic structure by X-ray diffraction (XRD) technique, and the XRD results revealed that the x value of the KxNa(1,x)NbO3 gradually increased with the increase in the ratio of K+ to Na+ in alkaline solution. The morphology and the microstructure were investigated by scanning electron microscopy, energy-dispersive spectroscopy, and transmission electron microscopy, and the results indicated that the ratio of K+ to Na+ in the solution had a great effect on the morphology and the size of products. Na0.5K0.5NbO3 with morphotropic phase boundary composition could be synthesized when the molar ratio of K+ to Na+ was between 4:1 and 6:1 in the solution. A possible formation mechanism of the KxNa(1,x)NbO3 crystal was also proposed based on the experimental results. [source] Hydrothermal Synthesis of Alpha Alumina (,-Al2O3) Powders: Study of the Processing Variables and Growth MechanismsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Wojciech L. Suchanek Alpha alumina (,-Al2O3) powders and ,-Al2O3/boehmite (,-AlOOH) mixtures with controlled ,-AlOOH contents were synthesized hydrothermally under alkaline or acidic conditions at 380°,435°C for 1,10 days, under 6.9,14.5 MPa pressure, from concentrated precursors without stirring. The precursors were formed by mixing different types of aluminum hydroxides with water, and optionally with ,-Al2O3 seeds, hydrogen peroxide, sulfuric acid, dopants (i.e., KMnO4), and/or other additives. The experiments were performed on industrial scale in large production autoclaves. The synthesized ,-Al2O3 powders exhibited up to 100% phase purity, 99.98% chemical purity, equiaxed morphology, low aggregation levels, narrow crystallite size distributions with primary particle sizes ranging between 100 nm and 40 ,m, and high reproducibility. Precursor types, seeds, chemical additives, and temperature/time of the hydrothermal synthesis were found to govern properties of the powders. Different growth mechanisms for nanosized and rough powders are discussed. Results of this study enable the use of hydrothermal ,-Al2O3 powders in a multitude of applications, and make their hydrothermal production a commercial reality. [source] Hydrothermal Synthesis and Spark Plasma Sintering of (K, Na)NbO3 Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Nan Liu A facile hydrothermal route was adopted for synthesis of lead-free piezoceramics (K, Na)NbO3 powders. The influences of temperature and KOH/NaOH concentration on the resultant powders were investigated. Although two similar perovskite phases appeared when K/Na ratio tended toward 1:1, the two-phase coexistence tendency was weakened by increasing hydrothermal reaction temperature, and consequently only one phase could be obtained after spark plasma sintering. Reasonably good ferroelectric and piezoelectric properties were obtained for the samples after postannealing, whose piezoelectric constant (d33) reached 135 pC/N. The optimal remnant polarization (Pr) and mechanical quality factor (Qm) were 26.2 ,C/cm2 and 164, respectively, which were both twice as much as those of the samples using powders prepared from solid-state reaction. [source] Solid-Based Hydrothermal Synthesis and Characterization of Alumina Nanofibers with Controllable Aspect RatiosJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009Shou-Cang Shen Nanofibers of AlOOH with controllable aspect ratios have been synthesized by a facile steam-assisted solid-phase crystallization route. The morphology and aspect ratios of resulting AlOOH nanofibers were significantly influenced by the alkaline medium used in the preparation of solid precipitates from Al(NO3)3 solution. When tetramethylammonium hydroxide was used for precipitation, straight rod-like nanofibers with aspect ratios of 10,20 were obtained. The use of other tetra-alkylated ammonium hydroxides, such as tetraethylammonium hydroxide, tetrapropylammonium hydroxide or tetrabutylammonium hydroxide, led to the formation of long wire-like nanofibers with aspect ratios up to 150. After thermal treatment at 600°C, the morphologies of the one-dimensional nanostructures were well preserved while the crystal structure was converted to ,-alumina. The wire-like nanofibers of alumina possessed higher thermal stability than alumina nanorods, and both exhibited much higher stability as compared with alumina micropowder. [source] Hydrothermal Synthesis of Ba-Hexaferrite NanoparticlesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2007Miha Drofenik Barium hexaferrite BaFe12O19 nanoparticles with a single-domain size were synthesized using a controlled hydrothermal process involving the LaMer,Dinger principle and the Ostwald ripening mechanism. Nanocrystalline particles of BaFe12O19 were obtained when the molar ratio of the precursor composition Ba(OH)2·8H2O/,-Fe2O3 was 0.3 and the concentration of the suspension was about 1 wt%. The as-synthesized crystalline BaFe12O19 platelets approximately 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 Am2/kg. [source] Hydrothermal Synthesis and Characterization of CdWO4 NanorodsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Yonggang Wang Cadmium tungstate (CdWO4) nanorods were successfully synthesized by a hydrothermal process at as low a temperature as 70°C. The products were characterized by X-ray powder diffraction, transmission electron microscopy, and photoluminescent spectra techniques. The results showed that the morphology of nanocrystallites significantly varied with the reaction temperature, and CdWO4 nanorods exhibited a better luminescent property than nanofibers. [source] Preparation of Tubular Silicalite Membranes by Hydrothermal Synthesis with Electrophoretic Deposition as a Seeding TechniqueJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2006Hideyuki Negishi Preparation of tubular silicalite membranes by hydrothermal synthesis with electrophoretic deposition (EPD) as a seeding technique was investigated. Two micrometers of small silicalite seeds were produced by an open-system hydrothermal synthesis at 100°C. These seeds were dispersed in 1-propanol and seeded on porous tubular stainless-steel supports by EPD; it had a high productivity and uniformity. The seeded support was then hydrothermally treated, and a tubular silicalite membrane was obtained. The pervaporation performance of this membrane showed a separation factor , of 70 with a total flux of 0.35 kg·(m2·h),1 for a 5 vol% EtOH aqueous solution at 30°C. [source] Hydrothermal Synthesis of Thin Films of Barium Titanate Ceramic Nano-Tubes at 200°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2003Nitin P. Padture§ A novel, low-temperature synthesis method for producing BaTiO3 thin films patterned in the form of nano-tubes ("honeycomb") on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (,200,300-nm thickness) of amorphous titanium oxide nano-tube (,100-nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2, where the nano-tube arrays serve as templates for their hydrothermal conversion to polycrystalline BaTiO3 nano-tubes. This opens the possibility of tailoring the nano-tube arrays and of using various precursor solutions and their combinations in the hydrothermal bath, to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic device applications but also in biomedical applications, where patterned thin films are also desirable. [source] Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide PowdersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Nan-Chun Wu Well-crystallized cerium(IV) oxide (CeO2) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO2 crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO2 crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO2 crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains. [source] Hydrothermal Synthesis of Tetragonal Barium Titanate from Barium Chloride and Titanium Tetrachloride under Moderate ConditionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Huarui Xu Tetragonal BaTiO3powders were prepared hydrothermally at 240°C, in only 12 h, using BaCl2·2H2O and TiCl4, which are rather easy to manipulate. Characterization via X-ray diffractometry, scanning electron microscopy, Brunauer,Emmett,Teller analysis, and differential scanning calorimetry confirmed that increasing the NaOH excess concentration (from 0.5M to 2.0M) and decreasing the initial TiCl4concentration (from 0.625M to 0.15M) promotes the formation of tetragonal BaTiO3powders. After reaction, the powders were proved to be phase-pure BaTiO3, with no impurities, such as Cl, and CO32,. [source] Hydrothermal Synthesis and Formation Mechanisms of Lanthanum Tin Pyrochlore OxideJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Jooho Moon Well-defined La2Sn2O7 with a phase-pure pyrochlore structure was produced by hydrothermal synthesis at temperatures as low as 200°C. Production of phase-pure La2Sn2O7 requires a pH above 10, and higher pH accelerates the crystallization process. The synthesis produced spherical particles of average particle size ,0.59 ,m (±0.12) and surface area ,14.1 m2/g. SEM and TEM observation for morphologic evolution and kinetic analysis during crystallization indicated that La2Sn2O7 formation probably proceeds via a two-step reaction. First a transient dissolution,precipitation occurs. Then the primary crystallites aggregate because of their colloidal instability, and heterocoagulation with the lanthanum hydrous oxide precursor particles also occurs. The sluggish reaction rate at the later stage of reaction is characterized by an insitu transformation, where the soluble tin species is diffused through the porous La2Sn2O7 aggregates to react with entrapped lanthanum precursors. [source] Sm3+ -Doped Bi2O3 Photocatalyst Prepared by Hydrothermal SynthesisCHEMCATCHEM, Issue 4 2009Jakkidi Krishna, Reddy Abstract Bi2O3 and Sm3+ -doped Bi2O3 visible-light-active photocatalysts with different Sm3+ loadings (0.5, 1.0, and 2.0,wt,%) were synthesized by a hydrothermal method. The structural properties of the prepared catalysts were studied by X-ray diffraction (XRD), BET surface area, UV/Vis diffuse reflectance (DRS), FTIR, and X-ray photoelectron (XPS) spectroscopic techniques. The XRD spectra of the Sm-doped Bi2O3 catalysts calcined at 550,°C show only the characteristic peaks of Bi2O3. A high red shift in the range 450,600,nm was detected in the DRS band, leading to a large decrease in the band-gap energy from 2.82 to 2.0,eV. This red shift increased with increasing Sm content. XPS results revealed that Sm interacted with Bi2O3, wherein both Bi and Sm were in the +3 oxidation state. The photocatalytic activities of the catalysts were evaluated for the degradation of methylene blue and phenol under solar irradiation. Of all of the catalysts prepared, the Sm3+ -doped Bi2O3 with a Sm loading of 1,wt,% gave the best photocatalytic activity. [source] ChemInform Abstract: Template-Free Hydrothermal Synthesis and Photocatalytic Performances of Novel Bi2SiO5 Nanosheets.CHEMINFORM, Issue 48 2009Ruigen Chen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Hydrothermal Synthesis of Vanadium Oxyfluoride Chains Incorporating Covalently Bound Copper Coordination Complexes.CHEMINFORM, Issue 51 2008Thushitha Mahenthirarajah Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A 2-D 3d,4f Heterometallic Compound: Hydrothermal Synthesis, Structure and Magnetic Properties.CHEMINFORM, Issue 40 2008Ning Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] | ||||||||||||||||