Mechanism of the nanocrystals formation of the spinel structure in the MgO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system under the hydrothermal conditions

Using the method of hydrothermal synthesis,the nanoparticles of magnesium-aluminum spinel were obtained with a crystallite size of 40–50 nm. The sequence was determined of the chemical transformations under hydrothermal conditions of the initial magnesium-aluminum hydroxides obtained by co-precipitation, leading to the formation of nanoparticles MgAl₂O₄.     

Synthesis of Si-MCM-41 from ternary SiO<Subscript>2</Subscript>–CTAOH–H<Subscript>2</Subscript>O system via dry gel conversion route

Steam assisted dry gel conversion method was employed for the synthesis of Si-MCM-41 from ternary SiO₂:CTAOH:H₂O systems wherein fumed silica was used as a source of silica. The influence of synthesis time, molar ratios of CTAOH/SiO₂ in dry gel and the water content at the bottom of autoclave on the quality and formation of mesophases has been investigated. Powder XRD, N₂ adsorption–desorption, TEM and hydrothermal stability test were the techniques used for sample characterization. Keeping molar ratio of CTAOH/SiO₂ constant, shorter synthesis time, lower unit cell parameter and d spacing were observed when steam assisted dry gel conversion method was employed in place of conventional hydrothermal method. There exists an optimum lower limit for water content at the bottom of autoclave for reducing the synthesis period. Keeping synthesis temperature and CTAOH/SiO₂ molar ratio fixed, Si-MCM-41 with improved hydrothermal stability was obtained by steam assisted dry gel conversion route.     

Thermal synthesis of the CeO<Subscript>2</Subscript>-PrO<Subscript>2</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>pigments

Summary The synthesis of new compounds based on the CeO₂-PrO₂-Nd₂O₃system, which can be used as pigments for colouring of ceramic glazes, is investigated in our laboratory. The optimum conditions for the syntheses of these compounds have been estimated. The methods of thermal analysis provided first information about the temperature region of the formation of the pigments investigated. The synthesis of these compounds was followed by thermal analysis using STA 449/C Jupiter (Netzsch, Germany).     

Kinetics of formation of barium tungstate in equimolar powder mixture of BaCO<Subscript>3</Subscript> and WO<Subscript>3</Subscript>

The formation of Barium monotungstate (BaWO₄) particles in equimolar powder mixtures of BaCO₃ and WO₃ was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO₂) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The x–t and x–T data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO₃ species across the product layer (BaWO₄), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.     

Synthesis and crystallization kinetics of the novel ion exchanger Na<Subscript>4</Subscript>Ti<Subscript>4</Subscript>Si<Subscript>3</Subscript>O<Subscript>10</Subscript> for cesium removal

Thermodynamics and crystallization kinetics of the hydrothermal synthesis of Na₄Ti₄Si₃O₁₀ (NaTS) were systemically studied by both experiments and model simulation. Experimental results showed that the curve of crystallinity with time was a characteristic signmoid in the shape that indicated the crystallization of Na₄Ti₄Si₃O₁₀ was a typical spontaneous nucleation process on the laboratory scale. Crystallization of NaTS belongs to the liquid-liquid transformation mechanism and the reaction is endothermic (ΔH = 15.3 kJ/mol). A mathematic model of crystallization kinetics was developed to simulate the synthesis of NaTS. Runge-Kutta and simplex methods were adopted to solve the partial differential equations. Model results fitted well with the experimental data and showed that the synthesis process belongs to spontaneous nucleation and crystal growth. Moreover, the very small crystal growth constant (5.6·10⁻⁷) and gel dissolution constant (7.0·10⁻⁷) indicate they are the rate-limiting steps of the whole synthesis process.     

One-pot synthesis and photoluminescence properties of core/porous-shell olive-like BaWO4 microstructure by a template-assisted hydrothermal method

Core/porous-shell olive-like crystalline BaWO₄ is synthesized by a combined simple hydrothermal method and soft template approach. The prepared product shows an olive-like shape with diameter of ～2 μm, length of ～4 μm, and the thickness of the shell of about 65 nm, which are orderly assembled by many nanoparticles. A possible formation mechanism of olive-like BaWO₄ microstructure involving interfacial recognization of ions, nucleation, aggregation, in situ growth and Ostwald ripening process is proposed. Polyacrylic acid sodium (PAAS) as a template plays an important role in inducing the nucleation and growth of olive-like BaWO₄ microcrystalline. Other shapes of BaWO₄ microcrystalline are also fabricated by varying the concentration of PAAS and Ba²⁺. The olive-like product with a core-shell structure which exists a large number of pores on crystal surface shows excellent photoluminescence property, which have potentially applied prospects in fields such as light display systems etc.     

Prenucleation formations in control over synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocrystalline powders

Nanocrystalline cobalt ferrite powders were synthesized by hydrothermal treatment of co-precipitated hydroxides in the conditions of an external heating of the autoclave and under microwave heating of the reaction medium. In the microwave-heating mode, the prenucleation clusters formed under ultrasonic treatment of a suspended mixture of cobalt and iron hydroxides is transformed into CoFe₂O₄ nanocrystals during the first minute of synthesis at a temperature satisfying the equilibrium-existence conditions of cobalt ferrite. In the case of a slow external heating of the autoclave, there is no effect of this kind, which is attributed to the disintegration of the prenucleation clusters before the dehydration of the hydroxides to give crystalline cobalt ferrite becomes thermodynamically favorable. The main factor determining the increase in the formation rate of crystallites of CoFe₂O₄ nanopowders and the decrease in their size is the generation of prenucleation centers in the starting mixture of cobalt and iron hydroxides.     

Effect of heat treatment on structural-chemical transformations in magnesium hydrosilicate [Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript>] nanotubes

The structural-chemical transformations in nanotubular magnesium hydrosilicate of composition Mg₃Si₂O₅(OH)₄ (chrysotile) obtained by hydrothermal synthesis were studied in heating to 1200°C.     

Hydrothermal synthesis of nanosized and amorphous alumina in the ZrO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-H<Subscript>2</Subscript>O system

The reciprocal influence of components on the chemical and structural transformations in the ZrO₂-Al₂O₃-H₂O system during nanoparticle formation under hydrothermal conditions is considered. The possibility of formation of amorphous aluminum oxide under hydrothermal conditions is found as a result of the influence of zirconia nanoparticles on the crystallization.     

NH<Subscript>4</Subscript>V<Subscript>3</Subscript>O<Subscript>7</Subscript>: Synthesis,morphology, and optical properties

The effect of the method used for the synthesis of NH₄V₃O₇ on its morphology, textural parameters, and optical properties was studied. Ammonium vanadate NH₄V₃O₇ was prepared by treating NH₄VO₃ in the presence of citric acid under hydrothermal (4.0 ≤ pH ≤ 5.5, T = 180–200°C, 48 h) and microwave–hydrothermal (3.5 ≤ pH ≤ 5.0, T = 180–220°C, 20 min) conditions. Self-assembled NH₄V₃O₇ microcrystals crystallizing in monoclinic system with unit cell parameters a = 12.247(5) Å, b = 3.4233(1) Å, c = 13.899(4) Å, β = 89.72(3)°, and V = 582.3(4) ų (space group P2₁) were shown to be formed independently of the method used to treat the reaction mixture. The morphology of NH₄V₃O₇ particles was shown to depend on рН of the reaction mass and the method of synthesis. The structural features of NH₄V₃O₇ were studied by IR, UV, and Vis spectroscopy, and the optical bandgap was determined.     

An alternative synthetic process of <Emphasis Type="Italic">p</Emphasis>-acetaminobenzenesulfonyl chloride through combined chlorosulfonation by HClSO<Subscript>3</Subscript> and PCl<Subscript>5</Subscript>

p-Aminobenzene sulfonamide (sulfanilamide, SN) is the simplest and most-used sulfonamide medicine. The key step of SN production via the commonly used chlorosulfonic acid routine is the synthesis of p-acetaminobenzenesulfonyl chloride (P-ASC). A large amount of HSO₃Cl has to be used in the traditional process, which results in serious environmental problems. In this study, an alternative chlorosulfonic acid process to synthesize P-ASC was investigated by partially substituting HSO₃Cl by PCl₅ as the chlorination agent. Compared with the traditional process, the molar ratio of HSO₃Cl to acetanilide (the main raw material) can be decreased from 4.96 to 2.1 using CCl₄ as the diluent; also, addition of a small amount of NH₄Cl was found to significantly increase the P-ASC yield. Operating conditions of the reaction were studied first by single-factor experiments and later by orthogonal experiments to obtain optimum operating conditions under which the P-ASC yield can reach as high as 86.3 %.     

Experimental Studies on Isonicotinato Cadmium(II) Complex [Cd(C<Subscript>6</Subscript>H<Subscript>4</Subscript>NO<Subscript>2</Subscript>)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>] and Density Functional Calculations

Isonicotinato cadmium(II) complex [Cd(C₆H₄NO₂)₂(H₂O)₄] has been synthesized by hydrothermal method and characterized by elemental analysis, electronic-spectra and thermogravimetric analysis. Density functional theory (DFT) method calculations of the structure, atomic charges distribution, electronic spectra, natural population analysis and the thermodynamic properties at different temperatures have been performed. The calculated results show the electronic transitions are mainly derived from the contribution of bands π → π^* and the decomposition of the title compound should first occur at the bond of Cd—O, then at the bond of Cd—N, which agrees very well with the experimental data.     

Development of Accurate Chemical Equilibrium Models for Oxalate Species to High Ionic Strength in the System: Na—Ba—Ca—Mn—Sr—Cl—NO<Subscript>3</Subscript>—PO<Subscript>4</Subscript>—SO<Subscript>4</Subscript>—H<Subscript>2</Subscript>O at 25 °C

The development of an accurate aqueous thermodynamic model is described for oxalate species in the Na—Ba—Ca—Mn—Sr—Cl—NO₃—PO₄—SO₄—H₂O system at 25 °C. The model is valid to high ionic strength (as high as 10 mol·kg⁻¹) and from very acid (10 mol·kg⁻¹ H₂SO₄) to neutral and basic conditions. The model is based upon the equations of Pitzer and co-workers. The necessary ion-interaction parameters are determined by comparison with experimental data taken from the literature or determined in this study. The proposed aqueous activity and solubility model is valid for a range of applications from interpretation of studies on mineral dissolution at circumneutral pH to the dissolution of high-level waste tank sludges under acidic conditions.     

Synthesis of CeVO<Subscript>4</Subscript> Crystals with Different Sizes and Shapes

Tetragonal CeVO₄ was prepared through hydrothermal treatment and sonication method with the same precursor in the absence of any catalysts or templates, and the products were characterized by XRD, TEM and Raman. It is found that microrods, nanoparticles, nanorods and nanoplates have been obtained. The bigger nanorods produced through hydrothermal treatment have average diameters of 15–25 nm and lengths of 20–60 nm. The smaller nanorods prepared through ultrasound treatment have average diameters of 6–12 nm and lengths of 10–18 nm. Uniform nanoplates have been produced. The nanoplates produced through hydrothermal method are composed of CeVO₄ and CeO₂. The mechanism of shape changing has been discussed. And the existing vanadium which is sensitive to the pH value of synthesis solution may be a key factor for the resulted sizes and shapes of the obtained nanocrystals. The samples prepared through hydrothermal treatment and sonication method were used as the catalysts for the combustion of trichloroethylene to test their catalytic activity.     

Phase equilibria and isomorphism in the LiVWO<Subscript>6</Subscript>-NaVWO<Subscript>6</Subscript> system

Compounds of composition Li _x Na_{1 − x} VWO₆ (0 ≤ x ≤ 1), which are synthetic analogues of brannerite-type minerals, were produced for the first time by solid-state synthesis at high temperatures. The structure of the compounds and their unlimited miscibility in the solid phase in the LiVWO₆-NaVWO₆ binary system were determined by X-ray diffraction. The phase equilibrium diagram was studied by differential thermal analysis together with thermodynamic modeling. It was found that the system under investigation is described by the regular solid solutions model.     

Structural and thermal studies on the solid products in the system MnSeO<Subscript>3</Subscript>-SeO<Subscript>2</Subscript>-H<Subscript>2</Subscript>O

The solubility of MnSeO₃-SeO₂-H₂O system was studied in the temperature region 25–300°C. The compounds of the three-component system were identified by the Schreinemaker’s method. The phase diagram of manganese(II) selenites was drawn and the crystallization fields for the different phases were determined. Depending on the conditions for hydrothermal synthesis, MnSeO₃·H₂O, MnSeO₃·3/4H₂O, MnSeO₃·l/3H₂O and MnSe₂O₅ were obtained. The different phases were proven and characterized by chemical, powder X-ray diffraction and thermal analyses, as well as IR spectroscopy. The kinetics of dehydration and decomposition of MnSeO₃·H₂O was studied under non-isothermal heating. Based on 4 calculation procedures and 27 kinetic equations, the values of activation energy and pre-exponential factor in Arrhenius equation were calculated for both processes.     

Synthesis and Electrocatalytic Properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanocrystallites with Various Morphologies

Co₃O₄ crystallites with particle, plate-, tube-, rod- and sheet-like morphologies were successfully prepared by the calcination of the corresponding precursors synthesized via a precipitation or hydrothermal procedure. The morphologies of the precursors and Co₃O₄ nano-tubes were detected by field emission scanning electron microscopy (FE-SEM). The as-obtained Co₃O₄ samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and special surface area measurement (BET). The electrocatalytic activity of p-nitrophenol reduction with the Co₃O₄ products decorated on a glassy carbon electrode (GCE) was tested, respectively, using cyclic voltammetry (CV) in a basic solution. The results indicated that p-nitrophenol was reduced with higher current density but almost at a constant potential on the Co₃O₄/GCE in contrast with that on a bare GCE at the same conditions. The highly catalytic activity of the as-prepared Co₃O₄ in a basic solution suggested their wide applications in environmental treatment or organic synthesis.     

Hydrolysis of cellulose by the heteropoly acid H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The potential of heteropoly acid H₃PW₁₂O₄₀ to catalyze the hydrolysis of cellulose to glucose under hydrothermal conditions was explored. This technology could contribute to sustainable societies in the future by using cellulose biomass. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. A remarkably high yield of glucose (50.5%) and selectivity higher than 90% at 453 K for 2 h with a mass ratio of cellulose to H₃PW₁₂O₄₀ of 0.42 were achieved. This was attributed to the high hydrothermal stability and the excellent catalytic properties, such as the strong Brønsted acid sites. This homogeneous catalyst can be recycled for reuse by extraction with diethyl ether. The results illustrate that H₃PW₁₂O₄₀ is an environmentally benign acid catalyst for the hydrolysis of cellulose.     

Hydrothermal synthesis,characterization, and thermal properties of alumino silicate azide sodalite,Na<Subscript>8</Subscript>[AlSiO<Subscript>4</Subscript>]<Subscript>6</Subscript>(N<Subscript>3</Subscript>)<Subscript>2</Subscript>

First time we report the synthesis, structural characterization and thermal behavior of an unusual N₃ ^? containing alumino-silicate sodalite mineral. Azide sodalite, Na₈[AlSiO₄]₆(N₃)₂ has been synthesized under hydrothermal conditions at 433 K in steel lined Teflon autoclave. The structural and microstructural properties of azide sodalite mineral was characterized by various methods including FT-IR, XRD, SEM, TGA, and MAS NMR. Crystal structure have been refined by Rietveld method in \(P\bar 43n\) space group, indicating that the N₃ ^? sodalite has cubic in lattice. High temperature study was carried out to see the effect of thermal expansion on cell dimension (a ^o) of azide sodalite. Thermal behavior of sodalite was also assessed by thermogravimetric method.     

Comparison of different soft chemical routes synthesis of submicro-LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> and their influence on its electrochemical properties

A comparative study of submicro-crystalline spinel LiMn₂O₄ powders prepared by two different soft chemical routes such as hydrothermal and sol–gel methods is made. The dependence of the physicochemical properties of the spinel LiMn₂O₄ powder has been extensively investigated by using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscope, cyclic voltammogram, charge–discharge test, and electrochemical impedance spectroscopy (EIS). The results show that the electrochemical performances of spinel LiMn₂O₄ depend strongly upon the synthesis method. The LiMn₂O₄ powder prepared by hydrothermal route has higher specific capacity and better cycling performance than the one synthesized from sol–gel method. The former has the max discharge capacity of 114.36 and 99.78 mAh g⁻¹ at the 100th cycle, while the latter has the max discharge capacity of 98.67 and 60.25 mAh g⁻¹ at the 100th cycle. The selected equivalent circuit can fit well the EIS results of synthesized LiMn₂O₄. For spinel LiMn₂O₄ from sol–gel method and hydrothermal route in the first charge process R _SEI remain almost invariable, R _e and R _ct first decreasing and then increasing with the increase of polarization potential.