Crystallization of hydrous zirconia and hafnia during hydrothermal treatment

The products of microwave-hydrothermal (MW-HT) treatment of amorphous hydrous zirconia and hafnia xerogels were studied by powder X-ray diffraction and thermal analysis. Decreasing gel precipitation pH leads to an increase in ZrO₂ and HfO₂ crystallization rates and enhances the formation of stable monoclinic ZrO₂.     

Transformations of hydrated titanium dioxide in hydrothermal treatment

X-ray diffraction analysis, transmission electron microscopy, IR spectroscopy, mass spectrometry, chemical analysis, and thermogravimetry were used to study transformations in the course of a hydrothermal treatment (150–240°C of samples of hydrated titanium dioxide produced by thermal hydrolysis of sulfuric acid solutions of titanium(IV) compounds), in water. The dependences of the dispersion and chemical composition of the samples obtained on the thermal treatment temperature were determined.     

Peculiarities of phase transformations in aqueous isopropanol solutions

Peculiarities of phase transformations in aqueous isopropanol solutions are studied in the range from room temperature to −15°C. It is found that solution cooling results in the formation of macroaggregates with regular geometrical shapes, which are dispersed in the liquid phase and directedly move in the field of a temperature gradient. In aqueous isopropanol solutions with concentrations of 10–30 vol %, the aggregates are formed at temperatures of −10 to −15°C. The average aggregate size is several millimeters. Under the action of a temperature gradient, the aggregates move to the region of higher temperatures. At temperature gradients of 1–2 K/cm, the aggregate velocity is 1–2 mm/s. The characters of the motion and interaction of aggregates are very sensitive to the temperature distribution in a solution. After the aggregate motion ceases, crystallization of the liquid phase that initially is outside of the aggregates is observed.     

Liquid-solid phase transformation of potassium iodide aqueous solutions of different concentrations held inside a porous material

Calorimetric analysis shows a succession of transformations inside and outside the pores, whose characteristics depend on the concentration of the solution and the amount of porous body present.For a given porous body, whatever the initial concentration of the solution, the capillary condensate concentration evolves systematically, during cooling, towards the eutectic concentration even if the initial salt concentration is higher than the eutectic one. It should be noted that this phenomenon indicates migration outside the pores of water or potassium iodide according to the initial concentration.For various samples whose pore size is decreasing, successive solidification of divided water and eutectic occurs at decreasing temperatures. The freezing temperature depression of water in divided KI solutions does not seem to be a function of the salt concentration but is dependent mainly on the division effect. A nearly linear relationship between pore radius and the reciprocal of temperature depression may experimentally be established for divided eutectic.

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Zusammenfassung Kalorimetrische Analyse zeigt eine Reihe von Umwandlungen inner- und außerhalb von Poren, wobei die Charakteristik der Umformungen von der Konzentration der Lösung sowie von der Menge des anwesenden porösen Körpers abhängt. Bei einem gegebenen porösen Körper verändert sich die Konzentration des Kapillarkondensates unabhängig von der Ausgangskonzentration systematisch immer in Richtung der eutektischen Konzentration, auch wenn die Salzkonzentration zu Beginn über der eutektischen Konzentration liegt. Man muß bemerken, daß diese Erscheinung je nach Ausgangskonzentration auf Migration von Wasser oder Kaliumjodid außerhalb der Poren hinweist.Für verschiedene Proben mit abnehmender Porengröße findet bei sinkender Temperatur ein nacheinanderfolgendes Erstarren von getrenntem Wasser und Eutektikum statt. Die Gefrierpunktserniedrigung von Wasser in derartig getrennten KI-Lösungen scheint nicht eine Funktion der Salzkonzentration zu sein sondern hauptsächlich vom Separierungseffekt abzuhängen. Für unterteilte Eutektika konnte ein annähernd linearer Zusammenhang zwischen dem Porenradius und dem Reziproken der Temperaturerniedrigung festgestellt werden.

     

Thermal transformations of hydrous titanium dioxide

During heating hydrous titanium dioxide with a general empirical formula TiO₂·xH ₂O·ySO ₃ prepared by hydrolysis of titanium sulphate solution drying, dehydration, desulphurization and anatase — rutile transformation proceed. The studies applying the DTA, TG, DTG methods have been carried out. To separate the particular effects damp samples, dried up to constant mass samples as well as samples after removing sulphur compounds have been used.

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Zusammenfassung Während des Erhitzens von wasserhaltigem Titandioxid der allgemeinen Formel TiO₂ ·xH₂O ·ySO₃, hergestellt durch Hydrolyse von Titansulfatlösung, verlaufen Trocknung, Dehydratation, Desulfurisation und eine Anatas — Rutil Umwandlung. Die Untersuchungen wurden unter Anwendung von DTA, TG und DTG durchgeführt. Zur Unterscheidung der einzelnen Effekte wurden feuchte, bis zur Massekonstantheit getrocknete als auch entschwefelte Proben verwendet.

     

Structural parameters of aqueous solutions of potassium fluoride under hydrothermal conditions

The structural parameters of aqueous KF solutions with concentrations of 10 and 20 wt % in the temperature range 473–623 K (p 18.7–24.6 MPa), obtained by the method of integral equations, are presented and compared with the structural parameters under standard conditions. Regularities of the structure formation of the systems under hydrothermal conditions, connected with ionic hydration and association, are elucidated. It is established that within the studied temperature range the number of contact associates in the solutions is stabilized, implying the possibility of formation of crystallization centers.     

The effect of the ionic environment during precipitation on the structure of hydrous titanium dioxide

Summary Samples of titanium dioxide have been prepared by hydrolysis of alkyl titanates in sulphuric acid solution of differing concentrations. The sulphate content of the resulting precipitate has been determined, and the specific surface and pore volume investigated by sorption methods. The results show that the surface properties of the oxide are determined by the conditions of hydrolysis and subsequent precipitation. It has been found possible to reproduce within a few per cents the surface area and the pore volume of the samples. A model has been put forward to account for the observed phenomena, and an equation relating the specific surfaceS of the precipitate with the activityn of sulphate ions in the hydrolysing medium has been deduced:S=S ₀−k√n whereS ₀ andk are constants.

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Zusammenfassung Proben von Titandioxyd wurden durch Hydrolyse von Alkylanaten in Schwefels?urel?sung verschiedener Konzentration pr?pariert. Die Sulfatgehalte des resultierenden Niederschlags wurden bestimmt und die spezifische Oberfl?che und das Porenvolumen durch Sorptionsmethoden untersucht. Die Ergebnisse zeigen, da\ die Oberfl?cheneigenschaften des Oxydes durch die Bedingungen der Hydrolyse und die anschlie\ende F?llung bestimmt werden. Es war m?glich, die Oberfl?che und das Porenvolumen der Proben innerhalb weniger Prozente zu reproduzieren. Es wurde ein Modell entworfen, die beobachteten Ph?nomene zu erkl?ren, und eine Gleichung abgeleitet, die die spezifische Oberfl?cheS des Pr?zipitates mit der Aktivit?tn der Sulfationen im hydrolysierenden Medium in Beziehung setzt:S=S ₀−k√n;S ₀ undk=const.

     

Removal of aqueous As(III) and As(V) by hydrous titanium dioxide

Dissolved arsenic in drinking water is a global concern as it causes serious health problems. The purpose of this research was to study the applicability of an industrial intermediate product, a mixture of titanium hydroxide and titanium dioxide for removing aqueous arsenic. The material is common, inexpensive, and non-toxic, making it an attractive choice for drinking water purification. The kinetics and equilibrium of removing both primary inorganic arsenic forms, As(III) and As(V), were studied by separate batch experiments. The tested material functioned well in removing both of these arsenic forms. The apparent values for Langmuir monolayer sorption capacities were 31.8 mg/g for As(III) and 33.4 mg/g for As(V) at pH 4. The studied TiO(2) performed the best in acidic conditions, but also reasonably well in other pH conditions.     

水相循环对玉米秸秆水热液化成油特性影响的研究

以玉米秸秆为原料,以去离子水为介质,研究水相循环对玉米秸秆水热液化成油特性的影响。循环过程中不额外添加去离子水,对循环前后的水相产物、生物原油和固体产物进行对比研究发现,水相循环产生有机酸的富集效应,促进酮酚类的转化,两者共同作用提高生物原油和固体产物的产率和品质。具体表现为:水相循环对水相pH值影响较小(3. 62-3. 91),但可以使乙酸和丙酸等有机酸不断累积,同时使酮类、酚类化合物含量逐渐减少;水相循环可以使生物原油产率从20. 42%逐步提高至24. 31%,且可略提升油品质;水相循环可以使固体产物的碳含量由60. 94%提升至61. 74%。     

1H NMR relaxation study of polymer-solvent interactions during thermotropic phase transition in aqueous solutions

The dynamic-structural changes and polymer - solvent interactions during the thermotropic phase transition in poly(vinyl methyl ether) (PVME)/D₂O solutions in a broad range of polymer concentrations (c = 0.1-60 wt.-%) were studied combining the measurements of ¹H NMR spectra, spin-spin (T₂) and spin-lattice (T₁) relaxation times. Phase separation in solutions results in a marked line broadening of a major part of polymer segments, evidently due to the formation of compact globular-like structures. The minority (∼15%) mobile component, which does not participate in the phase separation, consists of low-molecular-weight fractions of PVME, as shown by GPC. Measurements of spin-spin relaxation times T₂ of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute solutions where globules probably contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures to (in) PVME globular structures in semidilute and concentrated solutions was revealed from measurements of spin-spin and spin-lattice relaxation times of residual HDO molecules.     

Kinetics,isotherm and thermodynamics for Cr(III) and Cr(VI) adsorption from aqueous solutions by crystalline hydrous titanium oxide

The synthetic crystalline hydrous titanium(IV) oxide (CHTO), an anatase variety and thermally stable up to 300 °C, has been used for adsorption of Cr(III) and Cr(VI) from the aqueous solutions, the optimum pH-values of which are 5.0 and 1.5, respectively. The kinetic data correspond very well to the pseudo-second order equation. The rates of adsorption are controlled by the film (boundary layer) diffusion, and increase with increasing temperature. The equilibrium data describe very well the Langmuir, Redlich–Peterson, and Toth isotherms. The monolayer adsorption capacities are high, and increased with increasing temperature. The evaluated ΔG^° (kJ · mol^?1) and ΔH^° (kJ · mol^?1) indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (ΔS^° = positive), and the mean free energy (E_DR) values obtained by analysis of equilibrium data with Dubinin–Radushkevick equation indicate the ion-exchange mechanism for Cr(III) and Cr(VI)-adsorptions.     

Kinetics of the amorphous—anatase phase transformation in copper doped titanium oxide

Samples of TiO₂ doped with 2 and 5 mol% of Cu²⁺ were prepared by the sol-gel process. Titanium(IV) isopropoxide and copper(II) nitrate were used as precursors. The samples were prepared as monolithic shapes, dried at 80°C for 72 h and heat treated at various temperatures in the range 200–900°C for 2 h. The structural transformation and texture of the samples were investigated by X-ray powder diffraction (XRD) and nitrogen adsorption. Significant changes were observed during the crystallization process; on the one hand, the crystallization profiles show that crystallization occurs uniformly and is practically insensitive to the dopant concentration, but when the transformation at a given temperature is followed as a function of time, the rate of the amorphous-anatase transformation is larger for the sample containing 2 mol% Cu²⁺. Electron spin resonance (ESR) results show that in this sample there is no segregation of Cu²⁺ ions. The sample containing 2 mol% of Cu²⁺ was selected for the kinetic studies and the temperatures selected were 300, 325, 350, 375 and 400°C, which were taken from the amorphous to anatase crystallization profile. An activation energy of 137 ± 4 kJ/mol for the crystallization process was estimated from the kinetic data. These results showed that the effect of the open structure present in the TiO₂ amorphous phase provides the atomic mobility required for the crystallization. On the other hand, the differences in the crystallization rate due to the amount of Cu²⁺ were explained by the segregation of copper ions to the surface of the samples.     

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

Water soluble 2-azobenzenoxy-ethoxy-hydroxpropylcelluloses (azo-EHPC) were synthesized by etherification reaction of bromoethoxy-azobenzene (BEA) with hydroxypropylcellulose (HPC) to study their phase transition behavior in aq. solution. The degree of substitution (DS) of the water soluble azo-EHPCs was less than 0.066. Their chemical structure and thermal property were characterized by proton nuclear magnetic resonance (¹H-NMR), fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry. The azo-EHPC showed a reversible sol–gel transition behavior in its aq. solution, i.e. a clear azo-EHPC aq. solution became turbid when the solution temperature surpassed a lower critical solution temperature (LCST). The sol–gel transition phenomenon was investigated by optical microscopy and turbidimetric measurement. It was found that the LCST was related to the cis-/trans- conformation of the azobenzene side group, the type of cyclodextrin (CD), concentration of azo-EHPC, and NaCl concentration. The LCST of azo-EHPC was lower than that of HPC (36.6 °C) by at most 13.6 °C, and the LCST of trans-azo-EHPC was less than that of cis-azo-EHPC by ca. 3 °C. Additionally, the presence of CD in solutions displayed a positive effect on the LCST, i.e. increasing the LCST by 3–5 °C. And this impact was more profound on the azo-EHPC with higher DS values. The thermoreversible phase transition mechanism was discussed. We proposed that the effect of DS, conformation of azobenzene group, azo-EHPC concentration, salt concentration, and CD on the LCST of azo-EHPCs was a rearrangement of the hydrophilic/hydrophobic interaction between side azobenzene groups and water molecules.     

Characteristics of aggregation in aqueous solutions of dialkylpyrrolidinium bromides

Three pyrrolidinium-based ionic liquids-N-dodecyl-N-methylpyrrolidinium bromide, N-butyl-N-octylpyrrolidinium bromide, and N-butyl-N-dodecylpyrrolodinium bromide-were synthesized and characterized by their decomposition temperatures (T(d)) measured by thermogravimetric analysis, and by their melting point (T(m)), glass transition (T(g)) and crystallization temperatures (T(cryst)) determined by differential scanning calorimetry. Their self-aggregation properties in aqueous solution were studied and their behavior is compared with that of analogous conventional cationic surfactants, namely tetra-alkylammonium bromide salts. The critical micellar concentration, cmcs were obtained by isothermal titration calorimetry (ITC); which were further validated by measurements of interfacial tension, fluorescence and NMR spectroscopy. Enthalpies of micellization were measured at three different temperatures using ITC. The Taylor dispersion method and DOSY NMR were used to determine diffusion coefficients of the ionic liquid surfactants in aqueous solution at 298.15K. Several correlations between structural features of the surfactant species, such as the number and size of their alkyl chains, and the thermodynamic quantities of micellization-expressed by experimental values of cmc, counter-ion binding fraction, Δ(mic)G°, Δ(mic)°, and Δ(mic)S°-are established. We could interpret the different contributions of the two alkyl side chains to the aggregation properties in terms of the balance of interactions in homogeneous and micellar phases, contributing to understanding the aggregation behavior of ionic liquids in water and the parallel between these systems and traditional ionic surfactants.     

Adsorption of polymethacrylic acid from aqueous solutions on disperse titanium dioxide

The state of macromolecules of polymethacrylic acid adsorbed on the surface of disperse titanium dioxide was assessed using a combination of the differential concentration approach to the determination of adsorption and methods for determining the size of disperse adsorbents by dynamic light scattering and sedimentation analysis in the field of centrifugal forces. Three sections were found on the isotherm of adsorption: in the first, isolated islands of adsorbed macromolecules formed; in the second, layers of macromolecules with a different degree of deformation were observed; in the third, determining the adsorption of macromolecules is complicated by other accompanying processes, and assessing the state of macromolecules in the adsorption layer becomes difficult.     

Generation of phenylmethylketyl radicals in aqueous solutions and study of their transformation

Acetophenone and its intermediates formed upon the first electron transfer are studied by laser photoemission and traditional electrochemistry. It is shown that the intermediate reduction is affected by competition of the reactions of the formed radical-anions oxidation and their subsequent transformation to secondary products that are rapidly reduced at the electrode. From the comparison of the data obtained by the laser photoemission method and electrochemical measurements a conclusion was drawn that the product is a metastable complex (associate) of the radical-anion with water molecule; its formation rate constant is rather low (～6 × 10³ M^?1 s^?1). It was also concluded that bulk radical reactions dominate in aprotic media at moderate cathodic potentials; the acetophenone radical-anion is reduced at E ≤ ?1.9 V (SCE). This conclusion agrees with the results of the acetophenone preparative electrolysis in DMFA, where marked yield of pinacon was observed at the potentials of limiting current of the 1st reduction wave, while the stage of 2nd electron transfer occurred at E ≤ ?2.3 V (SCE).     

Removal of uranium(VI) from aqueous solutions by carboxyl-rich hydrothermal carbon spheres through low-temperature heat treatment in air

Carboxyl-rich hydrothermal carbon spheres were prepared by simply heating pristine hydrothermal carbon spheres (HCSs) at lower temperature in air, and the textural properties were characterized using Boehm titrations, scanning electron microscopy, Fourier transform infrared spectrometer (FT-IR) and elemental-analysis. The result of Boehm titrations indicated that the content of carboxyl groups on HCSs increased significantly from 0.53 to 3.81 mmol/g after heat-treatment at 300 °C, which was also confirmed by FT-IR and EA qualitatively. The ability of heat-treated HCSs has been explored for the removal and recovery of uranium from aqueous solutions, and the influences of different experimental parameters, such as heat-treatment temperature, contact time and ionic strength, on adsorption were investigated. The U(VI) sorption capacity of HCSs increased from 55.0 to 179.95 mg/g after heat-treatment at 300 °C for 5 h. Selective adsorption studies showed that the heat-treated HCSs could selectively remove U(VI), and the selectivity coefficients were improved after heat-treatment in the presence of co-existing ions, Na(I), Ni(II), Sr(II), Mn(II), Mg(II) and Zn(II). The adsorbent HCSs could be effectively regenerated by 0.05 mol/L HCl solution for the removal and recovery of U(VI). Complete removal (99.0 %) of U(VI) from 1.0 L industry wastewater containing 15.0 mg U(VI) ions was possible with 5.0 g heat-treated HCSs. In addition, a reaction mechanism for newly generating carboxyl groups on pristine HCSs surface during heat-treatment process and uranyl ion interaction with carboxyl-rich hydrothermal carbon spheres were also supposed.     

Thermoreversible gelation and phase separation in aqueous methyl cellulose solutions

We derived typical phase diagrams for aqueous solutions of methyl cellulose (MC) of different molecular weights via micro‐differential scanning calorimetry, small‐angle X‐ray scattering, and visual inspection. The phase diagrams showed the cooccurrence of gelation and phase separation and qualitatively agreed with the theoretically calculated diagrams. The sol–gel transition line and phase separation line of a lower critical solution point type shifted toward lower temperatures and lower concentrations with an increase in the MC molecular weight. The sol–gel transition line intersected at a temperature higher than the critical point of the phase separation; therefore, both sol–gel phase separation and gel–gel phase separation were possible, depending on the temperature. Specifically, through visual inspection of a high molecular weight MC sample in the critical temperature region, we observed phase separation into two coexisting gels with different polymer concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 91–100, 2001