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.

     

Sorption of uranyl ions on hydrous titanium dioxide

Summary The mechanism of the sorption of U on TiO₂ · x H₂O is investigated in absence and in presence of carbonate as function of pH. Speciation of U in solution and the state of the surface of TiO₂ · x H₂O are taken into account. In the experiments the mole fractions of the U species in presence of carbonate are the same as in seawater. Below pH 5 the sorption of U can be described in absence and in presence of carbonate by ion exchange of UO ₂ ²⁺ or alternatively by sorption of UO₂OH⁺, because hydrolysis and sorption are occurring simultaneously. Above pH 5 in absence of carbonate, first pH-independent sorption of (UO₂)₃(OH) ₇ ^– and then (above the isoelectric point of TiO₂ · x H₂O) pH-dependent sorption of (UO₂)₃(OH) ₇ ^– are observed. In the same pH range, but in presence of carbonate, two species of U are dominating in solution, first UO₂CO₃OH^– and then UO₂(CO₃) ₃ ^4– · UO₂CO₃OH^– is not sorbed in measurable amounts which causes a drastic decrease of the sorption ratio. UO₂(CO₃) ₃ ^4– , which begins to dominate above pH 6 (depending on the carbonate concentration), is sorbed either by formation of TiOUO₂ bonds or (at carbonate concentrations >10^–2 mol/l) via carbonate bridges.

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Sorption von Uranylionen an wasserhaltigem Titandioxid

     

Identification of degraded products of aldicarb due to the catalytic behavior of titanium dioxide/polyacrylonitrile nanofiber

Photocatalytic properties of fibers containing TiO₂ nanoparticles were explored for use as a self-decontaminating material using degradation of the pesticide aldicarb as the model toxin. During the analysis of the aldicarb treated sample by liquid chromatography (LC) with diode array detector (DAD), an unidentified peak was found at relative retention time (RT) 3.9 min when compared to aldicarb and major metabolites, aldicarb sulfoxide, and aldicarb sulfone. An analytical method was developed to confirm and identify this degradation product. LC–APCI/MS techniques were used first to analyze molecular ions and major fragments comparing retention times and spectra with those of known standards. FTIR and LC–MS/MS techniques were used to confirm the identity of the degradation product as 2-propenal, 2-methyl-, O-[(methylamino)carbonyl]oxime.     

Possible radiochemical separations of anionic radionuclides by amorphous hydrous titanium dioxide

Ion-exchange selectivities towards oxoanions and halide ions were studied for radio-chemical applications by an amorphous hydrous titanium dioxide (Am-HTDO) as functions of pH and concentration. The selectivity series was found to be Mo(VI)<W(VI)<P(V)<As(V)<Sb(V) for micro-amounts at pH 9 and Br^–Cl^–F^– for macro-amounts. A feasibility was suggested for radiochemical separations of³²P by³⁵Cl(n,)³²P and⁷⁷Br by⁷⁵As(, 2n)⁷⁷Br, and selective removal of anionic radionuclides.Synthetic Inorganic Ion-Exchange Materials. XLIII.     

Layered hydrous manganese dioxide saturated with alkaline-earth cations: Synthesis and sorption properties

Layered compounds based on hydrous manganese dioxides (hereafter, Mn-phases) saturated with alkaline-earth cations were synthesized at 3–6°C. These phases are analogues of manganese minerals from oceanic iron-manganese sediments (vernadite, birnessite, buserite-I, an asbolan-like phase, and a hybrid phase). All the Mn-phases, as a rule, had poorly ordered structures. The sorption properties of these phases were studied with respect to alkali-metal cations (Na⁺, K⁺), an s-metal cation (Ba²⁺), a p-metal cation (Pb²⁺), and d-metal cations (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺). The exchange capacities of the Mn-phases were 0.45–1.06 mg-equiv/g for the alkali cations and 0.94–5.78 mg-equiv/g for the other cations. The phase composition of the Mn-phase did not affect the alkali cation sorption but affected the divalent cation sorption. The divalent cation exchange capacity increased from well-ordered birnessite to poorly ordered vernadite.     

Distribution coefficients of lanthanide elements and some separations on layered hydrous titanium dioxide

Distribution coefficients /K_d/ of lanthanide elements on layered hydrous titanium dioxide, H₂Ti₄O₉.nH₂O /where n=1.2–1.3/, have been determined as a function of the pH of the aqueous phase. The plots of 1g K_d vs. pH gave straight lines with slopes equal to +3 except for the data for heavier lanthanides, suggesting ideal ion-exchange equilibria between tervalent cations in the aqueous phase and hydrogen ions in the hydrous oxide. Mutual separations of La–Cs and La–Ba have been achieved on a column of this material on the basis of large differences in affinities between the metal ion pairs.     

Sorption of cesium and strontium ions on hydrous titanium dioxide from chloride medium

Epiboron instrumental neutron activation analysis (EINAA) using flexible boron as thermal neutron filter, has been used to analyze several salt samples obtained from various markets in Ghana for iodine. The method involves the irradiation of samples in boron carbide-lined polyethylene vials at the outer irradiation site of the Ghana Research Reactor-1 (GHARR-1). The samples were then counted directly without any pre-treatment on a Canberra N-type HPGe detector. The qualitative and quantitative analyses were done using the 443 keV photopeak of ¹²⁸I. The precision and accuracy of the method have been evaluated and the detection limits of the various samples were calculated. The values of iodine determined in the iodized salt range between 10.0 and 210 ppm. For non-iodinated salts, iodine levels were below 500 ppb. The values obtained show great variations among the salt samples, sample collection time and from market to market. This results show that the method can be successfully applied in the determination of trace amount of iodine in salt samples without any chemical separation.     

Preparation of copper-based oxygen carrier supported by titanium dioxide

Chemical-looping combustion (CLC) is an indirect oxygen combustion strategy, considered to be the most cost-effective power generation technology with the carbon dioxide (CO₂) inherently concentrated. The oxygen carriers in the combustion process are subjected to severe environments, such as high temperatures, multi-cycle operations, and thermodynamic limitations. Thus, the preparation of an oxygen carrier with high durability and better kinetics under harsh environments could be an essential part of the development of the CLC process. In this study, copper oxide (CuO) was selected as an active ingredient, and was supported on the titanium-dioxide-based supporting materials, which was either directly from commercial titanium dioxide powder (TiO₂) (anatase 99 %) or from tetrabutyl titanate, depending on methods. Three preparation methods were applied, including mechanic mixing (MM), sol–gel (SG), and wet impregnation (WI). Test results indicated all prepared oxygen carriers functioned properly in the multi-cycles of reduction and oxidation (redox) in thermogravimetric under 800 °C. Characterization and activity tests revealed that the CuO, prepared by the SG method was well-dispersed, highly active, and thermally stable in redox reactivity than those by the MM and WI methods. Furthermore, nucleation and diffusion models could better describe kinetics of prepared oxygen carrier based on the SG method.     

A radiochemical study of the kinetics of ion exchange on hydrous titanium dioxide

This paper reports a radiochemical study of the kinetics of ion exchange of Na⁺ and Cs⁺ with H⁺ on hydrous titanium dioxide. The experimental conditions are set to favor the particle diffusion mechanism only, and this is confirmed by the Bt versus t plots. On the basis of these studies the various physical parameters such as the effective diffusion coefficients, activation energies and entropies of activation have been evaluated. Tentative explanations are given for these results, from which some conclusions are drawn.     

Thermal behavior of polyacrylonitrile and poly(vinylpyrrolidone-graft-acrylonitrile) blend

The role of hydrophilic poly(vinylpyrrolidone-graft-acrylonitrile) (PGA) copolymer and the plasticization effect of water in melting behavior of polyacrylonitrile (PAN)-PGA blend were investigated. The PAN-rich PGA blend was obtained by in situ polymerization of the PAN homopolymer and the PGA copolymer. Depression of the melting point of PAN in the presence of the PGA occurred, thereby involving an endothermic transition of the wet blend powder at atmospheric pressure. This was due to a plasticization effect of water inducted into PAN matrix by the PGA. X-ray scattering showed that in the blend powder the crystalline phase of PAN was unaffected by PGA and the amorphous phase of PAN contained PGA domain. On compressing with heating, the wet blend powder formed a transparent sheet, in which the crystalline structure of PAN was changed from hexagonal to orthorhombic lattice. The amount of PAN chain participating in thermal motion for melting varies with absorbed water content. © 1996 John Wiley & Sons, Inc.     

Synthesis of vanadium-phosphorus oxide catalysts supported on pyrogenic silica and titanium dioxide

Various methods for the preparation of vanadium-phosphorus oxide (VPO) catalysts supported on aerosils A-300 and A-50 and TiO₂ were studied: a traditional method (in an organic solvent under varying the support addition time, the nature of the reducing agent, and the degree of reduction of vanadium oxide) and barothermal and mechanochemical syntheses. With the use of XRD analysis, it was found that the composition of the resulting VPO phase depends on the time of support addition to the synthesis and the temperature of thermal treatment. Conditions for the formation of a supported phase of VOHPO₄·0.5H₂O, the precursor of the active component (VO)₂P₂O₇, were determined. The presence of vanadium in an oxidation state of +4 was demonstrated using EPR and UV-VIS spectroscopy. The specific surface areas and pore structures of the synthesized catalysts were determined. The catalytic properties of samples in the reactions of n-butane oxidation in an excess of the hydrocarbon and oxidative ethane dehydrogenation were studied. It was found that, as compared with traditional bulk VPO catalysts, the use of the synthesized supported VPO catalysts made it possible to improve the process characteristics of n-butane oxidation and did not change these characteristics in the reaction of oxidative ethane dehydrogenation.     

Thermal characterization of hydrous tungsten oxides and their behavior as ion exchanger

The preparation, and thermal characterization and ion exchanger behavior of hydrous tungsten oxides obtained from purified tungsten trioxide, by processing of a Brazilian scheelite ore were described. By an alkaline fusion of tungsten trioxide with an excess of sodium carbonate at 900°C an intermediate tungstate product is obtained. Acid lixiviation of the tungstate intermediary in different experimental conditions produces two different hydrous tungsten oxides I and II respectively. A third material was produced by thermal treatment of II, yielding the material IIA, a monohydrate species. The materials prepared were characterized by TG/DTG, X-ray diffractometry and by surface area measurements. Their ion exchange behavior was studied too, using Na⁺ and K⁺ ions as the exchanged species. The inorganic exchanger materials were partially regenerated and may be used consecutively. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.

     

Thermal behavior of polyacrylonitrile polymers synthesized under different conditions and comonomer compositions

Polyacrylonitrile (PAN) polymers are used as precursors for carbon fiber production. This process requires an oxidative stabilization step, which can be studied by differential scanning calorimetry (DSC). In this sense, thermal behavior of PAN based terpolymers by different polymerization processes, compositions and itaconic acid concentrations in the reaction media were investigated. The obtained results showed that the addition of itaconic acid and methyl acrylate as comonomers resulted a lower heat flow during the process comparing to the PAN homopolymer. It suggested that these comonomers aid the oxidative stabilization stage for all studied process. The redox system polymerization at 40°C resulted in a lower heat flow. Itaconic acid decreases slightly initial and peak temperatures of the terpolymer and heat flow until concentration of 3y. The cyclization temperature decreases when MAis incorporated into the terpolymer compared to the MMA terpolymer and increases when MAA is the acidic monomer. Among terpolymers the AN/MA/AA polymer showed the best thermal behavior for carbon fiber producing.     

Adsorption behavior of carboxymethyl starch on titanium dioxide surfaces

The adsorption of carboxymethyl starch (CMS) on titanium dioxide surface from aqueous solution of electrolyte was investigated by adsorption and electrokinetics mobility measurements. Zeta potential measurements showed that the addition of CMS resulted in a shift of isoelectric point to the more acidic region, indicating the adsorption of CMS from the aqueous solution onto titanium dioxide surface. The positively charged and hydrophilic surface sites of titanium dioxide favor the adsorption of CMS molecules. The adsorption capacity of CMS on titanium dioxide surface was found to be controlled by the number of functional group on CMS that promotes surface charge CMS adsorption in agreement with Langmuir isotherm. For the adsorption of CMS, the pseudo-second-order kinetics of chemical reaction provides the best correlation of the experimental data.     

Photocatalytic reduction of dichromate by titanium dioxide supported on hollow glass microbeads

The photocatalytic reduction of dichromate using TiO2/beads as a photocatalyst was studied. The results showed that 3.8 × 10-4 mol/dm3 of dichromate can be completely reduced into Cr3 after illumination for 35 min with a 375 W medium pressure mercury lamp. The effects of factors such as the amount of TiO2/beads , initial concentration of dichromate, initial pH, nitrogen and oxygen atmosphere, and concentration of Fe3 on the photocatalytic reduction of dichromate were investigated. A possible mechamism of the photocatalytic reaction was proposed. After illumination for 200 h, no significant loss of photocatalytic activity of TiO2/beads was observed.