Synthesis and magnetic properties of two-dimensional vanadium(IV) oxide nanostructures on silica surface

Vanadium(IV) oxide nanolayers on silica surface were prepared for the first time. Samples characterized by different degrees of surface coverage by vanadium(IV)-oxygen groups were studied. Samples containing only vanadium(IV) ions and both vanadium(IV) and vanadium(V) ions were obtained. The size effect on the phase transition parameters was determined by studying magnetic properties of vanadium(IV) oxide nanolayers. The phase transition temperature ranges from 140 to 220 K, depending on surface concentration of vanadium(IV) ions and their environment.     

Silver(I) sorption by silica gels chemically modified with mercaptopropyl or dipropyl disulfide groups

The sorption of silver(I) from nitric and hydrochloric acid solutions with silica gels chemically modified with mercaptopropyl groups (MPSG) and dipropyl disulfide groups (DDSG) has been studied. For nitric acid solutions, the highest silver(I) recovery factor (99.0–99.9%) is reached in the acidity range between 5 M HNO₃ and pH 8 for MPSG and between 2 M HNO₃ and pH 8 for DDSG. In the sorption of silver(I) from hydrochloric acid solutions with MPSG, the recovery factor is 99% at pH 2–7. The recovery of silver(I) from chloride solutions with DDSG depends significantly on the chloride ion concentration. The treatment of silver-containing DDSG with a water-ethanol or water-dimethylformamide solution of Michler thioketone yields an intensely colored, reddish claret, mixed-ligand silver(I) complex on the sorbent surface. The diffuse reflectance spectrum of this complex shows a band peaking at 520 nm.     

Adsorption of thorium (IV) by amorphous silica; response surface modelling and optimization

The amorphous SiO₂ (200–300 nm) was synthesized as an absorbent and thorium adsorption of SiO₂ was investigated using experimental and RSM method. The SiO₂ particles were made for the adsorption of thorium from aqueous solutions, and characterized by particle size measurement, XRD and SEM. The adsorption of thorium process was optimized with RSM method. The correlation between four variables was modeled and studied. Under optimum conditions, the adsorption capacity of SiO₂ particles was found to be 134.4 mg/g, the correlation coefficient (R²) and the F value was obtained 0.96 and 1.98?×?10^?6, respectively. In addition, the adsorption isotherms were examined.     

Textural and adsorption properties of silica modified with germanium(IV) oxide

Nitrogen low-temperature adsorption-desorption shows that the incorporation of germanium(IV) oxide into a silicate matrix under the conditions of the sol-gel transition gives rise to the formation of silica with a uniform mesoporous texture that has a predominating pore diameter of about 4 nm.     

Encapsulation of titanium(IV) oxide particles in hollow silica for size-selective photocatalytic reactions

A core-shell composite of TiO2 particles encapsulated in a hollow silica was fabricated, and the core-shell composite showed size-selective photocatalytic activity for decomposition of organics without reducing the intrinsic activity of the naked TiO2 core.     

Size-selective photocatalytic reactions by titanium(IV) oxide coated with a hollow silica shell in aqueous solutions

A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO(2)) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO(2) with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO(2), but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The unique size-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO(2) particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable floatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface.     

On the stabilization of niobium(V) solutions by zirconium(IV) and hafnium(IV)

Niobium cannot be separated from zirconium or hafnium when these elements occur together in solution with common anions such as chloride and sulphate. This is ascribed to the co-polymerization of niobium(V) and the hydrolysed ionic species of zirconium(IV) and hafnium(IV) to form colloidal particles. In hydrochloric acid the particles are positively charged, whereas in sulphate solution the Zr-and Hf-sulphate complexes confer a negative charge. The two cases are considered separately.     

Vanadium in Italian waters: monitoring and speciation of V(IV) and V(V)

In this work, a highly sensitive method was developed to separate vanadium (IV) from vanadium (V), which are both contained in water at trace levels. A suitable strong anionic exchange column (SAX) loaded with disodium ethylendiaminetetraacetic acid (Na₂EDTA) was used to trap both vanadium species dissolved in 10–100 ml of water at pH 3. The vanadyl ion was selectively eluted by means of 15 ml of an aqueous solution containing Na₂EDTA, tetrabutylammonium hydroxide (TBA⁺OH⁻), and isopropanol (ⁱPr-OH) and was subsequently determined by atomic absorption spectroscopy with electrothermal atomization. The concentration of vanadate ion was calculated by subtracting the vanadyl concentration from the total concentration of vanadium. The optimal conditions for a selective elution were evaluated. The recovery of vanadium (IV) was 95% or better. The proposed method provides a simple procedure for the speciation of vanadium in aqueous matrices. The collection of the two forms could easily be carried out at the sampling site. Therefore, the risk of changing the concentration ratio between vanadium species was widely reduced. The detection limits were 1 μg/l for both species, when a 10-ml sample was eluted through the column. The method was applied successfully to vanadium speciation on different kinds of Italian volcanic water: Mount Etna (Sicily), Lake Bracciano and Castelli Romani (Latium).     

Influence of surface oxygen groups on V(II) oxidation reaction kinetics

The role of surface oxygen groups on the kinetics of the V(II) oxidation reaction was studied on modified glassy carbon (GC) electrodes by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The reaction was found to be sensitive to the presence of oxygen groups on the electrode surface. Higher O/C ratios determined by X-ray photoelectron spectroscopy (XPS) corresponded to higher reactivities and lower charge transfer resistances measured in a 1 M V(II) electrolyte. The stability of an oxidised GC surface was also investigated in a 1 M V(II) electrolyte by potential holding and cycling experiments. It was found that after holding and cycling to successively more negative potentials up to − 0.8 V/RHE, the electrode surface lost its initial reactivity.     

含钒(IV)和钒(V)的钨锗混合价杂多酸盐的合成及其结构表征

报道了含钒(IV)和钒(V)的钨锗混合价杂多酸盐的合成、电子吸收光谱及单电子还原态的ESR谱。α-和β-[HGeV^I^VV2^VW9O40]^7^-的溶液ESR谱是由40余条超精细线组成的, 表明在阴离子中3个VO6八面体是角顶共用, 且其中一个桥氧原子是质子化的。     

含钒(IV)和钒(V)的钨锗混合价杂多酸盐的合成及其结构表征

报道了含钒(IV)和钒(V)的钨锗混合价杂多酸盐的合成、电子吸收光谱及单电子还原态的ESR谱。α-和β-[HGeV^I^VV2^VW9O40]^7^-的溶液ESR谱是由40余条超精细线组成的, 表明在阴离子中3个VO6八面体是角顶共用, 且其中一个桥氧原子是质子化的。     

Drying of films formed by ordered poly(ethylene oxide)-poly(propylene oxide) block copolymer gels

The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.     

Iodometric estimation of cerium(IV) by arsenious oxide

Summary Determination of cerium(IV), depending upon its reduction to cerium-(III) by KI and titration of the liberated iodine with standard arsenious oxide solution in a suitably adjusted p_H range, is described.Sincere thanks of the author are due to Professor S. S. Joshi for research facilities.     

Role of the phase transition at GaN QDs formation on (0001)AlN surface by ammonia molecular beam epitaxy

Journal of Thermal Analysis and Calorimetry - We report an original method of GaN/AlN quantum dots (QDs) formation with low density by ammonia MBE on the (0001)AlN...     

Investigation on Concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） Redox Reaction by Rotating Disc Voltammetry

The kinetic characteristics of the concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） couple have been studied at a glassy carbon electrode in sulfuric acid using rotating-disc electrode and cyclic voltammetry. The kinetics of the Ⅴ（Ⅳ）/Ⅴ（Ⅴ） redox couple reaction was found to be electrochemically quasi-reversible with the slower kinetics for the Ⅴ（Ⅴ） reduction than that for the Ⅴ（Ⅳ） oxidation. And, dependence of diffusion coefficients and kinetic parameters of Ⅴ（Ⅳ） species on the Ⅴ（Ⅳ） and H2SO4 concentration was investigated. It is shown that the concentration of active species Ⅴ（Ⅳ） should be over 1 mol·L^-1 for the redox flow battery application. Further, with increasing the Ⅴ（Ⅳ） and H2SO4 concentration, the diffusion coefficients of Ⅴ（Ⅳ） were gradually reduced whereas its kinetics was improved considerably, especially in the case of Ⅴ（Ⅳ） and H2SO4 up to 2 and 4 mol·L^-1.     

Separation of selenium(IV) and tellurium(IV) from mixtures by extraction chromatography with trioctylphosphine oxide

The reversed-phase extraction chromatographic separation of selenium(IV) and tellurium(IV) from several elements with trioctylphosphine oxide as extractant is reported. Selenium was extracted from 6M hydrochloric acid containing 7M lithium chloride was stripped with 4M hydrochloric acid, and tellurium was extracted from either the same medium as selenium or from 4M hydrochloric acid, and stripped with 1-2M hydrochloric acid. Selenium and tellurium can be separated from multicomponent mixtures.