A simple route to V2O5·xH2O bundle-like nanostructures

V₂O₅·xH₂O bundle-like nanostructures composed of nanobelts have been synthesized by a simple hydrothermal method with the aid of Co²⁺. The widths, thickness and lengths of V₂O₅·xH₂O nanobelts are 80–100 nm, 10–20 nm, and several micrometers, respectively. The morphologies and the crystallographic structures of the V₂O₅·xH₂O bundle-like nanostructures were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and electron diffraction (ED). The effects of the inorganic ions and reaction temperature on the morphologies of the resulting products have been investigated.     

Thermal decomposition of CuCrO4·2CuO·2H2O and phase relations in the Cu-Cr-O system

The compound, CuCrO₄·2CuO·2H₂O has been synthesized by precipitating it from the aqueous solution containing chromium (VI) oxide and basic copper (II) carbonate. Thermal decomposition of CuCrO₄·2CuO·2H₂O has been studied by thermogravimetry and differential scanning calorimetry in flowing air and pure oxygen between 298 and 1373 K. The formation of different phases after each stage of decomposition were identified by X-ray diffraction analysis. The compound CuCrO₄ was found to be non-stoichiometric. Based on the results obtained in this study and those reported earlier, the isothermal section of the phase diagram of the Cu-Cr-O ternary system has been composed at 600 and 1150 K. Scanning electron microscopy studies of CuCrO₄·2CuO·2H₂O precipitate showed rectangular plate-like morphology. The decomposition of CuCrO₄·2CuO·2H₂O at 798 K in air resulted in the formation of a mixture of fine powder of CuCr₂O₄+CuO (Adkin's catalyst) having a uniform spherical geometry and a particle size less than 0.1 m.     

Synthesis of uniformly sized Cu2O crystals with star-like and flower-like morphologies

Uniformly sized single-crystalline Cu₂O crystals with star-like and flower-like morphologies have been successfully prepared via the reaction of d-glucose, copper (II) chloride and sodium hydroxide in aqueous solution. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electron diffraction (ED).     

A simple solvothermal reduction route to copper and cuprous oxide

Pure copper nanocrystallites and cuprous oxide nanorods have been synthesized via solvothermal treatment of CuSO₄ or CuSO₄·5H₂O and NaOH in pure ethanol and mixed solution of ethanol and deionized water at 140 °C for 10 h, respectively. Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to investigate the different morphologies of the as-synthesized products. X-ray powder diffraction (XRD) and selected area electron diffraction (SAED) were applied to characterize the composition and crystal phases of the products. It was proposed that the reducibility of ethanol was influenced by temperature and the addition of deionized water in the formation of different phases, which were realized by carefully controlling the experimental conditions.     

Synthesis and morphological studies of ZnCuTe ternary nanowires via template-assisted electrodeposition technique

ZnCuTe nanowires have been successfully synthesized via template-assisted one step electrodeposition technique from an aqueous solution of zinc sulphate (ZnSO₄·7H₂O), copper sulphate (CuSO₄·5H₂O) and tellurium oxide (TeO₂) at room temperature (303?K). Nanowires of diameter 200, 100 and 50?nm have been synthesized on copper and indium tin oxide coated glass substrates using track-etch polycarbonate membranes (Whatman). The morphologies and structures of electrodeposited ZnCuTe nanowires were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). SEM confirmed the formation of nanowires and reveal that the morphologies of nanowires have diameter equal to the diameter of the templates used. The XRD pattern have shown a preferential growth of ZnCuTe nanowires along the (119) direction and the structure corresponding to hexagonal structure. Energy dispersive X-ray analysis confirmed that the zinc copper telluride nanowires are constituted of elements Zn, Cu and Te.     

Synthesis and characterization of micrometer Cu/PVP architectures

Micrometer-sized flower-like Cu/polyvinylpyrrolidone (PVP) architectures are synthesized by the reduction of copper (II) salt with hydrazine hydrate in aqueous solution in the presence of PVP capping agent. The resulting Cu/PVP architectures are investigated by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). The Cu/PVP flowers have uniform morphologies with an average diameter of 10 μm, made of several intercrossing plates. The formation of Cu/PVP flowers is a new kinetic control process, and the factors such as the amount of N₂H₄H₂O, reaction temperature, molar ratio of CuCl₂ to PVP and molecular weight of PVP have significant effect on the morphology of Cu/PVP architectures. A possible mechanism of the formation of micrometer Cu/PVP architectures was discussed.     

Flower-like zinc oxide deposited on the film of graphene oxide and its photoluminescence

The graphene oxide films have been fabricated by simply filtering the graphene oxide solution through the micropore filter. Then the flower-like ZnO grows on the graphene layer by immersing the seed-coated graphene oxide films in the dilute growing solution containing NH₃·H₂O and Zn(NO₃)₂·6H₂O. The morphologies of the as-obtained ZnO deposited on the graphene oxide layer are characterized by using scanning electron microscope (SEM), X-ray powder diffraction (XRD) and photoluminescence (PL). The formation mechanism of the flower-like ZnO has also been investigated. The results show that the morphology of the finally-obtained ZnO is tunable by seeds, the concentration of growing solution and the reaction time.     

Hydrothermal synthesis,characterization and luminescent properties of GdPO4·H2O:Tb nanorods and nanobundles

In this paper, the Tb³⁺-doped GdPO₄·H₂O nanorods and nanobundles have been synthesized by the hydrothermal method with and without glycine, respectively. The X-ray powder diffraction (XRD), thermogravimetric and differential thermal analysis (TG–DTA), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), energy-dispersive spectra (EDS) and photoluminescence (PL) were employed to characterize the as-obtained products. It was found that the addition of glycine and the pH value have crucial influences on the formation of the resulting morphologies and sizes. The possible formation mechanisms for GdPO₄·H₂O:Tb³⁺ nanorods and nanobundles were put forward. A detailed investigation on the photoluminescence of GdPO₄·H₂O:Tb³⁺ different samples revealed that the luminescent properties of products are strongly correlated with the morphologies, sizes, coordination environment and crystal field symmetry.     

Interface reactions in the system sialon-Cu-Cu2O

The interface reactions between an /gb-sialon ceramic and Cu, Cu₂O or a Cu-Cu₂O mixture have been studied. A fully dense sialon ceramic material prepared by pressureless sintering at 1775 ° C with 6 wt% Y₂O₃ as sintering aid, were coldpressed together with Cu, Cu₂O or Cu-Cu₂O mixtures into cylindrical tablets. These samples were heat treated at 700, 850 and 1000 ° C in evacuated silica tubes. The reaction zones formed between the sialon and the powder compacts were studied in a SEM equipped with an EDS system. No reaction between copper and sialon ceramic could be detected in spite of prolonged heat treatment at 1000 ° C. Cu₂O reacted with the ceramic at 850 and 1000 ° C to form a glass containing copper and all the other sialon components. The interaction between the sialon material and the Cu-Cu₂O powder compacts was characterized by a redox reaction. The sialon was thus oxidized to SiO₂ and N₂ while Cu₂O was reduced to copper. A glass phase containing silicon, aluminium, yttrium and copper was also formed in the reaction.     

Phase Composition of the Products of Fe Oxidation in Fe + C + NaCl + H2O + O2 Exothermic Mixtures

Using thermodynamic analysis of the Fe–C–NaCl–H₂O–O₂ system and experimental studies (x-ray diffraction and Mössbauer spectroscopy) of exothermic mixtures containing Fe metal, activated carbon, water, and NaCl, we identified the state of Fe and determined the phase composition of the reaction products at different stages of oxidation with atmospheric oxygen. The calculation and experimental results are in reasonable agreement. Under the conditions of restricted access for air, the main oxidation product is magnetite, Fe₃O₄. Free access for air leads to the formation of hydrous ferric oxide, Fe₂O₃ · nH₂O. The most stable phase under the conditions of interest is goethite, Fe₂O₃ · H₂O (-FeOOH). Storage of incompletely oxidized samples away from air for 7–14 days leads to partial reduction of iron(III) oxide phases to Fe₃O₄ and -Fe.     

Thermochemical preparation of W–25%Cu nanocomposite powder through a CVT mechanism

In order to produce a W–25%Cu nanocomposite powder manufactured by a thermochemical procedure a novel pair of precursors were used. Cu₂WO₄(OH)₂ and CuWO₄·2H₂O precipitates were first produced by reacting the copper nitrate and sodium tungstate aqueous solutions under certain pH and temperature. The precipitates were then dried and calcined in order to prepare CuWO_4 − x, CuO, and WO₃ oxide powders for the next step reduction. The reduction was carried out under a H₂ atmosphere to form the final W–Cu metal nanocomposite powder. Characteristics of the final powder such as distribution, uniformity and size were then discussed based thoroughly on the dominant mechanism of reduction; Chemical Vapor Transport. It was found that the average particle size of the reduced powder is 35 nm for W and 54 nm for Cu.     

The formation of ilmenite FeTiO3 powders by a novel liquid mix and H2/H2O reduction process

FeTiO₃ powder was prepared via a liquid mix and H₂/H₂O reduction process. First, an intermediate compound was synthesized by a liquid mix process. This precursor compound to FeTiO₃ was characterized by thermal analysis (TG/DTA) and Fourier Transform Infrared spectroscopy (FT-IR). Second, the precursor was annealed in the air, H₂/H₂O(g) mixing gas stream, respectively. The obtained powder was characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis spectroscopy (EDAX) and scanning electron microscope (SEM). It was showed that pure and homogenous FeTiO₃ was successfully obtained below 600 °C.     

Nanocomposites of cellulose/iron oxide: influence of synthesis conditions on their morphological behavior and thermal stability

Nanocomposites of cellulose/iron oxide have been successfully prepared by hydrothermal method using cellulose solution and Fe(NO₃)₃·9H₂O at 180 °C. The cellulose solution was obtained by the dissolution of microcrystalline cellulose in NaOH/urea aqueous solution, which is a good system to dissolve cellulose and favors the synthesis of iron oxide without needing any template or other reagents. The phases, microstructure, and morphologies of nanocomposites were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectra (EDS). The effects of the heating time, heating temperature, cellulose concentration, and ferric nitrate concentration on the morphological behavior of products were investigated. The experimental results indicated that the cellulose concentration played an important role in both the phase and shape of iron oxide in nanocomposites. Moreover, the nanocomposites synthesized by using different cellulose concentrations displayed different thermal stabilities.     

Green synthesis of bi-component copper oxide composites and enhanced photocatalytic performance

A facile and green route was proposed for the synthesis of bi-component copper oxide composite without any templates and additives. The effects of D-(+)-glucose amount, reaction temperature, and reaction time on the morphology and constitution of the products were investigated by SEM, X-ray diffraction, and UV-vis DRS in detail. The results indicate that a series of Cu₂O–CuO bi-component copper oxide composites with various morphologies can be easily obtained. Structure characterisation and photocatalytic tests show that the bi-component Cu₂O–CuO composites exhibited better photodecolouration of methylene blue than those of the Cu₂O, CuO, and Cu–CuO compounds owing to the existence of the synergistic effect between the CuO and Cu₂O.     

Synthesis of carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H2O for hydrogen generation

Synthesis of a carbon-iron(II) oxide layer on the surface of magnetite and its reactivity with H₂O for hydrogen generation reaction have been studied. X-ray diffractometry and chemical analysis showed that the carbon-bearing magnetite synthesized by the carbon-deposition reaction from CO₂ gas with the hydrogen-reduced magnetite, was magnetite with a carbon-iron(II) oxide layer (CIO layer-M; M is stoichiometric magnetite) represented by (Fe₃O₄)_1– (Fe₃O₃)C. The TG-MS spectra also showed the evidence for the formation of the CIO layer on the bulk stoichiometric magnetite. Some amorphous phase was formed in the CIO layer during the activation step (in vacuo at 300 °C for 30 min). This amorphous phase reacted with H₂O and evolved H₂ gas at 350 °C. This H₂ generation reaction resulted in the oxidation of the CIO layer into -Fe₂O₃ component and the release of a part of carbon in the CIO layer as CO₂. The X-ray diffractometry and Mössbauer spectroscopy indicated that the solid solution of Fe₃O₄--Fe₂O₃ was formed in the solid phase after the H₂ generation reaction. This shows the cation movement in the B site of the bulk magnetite of the activated CIO layer-M during the H₂ generation reaction. The TG-MS spectra also supported the above estimation.     

Production of alumina fibre through jute fibre substrate

Alumina fibre has been produced using jute fibre as substrate material at temperatures lower than 1600 C in a reducing atmosphere. Processed jute fibre was chemically pretreated by saturation with Al₂Cl₆ · 12H₂O, coked and then pyrolysed to obtain alumina fibre. Chemical pretreatment conditions have been determined by following weight loss measurements of the jute fibre at 0.1 to 0.6 N solutions of NaOH, KOH, NH₄OH, Na₂CO₃, K₂CO₃, HCl and acetic acid. The effect of heat treatment on the jute fibre and jute fibre + aluminium salt has been studied from 150 to 1600 C. Trace elements present (Fe₂O₃, SiO₂, K₂O, Na₂O, CaO, MgO, ZnO, MnO, V₂O₅, P₂O₅, CuO) on heat-treated products have been determined by atomic absorption spectrometry. Optical and scanning electron micrographs of representative samples showing growth mechanism are presented. The effect of copper, nickel and platinum catalysts and fluxing agents such as K₂O and Na₂O in fibre formation has also been examined. Particle size and surface area analyses of intermediate and final products have been carried out. Changes in 2 values are plotted for various products from X-ray diffraction studies. It is conceived that the porous surface of cellulosic fibrils in the jute fibre adsorbs the AlCl₃ molecules which decompose to oxide and are gradually shaped to the fibrous form during the course of thermal treatment in a reducing atmosphere and due to the high surface area.     

Low-temperature fabrication and electrical property of 10 mol% Sm2O3-doped CeO2 ceramics

Ten mol% Sm₂O₃-doped CeO₂ solid-solution (20SDC) powders have been synthesized via carbonate coprecipitation using ammonium hydrogen carbonate (AHC) and urea as the precipitants, respectively. Characterizations were achieved by elemental analysis, X-ray diffractometry, differential thermal analysis/thermogravimetry, and FESEM. An amorphous hydroxyl carbonate precursor (Ce,Sm)(OH)CO₃·2H₂O having nanosized (~10 nm) spherical particles was formed with AHC, while a mixture of crystalline (Ce,Sm)₂(CO₃)₂(OH)₂·H₂O and (Ce,Sm)₂O(CO₃)₂·H₂O phases exhibiting irregular particle morphologies was obtained with urea. Both the precursors convert to oxide solid solutions without any phase detected corresponding to Sm₂O₃ during calcination. The oxide powder processed via the AHC method can be sintered to >99% of the theoretical at a low temperature of 1200 ?C, due to the good dispersion and ultrafine size (~15 nm) of the particles, while that from the urea method can only reach ,67.2% dense at the same temperature. Electrical conductivity of the densified ceramic was measured in air in the range 400—700 ?C by the DC three-point method, and an activation energy of ~60.5 kJ/mol was derived from the experimental data.

© 2003 Elsevier Ltd. All rights reserved.     

Specific Features of Anodic Dissolution of Copper in H2SO4 + H2O and H2SO4 + CuSO4 + H2O Systems

We investigate anodic dissolution of copper in H₂SO₄ + H₂O and H₂SO₄ + H₂O + CuSO₄ systems, which model solutions for the electrochemical production of copper (+2) sulfate. Ultimate densities of anodic current in the temperature range 20–80°C for a voltage up to 8 V were found. We show that a concentration of copper ions ( Cu²⁺) of 1.5–2.0 moles/liter in the anolyte is the limiting one in the electrochemical production of solutions of copper (+2) sulfate.     

Liquid mutual diffusivities of the H2O/D2O system

The liquid-phase mutual diffusivities of the water (H₂O) and deuterium oxide (D₂O) system at 298.2 K were measured using an instrument based on the Taylor dispersion technique. The instrument has been designed to match, as closely as possible, the mathematical model of ideal Taylor dispersion, minimizing all the departures from the ideal model. The diffusivities were measured over the entire concentration range and the results follow a linear dependence on molar fraction given by 10⁹ D ₁₂ = , where D ₁₂ is in m²·s^–1. Comparison with highly accurate data obtained by a Rayleigh interferometer seems to indicate that the accuracy of the present instrument is 1%. The hard-sphere model was applied to the estimation of the mutual diffusivities of this system and good agreement was found with experiment, deviations being ±3.5%.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.     

Synthesis of single-crystalline Ce(CO3)(OH) with novel dendrite morphology and their thermal conversion to CeO2

Single-crystalline cerium carbonate hydroxide (Ce(CO₃)(OH)) with dendrite morphologies have been successfully synthesized by hydrothermal method at 150 °C using Ce(NO₃)₃·6H₂O as the cerium source, aqueous carbamide as both an alkaline and carbon source and poly(vinyl pyrrolidone) (PVP) as surfactant. Ceria (CeO₂) with dendrite morphologies have been fabricated by a thermal decomposition-oxidation process at 500 °C for 6 h using single-crystalline Ce(CO₃)(OH) dendrites as the precursor. The dendrite morphologies of Ce(CO₃)(OH) was sustained after thermal decomposition-oxidation to CeO₂. The as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TG).