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Dialysis and peptization, which are colloid chemical solution processes, are simple and effective techniques for controlling hydrolysis of hydrated metal cations. These synthetic processes preparation of stable sol with dispersion of doped oxide nanoparticles with wide molar fraction range from metal chloride aqueous and glycol solutions. Furthermore, control and introduction of lattice defects can be possible due to low temperature synthesis below 373 K. Design of optical and electrical characteristics of oxide nanoparticles by the solutions processes can be realized by controlling the situation of doping and lattice defects.

Porous materials were prepared by stacking needle-like titania particles. The uniform, needle-like titania particles were synthesized by hydrothermal treatment of titanium hydroxide gel containing ethylenediamine. A seeding technique controlled the particle size of them. The obtained particles were dispersed in aqueous solutions with various pH values and vacuum-filtered to form bulk materials. Porous materials with uniform microstructure were obtained when the pH of the suspension was adjusted to the value suitable for generating electrostatic repulsion between dispersed titania particles. Changing the size of component particles also controlled the pore size of the porous titania.

Changes in compositional fluctuation during sintering of PZT ceramics were studied both for ordinary sintering and for the spark plasma sintering (SPS) method. Generally, sintering is established by diffusion at high temperatures. In ordinary sintering, compositional fluctuation decreased with increasing bulk density. In contrast, compositional fluctuation changed little with increasing bulk density during SPS.

Zinc oxide particles were prepared by heating zinc hydroxide precipitate in a mixed solution of H2O and ethanol at 348 K for 2 h. When the molar fraction of ethanol in the solution increased, the particle size of the obtained zinc oxide decreased. The band-gap absorption edge of the UV-VIS spectra of the obtained zinc oxide particles also shifted to the shorter wave length with an increase of ethanol molar fraction in the mixed solution. When zinc hydroxide was heated in pure ethanol, zinc oxide nanoparticles whose average diameter was 41 nm were obtained. The zinc oxide nanoparticles can be obtained by heat treatment of zinc hydroxide in the neutral solution at 348 K.

Cerium oxide (CeO2) nanoparticles were obtained by heating a polyethylene glycol (PEG) solution of cerium nitrate hydrate [Ce(NO3)3 6H(2)O] at 383 K for 3 h. When the PEG, whose molecular weight was 20,000, was used for the preparation, the monodispersed CeO2, whose particle size was about 102 nm, was obtained. When the mixture of PEG20,000 and ethylene glycol (EG) was used to prepare the PEG solution of cerium nitrate hydrate, the average particle size increased from 102 nm to 660 nm with an increase in the EG content of the solution. The pore structure in the obtained CeO2 particles also depended on the weight ratio between EG and PEG20,000.

Aqueous solutions containing Zn(OH)(4)(2-) ions were prepared by adding 50 ml of 1.5 mol l(-1) aqueous alkali metal hydroxide (MOH: M = Li, Na, K, Cs) to 50 ml of 0.1 mol l(-1) aqueous zinc nitrate hydrate (Zn(NO3)(2).6H(2)O). Zinc oxide (ZnO) crystallites were obtained by heating aqueous solutions containing Zn(OH)(4)(2-) ions at greater than or equal to348 or 368 K for 3 h. The morphology depended on both of the heating temperature of the Zn(OH)(4)(2-) aqueous solution and the alkali metal hydroxide used to obtain Zn(OH)(4)(2-) ions. According to the result of the kinetics of the zinc oxide formation, it was shown that the decomposition of Zn(OH)(4)(2-) ions on the zinc oxide surface was the rate determining step when NaOH, KOH and CsOH were used to obtain Zn(OH)(4)(2-) ions. When LiOH was used to obtain Zn(OH)(4)(2-) ions, the rate determining step was the nucleation of zinc oxide and/or the adsorption of Zn(OH)(4)(2-) ions.

Aqueous solutions containing Zn(OH)(4)(2-) ions were prepared by adding 50 ml of 1.5 mol l(-1) aqueous alkali metal hydroxide (MOH: M = Li, Na, K, Cs) to 50 ml of 0.1 mol l(-1) aqueous zinc nitrate hydrate (Zn(NO3)(2).6H(2)O). Zinc oxide (ZnO) crystallites were obtained by heating aqueous solutions containing Zn(OH)(4)(2-) ions at greater than or equal to348 or 368 K for 3 h. The morphology depended on both of the heating temperature of the Zn(OH)(4)(2-) aqueous solution and the alkali metal hydroxide used to obtain Zn(OH)(4)(2-) ions. According to the result of the kinetics of the zinc oxide formation, it was shown that the decomposition of Zn(OH)(4)(2-) ions on the zinc oxide surface was the rate determining step when NaOH, KOH and CsOH were used to obtain Zn(OH)(4)(2-) ions. When LiOH was used to obtain Zn(OH)(4)(2-) ions, the rate determining step was the nucleation of zinc oxide and/or the adsorption of Zn(OH)(4)(2-) ions.

Monodispersed zinc oxide (ZnO) nanoparticle whose average diameter was ca. 20 nm was prepared by heating zinc peroxide (ZnO2) particles at 473 K for 1 h. After ZnO compact was prepared by pressing ZnO nanoparticles, the ZnO compact was sintered at the temperature in the range from 573 K to 1073 K to obtain the nonporous ZnO sintered compact. When the sintering temperature increased from 673 K to 1073 K, the average particle size of the obtained ZnO nanoparticle increased from 35 nm to 53 nm. The obtained ZnO sintered compact had nanopores. The average pore size of the inter-particle pores increased from 35 nm to 82 nm. The pore diameter was regulated by the sintering temperature.

A peroxo niobic acid sol was prepared by peptization of the niobic acid precipitate (Nb2O5.nH(2)O) with a H2O2 aqueous solution. Crystallized Nb2O5 nanoparticles and niobic acid nanoparticles were obtained by heating the peroxo niobic acid sol. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3] = 0.3 mol/l) was heated at 348 K for 1 week, Nb2O5 nanoparticles with a diameter of 4.5 nm and a SBET of 275 m(2)/g were obtained. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3] = 1 mol/l) was heated at 348 K for 1 week, niobic acid nanoparticles with a diameter of less than 2 nm were obtained. The pore structure and degree of crystallinity of the nanoparticles prepared by heating the peroxo niobic acid sol greatly depended on the concentration of the ammonia solution used for preparing the niobic acid precipitate. (C) 2003 Elsevier Inc. All rights reserved.

A peroxo niobic acid sol was prepared by peptization of the niobic acid precipitate (Nb2O5.nH(2)O) with a H2O2 aqueous solution. Crystallized Nb2O5 nanoparticles and niobic acid nanoparticles were obtained by heating the peroxo niobic acid sol. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3] = 0.3 mol/l) was heated at 348 K for 1 week, Nb2O5 nanoparticles with a diameter of 4.5 nm and a SBET of 275 m(2)/g were obtained. When peroxo niobic acid sol prepared by peptization of the niobic acid precipitate ([NH3] = 1 mol/l) was heated at 348 K for 1 week, niobic acid nanoparticles with a diameter of less than 2 nm were obtained. The pore structure and degree of crystallinity of the nanoparticles prepared by heating the peroxo niobic acid sol greatly depended on the concentration of the ammonia solution used for preparing the niobic acid precipitate. (C) 2003 Elsevier Inc. All rights reserved.

Ti-peroxy compound was synthesized from Ti(O-iPr)4 and H2O2. Anatase and rutile TiO2 nanoparticles were prepared by heating the Ti-peroxy compound diluted with a polyol aqueous solution at 368 K for 24 h. In this research, ethylene glycol, glycerin, erythritol, and D-mannitol were used as polyols in the diluting solution. The ratio of anatase/rutile of the TiO2 obtained depended on the polyol concentration in the diluting solution. Furthermore, the polyol concentration at which single-phase anatase could be obtained was lowest when the number of OH groups in the polyol molecule was the highest. With increasing polyol concentration, the obtained TiO2 nanoparticles showed increasing specific surface area and decreasing particle size.

Zinc oxide (ZnO) nanoparticles were obtained by firing the zinc peroxide nanoparticles at more than 473 K for 2 h. The zinc peroxide decomposed at 473 K to form ZnO that contained O22- ions. Furthermore, the ZnO nanoparticles without O22- ions were obtained by decomposition of the zinc peroxide at more than 513 K and the obtained ZnO contained oxygen vacancies. The increase of the unit cell parameter and the decrease of the activation energy for the electronic conduction were observed due to the oxygen vacancy. The ZnO nanoparticles also had lattice strain. The value of Δd/d decreased from 9.1 × 10-3 to 0 when the firing temperature was in the range from 473 K to 773 K.

CeO2(IV) fine particles were prepared by heating a polyethylene glycol solution of Ce(NO3)3·6H2O at 383 K for 3 h. When a polyethylene glycol whose molecular weight was 7500 or 20000 was used for the preparation, the obtained CeO2 particles were almost monodispersed.

An ethanol solution of Ti-peroxy compounds was prepared from the ethanol solution of titanium isopropoxide (Ti(O-iPr)(4)) and H2O2. Heating of the ethanol solution of the Ti-peroxy compounds at 348 K formed a Ti-peroxy gel, and heat treatment of the gel at 348 K for more than 6 h formed gels that consisted of anatase nanoparticles. The diameter of the anatase nanoparticles increased from 9 to 15 nm as the heating time increased from 6 to 48 h. According to the results of the N-2 adsorption measurement, the anatase nanoparticles had micropores, and the specific surface area (S-BET) was in the range of 254 to 438 m(2)/g. The particle size, lattice strain, specific surface area, and photocatalytic activity of the anatase nanoparticles can be regulated by the heating time of the Ti-peroxy gel at 348 K. (C) 2002 Elsevier Science (USA).

An ethanol solution of Ti-peroxy compounds was prepared from the ethanol solution of titanium isopropoxide (Ti(O-iPr)(4)) and H2O2. Heating of the ethanol solution of the Ti-peroxy compounds at 348 K formed a Ti-peroxy gel, and heat treatment of the gel at 348 K for more than 6 h formed gels that consisted of anatase nanoparticles. The diameter of the anatase nanoparticles increased from 9 to 15 nm as the heating time increased from 6 to 48 h. According to the results of the N-2 adsorption measurement, the anatase nanoparticles had micropores, and the specific surface area (S-BET) was in the range of 254 to 438 m(2)/g. The particle size, lattice strain, specific surface area, and photocatalytic activity of the anatase nanoparticles can be regulated by the heating time of the Ti-peroxy gel at 348 K. (C) 2002 Elsevier Science (USA).

Zinc peroxide sols were prepared by the peptization of Zn(OH)(2) using 1 mol/L of H2O2 aqueous solution at 348 K for 2 h. Firing the dried sol powder at 573 K for 2 h formed almost monodispersed ZnO nanoparticles whose average diameter was 19 nm.

Zinc peroxide sols were prepared by the peptization of Zn(OH)(2) using 1 mol/L of H2O2 aqueous solution at 348 K for 2 h. Firing the dried sol powder at 573 K for 2 h formed almost monodispersed ZnO nanoparticles whose average diameter was 19 nm.

Fe(III)-doped TiO2 (anatase) was prepared by the oxidation of FexTiS2. Two calcination methods were used to oxidize FexTiS2. In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO2 (anatase), forming Fe(III)-doped TiO2 (anatase), in the composition range of 0 less than or equal to Fe/Ti less than or equal to 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of FexTiS2. The electronic property and the valence stage of the Fe(III)-doped TiO2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO2 (anatase) was decreased by the Fe(III) doping.

A crystallized titania gel was prepared without gel-collapse and precipitation by heat treatment at 348K for 24h of an aqueous ethanol solution of the Ti-peroxy compound obtained from Ti(OiPr)(4) and H2O2. The structure of the TiO2 in the gel changed from rutile to anatase as the ethanol concentration in the gel increased.

Fe(III)-doped TiO2 (anatase) was prepared by the oxidation of FexTiS2. Two calcination methods were used to oxidize FexTiS2. In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO2 (anatase), forming Fe(III)-doped TiO2 (anatase), in the composition range of 0 less than or equal to Fe/Ti less than or equal to 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of FexTiS2. The electronic property and the valence stage of the Fe(III)-doped TiO2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO2 (anatase) was decreased by the Fe(III) doping.

A crystallized titania gel was prepared without gel-collapse and precipitation by heat treatment at 348K for 24h of an aqueous ethanol solution of the Ti-peroxy compound obtained from Ti(OiPr)(4) and H2O2. The structure of the TiO2 in the gel changed from rutile to anatase as the ethanol concentration in the gel increased.

Cr3+-M2+ (M=Ni, Zn, Co, Cu) oxalate complexes were obtained by heat treatment of a polyethylene glycol (PEG) solution of a metal nitrate hydrate at 353 K for 6 h. The relation between the cation mole fraction [M2+/(Cr3++M2+)] in the PEG solution and in the precipitate obtained depended on the molecular weight of the PEG. The structure and the cation arrangement in the oxalate precipitate also depended on the molecular weight of the PEG. Two different models for the process of precipitate formation were examined in which it is assumed that Cr3+ and M2+ coordinate to PEG independently of and cooperatively with each other, respectively. The calculated relation between the M2+ mole fraction of the PEG solution and that of the precipitate was compared with the relation obtained from the experimental results. The results obtained from the second model agreed quite well with the experimental results. We therefore conclude that Cr3+ and M2+ coordinate cooperatively to PEGs.

Cr3+-M2+ (M=Ni, Zn, Co, Cu) oxalate complexes were obtained by heat treatment of a polyethylene glycol (PEG) solution of a metal nitrate hydrate at 353 K for 6 h. The relation between the cation mole fraction [M2+/(Cr3++M2+)] in the PEG solution and in the precipitate obtained depended on the molecular weight of the PEG. The structure and the cation arrangement in the oxalate precipitate also depended on the molecular weight of the PEG. Two different models for the process of precipitate formation were examined in which it is assumed that Cr3+ and M2+ coordinate to PEG independently of and cooperatively with each other, respectively. The calculated relation between the M2+ mole fraction of the PEG solution and that of the precipitate was compared with the relation obtained from the experimental results. The results obtained from the second model agreed quite well with the experimental results. We therefore conclude that Cr3+ and M2+ coordinate cooperatively to PEGs.

Iron oxide films were prepared by the polymer precursor method with alkaline metal (Li, Na, and K) ion doping. Alkaline metal ions were used to regulate the thermal decomposition process of the cation-citrate complex, that is, the precursor of the film. The spinel iron oxide films were obtained by firing the precursor with the alkaline ion doping [Na/Fe (atomic ratio) greater than or equal to 0.2 and K/Fe (atomic ratio) greater than or equal to 0.2] at 773 K for 5 min in air. The formation mechanism of the spinel iron oxide films was investigated by differential thermal analysis (DTA) and x-ray photoelectron spectroscopy (XPS) measurements. Formation of the carbon-iron oxide complex was observed, and this reduction atmosphere induced the formation of the spinel iron oxide films. This method gave the spinel iron oxide films of which nanostructures are controlled.

Porous iron oxide films were prepared by the polymer precursor method with poly(vinyl alcohol) (PVA). Pore size distribution of the films was determined by the N-2 adsorption isotherm at 77K with the aid of the quartz crystal microbalance method. The crystal and pore structures of the iron oxide film varied with the amount of PVA in a coating solution; the crystal structure changed from alpha-Fe2O3 to gamma-Fe2O3 with an increase of PVA. XPS valence band spectra showed the presence of the layer of Fe3O4 in a mixed valence state on the surface of the microporous film. Also the temperature dependence of the electrical resistance of the film showed the presence of the Fe3O4 like layer on the film surface. The kinetics of the reduction of the porous iron oxide films was examined, and the activation energy of the reduction was determined. The Gibbs free energy of the film reduction of alpha-Fe2O3 to Fe3O4 decreased. Hence, it was shown that the surface energy of the porous films controls the crystal and surface structures of the film.

The lower valent cations were homogeneously doped in p-type oxide films. The prepared doped oxide systems were Mg-doped alpha-Cr2O3, Ni-doped alpha-Cr2O3, and Li-doped NiO. The Mg doping induced a homogeneous mixed valence state of Cr3+ and Cr6+ in the Cr2O3 film, reducing the Mg dopant to the metallic valence state in the Cr2O3 lattice, which is completely different from the powder or single crystalline system. The mixed valence state formation gave rise to a marked chromism. The mixed valence formation and perfect reduction of the lower valent dopants were evidenced by X-ray photoelectron spectroscopy, electrical conductivity change, and optical absorption. Ni-doped alpha-Cr2O3 and Li-doped NiO showed similar results. The reduction kinetics of the mixed valence state in the p-type oxide lattice with the aid of the electrical conductivity measurement suggested that the rate-determining step is not the diffusion of oxygen.

Ti4+-doped alpha-Fe2O3 films have been prepared by the sol-gel method. The dispersed state of the doped Ti ions in the film was compared with a Ti-doped powder prepared by a coprecipitation method in order to examine homogeneous dispersion effects of the sol-gel method. X-Ray diffraction (XRD) showed the highly oriented structure of the set-gel-derived Ti-doped alpha-Fe2O3 films. Ti doping can control the electrical conductivity of the film effectively. X-Ray photoelectron spectroscopy (XPS) valence band spectra evidenced the formation of the mixed valence with Ti doping. The data on electrical conductivity changes with doping indicated a distinct difference of Ti-dopant dispersion in the film and powder. The depth profile of the Ti dopants from the surface was measured with XPS using Ar-ion etching; the Ti dopants are more homogeneously distributed in the sol-gel-derived film than in the powder.

The surface of activated carbon fiber (ACF) was oxidized by a H2O2 solution or was reduced by H-2 gas and the change in the water adsorption isotherm as a result of such surface treatments was examined at 303 K. The surface oxidation by H2O2 increased the amount of adsobed water in the low-pressure region, while the reduction by H-2 decreased the low-pressure adsorption of water. The surface oxidation also increased slightly the intensity of the XPS C-1s tail in the high-energy region. The XPS ratio spectrum, using the spectrum of the reduced ACF as the standard, gave an explicit peak due to the presence of surface functional grops. The ratio peak area had a linear relationship with the amount of adsobed water in the low-pressure region.

Research News: The sol-gel method can be used to produce multicomponent oxide materials which have a homogeneous composition even at the atomic level. Thin transition metal oxide films are shown to exhibit different properties from those of the bulk material and both the crystal structure and the valence slate of the materials can be sensitively controlled by doping. Recent progress in the field is reviewed, including the production of highly oriented films, valence-controlled oxides, the control of instable phase formation and atmosphere-sensitive structural transformations.

The surface of activated carbon fiber (ACF) was oxidized by a H2O2 solution or was reduced by H2 gas and the change in the water adsorption isotherm as a result of such surface treatments was examined at 303 K. The surface oxidation by H2O2 increased the amount of adsobed water in the low-pressure region, while the reduction by H2 decreased the low-pressure adsorption of water. The surface oxidation also increased slightly the intensity of the XPS C18 tail in the high-energy region. The XPS ratio spectrum, using the spectrum of the reduced ACF as the standard, gave an explicit peak due to the presence of surface functional grops. The ratio peak area had a linear relationship with the amount of adsobed water in the low-pressure region. © 1995, American Chemical Society. All rights reserved.

Ultrafine Ti(IV)-doped alpha-FeOOH particles were dispersed on the high-surface-area carbon fibers of uniform micropores in order to elucidate the role of the surface electronic factor in the micropore filling of supercritical NO. EXAFS and XANES showed that dispersed Ti-doped alpha-FeOOH particles are ultrafine and have the same local structure as that of bulk alpha-FeOOH particles. The microporosity of the samples did not change significantly by the doping of Ti(IV) in dispersed alpha-FeOOH on the basis of N2 adsorption. Also, the surface acidic site concentration measured by the irreversible NH3 adsorption was almost constant regardless of the Ti doping. However, doping of Ti(IV) in the dispersed alpha-FeOOH enhanced the micropore filling of supercritical NO by 40%, at the maximum. The enhancement of the NO micropore filling by Ti doping was presumed to come from the increase of quasi-free electrons in the dispersed alpha-FeOOH fine particles due to mixed valence formation, which is enhanced by the surface segregation of Ti(IV) from the XPS examinations.

The electrical conductivity of the NiO film was controlled by doping Li ions. The junctioned oxide film of p-type Li-doped NiO and n-type TiO2 was prepared by the sol-gel method. The p-n junctioned oxide film showed clear rectification effect.