Morphological behavior of spherically granulated hydrated zirconium dioxide during its chemical and hydrothermal treatments

Hydrated zirconium dioxide samples were synthesized via original sol–gel route by two-step neutralization of zirconium oxychloride. Spherical granules of zirconia materials were prepared using a well-known “oil-drop” method. By the use of low temperature nitrogen adsorption, it is shown that surface fractal dimension of synthesized xerogels strongly depends on synthesis conditions, chemical and hydrothermal treatments. It is established that the change of synthesis conditions allows to obtain zirconium containing materials with developed porous structure: BET surface area—250–450 m²/g, pore diameter—2.0–4.2 nm, surface fractal dimension—2.28–2.63. It is shown that surface fractal dimension is an important parameter allowing to control the final properties of synthesized material and to determine the reasons of non-reproducibility of adsorptive, catalytic and other physical and chemical properties of zirconium containing oxides from synthesis to synthesis.     

Binary ZrO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> xerogels: Synthesis and properties

Binary systems of silica and zirconia xerogels have been prepared by hydrolysis of zirconium(IV) oxychloride in the silica gel matrix. Systems of various composition have been studied by ¹H NMR, IR spectroscopy, and thermogravimetry and have been tested in a model process of hydrogen peroxide decomposition. It has been shown that the physicochemical properties of binary oxide systems can be tailored by varying the component ratio.     

Highly anti–anti selective synthesis of bis-β-amino ketones via three-component direct Mannich-type reaction of terephthalaldehyde catalyzed by ZrOCl2·8H2O

At room temperature, zirconium oxychloride (ZrOCl₂·8H₂O) efficiently catalyzes the direct Mannich-type reaction of a variety of in situ generated bis-imines using terephthalaldehyde and anilines with ketones in a three-component reaction at room temperature. The reaction proceeds rapidly and affords the corresponding bis-β-amino ketones in good-to-high yields with good-to-excellent anti–anti selectivity.     

固体超强酸SO2-4/ZrO2的制备及其催化性能研究

以氧氯化锆为锆原,氨水为沉淀剂,硫酸溶液为浸渍液,通过沉淀-浸渍法制备SO2-4/ZrO2(SZ)酯化催化剂,其结构经BET、X-射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)及扫描电子显微镜(SEM)表征.结果表明:随着焙烧温度升高,催化剂的比表面积依次降低,孔径增大,氧化锆的晶态由无定形态转化为四方晶态再转化为单斜晶态;于600℃焙烧时,催化剂形成的S=O键红外吸收峰最强;于700℃焙烧时,催化剂结构被破坏.在丙烯酸与十八醇的酯化反应中对催化剂进行活性测试.结果表明:600℃焙烧的催化剂产率最高(96.4%).     

Porosity of some iron(III), chromium(III), and zirconium(IV) hydroxide oxide xerogels

Porosity and density in water are studied for xerogels prepared by drying iron(III), chromium(III), and zirconium(IV) hydroxide oxide (HO) hydrogels. The hydrogels are either freshly precipitated at pH 7–11 or aged in sodium chloride or sodium sulfate solutions. The space distribution in the xerogels between the volume occupied by the constituent ions and the interstitial volume (spaces between metal-oxygen chains, mesopores, micropores, and macropores) is determined. The meso-and micropore volumes of the chromium(III) HO xerogels are two to four times the volumes of iron(III) and zirconium(IV) HO xerogels. We suggest that the microstructure of the chromium(III) HO hydrogels is almost fully inherited by their xerogels.     

Changes in the zirconium local surrounding on ligand substitution in solutions

EXAFS and SAXS methods have been used to examine zirconium hydroxide and oxychloride aqueous solutions in the presence of sulfuric acid in a wide range of concentrations, as well as a zirconium sulfate aqueous solution. The structure of the complexes and their transformation regularities were determined. Structures of the given complexes and structures of zirconium hydroxide and zirconium oxychloride and hydroxide complexes in aqueous solutions were compared. Complexes in zirconium hydroxide and oxychloride aqueous solutions have identical structures in the presence of sulfuric acid. When the concentration ratio of sulfuric acid and the initial compound is low (20–30), the complex is an open trimer with zirconium atoms bonded by sulfate groups. Bridge sulfate groups form Zr-O-S-O-Zr bonds. Apart from the bridge sulfate groups, there are three terminal sulfate groups and three terminal hydroxyl groups for each zirconium atom. When the concentration of sulfuric acid is increased (up to a ratio of 40–100), closed trimers are observed in the solution.     

Reactions of Metal Salts and Alkali Metal Nitrates. Role of the Metal Precursors and Alkali Metal Ions in the Resulting Phase of Zirconia

Zirconia powders are prepared by reaction of a zirconium precursor with an alkali metal nitrate. The major part of the reactions takes place before the melting points and then the reactions go slowly to completion at 450°C in the molten salts. The roles of the precursor and the alkali metal ion are discussed considering the reaction between two precursors, octahydrated zirconium oxychloride and zirconium tetrachloride, and two nitrates, LiNO₃ and NaNO₃, and some resulting physico-chemical differences. The obtained zirconia powders contain very small amounts of alkali metal ions which act as stabilizing agent. Their effect on the balance tetragonal-monoclinic ZrO₂ depends upon the homogeneity of their distribution which is related to their ability to diffuse inside the bulk of particles and their polarizing power when located mainly on the surface.     

Effect of preparative conditions on the surface characteristics of mixed zirconium and titanium oxides

The surface characteristics of mixed zirconium and titanium oxides prepared from different starting materials are investigated. One mode of preparation entailed the use of zirconium sulfate and titanium oxysulfate as starting materials and ammonium hydroxide as precipitating agent. The produced oxides were washed to different extents to obtain samples with different sulfate content. A second preparative mode used zirconium oxychloride and titanous chloride as starting materials also with ammonium hydroxide as precipitating agent. The oxidation of the titanous to the titanic form for these oxides was carried out by means of oxygen gas. Resulting samples were heat treated at 400 °C and 600 °C, and textural characteristics determined from the adsorption of N₂ at 77 K, complemented by infrared and thermal studies. The samples precipitated from the oxychloride and chloride salts of zirconium and titanium, as well as those precipitated from the sulfate and oxysulfate salts and washed free of the sulfate ions displayed quite similar textural characteristics. The unheated samples and those heat-treated at 400 °C were mesoporous, with some microporosity, and relatively large surface areas in the order of 200–300 m²/g. Heat treatment to 600 °C led to a relative decrease in surface area, in the order of 100 m²/g, and to the disappearance of microporosity. The mixed zirconium and titanium oxides with a sulfate content of ≈17% displayed significantly lower surface areas, smaller than 10 m²/g, with a prevalence of micro and mesoporosity. Infrared and thermal studies indicated the presence of differently bounded sulfato groups, which seem to have a blocking effect on the pores, resulting in the observed smaller surface areas.     

Thermal behavior of the composite xerogels of zirconium oxyhydroxide and silicic acid

Gels were prepared via sol?Cgel method by addition of zirconium oxychloride solution into sodium metasilicate (SZ) and sodium metasilicate solution into zirconium oxychloride (ZS) at varying final pH. Si/Zr molar ratio equaled 1/1. Synthesized gels were dried with calcium chloride until they reached a constant mass. SEM and nitrogen adsorption analysis have shown that SZ gels have surface area 175?C200?m^2?g^?1, consist of 20?C30?nm grains. ZS samples have surface area about 1?m^2?g^?1, consist of grains smaller than 10?nm. Thermal and X-ray phase analysis have shown that transition of amorphous ZrO₂ to crystalline form shifts from 430 to 850?C870?°C for SZ gels. Unlike zirconia gels phase transitions that proceed in order: ??amorphous (430?°C)??tetragonal (800?°C)??monoclinic (1,000?°C) phases??, the monoclinic phase in ZS gels appears immediately after transition from amorphous to crystalline state; the tetragonal phase in SZ samples is stable until 1,000?°C.     

The Structure Formation of Zirconium Oxide Gels in Alcoholic Solution

Zirconium oxide gels were prepared by controlled hydrolysis and condensation of zirconium-n-propoxide in alcoholic solution. After completion of the gelation the aging and drying of the alcogel was observed in situ by Small and Wide Angle X-ray Scattering experiments at room temperature. The xerogels obtained have been annealed at different temperatures to crystallization. The structural changes were observed by using SAXS and WAXS. Structural models reproducing the experimental WAXS data have been simulated by the reverse Monte Carlo method. A comparison between zirconium oxide xerogels obtained under different thermal treatments was made and evidence was found that thermal treatment at higher temperatures and preparation conditions affect the atomic arrangement of these amorphous gels.     

Silica xerogels as a delivery system for the controlled release of different molecular weight heparins

In this work, we investigated a sol–gel derived silica matrix as a delivery system for the prolonged release of different molecular weight heparins, which allows the glycosaminoglicons to retain their whole biological activity. Several xerogels were obtained by embedding different molecular weight heparins into matrices prepared by using different amount of NH₄OH as a catalyst during gel formation. Gel synthesis parameters, drug release properties, and xerogels surface area were evaluated. Unfractionated, low and oligo-molecular weight heparins were embedded into xerogels and the effect of the molecular weight on the release kinetics and the retained biological activity has been investigated. The results show that the surface area of the matrix is a determinant parameter affecting drug release kinetics. This structural feature can be modified by varying the catalyst tetraethoxysilane molar ratio used during the matrix synthesis. In most cases release kinetics fitted the Higuchi diffusive model and a lower diffusion rate was observed from silica matrices characterized by a smaller surface area. In the case of matrices with lower surface area, loaded with unfractionated heparin, zero order kinetics was observed. In this paper, we have defined a heparin release silica xerogel system and we have pointed out how modulation of its synthesis parameters allows adjusting the release of heparin according to therapeutic needs.     

Role of graphene in structural transformation of zirconium oxide

Fine powders of zirconium oxide (ZrO₂) were prepared using zirconium oxychloride by combustion method. The crystalline size of pure ZrO₂ was in range of 14–45 nm. Graphene was incorporated in ZrO₂ using graphene oxide as precursor and reducing it with hydrazine hydrate. X-Ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analysis and Raman spectroscopy methods were used to characterize the samples. The role of graphene in structural transformation of ZrO₂ to monoclinic phase was clearly observed.     

Solvent effects on structural properties of SiO2 gel using n-octylamine as a catalyst

We have investigated the effect of solvent(ethanol, acetone, isopropanol) on the sol–gel process of tetraethylorthosilicate (TEOS) in which case, n-octylamine is used as polycondensation catalyst. Two sets of materials were prepared in the laboratory by using ethanol, acetone and isopropanol as solvents respectively: (1) xerogels from TEOS/n-octylamine, and (2) composites from TEOS/polyhedral oligomeric silsesquioxanes /n-octylamine. The chemical structure of xerogels was studied by FTIR, TG–DSC, scanning electronic microscope and nitrogen adsorption–desorption isotherms techniques. The results have shown that the solvents directly influence the gel time. Gel time is longer for acetone than that of ethanol and isopropanol. In the case of TEOS xerogels, the materials are essentially mesoporous when n-octylamine is used as a catalyst. Silica, when ethanol is used as a solvent, exhibits a more narrow pore size showing textures with a microstructure uniformly distributed with different porosity levels. However, when the aged-isopropanol gel is used, silica shows textures with a microstructure nonuniformly distributed.     

Preparation and characterization of microporous SiO2-ZrO2 pillared montmorillonite

SiO₂-ZrO₂ pillared montmorillonite (SZM) was prepared by the reaction of Na-montmorillonite with colloidal silica-zirconia particles which were prepared by depositing zirconium hydroxy cations on silica particles. By pillaring with the colloidal particles, the basal spacing of montmorillonite was expanded to ca. 45 Å and the calcined SZM samples showed large specific surface areas up to 320 m²/g at 400 °C. In spite of large interlayer separation, adsorption results indicated the presence of micropores generated between the colloidal particles. The microporous structure was maintained at least up to 600 °C and exhibited specific shape selectivity for the adsorption of large organic molecules, especially between toluene and mesitylene. According to the temperature-programmed-desorption (TPD) spectra of ammonia, the calcined SZM showed weakly acidic sites.     

Thermal evolution of (Zr,Ti)O2 gels synthesized at different basicpH

(Zr, Ti)O₂ gels as precursors of zirconium titanate (ZT) powders were prepared by the sol-gel method, which involves hydrolysis of ZrClO₂+TiCl₄ in the presence or absence of hydrogen peroxide, in twopH ranges, 8–9 or 11–12. Thermal evolution of these precursors has been studied by DTA, BET surface area, XRD and SEM. Differences in DTA curves, surface area and morphology were observed. In particular, ZT prepared atpH=8–9 with hydrogen peroxide was purer, more homogeneous and presented a different morphology compared to ZT processed atpH=11–12; hydrated/hydroxylated Zr?Ti species were formed to a greater extent in the latter case. Addition of hydrogen peroxide during chemical processing of these gels plays a key role in controlling the crystallization temperature of ZT.     

Utilization of natural anthocyanin pigments as photosensitizers for dye-sensitized solar cells

Inorganic–organic hybrid crack-free xerogels were obtained by using a surfactant n-octylamine as a catalyst containing tetraethoxyorthosilicate (TEOS) and hydroxyl-terminated polydimethylsiloxane as an additive. We studied the effect of gelling time and viscosity on PDMS–OH concentration. We have demonstrated that the addition of poly(dimethylsiloxane) (PDMS) to a silica oligomer associated with a neutral catalyst, in the presence of a surfactant, accelerated the gelling process; this reduction of the time needed for the product to gel in carbonate stones helped to achieve effective stone protection. It was found that PDMS–OH was chemically incorporated into the gel matrix via Si–O–Si bonds by FTIR analysis and an appreciable reduction of gel fracture for hybrids prepared from 3 % w/w of PDMS. Nitrogen adsorption–desorption isotherms of xerogels were measured, it showed the pore size of xerogels decrease with the addition of PDMS when concentration of PDMS was below 6 %, while xerogels showed pores in the macroporous range when adding 12 % w/w of PDMS. The protective performance evaluated by its ability to resist acid rain reveals that the protective effects were satisfying.     

Co-separation of hafnium with zirconium oxychloride using175,181Hf as radioactive tracer

Co-separation of hafnium with zirconium oxychloride has been studied from 0 to 60°C with the help of^175,181Hf. It was found that zirconium oxychloride undergoes two transitions, one at about 33°C and another at about 59.5°C. From the value of the partition factor it was clear that a separation method based on fractional crystallisation of the oxychloride will not be a successful line of approach. The transition points were verified by DTA study. It was found from the DTA curve that hafnium oxychloride undergoes transition near 90°C. The solubility of zirconium oxychloride and the break in the partition factor also corroborate the above findings.     

Preparation of polyzirconoxane from zirconium oxychloride octahydrate and ethylene glycol as a precursor for zirconia ceramics

An Erratum has been published for this article in Applied Organometallic Chemistry 2001; 15(4):317. The preparation of polyzirconoxanes (EG‐PZO) was investigated by a one‐pot reaction of zirconium oxychloride octahydrate with ethylene glycol. Triethylamine was added dropwise into a mixture of zirconium oxychloride octahydrate, ethylene glycol and methanol to give EG‐PZO with a good spinnability and stability to self‐condensation. The ¹H NMR spectrum, IR spectrum, analytical data and expanded X‐ray absorption fine‐structure analysis indicated that EG‐PZO consisted of Zr < (OH)₂ > Zr linkages as a main chain with pendant 2‐hydroxyethoxy groups, chloro groups and water. The 3Y₂O₃–97ZrO₂ ceramic fibers were prepared by sintering the precursor fibers after the addition of <?tw=97%>Y(acac)₃ (acac = acetoacetate) to EG‐PZO. Copy‐<?tw>­right © 2000 John Wiley & Sons, Ltd.     

Sur la thermogravimétrie des précipités analytiques: Dosage du hafnium

A zirconium-free oxychloride of hafnium was prepared. The hafnium can be determined gravimetrically from the thermolysis curves of the precipitate. In particular, the neutral selenate, the p-hydroxyphenylarsinate and the mandelate were studied, and the curves obtained were compared to those plotted of the homologous zirconium derivatives.     

Leaching of the Anthraquinone Dye Solvent Blue 59 Incorporated into Organically Modified Silica Xerogels

The effects of preparation method and precursor composition on the leaching behavior of the anthraquinone dye Solvent Blue 59 incorporated into silica based xerogels have been studied. Xerogels were prepared under acidic conditions from mixtures of 20 mol% of organically modified silicon alkoxides, R–Si(OR)3, in Si(OR)4 (R = methyl or ethyl, R = methyl, vinyl, phenyl). The dye was added at the beginning of the sol-gel reaction. The reaction was carried out by either hydrolysis under acidic conditions or acidolysis by formic acid. The dye incorporated was leached with refluxing ethanol using a Soxhlet extraction procedure to simulate the long-term stability of the samples prepared. With increasing size of organic substituent (methyl < vinyl < phenyl), the amount of dye leached decreases. Results from nitrogen adsorption experiments show that all samples characterized have about the same average pore diameter, but they differ in total pore volume and BET surface area. With increasing size of the organic residue, the pore volume decreases by an order of magnitude. Therefore, it is concluded that the microstructure of the xerogels prepared determines the retention behavior of dyes incorporated during the sol-gel reaction.