Sol Particles Research Articles

Kinetics of Sol-Gel Transformation for the Preparation of TiO<sub>2</sub> Ultrafiltration Membrane

The sol-gel technique is considered to be one of the most practical methods for producing ceramic membranes, and the properties of the sols could affect the microstructures of the desired products. Especially, optimized viscosity and a short gelation time can reduce the sol particles infiltrate into the pores of the support. So how to control the forming process of the gel is essential for fabricating the membranes. In this paper, we developed a kinetic equation of sol-gel transformation to study the relationships between viscosity and time of titanium sol systems by using N, N—Dimethylformamide (DMF) as solvent. Both the growth process of the sol particles and activation energy of the process were investigated according to the kinetic curves. The results indicate that the viscosity of sols decreases with the increment of R and temperature, but increases with rw, at the same time the gelation time decreases with rw, temperature and R. Furthermore, the growth of sol particles versus time accord with the NLG model, and the activation energy of gelation process decreased with R. When R changed from 2 to 6, the activation energy was decrease from 12.48KJ/mol to 9.35KJ/mol. According to the analysis of the results of the sol-gel transformation, a shorter gelation time could be obtained by increaseing the rw, R and the gelation’ temperature.

Preparation of organic/inorganic hybrid silica using methyltriethoxysilane and tetraethoxysilane as co-precursors

The preparation of a clear, organic/inorganic hybrid silica sol using methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) as co-precursors under alkaline conditions is reported. Two types of alkaline catalysts—ammonia and tetra-methyl-ammonium hydroxide (TMAH)—were examined for use in the preparation of colloidal sols of <100 nm in diameter, which are suitable for fabrication of nanoporous hydrophobic membranes. Factors that might influence sol preparation were investigated. When ammonia was used as the catalyst, the hydrolysis-polymerization reaction ratio decreased with both an increase in the molar ratio of MTES/TEOS, and a reduction in the water molar ratio. However, when TMAH was used as the catalyst, the water molar ratio had no effect on the hybrid sol preparation reactions. Even systems that employed higher molar ratios of MTES/TEOS or a lower water molar ratio relative to those of the original reactants, allowed for successful preparation of clear sols with a mean sol particle size of <40 nm.

Effect of the nature of anions of aluminum salts used to synthesize a precursor of the Al2O3-ZrO2 ceramics on the stabilization of the tetragonal modification of zirconium dioxide

Samples of a precursor for an aluminum oxide ceramics reinforced with zirconium oxide were synthesized by hydrolysis of various aluminum salts in the presence of a ZrO2 sol under conditions of urea decomposition at 90°C and pH < 4 maintained, with hydrolysis products deposited onto the surface of ZrO2 sol particles. It was found that the nature of a salt anion affects the interaction of hydrolysis products of the aluminum cation with the surface of ZrO2 sol particles. The structure of products formed in thermal treatment of samples of a precursor for Al2O3-ZrO2 (T = 1250°C) was characterized by X-ray phase analysis and scanning electron microscopy. The phase transition temperatures of the oxides Al2O3 and ZrO2 contained in the precursor were estimated using the results of thermal analysis of the samples in the temperature range 20–1300°C.

Electrophoretic Deposition/Infiltration of Natural Zeolite Particles on/into Various Substrates

Electrophoretic deposition (EPD) and infiltration (EPI) behavior of a natural zeolite (clinoptilolite, produced in Akita prefecture, Japan) particles on/into a steel and a porous glass substrates were investigated for the purpose of the environmental purification. The obtained deposit of the zeolite prepared by the EPD was less durable against peeling off compared with the EPI process, but it was improved by use of silica sol particles as a binder. Ion uptake efficiency of the EPD sample was superior to that of the EPI sample, that will be caused by the shape factor of the zeolite particle deposit.

Regularities of the change in colloid-chemical properties of silica hydrosols in the presence of alkali metal hydroxides

The effect exerted by type of alkaline hydroxide additive on the change in turbidity and on the formation of silica hydrosol spatial structures was studied. Silica depolymerization in an alkaline solution to form active silicic acids was studied depending on the aging time of the system, size of sol particles, and the type of alkaline hydroxide additive.

A study on the effect of synthesis parameters on the size of nickel particles in sol–gel derived Ni–SiO2–Al2O3 nanocomposites

The present work deals with the synthesis of Ni–SiO2–Al2O3 nanocomposites fabricated by embedding nickel oxide particles, obtained from hexahydrated nickel nitrate [Ni(NO3)2 · 6H2O], in matrixes with different molar percents of Silica/Alumina, through sol–gel method based on hydrolysis and condensation of tetraethylorthosilicate (TEOS) and Aluminum Isopropoxide [Al(OC3H7)3] alkoxides. Due to the various factors, e.g., pH, EtOH/TEOS/H2O ratio, Si/Ni ratio etc., influencing the nickel grain size of the nanocomposites, Taguchi robust design method of system optimization was used to determine the percent of contribution (%ρ) of each factor. The nanocomposites were reduced in a flow of hydrogen and nitrogen gas at 700 °C for half an hour. The nickel grain size in the nanocomposites was determined by utilizing Scherrer`s method and XRD patterns. The smallest nickel grain size obtained from the Taguchi orthogonal array was about 24 nm, later confirmed by TEM observations. After optimization of the controlling factors, a nickel grain size of 15.4 nm was obtained. It was found that the SiO2/Al2O3 molar ratio of the matrix had the most influence on the nickel grain size (29.22%) and the Water/TEOS molar ratio stood in second place (21.44%). It was illustrated that the starting temperature of the aluminum isopropoxide had the least influence on the nickel grain size.

An Experimental Study on the Free‐Radical Copolymerization Kinetics with Crosslinking of Styrene and Divinylbenzene in Supercritical Carbon Dioxide

AbstractA study on the effect of process conditions and composition of the reacting mixture on the kinetics and particle properties in the copolymerization of styrene and divinylbenzene in supercritical carbon dioxide is presented. Polystyrene‐block‐polydimethylsiloxane and Krytox 257 FSL (Dupont) were used as stabilizers, and their performance compared. A 38 mL, high‐pressure view cell, equipped with one frontal and two lateral sapphire windows, was used as the reacting vessel. The polymer product was characterized for total monomer conversion, gel content, molecular weight averages of the sol fraction and particle size distribution. Acceptable polymerization rates and partially‐agglomerated spherical particles were produced under the conditions tested.magnified image

Influence of pH value of TiO2 sol on surface gloss of corresponding TiO2 film coated on ceramic tiles

A series of TiO2 sols with different pH values prepared by the sol-gel method under acid conditions were coated onto the surfaces of ceramic tiles to obtain the corresponding TiO2 films respectively. The surface gloss and roughness of the as-prepared TiO2 films were measured by a glossmeter and an atomic force microscope (AFM) respectively. It has been found that the surface gloss of the as-prepared TiO2 films is decreased but its roughness is increased with the increase of the pH value of TiO2 sol. Moreover, the measurement result of the as-prepared TiO2 sols by Zetasizer shows that the ζ potential of TiO2 sol is increased with the increase of pH value of TiO2 sol. It is proposed that the increase of ζ potential will cause a stronger repulsion of particles in TiO2 sol, resulting in a rougher surface and then lower surface gloss of the corresponding TiO2 film.

Sol–gel dry spinning of mullite fibers from AN/TEOS/AIP system

Continuous mullite ceramic fibers were fabricated by a sol–gel dry-spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate, aluminum isopropoxide and tetraethylorthosilicate. The sol–gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature of the sol. Combined with size analysis of sol particles and TEM analysis, the growth characteristics of sol particle agglomeration and its structural evolution were examined. By adjusting the temperature, the gelation degree could be stabilized at a certain value, and the sol–gel transition could be transferred to the spinning line. Continuous fibers were obtained from such sols using a laboratory dry-spinning apparatus. Sintering of the precursor fibers at 1100 °C yielded crack-free mullite ceramic fibers when the solid content of spinnable sol was above 50%.

Photocatalytic degradation of methylene blue and acetaldehyde by TiO2/glaze coated porous red clay tile

Nanosized TiO2 sol synthesized by sol-gel method was successfully coated on the porous red clay tile (PRC tile) with micrometer sized pores. PRC tile was first coated with a low-firing glaze (glaze-coated PRC tile) and then TiO2 sol was coated on the glaze layer. A low-fired glaze was prepared at various blending ratios with frit and feldspar, and a blending ratio glazed at 700 °C was selected as an optimum condition. Then TiO2 sol synthesized from TTIP was dip-coated on the glazed layer (TiO2/glaze-coated PRC tile), and it was calcined again at 500 °C. Here, these optimum calcination temperatures were selected to derive a strong bonding by a partial sintering between TiO2 sol particles and glaze layer. Photocatalytic activity on the TiO2/glaze-coated PRC tile was evaluated by the extent of photocatalytic degradation of methylene blue and acetaldehyde. Methylene blue with the high concentration of 150 mg/l on the surface of TiO2/glaze-coated PRC tile was almost photodegraded within 5 hours under the condition of average UV intensity of 0.275 mW/cm2, while no photodegradation reaction of methylene blue occurred on the glaze-coated PRC tile without TiO2. Another photocatalytic activity was also evaluated by measuring the extent of photocatalytic degradation of gaseous acetaldehyde. The photodegradation efficiency in TiO2/glaze-coated PRC tile showed about 77% photocatalytic degradation of acetaldehyde from 45,480 mg/l to 10,536 mg/l after the UV irradiation of 14 hours, but only about 16% in the case of the glaze-coated PRC tile.

Lateral flow (immuno)assay: its strengths, weaknesses, opportunities and threats. A literature survey

Lateral flow (immuno)assays are currently used for qualitative, semiquantitative and to some extent quantitative monitoring in resource-poor or non-laboratory environments. Applications include tests on pathogens, drugs, hormones and metabolites in biomedical, phytosanitary, veterinary, feed/food and environmental settings. We describe principles of current formats, applications, limitations and perspectives for quantitative monitoring. We illustrate the potentials and limitations of analysis with lateral flow (immuno)assays using a literature survey and a SWOT analysis (acronym for "strengths, weaknesses, opportunities, threats"). Articles referred to in this survey were searched for on MEDLINE, Scopus and in references of reviewed papers. Search terms included "immunochromatography", "sol particle immunoassay", "lateral flow immunoassay" and "dipstick assay".

Serum cystatin C measured by a sol particle homogeneous immunoassay can accurately detect early impairment of renal function

A sol particle homogeneous immunoassay (SPIA) is a method to measure the serum cystatin C (cysC) level as a marker of the glomerular filtration rate (GFR). Recently, formulas to convert measured cysC to GFR have been developed. A total of 154 patients (46 +/- 18 years old) who had undergone renal biopsy, sodium thiosulfate clearance (C thio) and 24-h creatinine clearance (24-hCcr) tests were subjects for the study. Their serum cysC levels were determined by SPIA. Multiple regression analysis revealed C (thio) and age as independent variables for serum creatinine concentration (Cr), while only C thio affected cysC. The equations using Cr or cysC showed significant correlation with C thio. Receiver-operating curve ROC analysis revealed that cysC and 24-hCcr shared comparable power to detect patients with GFR < 90 or 60 ml/min/1.73 m2 (AUC = 0.862 and 0.943 vs. AUC = 0.842 and 0.943, respectively), while Cr (AUC = 0.881) and MDRD2 (AUC = 0.888) showed slightly inferior ability to detect 60 ml/min/1.73 m2 than other parameters in the female population. The cut-off point of cysC and Cr obtained from the ROC analysis demonstrated strong power to detect patients with C thio < 90 ml/min/1.73 m2 or C thio < 60 ml/min/1.73 m2. According to CKD stages, the mean values of each equation were significantly different, like that demonstrated by 24-hCcr. SPIA could determine cysC levels that detected early renal impairment. The accuracy of cysC to detect early renal impairment may be superior to that of Cr in females, while it would be comparable to that of CG or MDRD when they are corrected by sex and age. Both cysC itself and cysC equations are effective to monitor the progress of renal impairment. The future standardization of cysC measurements and development of novel equation of cysC would contribute to the further improvement of GFR estimation in clinical practice.

Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO2, tlm, after a thermal treatment (1250°C). The structure of samples in the system Al2O3-ZrO2 is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO2 sol particles in decomposition of urea. The coating of ZrO2 sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO2 sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al2O3-ZrO2 was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorption isotherms.

Influence of silica sol particle behavior on the magnesium anodizing process with different anions addition

Combining the processes of colloid chemistry and electrochemistry the anodic films were made in electrolytes with silica sol addition. Two basic electrolytes 1 M NaOH + 10 vol.% silica sol and 1 M Na 2SiO 3 +10 vol.% silica sol were chosen to investigate the silica sol particle behavior during the anodizing process. The anodic films were prepared separately in the two basic electrolytes with various Na 2CO 3 or Na 3PO 4 additions at 2 A/dm 2, 20 °C for 10 min. The micro-images and element contents of the specimen were characterized by SEM and EDS. The results showed that some cracks appeared on the films by adding PO 4 3− in both of the two basic electrolytes. And the films became compact and uniform with the addition of CO 3 2− in Na 2SiO 3 basic solution. Moreover, the film average thickness decreased with adding anions. It can be confirmed that the sol particle adsorbing behavior in the solution was influenced by the amount of anions' charges, size and structure.

Europium(III) Complexes Containing Organosilyldipyridine Ligands Grafted on Silica Nanoparticles

This work focuses on the grafting of transition metal complexes on silica surface nanoparticles. Nanoscale silica particles in aqueous sols are used as starting silicated materials. We have undertaken the synthesis of europium(III) complexes containing organosilyldipyridine ligands, (EtO)3Si(CH2)3NHCH2-bipy (1) and (EtO)(CH3)2Si(CH2) 3NHCH 2-bipy (2), in view of a direct grafting reaction on silica nanoparticles. Reaction of one molar equivalent of 1 and 2 with Eu(tmhd)3 (tmhd= 2,2,6,6-tetramethyl-3,5-heptanedionato), as precursor, leads to octacoordinated silylated europium(III) complexes [Eu(tmhd)3(1)] (3) and [Eu(tmhd)3(2)] (4) as white solids in 34-54% yields. Europium complexes were characterized by elemental analysis, mass spectrometry, FT-IR, UV, and luminescence spectroscopies. These new complexes are reacting in a 1:10 (v/v) water and ethanol mixture with silica nanoparticles colloidal sol. Elemental analysis and thermogravimetric data indicated grafting ratios of 0.41 and 0.26 mmol of europium(III) complexes per gram of silica. Functionalized silica nanoparticles were characterized by DRIFT spectroscopy and TEM microscopy. The first analysis shows that the chemical integrity of the complexes is retained on the silica surface together with the size and the monodispersity of the nanoscale particles. As expected for europium(III) complexes, luminescence is observed under UV irradiation. Emission and excitation spectra indicate that the metal coordination environment is not modified on the silica surface. Moreover, the sharpness of the luminescence bands and the strong antenna effect are maintained when complexes are covalently bonded to silica. New luminescent europium(III) complexes grafted on silica nanoparticles are therefore obtained from our approach.

Development of thin-film nano-structured electrolyte layers for application in anode-supported solid oxide fuel cells

This paper reports a study on the deposition of sol particles for the preparation of thin and ultra-thin electrolyte membrane layers (thickness < 5 μm–50 nm), which cannot be produced with regular powder-based processes. For the deposition process, a range of coating liquids with varying particle sizes, covering the complete range between standard suspensions with a particle size of several 100 nm and nano-particle sols, was prepared. In the first part, it is demonstrated that a colloidal sol route can be used for membrane formation on a regular macroporous SOFC anode (NiO/zirconia), when the sol particle size is adapted to the pore structure of the anode (particle size ∼ 200 nm). SEM characterization indicated a thickness in the range 3–4 μm after calcination at 600 °C and ca. 2 μm after sintering at 1400 °C, far below the limit for conventional powder-based deposition methods. In the second part, ultra-thin zirconia and ceria membrane films are prepared by spraying sols containing nano-particles (average size 5–6 nm). The layers show a thickness of ∼ 100 nm, a very narrow particle size distribution and tight ultra-microporous structure, which allows a sintering treatment below 1000 °C, and can be used as an additional electrolyte layer for improving the leak rate of the cell or as diffusion barrier.

Changes in the State of Silver Sol Particles after Low-Temperature Treatments

The influence of the low-temperature treatment of Ag hydrosol on the properties of silver particles was studied by electron absorption spectroscopy over the temperature range 77–230 K. Low-temperature treatment caused the aggregation of particles because of an increase in the number of defects on the surface of Ag observed as an increase in the damping coefficient of electron plasma oscillations. These processes depended on the temperature and initial concentration of disperse silver. Defect formation is explained taking into account the tunnel mechanism of the interaction of low-atomic mobile H+(H2O)nand OH-(H2O)nclusters with the surface of silver particles at low temperatures.

The sol–gel transition of mullite spinning solution in relation to the formation of ceramic fibers

Continuous mullite ceramic fibers were fabricated by a sol–gel dry spinning technique. The sol was prepared from an aqueous solution of aluminum nitrate (AN), aluminum isopropoxide (AIP) and tetraethylorthosilicate (TEOS). The sol–gel transition was investigated by measuring the volume, the solid content, the viscosity and the rheological properties of the solution. Shear viscosity η of the mullite sol varied dynamically with concentrating time and temperature. Combine size analysis of sol particles and TEM analysis on this basis, the growth character of sol particles agglomeration and its structural evolution were discussed. By adjusting the temperature, the gelling degree could stabilize at a certain value and the sol–gel transition could be transferred to the spinning line. Continuous fibers were spun from such sols immediately before gelling in a laboratory dry spinning apparatus. The spinneret contained thirty circular holes, each having a diameter of 0.2 mm. The temperature inside the spinning channel was 100–120 °C, the winding speed was 100–300 m/min. Sintering of the precursor fibers at 1,100 °C yields crack-free mullite ceramic fibers.

Preparation of anatase F doped TiO2 sol and its performance for photodegradation of formaldehyde

Anatase fluoride doped TiO2 sol (F-TiO2) catalyst was prepared by a modified sol-gel hydrothermal method, using tetra butyl titanate as a precursor. The influences of F doping, temperature of hydrothermal, values of medium pH on the morphology and crystallization were studied. The microstructure and morphology of sol sample were characterized by XRD, TEM, FTIR, UV–Vis–DRS, particle size distribution (PSD) and XPS. The results showed that F-TiO2 particles in sol were spherical and partly crystallized to anatase structure, and dispersed in the aqueous medium homogeneously and that the average particle size was ca. 10.5 nm calculated from XRD and TEM results. It was also found that the addition of fluorine could improve the crystallization and adsorption of particles significantly, the photocatalytic activity for decomposition of formaldehyde were enhanced remarkably with the doping of fluorine. Possible mechanism of anatase F-TiO2 formed under hydrothermal conditions was discussed.

Ultrathin, hydrogen-selective silica membranes deposited on alumina-graded structures prepared from size-controlled boehmite sols

A novel membrane is described consisting of an ultrathin 20–30 nm permselective layer of silica deposited on an intermediate multilayer γ-alumina substrate with a graded structure. The alumina substrate is formed on top of a macroporous alumina support by sequentially dipping and calcining a series of dilute solutions containing boehmite (AlOOH) sols of different particle sizes. The size of the sol particles is tuned by precisely controlling synthesis parameters including acid type, acid concentration and hydrolysis time. The topmost silica layer is deposited on top of the intermediate alumina layer by chemical vapor deposition of a silica precursor, tetraethylorthosilicate, in an inert atmosphere. Cross-sectional images of the membranes obtained from scanning electron microscopy (SEM) show that the intermediate alumina layers are formed from particles of progressively smaller size so as to form a smooth interface between the rough support and the topmost amorphous silica layer. The resulting silica-on-alumina composite membrane had high permeance of 5.0 × 10 −7 mol m −2 s −1 Pa −1 and good selectivities for hydrogen over CH 4, CO and CO 2 of over 1500 at 873 K.