Ludox Colloidal Silica Research Articles

Silicalite-1 synthesized with geothermal and Ludox colloidal silica and corresponding TiO2/silicalite-1 hybrid photocatalysts for VOC oxidation

Abstract Silicalite-1 samples of uniform sub-micron size with two distinct morphologies were prepared using colloidal silica extracted from geothermal fluids. The colloidal silica used was provided by a New Zealand Company, GEO40 Ltd, and was produced by them using their patented process for recovering colloidal silica from geothermal brine. Spherical crystals with an average size of ca. 250 nm (S1N) as well as typical MFI-type coffin-shaped crystals with a size of ca. 900 nm (S1M) were prepared from clear synthesis solutions made from colloidal silica and aqueous tetrapropylammonium hydroxide of different concentration. The silicalite-1 samples prepared showed very similar characteristics to samples prepared using a conventional silica sol, Ludox SM, as a silica source. Silicalite-1 samples prepared with geothermal and conventional silica sols were used as supports for TiO2 nanoparticles. The hybrid TiO2/silicalite-1 materials were tested as photocatalysts for the photocatalytic degradation of trichloroethylene for air pollution control. The hybrid samples reduced the formation rates of non-desirable reaction products, promoting the mineralization process in comparison with a reference TiO2 xerogel and high Si/Al ratio ZSM-5-based hybrid materials.

Analysis of the Oligomeric State of Surface-Localized Proton-Coupled Folate Transporter by Blue Native Polyacrylamide Gel Electrophoresis

Folate vitamins are essential for DNA replication and cellular proliferation. However, mammalian organisms are devoid of de novo folate biosynthesis and thus rely on dietary sources to meet their metabolic needs. The proton coupled folate transporter (PCFT/SLC46A1) has been recently identified as the molecular entity of the carrier mediated intestinal folate uptake pathway for folic acids from food sources. PCFT is also involved in the absorption of chemotherapeutically used antifolates. Currently, there is limited information about the structure and function of PCFT. Hydropathy analysis suggests that there are 10-12 transmembrane segments. Further, using the Substituted Cysteine Accessibility Method (SCAM) evidence was provided for a 12 transmembrane segment topology. Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE) is a technique for separation of protein complexes in a native state with high resolution. We expressed PCFT in Xenopus laevis oocytes. Oocyte plasma membranes were polymerized to the vitelline membrane using ludox colloidal silica solution and polyacrylic acid, isolated by centrifugation, and plasma membrane proteins subsequently solubilized with digitonin and separated by BN-PAGE. The separation characteristics of native PCFT were compared to a molecular ruler produced by partial dissociation of homopentameric 5-hydroxytryptamine type 3A (5HT3A) receptors. Under native conditions, 5HT3A subunits largely migrated as a pentamer and PCFT only as a monomer. Treatment with denaturing agents generated a ladder of five bands for 5HT3A subunits, which consisted of monomer, dimer, trimer, tetramer and pentamer. Addition of crosslinking agents resulted in migration of 5HT3A subunits as a pentamer, even in the presence of denaturing agents. In contrast, crosslinking agents did not induce oligomeric assemblies of PCFT. These results indicate that functional plasma-membrane bound PCFT is a monomeric protein.

Concentration of colloidal silica suspensions using fluorescence spectroscopy

A simple detection method based on fluorescence excitation-emission spectroscopy has been developed to quantify the concentration of Ludox colloidal silica nanoparticles having diameters ranging from 7 to 22 nm. The technique works for suspensions of nominally negatively (SM30, LS, and TM40) and positively (CL) charged colloid silica particles. Without pretreatment, the method detection limits are 1.4 mg/L SiO 2 for CL (12 nm) and TM40 (22 nm) suspensions and 12 mg/L SiO 2 for SM30 (7 nm) and LS (12 nm) suspensions at an excitation wavelength of 308 nm and an emission wavelength of 318 nm. The fluorescence intensities of all the colloidal silica particle suspensions are linear ( R 2 > 0.98) with concentration in the range of 0–300 mg/L SiO 2. The fluorescence intensity of the negatively charged particle suspensions is constant between pH 3 and 9. The fluorescence intensity of suspensions of particles that are nominally positively charged is constant above pH 5.5, where the particles become negatively charged.

Diffusion of Redox Probes in Hydrated Sol−Gel-Derived Glasses. Effect of Gel Structure

The diffusion coefficients of redox probes entrapped in a silica matrix prepared by the sol-gel process were measured using a combination of cyclic voltammetry and chronoamperometry at an ultramicroelectrode. In this study, the porosities of the gels were varied to assess the importance of constrained environments vs intermolecular interactions on the translational mobility of guests entrapped in this solid host matrix. The average pore diameter of the gels was varied from 40 to 400 A by utilizing different catalysts (HCl, NH3, NaF) or different silicon precursors (tetramethoxysilane or Ludox colloidal silica). The diffusion coefficients of cobalt(II) tris(bipyridine), ferrocenemethyltrimethylammonium ion, and dicyanobis(phenanthroline)iron(II) and their rate of change as the gel dried were found to be nearly identical for gels prepared from TMOS and catalyzed with either HCl, NH3, or NaF. When trapped in gels prepared from Ludox, ferrocenemethanol and potassium ferricyanide diffused at rates identical to that measured in solution. In contrast, Dapp for ferrocenemethyl(trimethylammonium) dropped 1 order of magnitude over a 30-day drying period. These results attest to the importance of intermolecular interactions in governing diffusion in sol-gel-derived materials.

Electrodeposition of Porous Silicate Films from Ludox Colloidal Silica

Electrodeposition of Porous Silicate Films from Ludox Colloidal Silica

Nucleation and growth of zeolite A under reagent controlled conditions. Part II

Broad differences in the synthesis kinetics and the morphology of zeolite A from two silicate sources (soluble silicate and Ludox colloidal silica) and two different aluminium sources (aluminium isopropoxide and freshly prepared aluminium hydroxide) are reported. The differences are attributed to different rate limiting steps in the syntheses. The reactions have been followed by small angle X-ray scattering from the time of first mixing of the constituents until the final separation of zeolite A crystals. The soluble silicate and Ludox/aluminium hydroxide syntheses produce excellent cubic crystals in the 300 nm–1 µm size range. The products of the first synthesis have an interesting texture on the scale of nanometres but with aluminium isopropoxide as the aluminium source, the resulting zeolite A has a spherical morphology of size ca. 100 nm. Possible reasons for the development of these morphologies are discussed.

Two-dimensional NMR study of surface water dynamics in hydrated silica spheres

Partially hydrated LUDOX silica spheres (LUDOX colloidal silica HS-40, E.I. DuPont de Nemours Co.) of 15 nm diameter represent a system where the wetting layer of water is quite well defined in the sense that the study of the structure and dynamics of this layered water is not obscured by the much stronger signal of bulk water. When placed in a homogeneous magnetic field, the magnetic susceptibility differences of the silica and water create a distribution of local magnetic fields at the solid-liquid boundary. These fields encode the NMR frequency of the resonant nuclei and label water molecules in the surface layer. The distribution of local fields was determined by the deuteron two-dimensional (2D) separation of interactions NMR technique. The characteristic autocorrelation time ${\ensuremath{\tau}}_{c}$ for the motion of water molecules in the surface layer was studied by measuring the deuteron quadrupolar spin-lattice and spin-spin relaxation times, and taking their ratio. The ${\ensuremath{\tau}}_{c}$ characterizing the fluctuations of the electric-field gradient tensor at the deuteron site was determined at room temperature for a set of hydrations corresponding to an estimated thickness of surface water from 2 to 22 water monolayers. The magnitude of ${\ensuremath{\tau}}_{c},$ which is on the order of ${10}^{\ensuremath{-}8}\mathrm{s},$ demonstrates that the quadrupolar relaxation mechanism is the intramolecular rotational diffusion. This dynamic process slows down only insignificantly with a decreasing thickness of the wetting layer. A search for slower motions was made by the 2D exchange NMR of deuterons in a 6% hydrated LUDOX. No slow molecular motions were detected within the observation window of the experiment, demonstrating that the motional frequencies are faster than $2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}{10}^{5}{\mathrm{s}}^{\mathrm{\ensuremath{-}}1}.$

Hydrothermal crystallization mechanism of sodium beidellite from amorphous gel

Beidellite is a dioctahedral member of the smectite group and sodium beidellite can be described by the general formula, NaxA12(Si4_xAlx)O10(OH)2.nH20. Natural beidellite has an average layer charge of 0.33, although theoretically values range from 0.2 to 0.6 [1]. Beidellite has been hydrothermally synthesized from a gel by several researchers [1-5]. Their methods can be classified into two groups depending on the silica source for the gel preparation: the procedure of Luth and Ingamells [6] used colloidal silica, and that of Hamilton and Henderson [7] used tetraethyl orthosilicate (TEOS). Kloprogge et al. [1, 5] used gels prepared from TEOS to prepare sodium beidellite and presented the properties of synthesized sodium beidellite and its stability in the Na20-A1203-SiO2-H20 system. They reported that pure phase of beidellite was obtained by hydrothermal treatment of the gel only in water, but low-quartz co-existed with beidellite under basic conditions. Furthermore, kaolinite and low-quartz were crystallized at low temperatures below 250 °C but not sodium beidellite. Koizumi and Roy [2] used colloidal silica to prepare gels and showed the formation of wellcrystallized beidellite at 300-350 °C by reaction of a small amount of water with the gel with ideal beidellite composition. Plee et al. [3] synthesized sodium beidellite under basic conditions from a gel prepared by using colloidal silica. This report disagreed with the results obtained by Kloprogge et al. [1, 5]. The aim of the work reported here was to clarify the crystallization mechanism of sodium beidellite from a gel prepared from colloidal silica. The starting materials were Al(NO3)3.9H20, NaNO3 (reagent grade, Wako Pure Chemical Industries Ltd, Japan) and Ludox colloidal silica (HS-40; E.I. du Pont Nemours & Co., USA), which contains 40% SiO2 and a small amount of Na with SiOJNa20 weight ratio of 95. Starting gel (gel 1) was prepared to obtain the composition of Na0.4A12 (Si3.6A10.4) O10(OH)2'nH20. Firstly, a solution was prepared by dissolving 150.052 g of Al(NO3)3.9H20

The pulmonary response and clearance of Ludox colloidal silica after a 4-week inhalation exposure in rats

Rats were exposed to Ludox colloidal silica (CS) at concentrations of 0, 10, 50, and 150 mg/m 3 for 6 hr/day, 5 days/week for 4 weeks. Rats were killed after 4 weeks of exposure and 10 days or 3 months postexposure (PE). The exposure concentration of 10 mg/m 3 Ludox CS is considered to be the no-effect concentration. There were no exposure-related clinical signs in any group. After 4 weeks exposure, lung weights were increased significantly in rats exposed to 50 and 150 mg/m 3 Ludox CS, but lung weights were similar to those of controls at 3 months PE. After 4 weeks exposure to 50 mg/m 3 Ludox CS, a slight alveolar macrophage response, polymorphonuclear leukocytic infiltration, and Type II pneumocyte hyperplasia in alveolar duct regions were present. After 3 months PE, these pulmonary lesions had almost disappeared with removal of most dust-laden alveolar macrophages (AMs). The pulmonary response to 150 mg/m 3 Ludox CS was similar in character but increased in magnitude from that seen at 50 mg/m 3. At 3 months PE, most particleladen AMs had disappeared and the remaining AMs were aggregated and sharply demarcated. A few aggregates of particleladen AMs appeared to transform into silicotic nodules comprising macrophages, epithelioid cells, and lymphocytic infiltration in some animals. Some silicotic nodules showed reticular fiber networks with minute collagen fiber deposition. Tracheobronchial lymph nodes were enlarged with aggregates of particleladen AMs and hyperplastic histiocytic cells. Lung-deposited Ludox cleared rapidly from the lungs with half-times of approximately 40 and 50 days for the 50 and 150 mg/m 3 groups, respectively.

Catalysts for the aromatization ofn-butane prepared by surface-contact transfer of gallium onto ZSM-5 zeolite particles

ZSM-5 zeolite particles into which 0.6 weight per cent or less of gallium oxide has been incorporated by surface-contact transfer, may exhibit very high activity in the aromatization ofn-butane. In some cases, the yield in aromatics is as high as that obtained with the hybrid catalyst wherein the cocatalyst is prepared by evaporation of a solution of gallium nitrate in Ludox colloidal silica.

The Pulmonary Response and Clearance of Ludox Colloidal Silica after a 4-Week Inhalation Exposure in Rats

The Pulmonary Response and Clearance of Ludox Colloidal Silica after a 4-Week Inhalation Exposure in Rats

Four-week inhalation toxicity study with Ludox colloidal silica in rats: Pulmonary cellular responses

This study was designed to complement a traditional subchronic inhalation toxicity study with Ludox colloidal silica. CD rats were exposed nose-only for 2 or 4 weeks at concentrations of 0, 10, 50, and 150 mg/m 3 Ludox (dried SiO 2). Additional groups of rats exposed for 4 weeks were given a 3-month recovery period. Following exposure and/or recovery, fluids and cells were recovered from the lungs by bronchoalveolar lavage (BAL) and measured for cellular and biochemical parameters. Additional groups of animals were processed for cell labeling studies or lung deposition studies. Inhaled doses of Ludox colloidal silica were measured after 4-week exposures and were found to be 489 μg/lung (10 mg/m 3 group), 2418 μg/lung (50 mg/m 3), and 7378 μg/lung (150 mg/m 3), respectively. Results showed that exposures to 150 mg/m 3 Ludox for 2 or 4 weeks produced pulmonary inflammation along with increases in BAL protein, LDH, and alkaline phosphatase values ( p < 0.05) and reduced macrophage phagocytosis. Inflammatory responses, evidenced by increased numbers of neutrophils, were also measured in the lungs of the 50 mg/m 3 group following 2 and/or 4 weeks of exposure. Most biochemical parameters for all groups returned to control values following a 3-month recovery period. Autoradiographic studies demonstrated that the labeling indices of terminal bronchiolar and lung parenchymal cells were generally increased in the 50 and 150 mg/m 3 groups after 2 and 4 weeks of exposure but, with one exception, returned to normal levels following a 3-month postexposure period. No significant alterations in any measured parameters were detected in rats exposed to 10 mg/m 3 Ludox at any time postexposure. The determination of a no-observable-effect level (NOEL) of 10 mg/m 3 was consistent with results obtained by conventional toxicology methods and affirms the utility of these biochemical, cellular, and autoradiographic techniques for providing a predictive screen to assess the toxicity of inhaled particles.

Four-Week Inhalation Toxicity Study with Ludox Colloidal Silica in Rats: Pulmonary Cellular Responses

Four-Week Inhalation Toxicity Study with Ludox Colloidal Silica in Rats: Pulmonary Cellular Responses

Small Angle X-ray Scattering Study of Sodium Montmorillonite Clay Suspensions

Suspensions of montmorillonite clay with concentrations of ½ and 2% have been investigated by small angle x-ray scattering, with two different centrifuge fractions being studied for each concentration. At a given concentration the scattering was observed to be the same for both centrifuge fractions. The scattered intensity was always proportional to the concentration. These results are what would be expected from dilute suspensions of thin platelets of identical thickness but different surface areas. When corrections for the finite height of the collimating slits are applied to the scattering curves, good agreement with the theoretical curves for thin platelets is obtained. From the deviation between the experimental and the theoretical curves at the largest observed scattering angles, the thickness of the platelets was calculated to be 9 A. An independent determination of the thickness can be made from a measurement of the zero angle scattered intensity from some material for which the ratio of the scattered intensity to the scattering from a single electron can be calculated. Two heavy gases, SF6 and C2Cl2F4 (Freon 114), were used for this purpose. The feasibility of using Ludox colloidal silica as a third standard was investigated. Within experimental accuracy, the thickness values calculated from these data agree with the values obtained from the shape of the scattering curves. Both values agree with the thickness determined from the light scattering experiments of M. B. M'Ewen and M. I. Pratt [Trans. Faraday Soc. 53, 535 (1957)]. Since the scattering curve for the clay is proportional to the inverse square of the angle at the smallest observed angles, the large dimensions of the particle must be at least 500 A.

Determination of size of small particles by light scattering. experiments on ludox colloidal silica

Four samples of Ludox colloidal silica were studied by the light transmission and angular scattering method and the size of particles determined. It was found essential for light scattering work to centrifuge the original Ludox solution in order to remove the aggregated material. After this treatment each Ludox sample regardless of age could be used successfully for calibration purposes. The apparent particle sizes in aqueous solutions of Ludox were smaller than those in 0.05 M NaCl solutions, the latter being in very good agreement with electron microscopic values. The refractive index increments of Ludox in water and 0.05 M NaCl were determined at three wavelengths. The influence of cell length and blackening of the cells in transmission measurements were also studied. Dissymmetries and depolarizations were small. All results indicated that particles of Ludox behave practically asRayleigh scatterers. The usefulness of these results for the calibration of light scattering photometers is discussed.

Electron microscopy of Ludox colloidal silica

The samples of Ludox colloidal silica, previously studied by light scattering, were examined in electron microscope. A considerable aggregation of particles was noted in solutions. The aggregates were efficiently removed by centrifugation, as was previously indicated by the decrease in dissymmetry of light scattered by the same sols. From the electron micrographs the distribution of particle diameters was evaluated and several averages of particle size calculated and compared with the light scattering results. A very good agreement between the two sets of results was found.

CONSTRUCTION AND USE OF A SEMIMICRO LIGHT-SCATTERING APPARATUS

A light-scattering apparatus requiring only 4 ml. of liquid was designed and built. The device has permitted the measurement of intensity for angles between [Formula: see text] and 135° to the incident beam. In this range the unpolarized, horizontal, and vertical components of the light emitted from a solution of fluorescein were constant to within ± 0.2%, 0.4%, and 0.6% respectively. The apparatus was calibrated with a suspension of Ludox colloidal silica which absorbed no light for λ = 3800 Å to 6000 Å. The suspension was found to possess all the properties of a Rayleigh scattering system except randomness. This condition was achieved by extrapolating the light-scattering and spectrophotometric functions to zero concentration when computing the calibration factor. The molecular weight of a sample of sodium carrageenate, determined by the method of Zimm, was 1,700,000. The distribution of intensity at. zero concentration fell between that for stiff rods and polydisperse coils.