Types Of Silica Gel Research Articles

Sorption characteristics of a novel polymeric desiccant

In this work, we present a new polymeric desiccant named super desiccant polymer (SDP). The sorption capacity and diffusivity of SDP are measured from 30 °C to 60 °C at relative humidity from 5% to 70% using uptake measurement method. In addition, a small SDP wheel sample is fabricated to confirm durability of dehumidification and regeneration performance. The results show that the sorption capacity of SDP is 2–3 times higher than those of various types of silica gel. The sorption capacity is found to be 128% at relative humidity of 67%. Fick's law is modified and applied to model kinetic behavior of SDP. The apparent diffusivity of SDP ranges from 6.4 × 10−13 to 5.9 × 10−11 m2 s−1. Furthermore, the SDP wheel sample displays an outstanding durability during 40,000 times sorption and regeneration process. Given these excellent properties, SDP has a great potential in the industrial application as an advanced desiccant material.

Sorption equilibria of CO2 on silica-gels in the presence of water

The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275 K with pressures from 0 to 3.7 MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO2 hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO2 sorption was about 2.5 mmol of CO2 per gram of dry sorbent at 275 K. Similarly, the highest sorption was about 2.7 mmol for wet SG-B with Rw=0.81. However, CO2 hydrate did not form on the wet surface of SG-C due to its large pore sizes.

Synthesis, characterization and visible-light photocatalytic activity of TiO2–SiO2 composite modified with zinc porphyrins

Three types of silica gel supported titanium dioxide particles immobilizing Zn(II) carboxylphenyl porphyrins appending p-CH3, p-H and p-Cl phenyl substituents (designated as ZnMP–TiO2–SiO2, ZnPP–TiO2–SiO2 and ZnCP–TiO2–SiO2, respectively) have been synthesized and characterized using SEM, XRD, IR, AFS, DRS, UV–Vis, XPS and TG. The photodegradation of α-terpinene in aqueous suspension was used to determine the photocatalytic activity of TiO2–SiO2 samples which had been impregnated with Zn(II) porphyrins, as sensitizers. The experimental results confirmed that the photocatalytic activitys of these composites are much higher than those of the nonmodified TiO2–SiO2 under visible light irradiation and follow the order of ZnMP–TiO2–SiO2 > ZnPP–TiO2–SiO2 > ZnCP–TiO2–SiO2.

Silica- and sulfate-bearing rock coatings in smelter areas: Products of chemical weathering and atmospheric pollution I. Formation and mineralogical composition

Black rock-coatings occur in proximity to smelters and roast yards of the Greater Sudbury area, Ontario, Canada and contain information about the past interactions between surface minerals, and gaseous and particulate atmospheric components, many of which were pollutants. Rock-coatings were collected from various locations within the Sudbury area and are characterized with scanning electron microscopy, transmission electron microscopy, X-ray diffraction, electron microprobe analysis, infrared spectroscopy and X-ray photoelectron spectroscopy. Acidic fumigations and rain, the result of vast quantities of SO2 released from smelting, increased the chemical weathering rate of exposed rocks in the Sudbury area. Non-stoichiometric dissolution of the silicate minerals under acidic conditions resulted in the accumulation of silicic acid and the subsequent formation of a silica–gel type coating. The silica gel transformed overtime into amorphous silica, opal (opal C and opal-CT) and cristobalite. Dissolution of the underlying rock and also of metal-bearing particles by sulfuric acid resulted in the in situ formation of metal–sulfate-rich layers on the interfaces between the atmosphere and the silica-rich coating (atmosphere–coating interface, ACI) and between the silica-rich coating and the underlying rock (rock–coating interface, RCI). These metal–sulfate-rich layers contain nanometer aggregates of Fe–Cu–sulfate–hydroxide, goldichite, mereiterite, guildite, butlerite and antlerite. The silica-rich matrix also contains a mix of detrital grains from adjacent rocks and soils (feldspar, quartz, hematite, chlorite, montmorillonite) and non-dissolved smelter-derived nano- to micro-size particulates (metal–silicates, metal–oxides, C-spheres). The apparent disequilibrium between the embedded particles and the Fe–Cu-sulfates suggests that trapped nanoparticles were encapsulated into pores which prevented their equilibration with acidic metal–sulfate-bearing fluids. An XPS depth profile indicates a gradual transition from lower to higher concentrations of metals from the coating surface towards the metal–sulfate-rich layer on the ACI, which suggests that the outer surface of the coatings is currently leached on an angstrom scale by surface waters.

Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

The hydroamination of alkenes with sulfonamides catalyzed by the recyclable silica gel supported triflic acid

The vast applications of triflic acid (TfOH) in catalysis are severely limited by its corrosive and fuming properties. Immobilization of TfOH on silica gel well solves these problems and affords efficient recovery and reusability of TfOH. Two types of supported TfOH, the prepared silica gel supported TfOH and the in situ silica gel adsorbed TfOH, both exhibit good catalytic activity and reusability in the hydroamination of alkene with sulfonamide. The in situ silica gel adsorbed catalyst has been used for 5 runs with maintained reactivities and yields, which are superior to the performance of the prepared silica gel supported TfOH. For a series of alkenes and various sulfonamides, the heterogeneous hydroamination reactions catalyzed by both types of silica gel supported TfOH to afford similar moderate to excellent yields.

Theoretical insight of adsorption cooling

This letter proposes and presents a thermodynamic formulation to calculate the energetic performances of an adsorption cooler as a function of pore widths and volumes of solid adsorbents. The simulated results in terms of the coefficient of performance are validated with experimental data. It is found from the present analysis that the performance of an adsorption cooling device is influenced mainly by the physical characteristics of solid adsorbents, and the characteristics energy between the adsorbent-adsorbate systems. The present study confirms that there exists a special type of silica gel having optimal physical characteristics that allows us to obtain the best performance.

Barium Chloride Dispersed on Silica Gel Nanoparticles: An Efficient Catalyst for the Preparation of 2,4,6-Triarylpyridines under Solvent-Free Conditions

BaCl2 dispersed on a nano-structural type of silica gel (BaCl2-nano SiO2) was found to be an effective catalyst for the rapid and high yielding preparation of substituted 2,4,6-triarylpyridine frameworks by the reaction of various acetophenones, benzaldehydes and ammonium acetate. The prepared catalyst was characterised by X-ray diffraction and scanning electron microscopy analysis.

Different dispersion behavior of glucose and sucrose on alumina and silica surfaces

Phenomena of spontaneous monolayer-dispersion have been found in many salt and oxide/support systems as well as in organic compound/support systems. In this paper, the dispersion behaviors of glucose and sucrose have been systematically compared using three types of alumina with different textures and one type of silica gel, as supports. The dispersion capacity of the saccharides was determined by XRD quantitative phase analysis and confirmed by DTA-TG and FT-IR results. The pore size distribution of carbon-covered alumina (CCA) derived from the saccharide/alumina composite was employed to evaluate the dispersion state of the saccharide precursor. It was found that both sucrose and glucose are dispersed on the alumina and silica surfaces as a monolayer when their loading is kept under the monolayer-dispersion capacity. However, at higher saccharide content, glucose and sucrose are dispersed differently. Just like other monolayer-dispersion systems, sucrose begins to form in the crystalline phase when its loading exceeds the monolayer-dispersion capacity. In contrast, glucose aggregates in an amorphous state in the pores of the supports until these pores are filled, and only then forms crystalline glucose.

Method development for identification of ketobemidone metabolites in microdialysate samples by coupled-column capillary liquid chromatography–tandem mass spectrometry

Methodologies for identification of ketobemidone metabolites in microdialysate samples utilizing coupled-column capillary liquid chromatography–electrospray quadrupole time-of-flight tandem mass spectrometry are presented. Two different methods were developed to efficiently analyze the metabolites norketobemidone, ketobemidone N-oxide and hydroxyketobemidone, respectively. Both methods include on-line desalting and trapping of the analytes on micro-solid-phase extraction columns with different retention mechanisms. Norketobemidone and ketobemidone N-oxide were trapped on a C18 column and then eluted by back-flush followed by isocratic separation on a fluorinated reversed-phase type silica gel column (Fluofix). Retention equations are proposed for the chromatographic observations made on the Fluofix column. Hydroxyketobemidone was trapped on a phenylboronic acid column by complex formation at basic pH and then eluted at acidic pH directly into to the mass spectrometer. Oxidation of hydroxyketobemidone to its corresponding quinone was also observed. The methods were successfully used to analyze synthetic ketobemidone metabolites in dilute low-volume microdialysis samples.

Computational study of a novel continuous solar adsorption chiller: performance prediction and adsorbent selection

A novel solar adsorption chiller intended for domestic use is presented. The chiller can be integrated with existing solar systems based on flat plate collectors, and, contrary to commercial chillers, it operates continuously. A detailed analysis of both the simple and the heat-integrated cycle is carried out so as to select the optimal adsorbent and operating conditions. The employed integral thermodynamic model takes into account the inert masses that limit the performance of the chiller, such as the metal frame, the thermo-fluid, and the non-adsorbed steam, by introducing heat capacity effects. Given the adsorption equilibrium data, the energy balances, the performance, and the useful thermal loads of the system can be calculated at any operating conditions. The results indicate that silica gel Type A is a more efficient adsorbent compared to silica gel Type RD or Type 3A. Furthermore, the total porosity has a slight effect on system performance, while optimal operation can be achieved when the condenser temperature is less than 326 K and the evaporator temperature greater than 280 K. Copyright © 2006 John Wiley & Sons, Ltd.

Structural Investigations of Silica Polyamine Composites: Surface Coverage, Metal Ion Coordination, and Ligand Modification

Silanization of the silica gel surface in the synthesis of silica gel polyamine composites uses (chloropropyl)trichlorosilane (CPTCS). It is possible to substitute a molar fraction of reagent CPTCS with methyltrichlorosilane (MTCS), creating a mixed silane surface layer. Two types of silica gels were modified with a series of MTCS:CPTCS molar ratios. Solid-state CP/MAS 29Si and 13C NMR spectroscopies were used to evaluate the surface silane composition. Surface silane coverage was markedly improved for the resulting gels. When polyamines were grafted to the resultant MTCS:CPTCS silane layers, it was shown that the decrease in the number of propyl attachments to the polyamine resulted in increased quantities of “free amines”. Optimum MTCS:CPTCS ratios were determined for three polyamines grafted onto one silica gel. A substantial free amine increase was observed for poly(allylamine) (PAA). Metal uptake studies show increases in Cu(II) capacity and/or an improvement in Cu(II) mass-transfer kinetics. The effect of polymer molecular weight upon Cu(II) capacity was investigated for each polyamine. Substantial differences in Cu(II) capacity between 50 000 MW poly(vinylamine) (PVA) and >1000 MW PVA were evident. Similar differences between 25 000 MW poly(ethyleneimine) (PEI) and 1200 MW PEI were found. The mass-transfer kinetics was shown to be improved for composites prepared using a large fraction of MTCS in the reagent silane mixture. This resulted in substantial improvements in the 10% breakthrough Cu(II) capacity for PVA (50 000 MW). PEI composites were further modified to form an amino−acetate ligand. The impact of the MTCS:CPTCS silane ratio on the acetate ligand loading and ultimately on the Cu(II) capacity at pH = 2 was investigated. A ratio of 12.5:1 was shown to result in an acetate modified PEI composite with a Cu(II) capacity 140% of the Cu(II) capacity of the same composite prepared with “CPTCS only”.

Use of a Lipase to Synthesize Silica Gels in a Hydrophobic Organic Solvent

Biocatalytic and chemical catalytic reactions in solutions of lauric acid, 1-octanol and tetramethoxysilane (TMOS) in hydrophobic isooctane and in the presence of the lipase from Burkholderia cepacia, was studied by gas chromatography. Two types of silica gels could be obtained and the chemical and biochemical transformations leading to their formation were elucidated. In a first type of gelation, biocatalytic esterification between lauric acid and alcohol slowly produced some water which in turn hydrolyzed TMOS. Simultaneously, a transesterification reaction between 1-octanol and TMOS grafted octyl groups on the silica precursor. This induced a gelation of hydrophobic silica throughout the complete isooctane solvent volume. A second type of silica gel formed when no 1-octanol was added and only in the presence of the enzyme. This type of gel was hydrophilic and separated from the isooctane layer. Gas chromatographic analysis showed that it could only be formed as a result of hydrolysis reaction between lauric acid and TMOS, directly catalyzed by the lipase itself. Therefore, in this second type of gelation process, the metal-organic compound TMOS itself appeared as a direct enzymatic substrate.

Covalent Immobilization of Glucose Oxidase onto New Modified Acrylonitrile Copolymer/Silica Gel Hybrid Supports

New polymer/silica gel hybrid supports were prepared by coating high surface area of silica gel with modified acrylonitrile copolymer. The concentrations of the modifying agent (NaOH) and the modified polymer were varied. GOD was covalently immobilized on these hybrid supports and the relative activity and the amount of bound protein were determined. The highest relative activity and sufficient amount of bound protein of the immobilized GOD were achieved in 10% NaOH and 2% solution of modified acrylonitrile copolymer. The influence of glutaraldehyde concentration and the storage time on enzyme efficiency were examined. Glutaraldehyde concentration of 0.5% is optimal for the immobilized GOD. It was shown that the covalently bound enzyme (using 0.5% glutaraldehyde) had higher relative activity than the activity of the adsorbed enzyme. Covalently immobilized GOD with 0.5% glutaraldehyde was more stable for four months in comparison with the one immobilized on pure silica gel, hybrid support with 10% glutaraldehyde and the free enzyme. The effect of the pore size on the enzyme efficiency was studied on four types of silica gel with different pore size. Silica with large pores (CPC-Silica carrier, 375 A) presented higher relative activity than those with smaller pore size (Silica gel with 4, 40 and 100 A). The amount of bound protein was also reduced with decreasing the pore size. The effect of particle size was studied and it was found out that the smaller the particle size was, the greater the activity and the amount of immobilized enzyme were. The obtained results proved that these new polymer/silica gel hybrid supports were suitable for GOD immobilization.

Assessment of adsorption-desorption characteristics of adsorbents for adsorptive desiccant cooling system

The performance of various dehumidification materials was assessed in terms of effective adsorption amount of water vapor based on the adsorption isotherms to find a suitable dehumidification element for an economical adsorptive desiccant cooling system being developed. The effective adsorption amount is an important factor for regeneration at lower temperatures. Three types of silica gels, S(a), S(b), and S(c), with different pore volumes and pore size distributions, and zeolite with various molar ratios of Si/Al, 5.6, 29, 47, 91, and 220, prepared from a Y-type zeolite treated with hydrochloric acid, an activated carbon with silica gel added to improve the hydrophobic surface, and MCM-41 were examined. Silica gels having effective adsorption amounts of 0.25 g/g, and activated carbon with silica gel added were assessed to be candidate desiccant materials.

Uses of Ozone in a Three-Phase System for Water Treatment: Ozone Adsorption

A new technique of using ozone for water treatment is presented. This new technique consists of using a three-step-process composed firstly of ozone adsorption on an appropriate adsorbent, secondly water treatment, and thirdly regeneration of the adsorbent. Results regarding ozone adsorption (the first step) are presented in this paper. Different types of silica gel and a type of TiO2 have been tested for ozone adsorption. It was found that the physical characteristics of the silica gel affect its capacity for ozone. Titanium dioxide has shown ozone decomposition instead of adsorption as it contains Lewis acid sites. An exponential decrease of the silica gel capacity with its moisture content has been found. Linear isotherms in the range of ozone concentrations less than 100 g/m3 NTP have been found. A particle diffusion model with linear equilibrium isotherm has been used to model the breakthrough curves in fixed bed columns.

Gelation Time Depending on the Functionality and the Concentration of Monomers Simulated by a CCA Model

We study the gelation process by simulation of a cluster–cluster aggregation (CCA) model, in which networks of gels are constructed through clustering of two-functional or four-functional monomers. We find that gelation time increases when the initial concentration of monomers decreases, while it decreases when the fraction of four-functional monomers increases. At a small initial concentration, gelation time does not markedly depend on the functionality of monomers. This can be related to the forms of clusters: for a large functionality case, the clusters should be tight and should aggregate into compact structures, while for a small functionality case, clusters should form linear chains so that they can easily associate with each other. Numerical observations are compared with experimental results on gelation time for the two types of silica gels under acidic and basic conditions.

Adsorption Characteristics of Silica Gel + Water Systems

The adsorption characteristics of pure water vapor onto two different types of silica gel at temperatures from (298 to 338) K and at different equilibrium pressures between (500 and 7000) Pa were experimentally studied by a volumetric technique. The thermophysical properties such as the skeletal density, Brunauer−Emmett−Teller surface area, pore size, pore volume, and total porosity of silica gel were determined. The Tóth isotherm model is found to fit all of the experimental data within the experimental errors. The experimental isotherms and the computed enthalpies of adsorption are compared with those of various researchers and found to be consistent with a chiller manufacturer's data.

Effect of Surfactants on the Immobilization of 4-(2-Pyridylazo)resorcinol on Silochroms

The effect of cationic surfactants (cetyltrimethylammonium bromide, cetylpyridinium bromide, and tetrabutylammonium perchlorate) and a nonionic surfactant (OP-7) on the conditions of the immobilization of 4-(2-pyridylazo)resorcinol (PAR) on three types of silica gel (Silochrom S-120 (200–350 μm), Silochrom S-120 (315–500 μm), and Silochrom S-80 (200–350 μm)) was studied. It was found that OP-7 does not affect the adsorption of surfactants. The effect of cationic surfactants increases in the order tetrabutylammonium perchlorate < cetyltrimethylammonium bromide < cetylpyridinium bromide. The adsorption activity of silica gels increases in the order Silochrom S-120 (315–500 μm) < Silochrom S-80 (200–350 μm) < Silochrom S-120 (200–350 μm). Cetylpyridinium bromide provides full immobilization of PAR on silica gel Silochrom S-120 (200–350 μm) in the pH range 2–9.

インクジェット用紙の印字特性に対する塗工顔料の影響

Characteristics of inkjet-grade paper coating were evaluated by applying various coating layers on a plastic substrate instead of paper. The poly (ethylene terephthalate) (PET) film had to be hydrophilized by precoating. Precoating with poly (vinyl alcohol) (PVA) was found effective for this purpose, but resulted in crack formation after the main coating. This problem could be avoided by adding optimized amount of clay to the precoating color. Four types of silica gel, a plate-shaped aluminum hydroxide, and a plate-shaped clay were tested as main coating pigment, with PVA as binder. The latter two pigments gave poor inkjet print qualities due to slow absorption of ink leading to significant dot gain and mottling. On the other hand, silica gel pigments generally gave satisfactory print quality, but it showed certain variation with the type of pigment. The time dependence of water contact angle against various coated layers showed correlations with dot shape and optical properties in inkjet printing.