Pore Size Of Silica Gel Research Articles

Composite of ZIF-8 and totally porous silica gel for HPLC stationary phase

Abstract Metal-organic frameworks (MOFs) supported on silica gels have been proved to be promising stationary phases for high performance liquid chromatography (HPLC). However, up to now, the stationary phases still face the problems of uneven dispersion of MOFs on traditional spherical silica gels and the poor separation performance. In this work, the effect of the silica gel pore size on the dispersion of ZIF-8 on totally porous silica gel was systematically investigated and the highly uniform dispersion of ZIF-8 was gained on the silica gel with the pore diameter of 80 nm. Moreover, the distribution of ZIF-8 nanoparticles on the surface of wide pore silica could be further improved by adjusting the proportion of DMF and methanol solution. When the well packed ZIF-8@SiO2 composite column was used to separate hydroquinone and p-benzoquinone, its resolution reached an outstanding value of 5.47, while there was no baseline separation on the C18 column. Finally, the separation mechanism was also studied by testing the separation of the mixture of 1-phenylethanol and acetophenone. This work would provide an easy way to disperse MOFs on traditional silica gels and could provide a composite column for separation of hydroquinone and p-benzoquinone.

Cycloaddition of hexacene and fullerene[60

The [4+2] cycloaddition of hexacene and C60 yielded 1:1 and 1:2 adducts. The highest yield of 1:1 adduct was 90% by heating hexacene and C60 in toluene. The formation of 2 was achieved by reacting 1 with an excess amount of C60 in the presence of silica gel 60 with a yield up to 69%. The function of silica gel was rationalized by the effect of concentration enhancement inside the pore of silica gel. The reaction was examined systematically by changing the parameters of solvent, temperature, reaction time, and the pore size of silica gel. Both purified compounds 1 and 2 can be used for the fabrication of bulk heterojunction solar cells.

Phase Behavior and 13C NMR Spectroscopic Analysis of the Mixed Methane + Ethane + Propane Hydrates in Mesoporous Silica Gels

In this study, the phase behavior and quantitative determination of hydrate composition and cage occupancy for the mixed CH(4) + C(2)H(6) + C(3)H(8) hydrates were closely investigated through the experimental measurement of three-phase hydrate (H)-water-rich liquid (L(W))-vapor (V) equilibria and (13)C NMR spectra. To examine the effect of pore size and salinity, we measured hydrate phase equilibria for the quaternary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + water mixtures in silica gel pores of nominal diameters of 6.0, 15.0, and 30.0 nm and for the quinary CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) + NaCl + water mixtures of two different NaCl concentrations (3 and 10 wt %) in silica gel pores of a nominal 30.0 nm diameter. The value of hydrate-water interfacial tension for the CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) hydrate was found to be 47 ± 4 mJ/m(2) from the relation of the dissociation temperature depression with the pore size of silica gels at a given pressure. At a specified temperature, three-phase H-L(W)-V equilibrium curves of pore hydrates were shifted to higher pressure regions depending on pore sizes and NaCl concentrations. From the cage-dependent (13)C NMR chemical shifts of enclathrated guest molecules, the mixed CH(4) (90%) + C(2)H(6) (7%) + C(3)H(8) (3%) gas hydrate was confirmed to be structure II. The cage occupancies of each guest molecule and the hydration number of the mixed gas hydrates were also estimated from the (13)C NMR spectra.

Adsorption of Cu2+ on Amino Functionalized Silica Gel with Different Loading

Silica gel (G) and amino functionalized silica gel with three different loading of an aminopropyl group viz. 0.51, 1.01, and 1.45 mmol/g, (GN1, GN2, and GN3) were synthesized, characterized, and used as adsorbents for the adsorption of Cu2+ ions from aqueous solution. The specific surface area, pore volume, and BJH pore size of silica gel decreased with an increase in the loading of aminopropyl groups. Kinetic of adsorption of Cu2+ on GN2 followed pseudosecond order. Adsorption isotherms of Cu2+ on functionalized silica samples were best fit by the Sips model for all the three functionalized silica gels, among the four models used to describe the Cu2+ adsorption isotherms. The monolayer copper adsorption capacity for the gel GN1 (0.515 mmol Cu2+/g) and GN2 (0.55 mmol Cu2+/g) were found to be almost similar even when the loading of the amino group increased from 0.51 to 1.01 mmol/g. The NH2/Cu mole ratio was found to be around 1 and 2 for GN1 and GN2, respectively. In the case of GN3 (1.45 mmol NH2/g), the...

Sulfated and sulfonated polysaccharide as chiral stationary phases for capillary electrochromatography and capillary electrochromatography–mass spectrometry

The applications of polysaccharide phenyl carbamate derivatives as chiral stationary phases (CSPs) for capillary electrochromatography (CEC) are often hindered by longer retention times, especially using a normal-phase (NP) eluent due to very low electroosmotic flow (EOF). Therefore, in this study, we propose an approach for the aforementioned problems by introducing two new types of negatively charged sulfate and sulfonated groups for polysaccharide CSPs. These CSPs were utilized to pack CEC columns for enantioseparation with a NP eluent. Compared to conventional cellulose tris(3,5-dimethylphenyl carbamate) or CDMPC CSPs, the sulfated CDMPC CSP (sulfur content 4.25%, w/w) shortened the analysis time up to 50% but with a significant loss of enantiomeric resolution (∼60%). On the other hand, the sulfonated CDMPC CSP (sulfur content 1.76%, w/w) not only provided fast throughput but also maintained excellent resolving power. In addition, its synthesis is much more straightforward than the sulfated one. Furthermore, we studied several stationary phase parameters (CSP loading and silica gel pore size) and mobile phase parameters (including type of mobile phase and its composition) to evaluate the throughput and enantioselectivity. Using the optimized conditions, a chiral pool containing 66 analytes was screened to evaluate the enantioselectivity under three different mobile phase modes (i.e., NP, polar organic phase (POP) and reversed-phase (RP) eluents). Among these mobile phase modes, the RP mode showed the highest success rate, whereas some degree of complementary enantioselectivity was observed with NP and POP. Finally, the feasibility of applying this CSP for CEC–MS enantioseparation using internal tapered column was evaluated with NP, POP and RP eluents. In particular, the NP-CEC–MS provided significantly enhanced sensitivity when methanol was replaced with isopropanol in the sheath liquid. Using aminoglutethimide as model chiral analyte, all three modes of CEC–MS demonstrated excellent durability as well as excellent reproducibility of retention time and enantioselectivity.

Room temperature ionic liquids as templates in the synthesis of mesoporous silica via a sol–gel method

With various RTILs as templates, amorphous mesoporous silica gel materials were synthesized according to a proper sol–gel method. The materials display pore diameter of 3–12 nm, pore volume of 0.4–1.3 cm 3/g and BET surface area of 300–800 m 2/g. The effect of variations of the anions and cations of ILs, the alkyl chain length on imidazolium cation and IL concentration in the reaction system on the pore structure and thermal stability of the silica gel materials was preliminarily studied. It is suggested that, the pore size of silica gel can be tuned by variations of ILs and IL content. The different kind of the anions of ILs could largely impact the properties of the obtained silica gel materials. The mesoporous silica gels with 1-alkyl-3-methylimidazolium tetrafluoroborate as templates possessed larger pore sizes of 5–12 nm and higher thermal stability than the materials obtained with other ILs as templates.

Dependence of the Pore Size of Silica Gels on the Acidity of the Medium

The influence of the acidity of the medium of the initial sol–gel system on the pore size of a silica gel prepared by the organic sol–gel synthesis form tetramethoxysilane is investigated.

Manipulation of pore size distributions in silica and ormosil gels dried under ambient pressure conditions

Sol–gel derived silica and organically modified silica gels were solvent-exchanged and dried from various solvent mixtures in order to control the magnitude of capillary stress imposed on the gel, and to limit shrinkage during the drying process. A collection of trends was identified in the evolution of porosity, pore size distributions, and surface area of gels dried from various alcohols and acetone/alkane mixtures. By selecting n-alcohols of increasing length from 2 to 5 carbon units, the average pore size of silica gels was adjusted systematically from 4.1 to 3.1 nm with a relatively narrow pore size distribution. The use of acetone/alkane mixtures to modify the capillary stresses that are experienced by drying gels was demonstrated to be effective in controlling pore size and pore volume at high fractions of alkane. Ambient pressure drying thus provides an efficient method of porosity control in materials derived from the sol–gel process.

The effect of pore size of silica gel and concentration of buffer on capillary chromatographic and capillary electrochromatographic enantioseparations using cellulose tris(3,5-dichlorophenylcarbamate)

A comparative study was performed on the effect of the pore size of silica gel and the concentration of the buffer on enantioseparations in capillary liquid chromatography (CLC) and capillary electrochromatography (CEC). Cellulose tris(3,5-dichlorophenyl-carbamate) was used as chiral selector in combination with nonaqueous methanolic buffers. Thiourea has proven not to be a suitable marker for the electroosmotic flow (EOF) in the present separation system. Optimization of the separation conditions led to plate numbers above 400 000 per meter as well as almost baseline enantioseparations with an analysis time of less than 1 min for the first time in chiral CEC with pakked capillaries.

Photoinduced Reactions of Pyrene with Carbon Tetrachloride on Porous Silica Gel

Polyaromatic compounds such as pyrene are adsorbed to the porous silica gel surfaces, and the photoinduced reactions of these species on these surfaces are studied. The pyrene singlet excited state and triplet state are quenched on the surface with coadsorbed carbon tetrachloride (CCl4). Temperature studies with evacuated samples indicate that quenching occurs by CCl4 adsorbed on the surface and not by bombardment from the gas phase. The dynamic quenching rate constant of the pyrene singlet excited state increases after high-temperature pretreatment of the silica. It is suggested that this results from an increase in the rate of diffusion of carbon tetrachloride on the surface after the high-temperature removal of surface silanol groups. The dynamic quenching rate constant of the singlet excited state increases with the silica gel pore size, and the highest rate constant is observed on the 150 A silica surface, which has been pretreated at 600 °C. A large pore size (smaller surface area) and a dehydroxyla...

Separation of enantiomers on a chiral stationary phase based on ovoglycoprotein: I. Influences of the pore size of base silica materials and bound protein amounts on chiral resolution

The influences of the pore size of base silica gels and the bound amounts of ovoglycoprotein (OGCHI) on the chiral resolution of racemates have been investigated. To the 12-, 20- and 30-nm pore size silica gels, aminopropyl groups were introduced, activated with N,N′-disuccinimidyl carbonate and then reacted with OGCHI followed by blocking with d-glucosamine. For the OGCHI material prepared with the same pore size silica gel, a linear correlation was obtained between the capacity factor of each enantiomer and the amount of bound OGCHI. Enantioselectivity and resolution obtained with the reaction of 40 mg OGCHI per 1 g silica gel were lower than those obtained with the reaction of 80, 160 and 320 mg OGCHI, when the same pore size silica gel was used. This is due to the superfluous achiral interaction with base silica gels and/or spacers because of lower protein coverage. With regard to comparison of the pore sizes of silica gels, the OGCHI materials prepared with the 12-nm pore size silica gel gave the largest capacity factor, and the highest eantioselectivity and/or resolution for the racemates tested, when the same amount of OGCHI was reacted. Thus, the OGCHI materials were prepared with the reaction of 80 mg OGCHI per 1 g silica gel having a 12-nm pore size followed by blocking with d-glucosamine. By diminishing the superfluous achiral interaction with base silica materials and/or spacers, much more efficient OGCHI materials should be obtainable.

Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases II. Influence of the porosity of the silica gel matrix on performance

Two cellulose derivatives bearing simultaneously 10-undecenoyl and 3,5-dimethylphenylaminocarbonyl groups in different ratios were chemically bonded on allylsilica gels of different porosity. The systematic study of the effect of the silica gel pore size on the bonding of the polysaccharide derivative and on the performance of the resulting chiral supports is presented.

HPLC enantioseparation on cellulose tris(3,5-dimethylphenylcarbamate) as a chiral stationary phase: Influences of pore size of silica gel, coating amount, coating solvent, and column temperature on chiral discrimination

Cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) was coated on large-pore silica gels and used as a chiral stationary phase (CSP) for high-performance liquid chromatographic separation of enantiomers. The influences of pore size of silica gel, coating amount of CDMPC, coating solvent, and column temperature on chiral discrimination were investigated. CSPs prepared with a large-pore silica gel having a small surface area showed higher chiral recognition. The amount of CDMPC adsorbed on the silica gel influenced the chiral recognition of some racemates. Loading capacity of racemates increased with an increase of the amount of CDMPC supported on the silica gel, and a CSP coated with 45% CDMPC by weight can be used for both analytical and semi-preparative scale separations. The CDMPC, coated using acetone as the coating solvent, exhibited, in many cases, higher enantioselectivity than that obtained with tetrahydrofuran F as the coating solvent. © 1996 Wiley-Liss, Inc.

HPLC enantioseparation on cellulose tris(3,5‐dimethylphenylcarbamate) as a chiral stationary phase: Influences of pore size of silica gel, coating amount, coating solvent, and column temperature on chiral discrimination

HPLC enantioseparation on cellulose tris(3,5‐dimethylphenylcarbamate) as a chiral stationary phase: Influences of pore size of silica gel, coating amount, coating solvent, and column temperature on chiral discrimination

Stabilization and Electron Spin Resonance Characterization of Ru(bpy)33+in Silica Gel by Chemical Oxidation and Photoinduced Electron Transfer

The stabilization of Ru(bpy){sub 3}{sup 3+} from Ru(bpy){sub 3}{sup 2+} at both 77 K room temperature in silica gel by chemical oxidation with chlorine gas and by photoinduced electron transfer to suitable electron acceptors is reported. Stabilization at room temperature is of particular interest for potential light energy storage systems. Paramagnetic Ru(bpy){sub 3}{sup 3+} is characterized by electron spin resonance spectroscopy. The RU(bpy){sub 3}{sup 3+} yield formed by chlorine gas oxidation can be controlled by the silica gel pore size and decreases with increasing pore size. The Ru(bpy){sub 3}{sup 3+} yield is 1 order of magnitude smaller in 14.0 nm pore silica gel compared ro 2.5 nm pore silica gel. The Ru(bpy){sub 3}{sup 3+} yield gradually decreases by preheating the silica gel to higher temperatures before impregnation with Ru(bpy){sub 3}{sup 2+}. These results suggest that the oxidation of Ru(bpy){sub 3}{sup 2+} with chlorine gas takes place via a silica gel surface mediated reaction and that the direct reaction of adsorbed Ru(bpy){sub 3}{sup 2+} with chlorine molecule in the gas phase is less effective. Ru(bpy){sub 3}{sup 3+} can also be stabilized in silica gel by photolysis in the presence of the electron acceptor S{sub 2}O{sub 8}{sup 2-} (persulfonate ion) with amore » 50% yield or tetrachloro-1,4-benzoquinone (p-chloranil) with a lower yield. 31 refs., 10 figs., 1 tab.« less

Photooxidation of Phenothiazine Derivatives in Silicas of Different Pore Sizes

Methylphenothiazine and other N-alkylphenothiazines were introduced into silica gel pores by impregnation and sol-gel synthesis. The alkylphenothiazines were photooxidized at room temperature by 320-nm irradiation to form stable alkylphenothiazine cation radicals detected by electron spin resonance and diffuse reflectance spectroscopies. The silica gel framework is suggested to be the electron acceptor. The photoyield and stability of the methylphenothiazine cation radical depend on the silica gel pore size. In a small-pore silica gel the methylphenothiazine cation radical has a larger photoyield and is more stable with a longer lifetime than in a large-pore silica gel. Increasing the alkyl chain length up to hexadecyl does not affect the alkylphenothiazine cation photoyield or stability. However, addition of an anionic sulfate group to the alkyl chain of an alkyphenothiazine doubles its photoyield and increases the stability of the photoproduced radical. It is suggested that the mobility of the alkylphenothiazine cation radical in the silica gel pores controls its photoyield and stability. 30 refs., 9 figs.

Determination of Ammonium and Other Major Cations in River and Rain Water by Ion Chromatography Using Silica Gel as an Ion Exchanger

The separation of NH4+ from Na+, K+, Mg2+ and Ca2+ on silica gel columns was investigated using natural water samples and lithium oxalate as a retention modifier. The pore size of silica gels was found to be the most important factor affecting the retention of the cations. When a 0.0025 mol dm−3 lithium oxalate solution of pH 7 was used as the mobile phase these cations could be completely separated on a short silica-gel column (Develosil 30-3, 35 mm×4.0 mm i.d.) within about 20min. NH4+ contents in river (0.01–0.27 ppm) and rain (1–1.8 ppm) water samples were determined successfully.

Characterization of di-phasic nanoscale composites derived from xerogels

Di-phasic xerogel-derived composites, such as SiO2AgCl, SiO2-AIPO4, SiO2-CePO4, SiO2 -Nd2O3, SiO2-CdS, SiO2CrPO4, SiO2-BaSO4 and SiO2-PbCrO4 have been characterized in detail by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) techniques. The SiO2-AgCl photochromic composites with small amounts of AgCl did not show any crystallinity either by XRD or by SAED. Thin edges of these SiO2-AgCl composites did not reveal discrete AgCl particles because these are too small to be resolved even by TEM and are expected to be in the range 1.5 to 2.5 nm in size based on the pore size of silica gel. A few large AgCI-Ag particles precipitated on the outside of silica gel were, however, detected by TEM-SAED in silica gels with higher concentrations of AgCl. The SiO2-AIPO4 and SiO2-Nd2O3 composites are noncrystalline and did not show any periodic structure by TEM and SAED. Heat treatments to 400 or 600° C did not crystallize the AIPO4 or Nd2O3 phases. On the other hand, SiO2-CePO4 and SiO2-CdS composites showed lath-like particles of CePO4 and irregular particles of presumably CdS on the surfaces of silica gels. The SiO2-BaSO4 and SiO2-PbCrO4 composites showed crystals of BaSO4 and PbCrO4 which are too large to be incorporated in the silica gel pores. These results show that the size and crystallinity of a second phase within silica gels can be controlled by the appropriate manipulation of the different parameters, and to do so is an important advantage for this new class of diphasic nanoscale composite xerogel materials.

Influence of silica gel structure on hydrocarbon separation by gas chromatography

IN GAS-ADSORPTION chromatography, silical gel has been widely used for the separation of light hydrocarbons as a sufficiently homogeneous adsorbent [1-3]. Static studies showed that adsorption of hydrocarbons increases with the diminution in size of silica gel pores [4, 5]. I t was found of interest to study the effect of structure and surface chemistry on the gas-chromatographic separation of hydrocarbon mixtures. The effect of the surface chemistry of silica gels on the gas-chromatographic separation of hydrocarbons was studied in papers [6-11]. Similar investigations of porous glasses [12-15] are closely related to these papers. The effect of silica gel structure on the gas-chromatographic separation of light hydrocarbons formed the subject of paper [16]. With an increase of specific surface and reduction of silica gel pore size, more complete separation was achieved. By t rea tment of silica gels with HC1 and KOH solutions, adsorption was reduced as a result of increased pore sizes and reduced specific surface. With the removal of imp.urities polymerization of propylene and butenes on untreated silica gel was eliminated. I t was also shown in paper [17] that during t reatment of silica gels with acids and alkalies, the fine pores are reduced and the large ones increased. Paper [18] studies the effect on the separation of hydrocarbon gases of calcining silica gels of varying structure at 110-800°C. On increasing the temperature of treatment, silica gel activity increased to a maximum and then rapidly decreased. In the case of ethylene, activity increase was observed only before the elimination of adsorbed water, on eliminating the chemically combined water, activity markedly decreased. Ttmse results can be explained by the reduction of silica gel surface during sintering and by the reduction of adsorption energy of unsaturated (and aromatic) hydrocarbons during dehydroxylation of the surface as a consequence of the reduced specific interaction of ~-electron bonds with the hydroxyl groups on the silica surface [4, 12, 19-21]. In paper [18] a study was made of methods of obtaining symmetrical peaks on active silica gels by increasing working temperatures and deactivation of

Effect of Pore Size of Silica Gels on the Separation of Hydrocarbons.

Effect of Pore Size of Silica Gels on the Separation of Hydrocarbons.