Characterization of chemically modified silica gels by DRIFT spectroscopy

Chemically modified silica gels are investigated with respect to identity, purity and degree of surface coverage using diffuse reflectance FTIR (DRIFT) Spectroscopy. We report the results for two bonded HPLC phases, pyrene butyric acid propylamido- and octadecyl-groups grafted on irregular porous silica gel. For quantitative determination calibration standards are prepared by adsorbing structurally similar ligand compounds onto the surface of the silica gel; these coated materials give linear calibration curves up to a concentration of 1 mmol/g modified silica gel.     

Synthesis and characterization of functional chemically modified silica fillers

Elaborated methods of synthesis of chemically modified silicas with grafted silicon hydride and amino groups are analyzed. Experimental results on use of modified silicas with bonded amino groups as fillers of carboxyl-containing rubbers and epoxy resins are reported. It was shown that modified silica fillers with grafted silicon hydride groups could be applied for carrying out processes of catalytic solid-phase hydrosilylation of 2-hydroxyethylmethacrylate and some other functional olefins.     

Thermogravimetric study of silica with a chemically modified surface

Thermal methods were used to determine the thermal stability of organic groups introduced into the surface of silica precipitated following its reactions with dimethyl-dichlorosilane (DDS), methyltrichlorosilane (MTS) and methyltriethoxysilane (MTES).It was found that modification with MTS or DDS leads to a permanent hydrophobic film on the silica surface.

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Zusammenfassung Thermische Methoden wurden benutzt, um die thermische Stabilität von organischen Gruppen zu bestimmen, die auf die Oberfläche von ausgefällter Kieselsäure durch die Reaktion mit Dimethyldichlorsilan (DDS), Methyltrichlorsilan (MTS) und Methyltriäthoxysilan (MTES) eingebracht wurden. Die Modifizierung mit MTS oder DDS verursacht auf der Oberfläche der Kieselsäure eine permanente hydrophobe Schicht.

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Extraction of copper ions using silica gel with chemically modified surface

The applicability of silica gels for the application in solid-phase extraction was tested. Silica was modified with ketoimine groups. Surface characteristics of the modified silica were determined by elemental analysis, NMR spectra of solid phases (²⁹Si CP MAS NMR), analysis of pore size distribution of the silica support, and nitrogen adsorption-desorption. Newly proposed sorbents with ketoimine groups were applied in the preconcentration of trace amounts of the Cu (II) ions from lake water, post-industrial water, and demineralized water unburdened back to the lake. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Low-temperature sorption-luminescence determination of platinum using silica chemically modified with dithiocarbamate groups

Application of silica chemically modified with dithiocarbamate groups (DTCS) has been proposed for the low-temperature sorption-luminescence determination of platinum. The establishment of a sorption equilibrium in the platinum(IV) and platinum(II) extraction with DTCS from hydrochloric acid solutions takes 20 and 2 min, respectively. If the duration of the phase contact is optimal, the recovery achieves 99% in the acidity range from 4 M of HCl to pH 5. The sorption of platinum(IV) and platinum(II) results in the formation of coordination compounds of platinum(II) on the surface of the adsorbent which are luminescent in ultraviolet light when frozen (77 K). A procedure has been developed for low-temperature sorption-luminescence determination of platinum with the detection limit of 0.5 ??g of platinum per 0.1 g of the adsorbent and linearity of the calibration curve to 25 ??g/0.1 g. The developed procedure has been applied to the determination of platinum in the samples of alumoplatinum catalyst.     

Probing of chemically modified silica surfaces by solvatochromic pyridinium N-phenolate betaine indicators

The state of betaine indicators, 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate and 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate, on the surfaces of aminosilicas, silica modified with aminodiphosphonic acid, and unmodified silica gel is studied with diffuse reflectance spectroscopy. The normalized polarity parameters are calculated for the surface layers of the sorbents. It is revealed that regions with substantially different polarity and acidity are present on the surface of chemically modified silicas.     

Solid-phase luminescence determination of tetracycline in bottled water using chemically modified silica

Possibility of using chemically modified silica (CMS) with covalently immobilized sulfonic and ethylenediaminetriacetate (ED3A) groups for the adsorption preconcentration and extraction of tetracycline (TC) from aqueous solutions is studied. The conditions of complex formation by europium(III) ions on the surface of these adsorbents are optimized. The effect of citrate and Eu³⁺ ions on the luminescence intensity of the Eu–TC complex is shown. The luminescence properties of SiO₂ED3AEu and SiO₂SO₃HEu systems with tetracyclines are studied depending on the acidity of the medium, time of phase contact, the ratio of the volume of the solution to the weighed portion of the adsorbent, and concentrations of the adsorbed substances. It is found that tetracycline is quantitatively extracted by CMS as a complex with europium(III) ions in pH range 6.5–8.0; adsorption capacity to tetracycline in the Henry region is as high as 0.07–0.09 mmol/g and partition coefficients are 10³–10⁴ mL/g. A procedure is developed for the solid-phase luminescence determination of tetracycline using SiO₂SO₃HEu and SiO₂ED3AEu systems with limits of detection of 0.8 and 2.0 nM, respectively; linearity range is 1 × 10^–9–1 × 10^–5 M. The procedure is tested in the analysis of model mixtures and samples of bottled water.     

Extraction of metal ions using chemically modified silica gel: a PIXE analysis

Organic ligand with carboxyhydrazide functional group was immobilised on the surface of silica gel and the metal binding capacity of the ligand-embedded silica was investigated. The functional group was covalently bonded to the silica matrix through a spacer of methylene groups by sequential reactions of silica gel with dibromobutane, malonic ester and hydrazine in different media. Surface area value of the modified silica was determined. The changes in surface area were correlated with the structural change of the silica surface due to chemical modifications. A mixture solution of metal ions [K(I),Cr(III),Co(II),Ni(II),Cu(II),Zn(II),Hg(II) and U(VI)] was treated with the ligand-embedded silica in 10(-3) M aqueous solution. The measurement of metal extraction capacity of the silica based ligand was done by multielemental analysis of the metal complexes thus formed by using Proton Induced X-ray Emission (PIXE) technique.     

Low-temperature sorption-luminescence determination of silver using silica gel chemically modified with mercaptopropyl groups

Silica gel chemically modified with mercaptopropyl groups extracts silver(I) from solutions in the acidity ranges from 4 M HNO₃ to pH 8 and from 0.01 M HCl to pH 7. The time it takes to attain a sorption equilibrium is no more than 2 min; distribution coefficient is 1 × 10⁵ cm³/g. Yellow-orange luminescence was produced in the adsorbent phase upon the UV irradiation of wet adsorbates cooled to the liquid-nitrogen temperature (77 K). This effect was used for the development of a procedure for the low-temperature sorption-luminescence determination of silver. The calibration graph was linear in the range 1–80 µg Ag per 0.1 g of adsorbent. The detection limit was 0.05 µg per 0.02 g of adsorbent. The relative standard deviation was no more than 6% for silver amounts higher than 5 µg.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 4, 2005, pp. 390–393.Original Russian Text Copyright © 2005 by Losev, Elsuf ev, Trofimchuk.     

Comparison of the complexation abilities of bifunctional polysiloxane xerogels and chemically modified silica gels

Complexation of copper(II) on the surface of chemically modified silica gels and polysiloxane xerogels both containing the same functional groups, 3-aminopropyl and 3-mercaptopropyl, was studied. The composition of the complexes formed on the surface of these two classes of sorbents was determined by ESR and electronic spectroscopies.     

Sorption-spectrometric determination of palladium and gold using silica chemically modified with dipropyl disulfide groups

It has been found that silica chemically modified with dipropyl disulfide groups (DPDSS) quantitatively extracts palladium(II) from solutions in the acidity range from 4 M HCl to pH 4 and gold(III) in the range from 1 M HCl to pH 2 with a partition coefficient at the level of n × 10⁴ cm³/g. The adsorption of palladium(II) and gold(III) at room temperature is highly selective, whereas non-ferrous and other platinum metals are not adsorbed. Sorption-atomic absorption, sorption-ICP-atomic emission, and sorption-photometric methods for the determination of palladium and gold have been developed using DPDSS. The accuracy of the methods was tested by the analysis of certified reference samples.     

Adsorption and preconcentration of 2,4-dichlorophenoxyacetic acid on a chemically modified silica gel surface

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), chemically anchored to a silica gel surface, was used to adsorb and preconcentrate the same herbicide from aqueous solutions at room temperature. From a series of adsorption isotherms adjusted to a modified Langmuir equation, the maximum number of moles adsorbed was calculated as 4.67 x 10(-5) mol g(-1), with the highest retention capacity at pH 5. This modified silica gel was used in a column for preconcentrating trace levels of 2,4-D. The preconcentrated herbicide can be directly eluted with methanol with a recovery efficiency higher than 97%. The concentration factor was 8.33.     

Open tubular capillary electrochromatography migration behavior of enkephalins in etched chemically modified fused silica capillaries

Fused silica capillaries for use in electrophoretic analyses are etched with ammonium bifluoride in the presence of a second inorganic salt (CuCl(2), CrCl(3), NaNO(3), or (NH(4))(2)CO(3)). The effects of the presence of these inorganic components in the surface matrix on the electromigration behavior of enkephalins are evaluated. Resolution, efficiency and peak shape are used to compare the various columns. In some cases the etched surface is then modified by the addition of an octadecyl moiety using a silanization/hydrosilation procedure. The surface properties of the etched capillaries can also be evaluated by electroosmotic flow measurements. RSDs of migration times under identical experimental conditions were <1%.     

Proton conductivity of composites based on Nafion and silica matrices with a chemically modified surface

The surface of aerosilogel and macroporous and microporous glasses was modified with aromatic sulfo groups (≡Si(CH₂)₂-C₆H₄-SO₃H) by the chemical assembly method. Composite solid electrolytes containing Nafion were prepared from the silica matrices with a chemically modified surface. The proton conductivity of the materials was studied by impedance spectroscopy. Composite materials based on Nafion and aerosilogel matrices and macroporous glasses with grafted ≡Si(CH₂)₂-C₆H₄-SO₃H groups showed the highest proton conductivity.     

Determination of enantiomeric catecholamines by ligand-exchange chromatography using chemically modified L(+)-tartaric acid silica gel

Summary Studies on the separation of catecholamine racemates by chiral ligand exchange chromatography (CLEC) on a new chemically bonded chiral phase are described. The stationary phase consists of a silica support to which l(+)-tartaric acid as chiral component is bonded via 3-(trimethoxysilyl)-propylamine.After cleavage of the protecting groups and treatment with copper(II)-ions the l(+)-tartaric acid modified silica gel is able to resolve enantiomers of catecholamines.Parameters, influencing the retention and enantioselectivity, are the pH, ionic strength of the mobile phase and its composition as well as the temperature.Examples for the separation of racemic mixtures are described.

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Bestimmung enantiomerer catecholamine durch Ligandenaustausch-Chromatographie an chemisch gebundenem L(+)-Weinsäurekieselgel

Zusammenfassung Untersuchungen zur Trennung von Catecholaminracematen durch chirale Ligandenaustausch-Chromatographie an einer neuen chemisch gebundenen chiralen Phase werden beschrieben. Die stationäre Phase besteht aus einer Kieselgelmatrix, an welche l(+)-Weinsäure als chirale Komponente über 3-(Trimethoxysilyl)-propylamin gebunden ist. Nach Abspaltung der Schutzgruppen und Behandlung mit Cu(II)-ionen ist das mit l(+)-Weinsäure modifizierte Kieselgel in der Lage, enantiomere Catecholamine zu trennen.Parameter, die Einfluß auf Retention und Enantioselektivität haben, sind der pH-Wert, die Ionenstärke der mobilen Phase sowie deren Zusammensetzung und Temperatur. Beispiele für die Trennung racemischer Mischungen werden beschrieben.

     

Quantitative 1H NMR analysis of reacted silanol groups in silica nanoparticles chemically modified with monochlorosilanes

Quantitative analysis of reacted silanol groups in silica nanoparticles modified chemically with monochlorosilanes was performed by ¹H NMR after treatment with cesium fluoride. Silica nanoparticles were modified chemically by the reaction between the silanol groups and monochlorosilanes, and the structure of the organic moiety anchored onto the silica surface was confirmed with solid‐state ¹³C NMR. As monochlorosilanes react with silanol groups at 1:1 ratio unlike di‐ or trichlorosilanes, the number of the silanes introduced into silica nanoparticles equals that of reacted silanol groups. Organically modified silica nanoparticles were dissolved using cesium fluoride, and the amount of the soluble organic compounds originated from the introduced silanes was determined by a ¹H NMR internal standard method using pyrene as the reference. Those values determined by ¹H NMR were in good agreement with those determined by elemental analysis. Thus, the number of reacted silanol groups per one particle was calculated on the basis of the results obtained by the ¹H NMR method, and the values were highly dependent on the steric structure of the introduced silanes. Copyright © 2010 John Wiley & Sons, Ltd.