Showing papers on "Silica gel published in 1974"

Hydrogen bond strengths and acidities of hydroxyl groups on silica–alumina surfaces and in molecules in solution

Abstract: The properties of hydroxyl groups on mixed silica–alumina gels (0–50 % Al2O3) have been studied by adsorbing weak H bond accepting molecules onto the gels and recording the OH stretching infrared band.Additional measurements on silica gel and compilation of numerous literature data have shown that frequency shift measurements, or series of Δtext-decoration:overlinevOH measurements condensed into BHW (Bellamy, Hallam and Williams) slopes, provide a reliable estimate of the OH acidity. The resulting scale is independent of the atom to which the hydroxyl is attached; it may be used for surfaces of solids as well as for solutions.The results obtained for silica–alumina show that two distinct populations of hydroxyl groups are present. Hydroxyl groups of type 1 are identical with those present on the surface of silica. The spectra show the presence of hydroxyl groups of a second type, the proportion of which increases as the Al content of the gel rises; their acidity corresponds to a pKa between –4 and –8 and they are presumably the sites responsible for the protonation observed upon adsorption of pyridine or ammonia.

Semipermeable microcapsules containing a silica gel

Abstract: Described are semipermeable microcapsules which comprise an outer semipermeable polymeric skin encapsulating a silica gel These microcapsules may be used as chromatographic media or may be modified to contain a homogeneous or heterogeneous catalyst and/or a ferromagnetic material

Identification of Flavor Constituents in Carbonyl, Non-Carbonyl Neutral and Basic Fractions of Aqueous Smoke Condensates

Abstract: Carbonyl, non-carbonyl neutral and basic fractions obtained from commercial aqeuous smoke condensates were separated by GC and/or silica gel column chromatography.Ninety-eight constituents were identified (thirty-one compounds were not previously reported in smoke condensate) and twenty-two were tentatively identified on the basis of tR of GC, IR, MS (GC–MS) and NMR data.The yields of all the smoky aroma constituents (four aliphatic alcohols, five aliphatic ketoalcohols, six aliphatic ketones, twenty cyclic monoketones, three cyclic diketones, ten acids, two esters, twelve lactones, nine furan derivatives, six N-compounds, four aromatic hydrocarbons, two aromatic alcohols, nine aromatic carbonyls, twenty-four phenols and phenol ethers and five pyrocatechols) detected in commercial wood vinegar were estimated.

Alumino‐silicate polyacrylic acid and related cements

Abstract: The composition and setting reaction of cements formed from aluminosilicates and poly(acrylic acid), the ASPA cements, are described. Setting and hardening results from interactions between specially-formulated, complex, fluorine-containing calcium aluminosilicate glasses and aqueous solution of poly(acrylic acid) or similar poly(alkenyl carboxylic acids). Protons from the polyacid penetrate the surface of the glass decomposing the negatively charged aluminosilicate network to a siliceous hydrogel and releasing Al3+, Ca2+ and F- ions. These ions migrate, probably as complexes, such as AlF2+, AlF2+ and CaF+, into the polyelectrolyte phase where they cross-link polyanionic chains, by ionic and possibly chelate binding, causing the cement to gel and set. Overall the reaction may be seen as one where flexible hydrogen bonds, in the liquid, are progressively replaced by more rigid ionic ones, leading to gelation. The set cement is a composite of glass particles sheathed by a silica gel bound by a metal poly anionic matrix. ASPA cements can attain a compressive strength of 200 N/mm2 in 24 h and are adhesive under oral conditions to tooth materials. They find a number of applications in conservative and preventive dentistry. Certain naturally-occurring aluminosilicate minerals react with poly(acrylic acid) to form cement but these are much weaker (not exceeding a compressive strength of 30 N/mm2) and are weakened by water.

Improved inorganic ion-exchangers

Abstract: The possibility of using the sol-gel method for preparation of inorganic ion-exchangers with a silica gel matrix has been demonstrated on the ammonium molybdophosphate-silica gel (AMP-SG) system. For the preparation of the ion-exchanger a sodium silicate solution, containing AMP and components to cause gelling to silica gel after increase of the temperature of the solution, is poured into a hot stirred silicone oil. The solution forms droplets, which are filtered off after their gelling, washed and dried. Beads containing 65 wt.% of AMP per gram of dry material have been prepared by this method and tested in ion-exchange columns for caesium removal from nitric acid solutions. Caesium may easily be desorbed with ammonium chloride or nitrate solutions. The ion-exchanger is suitable for long-time reversible column operation, having not only good chemical, thermal and radiation stabilities but also good mechanical and hydrodynamic properties and resistance to abrasion. It combines the advantage of the good kinetics of ion-exchange obtained with microparticles of precipitated inorganic ion-exchanger, with the low flow resistance of large particles.

Diffusion into and adsorption of polyethylenimine on porous silica gel

Abstract: The polyethyleneimine (PEI)–water–silica gel absorption system was used as a model system to investigate the relationship between diffusion into the porous structure, adsorption rate, and molecular weight of the polymer. Three silica gels, Porasil A, B, and and C having a range of characteristic porosity were used as adsorbents. Adsorption of PEI on Porasil C, which has the majority of its pores much larger than the dimensions of the adsorbate molecule, increased initially with increased molecular weight but became nearly constant at higher molecular weight. Little increase in adsorption occurred for this silica gel with increased ionic strength or with increased pH between 9.5 and 10.8. In contrast, adsorption increased sharply with increased ionic strength and for the same pH range on Porasil A. Molecular weight dependence was reversed. Adsorption decreased with increased molecular weight on Porasil A. In this case, the molecular size of PEI investigated was the same as the majority of pore apertures in the adsorbent. Solution environments (i.e., pH and ionic strength) that decrease the size of the PEI molecule and its affinity for the anionic silica gel surface, thus enabling it to more readily diffuse into the smaller porous regions of the adsorbent, are the apparent causes of the very large adsorption increase. Electrostatic repulsion between PEI molecules do not appear greatly to affect adsorption. Similar adsorption behavior has been reported in the literature for the PEI–cellulosic fiber adsorption system. Maximum adsorption on Porasil A occurred at pH 10.8, the same maximum generally reported for adsorption of PEI on cellulosic fibers. In this case, the silica gel (Porasil A) was found to have a pore size distribution and specific surface area of the same magnitude as cellulosic fibers prepared in the expanded state.

Modified silica gels as selective adsorbents for sulphur dioxide

Abstract: Silica gel modified by –CH2CH2CH2NH3X where X is chlorid, bromide, or iodide adsorbs sulphur dioxide selectively to form the halogenosulphinate ion SO2X–; the process reverses upon warming.

Adsorption and Desorption of Trifluralin, Triallate, and Diallate by Various Adsorbents

Abstract: The relative adsorption of trifluralin (a,az,a-trifluoro- 2,6-dinitro-N,N-dipropyl-p-toluidine), triallate (S-(2,3,3-tri- chloroallyl)-diisopropylthiocarbamate), and diallate (S-(2 ,3- dichloroallyl)diisopropylthiocarbamate) was studied on sev- eral adsorptive surfaces. The herbicides were strongly ad- sorbed, with the following general trend: activated charcoal > peat moss > wheat straw (Triticum aestivum L.) X cellulose triacetate > cation exchange resin > anion exchange resin > silica gel XV cellulose powder > kaolinite Xv montmorillonite. Trifluralin and triallate were readily desorbed from montmoril- lonite by water, with miniminal desorption for peat moss, cellulose triacetate, and wheat straw.

The Thermal Behavior of Silanol Groups of Silica Gel as Studied by Infrared Spectroscopy. I

Abstract: The thermal behavior of the silanol of silica gel has been studied by quantitative infrared spectroscopy. Transparent and glass-like plates of silica gel of high purity, after they had been heat-treated at various temperatures below 680 °C, were used for the measurement of OH stretching vibrations ranging from 3100 to 3800 cm−1. These absorption bands were analysed into the several component bands by the simulation method using a Dupont Co. Curve Resolver. The intensity of these bands in area were proportional to the OH concentrations as measured by the thermal method. Each component band disappeared at a temperature which was roughly equal to that obtained from the dielectric and conductivity measurements. From these results, assignment was attempted on the basis of these bands.

The separation of arsenic-77 in a carrier-free state from the parent nuclide germanium-77 by a thin-layer chromatographic method

Abstract: 77As(III) and77As(V) were separated from neutron-irradiated GeO2 by a thin-layer chromatographic method, in which silica gel was used as adsorbent and a 2∶1 mixture of methanol and 5N HCl as developer. The Rf values of these nuclides were as follows: 0.00 for77Ge, 0.50 for77As(III) and 0.94 for77As(V). The influence of As(III) carrier added before the separation was investigated on the oxidation state of77As recoiled from the parent nuclide. The radiochemical purity of77As thus separated was more than 99.9% and the activity due to77As could easily be eluted with water from the adsorbent, with 93% recovery.

Thin-Layer Chromatographic Separations of Butadiene-Styrene Copolymers on the Basis of Composition and Molecular Weight

Abstract: Experimental methods have been developed for thin-layer Chromatographic separation of butadiene-styrene copolymers according to (i) composition and (ii) molecular weight. The technique of separation according to composition is based upon exploiting the adsorption of polymers from their solutions with less polar solvents through the greater adsorptivity of the relatively polar styrene units. The specific method involved is an elution gradient procedure based upon addition of a good, relatively polar solvent for both polymers (CHCls) to the nonpolar solvent CCl4. Adsorption onto silica gel during the development increases with styrene content so that high Rf values are associated with low styrene contents. The separation method for determining molecular weight distributions is based upon using solvents of marginal solubility and involves adding a highly polar nonsolvent to an initial polar solvent which precipitates the polymer during the development. Specifically, CH3OH is used as the nonsolvent, ...

New Possibilities of Investigating Adsorption Phenomena by Gas Chromatography: Estimation of Adsorbent Heterogeneity from the Pressure Dependence of Retention Data

Abstract: A new method is proposed for evaluating the distribution of adsorption energy on heterogeneous surfaces from the pressure-dependence of the retention volume: VN=VN(p). For this purpose Hobson's theoretical method has been adopted as most useful for testing the possibility of using gas chromatography data. Moreover, this method has been extended to a more realistic treatment of adsorption, without any loss of its basic advantages from the point of view of gas chromatography. The utility of our new method is demonstrated for two adsorption systems, using cyclohexane and cyclohexene as adsorbates, and some micro-porous silica gel as adsorbent.

Separation of germanium from some elements by adsorption on silica gel

Abstract: In the search for an efficient method of recovery of germanium from concentrated mineral acid solutions, silica gel has been found to be a selective adsorbent for this element. A method of quantitative separation of gallium from germanium is described which can be applied for the preparation of68Ge−68Ga isotope generator and for the isolation of68Ge from a zinc target. The applicability of the present method was also studied for the separation of a gertarget. The applicability of the present method was also studied for the separation of a germanium matrix in determining admixtures in semiconductor germanium samples by activation analysis.