Adsorbents silica

Noncrystalline Silicas. The noncrystalline forms of silica iaclude bulk vitreous silica and a variety of other amorphous types, which are of substantial commercial importance (see SiLiCA, AMORPHOUS SILICA SiLiCA, VITREOUS SILICA). A review discussiag the occurrence, synthesis, properties, and apphcations of the various forms of silica adsorbents is available (71). 

Neon [7440-01-9] M 20,2, Passed through a copper coil packed with 60/80 mesh 13X molecular sieves which is cooled in liquid N2, or through a column of Ascarite (NaOH-coated silica adsorbent). 

Mcntasty el al. [35] and others [13, 36] have measured methane uptakes on zeolites. These materials, such as the 4A, 5A and 13X zeolites, have methane uptakes which are lower than would be predicted using the above relationship. This suggests that either the zeolite cavity is more attractive to 77 K nitrogen than a carbon pore, or methane at 298 K, 3.4 MPa, is attracted more to a carbon pore than a zeolite. The latter proposition is supported by the modeling of Cracknel et al. [37, 38], who show that methane densities in silica cavities will be lower than for the equivalent size parallel slit shaped pore of their model carbon. Results reported by Ventura [39] for silica xerogels lead to a similar conclusion. Thus, porous silica adsorbents with equivalent nitrogen derived micropore volumes to carbons adsorb and deliver less methane. For delivery of 150 V./V a silica based adsorbent would requne a micropore volume in excess of 0.70 ml per ml of packed vessel volume. 

It has been outlined by several authors that the single macromolecule may be irreversibly bound because of the large number of weakly interacting segments. The first papers on the construction of polymer-coated silica adsorbents involved the physical adsorption of water-soluble polymers. Polyethylene oxides [28, 29] and poly-/V-vinylpyrrolidone [30] are examples of the stationary phases of this type. 

V. Hlady and J. D. Andrade, A TIRF titration study of l-anilinonaphthalene-8-sulfonate binding to silica-adsorbed bovine serum albumin, Colloids Surf. 42, 85-96 (1989). 

Carr, J.W. and Harris, J.M., In situ fluorescence detection of polycyclic aromatic hydrocarbons following pre-concentration on alkylated silica adsorbents. Anal. Chem., 60, 698, 1988. 

Gritti, F. and Guiochon, G, Influence of the pressure on the properties of chromatographic columns i. Measurement of the compressibility of methanol-water mixtures on amesoporous silica adsorbent, J. Chromatogr. A, 1070, 1, 2005. 

Slowly put sand over the cotton until you have at least one centimeter. Next, very slowly add the adsorbent (alumina, silica). Adsorbents liberate heat, possibly causing the eluent to boil, ruining the column. Add the adsorbent slowly. Use about 25 g of adsorbent for every 1 g of mixture you want to separate. When the alumina settles, add another 1 cm of sand to the top. During the entire procedure the level of the eluent must be higher than any solid material placed in the column,... 

Adsorption of solvent on silica gel. Attempts to use this adsorbent failed since activated silica adsorbs moisture from air more strongly than alcohol and ether vapour. 

As shown in Fig. 6, the differential heat of adsorption of NH3 was initially around 200 kJ mol 1 for all the mesoporous silica samples, indicating that mesoporous silica adsorbs NH3 as strong as HZSM-5. However, the differential heat decreased with an increase in the amount of adsorbed NH3 especially in the case of MCM-41P, the differential heat decreased very steeply. In the cases of MCM-41 and FSM-16, the differential heat gradually decreased and became almost constant at the adsorption amount of ca. 0.05 mmol g1 which was dose to aluminum content (0.051 and 0.068 mmol g 1 for MCM-41 and FSM-16, respectively). This is in contrast to the result on HZSM-5 where the differential heat was almost constant up to the adsorption amount of ca. 0.06 mmol g 1 which was close to aluminum content (0.062 mmol g ). 

The first experimental application of this concept was reported in the seminal work of Dickey, who, in 1949, stated that silica, adsorbed with methyl orange, showed preferential absorption properties towards the same structure. Dickey, hypothesising the mechanism with which the specific adsorption was generated, invoked Pauling s antibody formation theory This mechanism is the same as that proposed by Pauling for the formation of antibodies with use of antigen molecules as a template. [4],... 

Ueno, Y., Horiuchi, T., Tomita, M., Niwa, O., Zhou, H., Yamada, T., Honma, I., Separate detection of BTX mixture gas by a microfluidic device using a function of nanosized pores of mesoporous silica adsorbent. Anal. Chem. 2002, 74,... 

Activated carbon is by far the most widely used adsorbent. It is available in a wide range of different forms that differ mainly in pore size and pore size distribution. The carbon surface is essentially nonpolar although some polarity can be imparted by surface oxidation or other pre-treatments. It is widely used for removal of low concentrations of organics, either from aqueous streams (for example, decolorization of sugar or water treatment) or from vapor streams (for example, in range hoods and other pollution-control devices). Crystalline silica adsorbents such as silicalite are also organophilic but are substantially more expensive than activated carbon so their application is generally limited to situations where, for some reason, the use of carbon is not appropriate. 

Subsequently, using the Gurvich rule [2], it is possible to obtain the relation Nm = W/VNH3, which allows the calculation of the maximum amount of NH3 that could be adsorbed in the stabilized silica samples. Then, the maximum amount of NH3 that could be adsorbed in both samples is approximately Nm = 40.1 mmol/g. Since each molecule of ammonia contains three hydrogen atoms, 0.120 grams of hydrogen is stored in the form of NH3 per gram of the silica adsorbent, that is, 0.120 g/g. 

Quinolones (including ciprofloxacin) have been shown to be separable by TLC using thin layers of Diol-silica adsorbent, and solutions of di-(2-ethylhexyl)-orthophosphoric acid (HDEHP, an ion-pairing reagent) in polar solvents as the mobile phase [23]. Retention and selectivity in the adsorption-ion-association system can be controlled by adjusting the concentration of HDEHP (typically 5 10%), or by changing the polar diluents. 

V. M. Gun ko and R. Leboda, Carbon-Silica Adsorbents, in Encyclopedia of Surface and Colloid Science, edited by A.T. Hubbard, pp. 864-878 (Marcel Dekker, 2002). 

Before pyrolysis silicas were dried at 200°C and cooled to room temperature. Different amounts of organic precursors were deposited on dry silica (weight 5 g) to obtain carbon-silica adsorbents (carbosils) with different amounts of carbon deposits. Samples based on acenaphthene (Tables 1 and 2), acetylacetone and glucose (Table 3), were pyrolysed under static conditions in a stainless steel autoclave (0.3 dm3) at 773 K for 6 h. After reaction, all the prepared carbosils were washed in a Soxhlet apparatus with N,N-dimethylformamide and acetone, and then dried at 200°C. 

Table 1 presents the structural characteristics of adsorbents prepared with Si-40 and acenaphthene.15 Larger changes in the Si-40 structure are caused by hydrothermal treatment, despite a relatively low temperature (150°C), than by heating at 500°C. However in the case of carbon-silica adsorbents, both hydrothermal modification and high-temperature pyrolysis changes the pore structure to a large extent. 

R. Leboda, A. Gierak, B. Charmas, and Z. Hubicki, Complex carbon-silica adsorbents preparation, properties and some applications as model adsorbents in Fundamentals of Adsorption, edited by M. D. Le Van (Kluwer Academic Publishers, Boston, 1996), pp. 497-504. 

J. Skubiszewska-Zieba. R. Leboda, O. Seledets, and V. M. Gun ko, Effect of preparation conditions of carbon-silica adsorbents based on mesoporous silica gel Si-100 and carbonized glucose on their pore structure, Colloids Surf. A 231(1-3), 39-49 (2003). 

Abstract. Several series of pyrocarbon/silica adsorbents were prepared using fumed oxides of different specific surface areas, and mesoporous silica gel Si-100, as inorganic matrices. Different synthetic and natural polymers as well as glucose were used as carbon precursors. Solutions of phosphoric acid at various concentrations were utilized to prepare functionalized hybrid carbon-silica adsorbents. Nitrogen, p-nitrophenol and Cd(II) adsorption isotherms as well as AFM, XRD and XRF methods were used to estimate the structural and adsorption characteristics of the adsorbents. 

Keywords carbon-silica adsorbents, fumed silica, pyrolysis, glucose, starch, cellulose, phosphoric acid, polyvinylpyrrolidone, polystyrene, structural characteristics. 

Carbon/silica adsorbents with pure or functionalized carbon deposits, or functionalized silica surfaces, are of interest for many purposes, An improvement of the structural and adsorption characteristics of carbon deposits is desirable.1 Pyrocarbon deposits formed by carbonization of low-molecular organic precursors (dichloromethane, cyclohexene, alcohols, acetylacetone, acenaphthene, etc) at oxide surfaces typically possess a low inner specific... 

Table 1. Structural characteristics of initial fumed silicas and hybrid pyrocarbon/silica adsorbents prepared from liquid solutions of polymers and subsequent carbonization.5...

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