Adsorbent modified layer silicates

Amount of adsorbed cations a (meq/g), interplanar spacing door (nm) and specific surface area S (m /g) of modified layer silicates... 

The studies presented here are based essentially on the principle of comparison of the thermodynamic characteristics of adsorption measured on a number of organoderivatives of layer silicates and silica, with the data obtained from the molecular statistic calculations involving the portions of surface, which model the real surface of the materials studied. These surface portions were chosen on the basis of the adsorbent structure analysis and complex physico-chemical studies of the modifying layers structure. 

Using the value of the specific surface area of the kaolinite specimen prior to modification (70 m /g), the area occupied by each cation (1.2 nm ) and the amount of adsorbed modifier, we have estimated the thickness of the modifying layer covering the surface of the silicate, assuming that no defects exist in this layer. The resulting values, together with the experimental data on the Henry s constants and the differential heats of adsorption obtained as reported in [47] are listed in Table 10 for the two specimens considered. 

In the table, it can be seen that the adsorption characteristics remain virtually unchanged when the thickness of the layer of modifying cations is increased by a factor of almost two. Hence, since the adsorbed molecules are separated quite considerably from the surface of the original layer silicate, we conclude that it is interaction with the modifier which contributes mainly to the thermodynamic characteristics of adsorption, while details of the adsorbate - silicate interaction potential play only a marginal role. 

We had taken this fact into account in performing the calculations for the thermodynamic quantities. The model adopted for this system was the basal plane of the kaolinite covered with three or five monolayers of octadecylammonium cations in their trans conformation closely packed with each other. This implies the existence of atomic sheets in the modifying layer as well as in the silicate layer nearest to the surface the deeper silicate layers were included into the calculations in the bulk approximation. The data [11] were used for the BC potential coefficients employed for the interaction between the H and C atoms of the adsorbate molecule and H and C atoms of the modifier alkyl chain for the coefficients describing the interaction between the alkane atomic species and the ions constituting the silicate lattice, we used the values reported in [13]. The coefficients for the interaction with the N atom in the modifying layer were estimated using the quantum-... 

This property of layer silicate clays has been used to modify smectites so that they can adsorb and retain non-polar pollutants in water, such as chlorinated benzene. 

Epoxy-clay nanocomposites were studied extensively, but only ordered exfoliated nanocomposites were reported with in situ polymerization. Two recent works showed that disordered and highly exfoliated epoxy-clay nanocomposites can be prepared using an exfoliation-adsorption process." In this method the organo-modified clay is first dispersed in a solvent. It is well known that due to the weak forces that stack the layers together, layered silicates can easily be swelled and eventually delaminated in an adequate solvent. The polymer then adsorbs onto the delaminated sheets, and when the solvent is evaporated, a highly disordered structure is obtained before starting the standard in situ polymerization. 

Synthetic Insoluble Silicates. Insoluble crystalline siUcates, ie, mineral-type compounds, are synthesized from soluble siUcates by precipitation, gelation, ion exchange, and hydrothermal techniques. Hydrothermal treatment of partially neutralized, high mole ratio (m = 12—50), sodium siUcate solutions yields neutral alkaU polysiUcates that exhibit a layered stmcture and high ion-exchange capacity (135,136). These and other lamellar siUcates can be utilized either alone or modified via pillaring (137) as adsorbents and catalysts. 

However, when replacing two-thirds of the potassium sihcate, the resulting DPU resistance was dramahcally improved. The reason for this can be that on a nanoscale it takes a minimum amount of silica nanoparticles to substantially cover/modify the surface of the pigment and fillers, micron-sized particles, in the silicate paint. Unless the surface of the silicate film is completely protected by a thin layer of glycerolpropyl-modi-fied silica nanoparticles, dirt particles can be adsorbed on the unprotected parts of the surfaces in the sihcate paint film. In addition, stress forces during the paint drying process were... 

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