The study of phosphate ions sorption from silicon dioxide solutions obtained by using acid decomposition of nepheline

The process of sorption of phosphate ion by silicon dioxide obtained by acid decomposition of nepheline is studied. The experimental data were processed using the Freundlich and Langmuir sorption equations, which showed that the sorption process is fairly accurately described by both equations, while the use of the Langmuir monomolecular adsorption equation is preferable in the calculations. The capacity of the adsorption monolayer of the synthesized sample relative to the РО43–-ion and the adsorption equilibrium constant are calculated. Based on the obtained data, various options for sorption treatment of municipal wastewater from РО43--ion to normalized MPC values were evaluated.

Adsorption of phosphate ions from aqueous solutions by layered magnesium and aluminum double hydroxide obtained by solid-phase synthesis

A layered double hydroxide of magnesium and aluminum was obtained by solid-phase synthesis.It was found that it has a predominantly mesoporous structure with cylindrical and wedge-shaped pores, as well as a specific surface area of 50 m2/g. The process of phosphate ion sorption by a synthesized sample is studied. Processing of experimental data on the Freundlich and Langmuir sorption equations showed that the process is described fairly accurately by the Langmuir monomolecular adsorption equation. The capacity of the adsorption monolayer of the synthesized sample with respect to the РО43--ion and the adsorption equilibrium constant are calculated.

The equivalence of quasi-chemical and statistical description of adsorbate molecule association in a localised adsorption monolayer on a homogeneous solid surface

The analysis of Berezin and Kiselev’s concept assuming linear association of molecules in a localised adsorption monolayer on the homogeneous surface of a solid adsorbent was carried out. An inconsistency due to the lack of consideration of equilibrium concentration of free adsorption sites in the formulation of the expression for the association constant has been pointed out. It was shown that the correct form of this function leads to the final adsorption equation being identical to the specific case of the Fowler-Guggenheim equation. The obtained result has been generalised to cases of branched adsorbateadsorbate associations. A new adsorption equation limiting the association to at most the dimers has been introduced. Critical conditions for the two-dimensional condensation of the adsorption layer were determined. By applying the formalism of canonical ensemble, full equivalence of the phenomenological and statistical methods was demonstrated in the description of the intermolecular interactions in the localised adsorption monolayer.

A role of free silanol groups of nanosilica surface in interaction with poly(vinyl pyrrolidone)

In this work, a role of the number of free silanol groups at a nanosilica surface (specific surface area S_BET = 250 m²/g, initial amount of silanols α_ОН = 0.60-0.62 mmol/g) was analyzed in interaction with poly(vinyl pyrrolidone) (PVP) vs. the degree (Q_TMS) of silica hydrophobization by hexamethyldisilazane at 100 ^oC. The value of Q_TMS was 0.07, 0.42, 0.67, 0.81, 0.82, and 1.0. Adsorption of PVP onto a nanosilica surface was carried out from a water and water-ethanol (1:1) solutions of the polymer. It was shown that free silanol groups play a crucial role in the adsorption of poly(vinyl pyrrolidone). The value of the maximal adsorption (monolayer capacity) on completely hydrophobic nanosilica surface is approximately by 6.5 times lower than that for unmodified nanosilica

Description of the Adsorption Equilibrium with Consideration to the Decreasing Availability of Space in the Course of Mobile Adsorption of a Single Gas on a Homogenous Surface of Solid

The subsequent stages of the process of formulation of the equation for gas adsorption on a homogenous surface of a solid adsorbent were presented based on the general expression for the canonical ensemble of the mobile single-component adsorption monolayer. The method of formulating the configuration integral of the proposed model was discussed in detail where the role both of the attraction and repulsion between adsorbed molecules was emphasised. The expression for the probability of finding a molecule in a specified point on a surface of an adsorbent was modified by determining its magnitude by the adsorbent concentration. The expression for the so-called effective surface of the adsorbent was obtained by adapting a two-dimensional analogue equation of state hard spheres – Van der Waals equation (2D-vdW) and Reis-Frisch-Lebowitz equation accordingly (2D-RFL). As a result, two new adsorption equations were formulated which differ in detail concerning the adsorbate-adsorbate repulsion. On each of these equations theoretical analysis was performed in terms of two-dimensional phase transformation. In both cases it was proved that the proposed solution allows for the presence of two-phase transformations of the first type which is the gas-liquid condensation and solidification liquid-solid. The verification of the given approach was supplemented by the description of the experimental data given in reference literature and by obtaining a very good correlation between the theory and experiment.

Influence of milling and extrusion on the sorption properties of sorghum

The processing to which a material is subjected can affect its physical or chemical structures, resulting in products with different hygroscopic behaviours. The present work studied the water adsorption properties of sorghum subjected to different types of processing: raw flour (produced by milling whole grain), extrudates (obtained using a double screw extruder) and extruded flour (obtained by milling the extrudates). The isotherms were obtained using an automated instrumental method. The tests were run in duplicate at 25 °C with relative humidity values ranging between 11 and 84%. The water adsorption data fitted the GAB model well, showing high coefficients of determination. The estimated water contents of the adsorption monolayer ranged from 5.3 to 6.9 g of water per 100 g of dry material. The sorption isotherms were affected by the type of processing, extrusion cooking resulting in products with less water in the monolayer (less hygroscopic). The milling process yielded high water contents in the monolayer, probably due to the breakdown of some polymer-polymer interactions, which exposed the binding sites. To ensure microbiological stability, the water contents in the materials should not exceed 6.9 g of water per 100 g of dry material for raw sorghum flour, 5.3 g of water per 100 g for sorghum extrudates and 6.7 g of water per 100 g for extruded sorghum flour.

THEORETICAL STUDY ON ADSORBATE-INDUCED SURFACE STRESS IN THE SELF-ASSEMBLY OF ALKANETHIOLS ON GOLD

By using established statistical thermodynamic theory of adsorbate-induced surface stress of adsorption monolayer on metal surface, the surface stress Δg in the self-assembly of alkanethiols on Au (111) surface has been calculated. The quantitative relations of the surface stress Δg with the length N of the alkyl chain of the molecule and with the coverage θ of molecules on Au (111) have been theoretically studied, respectively. The calculated results agree with Berger et al.'s experiment. The qualitative discrepancy between the theory and experiment on the sign of the surface stress has been resolved. Among various components of the adsorbate–adsorbate interaction energies in the adlayer, the substrate-mediated interaction is significant for the adsorbate-induced surface stress, which shows that indirect contribution of the adsorption energy of alkanethiols through the substrate-mediated interaction is very important.