Adsorption interactions

Three typos of interactions control the adsorption of an adsorbate by activated carbon from water i) adsorbate-activated carbon, ii) adsorbate-water, and iii) activated carbon-water. 

Sample Surface Area Pore Volume pHpzc NaOH Uptake HCl Uptake H2O Uptake C N 0 

Adsorption of TCE by various heat-treated activated carbons and carbon fibers was also mvestigated [40]. Since all carbons were hrat-treated, the impact of carbon surfece polarity on the TCE ifrtake was less important than the impact of carbon porosity. When the correlations between flie TCE uptake and the pore volumes in different regions of raibon micropores were examined, the best correlation was obtained for 0.5-0.8 nm (Fig. 3). Overall, these results indicate that both pore volume and size distributum in pores less than 1 nm are important for TCE adsorption. The positive effect of carbon microporosily on the SOC adsorpticm has also been observed in other studies [41]. 

It is often necessary to compare the adsorption of DOM by different activated carbons one approach is to plot surface area or pore volume normalized Isoflrerms. To do so, it is necessary to identify the pore regions accessible to DOM, which is challenging as a result of the size distribution of both carbon pores and DOM components. The results obtained with uniform pore size carbon fibers Indicate that carbon pores smaller than 1 nm are most likely not accessible for DOM molecules. Therefore, as a result of their different sizes, different DOM components will adsorb in different regions of carbon pores larger than 1 nm. 

When activated carbon is applied prior to conventional treatment processes, the composition of DOM components is the same as that in the source water. However, the concentration and molecular weight distribution of DOM in water changes during treatment operations since DOM components are selectively removed by conventional treatment processes. As a result, the composition of DOM in contact with activated carbon depends on the location of application. Conventional water treatment processes preferentially remove hlgli molecular weight and more hydrophobic components of DOM from water [17,19], Therefore, when activated carbon is applied in filters after conventional treatment process, it is exposed to a DOM mixture that consists of smaller molecular weiglit and more hydrophilic DOM components, having a lower DOC concentration as compared to the raw water (Fig. 1). 

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The total potential energy of adsorption interaction may be subdivided into parts representing contributions of the different types of interactions between adsorbed molecules and adsorbents. Adopting the terminology of Barrer (3), the total energy of interaction is the sum of contributions... 

Nowadays, almost all commercially available HPLC stationary phases are also applicable to planar chromatography. In addition to the polar hydroxyl groups present on the surface of native silica, other polar functional groups attached to the silica skeleton can also enter into adsorptive interactions with suitable sample molecules (34). Silica with hydrophilic polar ligands, such as amino, cyano, and diol functions, attached to the silica skeleton by alkyl chains, all of which have been well proven in HPLC, have also been developed for TLC (34). 

Recent developments in the mechanisms of corrosion inhibition have been discussed in reviews dealing with acid solutions " and neutral solu-tions - . Novel and improved experimental techniques, e.g. surface enhanced Raman spectroscopy , infrared spectroscopy. Auger electron spectroscopyX-ray photoelectron spectroscopyand a.c. impedance analysis have been used to study the adsorption, interaction and reaction of inhibitors at metal surfaces. 

Moreover, the interaction of the surface of the fillter with the matrix is usually a procedure much more complicated than a simple mechanical effect. The presence of a filler actually restricts the segmental and molecular mobility of the polymeric matrix, as adsorption-interaction in polymer surface-layers into filler-particles occurs. It is then obvious that, under these conditions, the quality of adhesion can hardly be quantified and a more thorough investigation is necessary. 

The strength of the adsorptive interaction as expressed in values of AG jj depends on the mode of interaction between the adsorbate molecule and the electrode surface. Weak adsorption (physisorption) is based mostly on van-der-Waals-interactions. It shows t5q)ically values of AG jj > - 20 kJ mol Stronger... 

Perrin model and the Johansson and Elvingston model fall above the experimental data. Also shown in this figure is the prediction from the Stokes-Einstein-Smoluchowski expression, whereby the Stokes-Einstein expression is modified with the inclusion of the Ein-stein-Smoluchowski expression for the effect of solute on viscosity. Penke et al. [290] found that the Mackie-Meares equation fit the water diffusion data however, upon consideration of water interactions with the polymer gel, through measurements of longitudinal relaxation, adsorption interactions incorporated within the volume averaging theory also well described the experimental results. The volume averaging theory had the advantage that it could describe the effect of Bis on the relaxation within the same framework as the description of the diffusion coefficient. 

Thus, as of today, there is no reliable classification of various types of adsorption. Presumably, it would be most correct to consider various types of adsorption interactions consistent with classification of chemical bonds [19]. 

For each of the model compounds, some material will have leached deeper Into the soil than Is shown in the table. The model calculates only the position of maximum concentration. For a compound like DBCP, which has a very weak adsorption interaction with the soil, the concentration profile will be spread out. DBCP would probably be found at low concentrations at the 1017 cm level. For the strongly adsorbed compounds, such as toxaphene and methoxychlor, the concentration peak will be narrow, and the depth of maximum concentration is the depth where most of the material is. 

As has been pointed out, both entropic and enthalpic interactions affect the chromatographic behavior of macromolecules. They are adjusted to the required type of separation by selecting appropriate stationary and mobile phases. In a third mode of liquid chromatography of polymers, liquid chromatography at the critical condition (LCCC) (Entelis etal., 1985,1986 Pasch, 1997), the adsorptive interactions are fully compensated by entropic interactions. This mode is also referred to as liquid chromatography at the critical point of adsorption. Hence, TAS is equal to AH and therefore, AG becomes zero. K is 1 irrespective of molar mass and, consequently, homopolymer molecules of different molar masses coelute in one chromatographic... 

There is a wide range of adsorption enthalpies AH(adsi, ranging from effectively zero to as much a 600 kJ per mole of adsorbate. The adsorptive interaction cannot truly be said to be a bond if the enthalpy is small the interaction will probably be more akin to van der Waals forces, or maybe hydrogen bonds if the substrate bears a surface layer of oxide. We call this type of adsorption physical adsorption, which is often abbreviated to physisorption. At the other extreme are adsorption processes for which A//(ads) is so large that real chemical bond(s) form between the substrate and adsorbate. We call this type of adsorption chemical adsorption, although we might abbreviate this to chemisorption. 

Before we start, we assume that the dye stains the surface by forming an adsorptive interaction. The majority of dyes in the kitchen come from vegetables. A particularly intense dye is f-carotene (II), which colours carrots, the golden leaves of autumn and some flowers. The intensity of the f -carotene colour arises from the extended conjugation. 

As shown in Fig. 7.7d polymers can destabilize colloids even if they are of equal charge as the colloids. In polymer adsorption (cf. Fig. 4.16) chemical adsorption interaction may outweigh electrostatic repulsion. Coagulation is then achieved by bridging of the polymers attached to the particles. LaMer and coworkers have developed a chemical bridging theory which proposes that the extended segments attached to one of the particles can interact with vacant sites on another colloidal particle. 

The electrochemical oxidation of polyhydric alcohols, viz. ethylene glycol, glycerol, meso-erythritol, xilitol, on a platinum electrode show high reactivity in alkaline solutions of KOH and K2C03 [53]. This electro-oxidation shows structural effects, Pt(lll) being the most active orientation. This results from different adsorption interactions of glycerol with the crystal planes [59]. 

It has been supposed that the surface diffusion is a form of molecular diffusion, restricted by adsorption interaction. Consequently ... 

M.M. Davila-Jimenez, M.P. Elizalde-Gonzalez and A.A. Pelaez-Cid, Adsorption interaction between natural adsorbents and textile dyes in aqueous solution. Coll. Surf.A Eng. Asp., 254 (2005) 107-114. 

How exactly the molecules are oriented inside the channels depends on their specific shape and on the adsorption interaction between the dyes and the channel walls or charge compensating cations. Because of the dye s oblongness, a double-cone-like distribution in the channels is a reasonable model. This distribution is illustrated in Fig. 19a. The arrows represent the transition moments of the dyes and a describes the half-opening angle of the double cone. The hexagonal structure of the zeolite L crystal hence allows six equivalent positions of the transition moments on this double cone with respect to the channel axis. 

The monomeric catalyst fraction showed similar R[ values as the metathesis products, which complicated the chromatographic separation and recycling procedure. Immobilization of the ruthenium catalyst on a dendrimer was anticipated to facilitate the chromatographic separation. Indeed, the presence of multiple (polar) organometallic sites on the dendrimer periphery resulted in stronger adsorption interactions between the dendritic catalyst and the silica and thus a better separation from the product. Two types of dendritic catalysts were prepared in which... 

In addition to proton adsorption, interactions between the ions of the inert electrolyte (counter ions, section 10.3) and the oxide surface lead to ion pair formation which influences the electrochemical properties of the oxides and the determination of pKa values. Ion pair formation involves outer sphere surface complexes (see Chap. 11), e.g. 

Most chelation and adsorption interactions can be circumvented by separating doses of the interacting drugs by a period of several hours, although note that this may not be wholly effective with drugs that undergo enterohepatic recirculation. 

When entrapment methods are being used for heterogenization, the size of the metal complex is more important than the specific adsorptive interaction. There are two different preparation strategies. The first is based on building up catalysts in well-defined cages of porous supports. This approach is also called the ship in a bottle method [29]. The other approach is to build up a polymer network around a preformed catalyst. 

Adhesion is created by primary and secondary forces according to the theory of adsorption interaction. This theory is applied the most widely for the description of interaction in particulate filled or reinforced polymers [30]. The approach is based on the theory of contact wetting and focuses its attention mainly on the influence of secondary forces. Accordingly, the strength of the adhesive bond is assumed to be proportional to the reversible work of adhesion (W ), which is necessary to separate two phases with the creation of two new surfaces. 

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