Specific adsorption surface

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

Proteins, like other macromolecules, can be made into monolayers at the air-water interface either by spreading, adsorption, or specific binding. Proteins, while complex polymers, are interesting because of their inherent surface activity and amphiphilicity. There is an increasing body of literature on proteins at liquid interfaces, and here we only briefly discuss a few highlights. 

The alkali promotion of CO dissociation is substrate-specific, in the sense that it has been observed only for a restricted number of substrates where CO does not dissociate on the clean surface, specifically on Na, K, Cs/Ni( 100),38,47,48 Na/Rh49 and K, Na/Al(100).43 This implies that the reactivity of the clean metal surface for CO dissociation plays a dominant role. The alkali induced increase in the heat of CO adsorption (not higher than 60 kJ/mol)50 and the decrease in the activation energy for dissociation of the molecular state (on the order of 30 kJ/mol)51 are usually not sufficient to induce dissociative adsorption of CO on surfaces which strongly favor molecular adsorption (e. g. Pd or Pt). 

During ball milling the mean particle diameter, d, gas adsorption isotherm specific surface area (BET) and contamination (wt% contaminant) conform to the general law ... 

The availability of thermodynamically reliable quantities at liquid interfaces is advantageous as a reference in examining data obtained by other surface specific techniques. The model-independent solid information about thermodynamics of adsorption can be used as a norm in microscopic interpretation and understanding of currently available surface specific experimental techniques and theoretical approaches such as molecular dynamics simulations. This chapter will focus on the adsorption at the polarized liquid-liquid interfaces, which enable us to externally control the phase-boundary potential, providing an additional degree of freedom in studying the adsorption of electrified interfaces. A main emphasis will be on some aspects that have not been fully dealt with in previous reviews and monographs [8-21]. 

Figure 1. A schematic representation of the synthesis of the electrochemical double layer in UHV a) adsorption of specifically adsorbed ions without solvent b) addition of hydration water c) completion of the inner layer d) addition of solvent multilayers, e) model for the double layer at an electrode surface in solution.

The determination of the specific surface area of a zeolite is not trivial. Providers of zeolites typically give surface areas for their products, which were calculated from gas adsorption measurements applying the Brunauer-Emmet-Teller (BET) method. The BET method is based on a model assuming the successive formation of several layers of gas molecules on a given surface (multilayer adsorption). The specific surface area is then calculated from the amount of adsorbed molecules in the first layer. The space occupied by one adsorbed molecule is multiplied by the number of molecules, thus resulting in an area, which is assumed to be the best estimate for the surface area of the solid. The BET method provides a tool to calculate the number of molecules in the first layer. Unfortunately, it is based on a model assuming multilayer formation. Yet, the formation of multilayers is impossible in the narrow pores of zeolites. Specific surface areas of zeolites calculated by the BET method (often termed BET surface area) are therefore erroneous and should not be mistaken as the real surface areas of a material. Such numbers are more related to the pore volume of a zeolite rather than to their surface areas. 

Another possible factor for the decrease of If is adsorption that is excess of G on a surface of H. According to Gibbs, the isotherm of adsorption (the specific surface excess of /th guest) has a form ... 

The net charge at the hydrous oxide surface is established by the proton balance (adsorption of H or OH" and their complexes at the interface and specifically bound cations or anions. This charge can be determined from an alkalimetric-acidimetric titration curve and from a measurement of the extent of adsorption of specifically adsorbed ions. Specifically adsorbed cations (anions) increase (decrease) the pH of the point of zero charge (pzc) or the isoelectric point but lower (raise) the pH of the zero net proton condition (pznpc). 

The WDMSPR sensor approach offers the benefit of multichannel performance without increasing complexity and costs of the sensor system. In addition, the WDMSPR sensors make it possible to discriminate effects occurring in the proximity of sensor surface (specific binding, non-specific adsorption) from those occurring in the whole medium (interfering background refractive index fluctuations) which is a prerequisite for robust referencing ". ... 

Spectroscopic investigations to determine the structure of the surface complexes formed through adsorption and to help distinguish between adsorption of metals and their surface precipitation. Various surface-specific spectroscopic techniques are now used for this purpose, in particular IR, XPS, EPR and XAS (see Chap. 7). Eor reviews see Brown (1990), Manceau et al. (1992), Brown et al. (1995) and Blesa et al. (2000). 

The measurement of heats of adsorption by means of microcalorimetry has been used extensively in heterogeneous catalysis in the past few decades to gain more insight into the nature of gas-surface interactions and the catalytic properties of solid surfaces. Specific attention will be focused on group IIIA containing samples in this section. 

Lignite GAC This presents a total surface area of 650 m2/g and an apparent density of 0.50 g/cm3, approximately. It is usually used for liquid-phase adsorption, and specifically, in decolorizing applications because it has a higher percentage of meso (transitional) and macro pores than bituminous GAC, and therefore is appropriate for larger molecules. 

For example, the Langmuir adsorption isotherm specifically describes adsorption of a single gas-phase component on an otherwise bare surface. When more than one species is present or when chemical reactions occur, the functional form of the Langmuir adsorption isotherm is no longer applicable. Thus, although such simple functional expressions are very useful, they are not generally extensible to describe arbitrarily complex surface reaction mechanisms. 

The classical method involves admitting a known quantity of gas to the sample chamber, which is usually maintained near the condensation point of the gas. Adsorption of the gas on the surface of the solid occurs, decreasing the pressure in the chamber until the adsorbed gas is in equilibrium with the free gas phase. The volume of gas adsorbed is determined by subtracting the volume of gas required to fill the free space (dead space) at equilibrium pressure from the volume of gas admitted. The dead space is obtained by precalibration of the chamber volume or by repeating the determination with a sample of negligible adsorption. The specific surface area (S), in m2/g, is given by the following... 

It is rare that a catalyst can be chosen for a reaction such that it is entirely specific or unique in its behaviour. More often than not products additional to the main desired product are generated concomitantly. The ratio of the specific chemical rate constant of a desired reaction to that for an undesired reaction is termed the kinetic selectivity factor (which we shall designate by 5) and is of central importance in catalysis. Its magnitude is determined by the relative rates at which adsorption, surface reaction and desorption occur in the overall process and, for consecutive reactions, whether or not the intermediate product forms a localised or mobile adsorbed complex with the surface. In the case of two parallel competing catalytic reactions a second factor, the thermodynamic factor, is also of importance. This latter factor depends exponentially on the difference in free energy changes associated with the adsorption-desorption equilibria of the two competing reactants. The thermodynamic factor also influences the course of a consecutive reaction where it is enhanced by the ability of the intermediate product to desorb rapidly and also the reluctance of the catalyst to re-adsorb the intermediate product after it has vacated the surface. 

The flotation process is applied on a large scale in the concentration of a wide variety of the ores of copper, lead, zinc, cobalt, nickel, tin, molybdenum, antimony, etc., which can be in the form of oxides, silicates, sulfides, or carbonates. It is also used to concentrate the so-called non-metallic minerals that are required in the chemical industry, such as CaF2, BaS04, sulfur, Ca3(P03)2, coal, etc. Flotation relies upon the selective conversion of water-wetted (hydrophilic) solids to non-wetted (hydrophobic) ones. This enables the latter to be separated if they are allowed to contact air bubbles in a flotation froth. If the surface of the solids to be floated does not possess the requisite hydrophobic characteristic, it must be made to acquire the required hydrophobicity by the interaction with, and adsorption of, specific chemical compounds known as collectors. In separations from complex mineral mixtures, additions of various modifying agents may be required, such as depressants, which help to keep selected minerals hydrophilic, or activators, which are used to reinforce the action of the collector. Each of these functions will be discussed in relation to the coordination chemistry involved in the interactions between the mineral surface and the chemical compound. 

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