Adsorption synergistic

Synergistic adsorption — Coadsorption of two or more components under conditions (e.g., at concentrations) where neither of them adsorbs alone. 

In heterogeneous catalysis, all adsorbed species can be said to act as inhibitors by occupying parts of the catalyst surface, making it inaccessible to other molecules (synergistic adsorption is the exception). Thus, a reactant not only promotes conversion in the normal way, but also inhibits it. Both these opposing effects decrease with conversion, but their balance shifts. 

In this paper we examine the role of mixed surfactants in the demulsification of water-in-Leduc oil emulsion by application of the spreading rate method which is then correlated with the electroacoustic results and centrifugation. Microelectrophoresis using the reverse emulsion was also used to investigate the adsorption process. The results show both a very good correspondence between the various techniques and provide insight on the synergistic adsorption behavior of the hydrophobic and hydrophilic surfactants. 

Zhou Q, Somasundaian P (2009) Synergistic adsorption of mixtures of cationic gemini and ntmitmic sugar-based surfactant on silica. J Colloid Interface Sci 331 288-294... 

Although quantitative thin-film force measurements of polymer/surfactant-containing systems are relatively new, quite fascinating behaviour has already been found. In particular, the strongly interacting synergistic adsorption system (e.g. Case II) containing an anionic polyelectrolyte and a cationic surfactant has been extensively studied. This system has revealed both oscillatory force versus distance profiles, and interfacial gel formation within individual films. 

What is the difference between synergistic adsorption and chemisorption ... 

In the first case, an ion Me" does not form a surface-active complex with L, but the complex is formed between the oxidized, or reduced, ion Me"" and the adsorbed ligand Lads Synergistic adsorption may occur in the presence of a chelat-... 

It has been found that particulate pollution, while causing soiling of materials, may also be responsible for increasing corrosion levels (compared to the corrosion that would be caused by the same level of acid impingement alone) by a process of adsorption. Also, particulates can react synergistically with the acid deposition to cause much greater damage. 

In the case of ions, the repulsive interaction can be altered to an attractive interaction if an ion of opposite charge is simultaneously adsorbed. In a solution containing inhibitive anions and cations the adsorption of both ions may be enhanced and the inhibitive efficiency greatly increased compared to solutions of the individual ions. Thus, synergistic inhibitive effects occur in such mixtures of anionic and cationic inhibitors . These synergistic effects are particularly well defined in solutions containing halide ions, I. Br , Cl", with other inhibitors such as quaternary ammonium cations , alkyl benzene pyridinium cations , and various types of amines . It seems likely that co-ordinate-bond interactions also play some part in these synergistic effects, particularly in the interaction of the halide ions with the metal surfaces and with some amines . 

The synergistic elfect seen in Pt-Rn alloys has aronsed great interest, since it opened perspectives for their nse in efficient methanol fnel cells. Many studies were performed to elucidate the origins of this effect. Some workers believe that it is due to changes in the electron strnctnre of platinnm npon alloy formation with ruthenium. A popular interpretation is the bifunctional mechanism, according to which the organic species are preferentially chemisorbed on platinnm sites while the ruthenium sites facilitate the adsorption of the species needed for oxidation of the orgaiuc species. 

LDAO/SDS Interaction. Mixing of cationic and anionic surfactant solutions results In the formation of a mixed species that Is more surface active than the Individual species. The enhanced synergistic effect has been explained (2,3) by showing that a close-packed adsorption of electroneutral R R takes place (R" " and R represent the long chain cation and anion respectively). In the case of Ci2 and C14-DAO, a 1 1 LDAO/SDS molar ratio produces a minimum In surface tension and Is accompanied by an Increase In pH In the bulk solution the association seems to be of the type R R", and the absence of visible precipitate may be attributed to the solubilization of the R R" complex In the solution. In the region where LDAO Is In excess, the structure Is probably [cationic (LDAOH ) anionic (SDS)] nonlonlc (LDAO), while [cationic (LDAOH anionic (SDS)] anionic (SDS) Is formed when SDS Is In excess. Equal molar concentration results In cationic (LDAOH ) anionic (SDS) complex which should favor precipitation. However, at pH >9, there Is no Indication of precipitation (even when the total solute concentration Is 0.35 M). When the pH Is below 9, then precipitation will take place. 

Figure 9. (A) Synergistic effect observed for the adsorption of CBH I/CBH II onto Avicel (pH 5.0, 25°C). In ordinate the relative increase of adsorption (nmoles per mg Avicel) for each component ((enzyme)ai,, S) in a mixture of CBH I and CBH II as compared to the adsorption of each enzyme present as single component ((enzyme)ad, ). Syn. effect =...

C) Synergistic effect observed for the adsorption of core I/CBH II onto Avicel. Same conditions as in (A). 

Our chromophoric substrates proved to be valuable in the study of several aspects of the enzymology of these cellulases. A rapid and specific method for purification (affinity chromatography) has been developed. Following our collaboration with several groups, new insights into the domain arrangement and tertiary structures of two cellulases were obtained. Contributions to the elucidation of the synergistic action (adsorption-hydrolysis) of these enzymes were achieved. 

In systems containing two or more adsorbates, either competitive or synergistic effects may operate. The commonest synergistic effect is that of ternary adsorption (11.5.4). Competitive behaviour may involve competition for the same surface sites, indirect effects due to the change in the electrostatic properties of the oxide/water interface and in some cases, formation of non sorbing, metal-ligand complexes in solution. 

---