Adsorption, In situ

By well defined we mean that all the steps of the catalyst synthesis have been followed stepwise (physisorption and chemisorption of the starting organometallic, chemical transformation on the surface, etc.) by an adequate variety of chemical and physical tools at the disposal of chemists such as the mass balance of any reaction occurring during adsorption, in situ IR, NMR, EXAFS, UV-visible, chemical analysis, and so on. 

TIRF occupies a unique niche, providing a noninvasive method for studying protein adsorption in situ and in real time. The TIRF technique, as it is applied in our laboratory, has been used successfully to study both macroscopic and molecular aspects of protein adsorption. The present goal of this laboratory is to elucidate the interactions occurring when a protein adsorbs to a solid surface using the TIRF technique. It is hoped that, eventually, a complete, general description of the protein adsorption process will be attained. 

Kinetics of monolayer formation have been intensively studied. SPR and QCM are the simple methods allowing monitoring of the adsorption in situ. It was shown that deposition usually proceeds through a two-step process (Figure 6). The first step is first order with respect to the concentration of adsorbate and is well described by a Langmuir isotherm. This is a fast reaction comprising adsorption and desorption processes in equilibrium. 60-80% of material adsorbs during this step. It is usually accepted that this first step produces physi- or chemisorbed structures with alkane chains in a relatively disordered state. ... 

Asada M, Shuler ML (1989) Stimulation of ajmalicine production and exaetirai from Catharanthus roseus effects of adsorption in situ, elicitors, and alginate immohilization. Appl Microbiol Biotechnol 30 475-481. doi 10.1007/BF00263851... 

These materials, unlike the other nanophase materials described in this chapter, are nano-sized in only one dimension and thereby act as nanoplatelets that sandwich polymer chains in composites. Mont-morillonite (MMT) is a well-characterized layered silicate that can be made hydrophobic through either ionic exchange or modification with organic surfactant molecules to aid in dispersion [5,23]. Polymer-layered silicates may be synthesized by exfoliation adsorption, in situ intercalative polymerization, and melt intercalation to yield three general types of polymer/clay nanocomposites. Intercalated structures are characterized as alternating polymer and siHcate layers in an ordered pattern with a periodic space between layers of a few nanometers [13], ExfoHated or delaminated structure occurs when silicate layers are uniformly distributed throughout the polymer matrix. In some cases, the polymer does not intercalate... 

The four main strategic processes for preparing polymer/layered silicate nanocomposites are exfoliation-adsorption, in situ intercalative polymerization, melt intercalation and template synthesis. ... 

Wang J, Ocko B M, Davenport A J and Isaacs H I 1992 In situ diffraction and reflectivity studies of the Au(111 )/electrolyte interface Reconstruction and anion adsorption Phys. Rev B 34 10 321-38... 

Pettinger B, Lipkowski J and Mirwald S 1995 In situ SFIG studies of adsorption induced surface reconstruction of Au (111 )-electrodes Electrochim. Acta 40 133-42... 

Wohimann B, Park Z, Kruft M, Stuhimann C and Wandeit K 1998 An in situ and ex situ study of chioride adsorption on Cu(111) eiectrodes in diiute FICi soiutions 1998 Colloids Surfaces A 134 15-19... 

The third generation are latices made with independentiy prepared surfactant to mimic the in situ prepared functional monomer surfactant. These emulsifiers are often A—B block polymers where A is compatible with the polymer and B with the aqueous phase. In this way surface adsorption of the surfactant is more likely. These emulsions are known to exhibit excellent properties. 

It is common practice to exclude from consideration as leaching the elution of surface-adsorbed solute. This process is treated instead as a special case of the reverse operation, adsorption. Also usually excluded is the washing of filter cakes, whether in situ or by reslurrying and refiltration. 

Because silver, gold and copper electrodes are easily activated for SERS by roughening by use of reduction-oxidation cycles, SERS has been widely applied in electrochemistry to monitor the adsorption, orientation, and reactions of molecules at those electrodes in-situ. Special cells for SERS spectroelectrochemistry have been manufactured from chemically resistant materials and with a working electrode accessible to the laser radiation. The versatility of such a cell has been demonstrated in electrochemical reactions of corrosive, moisture-sensitive materials such as oxyhalide electrolytes [4.299]. 

Fig. 5.10. Series of sequential in-situ AFM images of the growth of ODS on silicon. The numbers indicate the adsorption time in minutes.

Several methods have been employed to study chemical reactions theoretically. Mean-field modeling using ordinary differential equations (ODE) is a widely used method [8]. Further extensions of the ODE framework to include diffusional terms are very useful and, e.g., have allowed one to describe spatio-temporal patterns in diffusion-reaction systems [9]. However, these methods are essentially limited because they always consider average environments of reactants and adsorption sites, ignoring stochastic fluctuations and correlations that naturally emerge in actual systems e.g., very recently by means of in situ STM measurements it has been demon-... 

The very new techniques of scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) have yet to establish themselves in the field of corrosion science. These techniques are capable of revealing surface structure to atomic resolution, and are totally undamaging to the surface. They can be used in principle in any environment in situ, even under polarization within an electrolyte. Their application to date has been chiefly to clean metal surfaces and surfaces carrying single monolayers of adsorbed material, rendering examination of the adsorption of inhibitors possible. They will indubitably find use in passive film analysis. 

In general, a Raman adsorption cell consists of a length of pyrex or silica tubing, one end of which is sealed with an optical flat, and the other either connected to a gas line for admitting the adsorbate or to a vacuum line for evacuating the cell. Activation of the samples may then be carried out in situ 27). 

In situ Fourier transform infrared and in situ infrared reflection spectroscopies have been used to study the electrical double layer structure and adsorption of various species at low-index single-crystal faces of Au, Pt, and other electrodes.206"210 It has been shown that if the ions in the solution have vibrational bands, it is possible to relate their excess density to the experimentally observed surface. 

According to the data obtained with SXRS in salt solutions,519 520 at a < 0 the surface of Au(lll) forms a ( 3 x 22) structure as in a vacuum. At a > 0 the reconstruction disappears and the (1 x 1) structure is observed. On the reconstructed Au(l 11) surface there are 4.4% more atoms than on the (1 x 1) structure and on the reconstructed Au( 100) there are 24% more atoms than on the (1 x 1) structure.506,519 This phase transition shifts in the negative direction with the adsorbability of the anion. The adsorption-induced surface reconstruction of Au(l 11) electrodes has been studied in situ by second harmonic generation by Pettinger et al.521... 

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