Situ Techniques

The presented examples clearly demonstrate tliat a combination of several different teclmiques is urgently recommended for a complete characterization of tire chemical composition and tire atomic stmcture of electrode surfaces and a reliable interiDretation of tire related results. Stmcture sensitive metliods should be combined witli spectroscopic and electrochemical teclmiques. Besides in situ techniques such as SXS, XAS and STM or AFM, ex situ vacuum teclmiques have proven tlieir significance for tlie investigation of tlie electrode/electrolyte interface. 

Ex situ bioremediation may use various biological wastewater treatment processes, soil piles, or land appHcation. With in situ bioremediation, the basic process is the same microbes, soil, and water working together as a bioreactor. Where the in situ techniques differ are in how contaminants and microbes are brought in contact and how oxygen, nutrients, and other chemical supplements ate distributed in the soil—water—air matrix. Typical in situ bioremediation techniques include natural or intrinsic attenuation, air sparging, and bioventing. 

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

The electrodesposition process of conducting polymers can be monitored by spectroelectrochemical in situ techniques Especially useful are ellipsometric... 

Transmission infrared spectroscopy is very popular for studying the adsorption of gases on supported catalysts and for studying the decomposition of infrared active catalyst precursors during catalyst preparation. Infrared spectroscopy is an in situ technique that is applicable in transmission or diffuse reflection mode on real catalysts. 

The second approach is to study real catalysts with in situ techniques such as infrared and Mossbauer spectroscopy, EXAFS and XRD, under reaction conditions, or, as is more often done, under a controlled environment after quenching of the reaction. The in situ techniques, however, are not sufficiently surface specific to yield the desired atom-by-atom characterization of the surface. At best they determine the composition of the particles. 

The dilemma is thus investigations of real catalysts under relevant conditions by in situ techniques give little information on the surface of the catalyst, while techniques that are surface sensitive can often only be applied on model surfaces under vacuum. Bridging the gap between UHV and high pressures and between the surfaces of single crystals and of real catalysts is therefore an important issue in catalysis. 

It is only since 1980 that in situ spectroscopic techniques have been developed to obtain identification of the adsorbed intermediates and hence of reliable reaction mechanisms. These new infrared spectroscopic in situ techniques, such as electrochemically modulated infrared reflectance spectroscopy (EMIRS), which uses a dispersive spectrometer, Fourier transform infrared reflectance spectroscopy, or a subtractively normalized interfacial Fourier transform infrared reflectance spectroscopy (SNIFTIRS), have provided definitive proof for the presence of strongly adsorbed species (mainly adsorbed carbon monoxide) acting as catalytic poisons. " " Even though this chapter is not devoted to the description of in situ infrared techniques, it is useful to briefly note the advantages and limitations of such spectroscopic methods. 

Dott W, D Eeidieker, M Steiof, PM Beckerm, P Kampfer (1995) Comparison of ex situ and in situ techniques for bioremediation of hydrocarbon-polluted soils. Int Biodet Biodeg 35 301-316. 

STM, X-ray reflectivity, and AFM are excellent in situ techniques for studying surface topography and morphology. Scanning electron microscopy is a useful ex situ technique. 

A wide variety of in situ techniques are available for the study of anodic hhns. These include reflectance, eUipsometry, X-ray reflectivity, and SXRD. X-ray reflectivity can be used to study thick surface layers up to 1000 A. The reflectance technique has been used to study oxide growth on metals, and it yields information on oxide thickness, roughness, and stoichiometry. It the only technique that can give information on buried metal-oxide interfaces. It is also possible to get information on duplex or multiple-layer oxide hhns or oxide hhns consisting of layers with different porosity. Films with thicknesses of anywhere from 10 to 1000 A can be studied. XAS can be used to study the chemistry of dilute components such as Cr in passive oxide hhns. 

The advantages of elUpsometry are that it is an in situ technique that can be used to study film growth on electrodes. The main disadvantage is that it does not provide chemical information. 

Christensen, P, and A. Hamnett, In-situ techniques in electrochemistry ellipsometry and FTIR, Electrochim. Acta, 45, 2443 (2000). 

The industrial catalyst for n-butane oxidation to maleic anhydride (MA) is a vanadium/phosphoras mixed oxide, in which bulk vanadyl pyrophosphate (VPP) (VO)2P207 is the main component. The nature of the active surface in VPP has been studied by several authors, often with the use of in situ techniques (1-3). While in all cases bulk VPP is assumed to constitute the core of the active phase, the different hypotheses concern the nature of the first atomic layers that are in direct contact with the gas phase. Either the development of surface amorphous layers, which play a direct role in the reaction, is invoked (4), or the participation of specific planes contributing to the reaction pattern is assumed (2,5), the redox process occurring reversibly between VPP and VOPO4. 

Currently, most remediation projects are carried out using ex situ technologies, both in the U.S. and in Europe. However, there is an increasing trend toward the application of in situ technologies because of their considerable advantages over ex situ techniques, such as less disturbance of the site, lower treatment costs, and so on. 

Frick, C.M., Farrel, R.E. and Germida, J.J., Assessment of Phytoremediation as an In-Situ Technique for Cleaning Oil-Contaminated Sites, Petroleum Technology Alliance of Canada, Calgary, AB, 1999. 

The various examples discussed above and several others, not mentioned in this necessarily incomplete chapter, demonstrate that XPS and also UPS assist and improve our understanding of the electrode/electrolyte interface and of electrochemical reactions. XPS, UPS and other ex situ techniques will continue to play a key role in providing information about the structure and composition of the electrochemical interface on a microscopic scale. 

In order to put the various ex situ techniques on a safer basis, the effects of electrode emersion and transfer deserve further clarification. Preferably those techniques which can be applied in both environments, in situ as well ex situ, will serve this purpose. 

Incorporating reinforcing particles that respond to a magnetic field is important with regard to aligning the particles to improve mechanical properties anisotropically [223-226]. In related work, some in-situ techniques have been used to generate electrically conducting fillers such as polyaniline within an elastomeric material [227],... 

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