In-Situ Spectroscopic Investigations

According to Sec. 3, the characterization of interface states at semiconductor electrodes is a key question since these states influence the behavior of the interface [76, 77]. The many different techniques of characterization have been reviewed [35, 76, 77] for the solid/liquid interface. True STS has not been applied until now. In first attempts to derive energy information the sample voltage was scanned to avoid problems with the electrochemical current at the tip extremity. The possibility of scanning the tip bias is discussed later. 

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Figure 3.80 Values of n, k and thickness L obtained t ia three parameter fits to the A, T and intensity data obtained during the growth of a polypyrrole film on a sputtered Pt electrode in N2-saturated I M NaCIO4/0,l M pyrrole. The potential was stepped from OV to 0.8 V vs, SCE for 15 s, and readings taken every 20 ms. Reprinted from tkarochimica Acia, 36. P,A. Christensen and A. Hamnett, In situ Spectroscopic Investigations of the Growth, Electrochemical Cycling and Overoxidation of Polypyrrolc in Aqueous Solution, pp. 1263-1286 (1991), with kind permission from Pergamon Press Ltd., Headington Hill Hall. Oxford 0X3 OBW, UK.

Figure 3.84 (a and b) The spectra in Figure 3,83 except only up to —0,2 V. (a) Full spectral range, spectra in Figure 3.83 collected at potentials > -0.2 V normalised to that taken at -0.2 V. (c) Full Reprinted from Electrochimica Act, 36, PA. Christensen and A, Hamnett, In. situ Spectroscopic Investig Cycling and Ovcroxidation of Polypyrrok in Aqueous Solution, pp.1263 1 86 (1991), with kind pc... 

Weissmahr, KW, Haderlein SB, Schwarzenbach RP, Hany R, Nuesch R (1997) In situ spectroscopic investigations of adsorption mechanisms of nitroaromatic compounds at clay minerals. Environ Sci Technol 31 240-247... 

The most powerful methods for the study of adsorption mechanism of nitroaromatic compounds on clay minerals have become in situ spectroscopic investigations. Handerlein et al. [152, 153] and Weissmahr et al. [154-156] have investigated the adsorption of NACs particularly on illites, montmorillonites and homoionic kaolinites. The substituted nitrobenzenes on the surface of smectites were investigated by Boyd et al. [157, 158], The main focus in the experimental study of adsorption of NACs on the surface of clay minerals is the influence of the type of clay mineral, the effect of exchangeable cation of the mineral, the effect of the structure and the kind of substituents of NAC compound on the position and orientation of NACs to the surface of mineral, the character of interaction between NACs and the surface of mineral, the adsorption energy. 

Cr2+/SiC>2 is an efficient catalyst for ethene polymerization, even at room temperature (in the industrial process the temperature is about 380 K). For this reason, it is an ideal system for in situ spectroscopic investigations of a working catalyst. 

Spectroscopic studies may be carried out under the actual catalytic conditions. These are referred to as in situ spectroscopic investigations. However, if the catalytic conditions are too drastic, it may not be possible to record spectra under such conditions. In such cases spectroscopic monitoring is done under less severe conditions. 

Obviously, having common NMR spectroscopical techniques routinely at hand, not only the ionic liquids themselves are interesting targets for in situ spectroscopic investigations. Since ILs are frequently used as solvents for chemical transformations, reactions in these media as well as the formation and the stability of transition metal complexes are studied (Fig. 11)... 

In this chapter, the local structures of the transition metal oxides, Ti, V, Mo, and Cr oxide single-site species, incorporated within zeolites or mesoporous sUica framework structures as well as the local structures of transition metal ions such as Ag" " exchanged into zeohte cavities were discussed, based on the results of various in situ spectroscopic investigations such as ESR, UV-Vis, photoluminescence and XAFS (XANES and EXAFS). 

ATR-FTIR/UV-vis/Raman spectroscopy has been applied for mechanistic studies of the heterogeneously catalyzed hydrogenation of imines and of formal [3+3] cyclocondensation reactions catalyzed by Lewis adds [11, 33]. In the latter reaction, different products were obtained dependent on the Lewis acid used. It could be elucidated by in situ spectroscopic investigations that the intermediate complex formed between the ketene acetal component and the Lewis acid (an acid-catalyzed rearrangement reaction occurs in the case of trimethylsilyltrifluoromethanesulfonate (TM SOTf), forming a bischelate complex with TiCl4) controls the subsequent attack of the second reactant in the form of a diene, and consequently, the mechanism of product formation [33]. 

Zakzeski J, Bruijnincx PCA, Weckhuysen BM (2011) In situ spectroscopic investigation of the cobalt-catalyzed oxidation of lignin model compounds in ionic liquids. Green Chem 13 671... 

In Situ Spectroscopic Investigations, Specialized Experimental Set-Ups, Chemometrics... 

Figure 14.8 Optical absorption spectra of a PEDOT electrochemical cell for different applied voltages. Reprinted from j. C. Custafsson, B. Liedberg and O. Inganas, In situ spectroscopic investigations of electrochromism and ion transport in a poly(3,4-ethylenedioxythiophene) electrode in a solid state electrochemical cell, Solid State Ionics 69, 145-152 (1994), Copyright 1994, with permission from Elsevier...

Zhang H-X, Wang S-H, Jiang K, Andre T, Cai W-B (2012) In situ spectroscopic investigation of CO accumulation and poisoning on Pd black surfaces in concentrated HCOOH. J Power Sources 199 165-169... 

Christensen, P. A., and Hamnett, A., In situ spectroscopic investigations of the growth, electrochemical cycling and overoxidation of polypyrrole in aqueous solutions, Elec-trochim. Acta, 36, 1263-1286 (1991). 

Conventional spectroelectrochemistry involves bulk electrolysis of an analyte in a low volume cell combined with simultaneous or subsequent in situ spectroscopic investigation. The key point is that investigations are in situ with spectroscopic studies undertaken within an electrochemical cell that is under potential control. Spectroelectrochemical experiments are frequently qualitative and are used to structurally characterize an intermediate redox state. Quantitative measuronents can be experimentally challenging because they require rigorous geometric arrangement of the cell to avoid problems such as iR drop and low current densities as a consequence of the relative size of the working electrode and its orientation with respect to the other electrodes. 

A challenge in using bulk electrolysis to generate redox states for in situ spectroscopic investigations is to minimize the time for exhaustive electrolysis. The most common... 

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