SEIRAS

SEIRAS is emerging as a powerful technique for interfacial studies in electrochemistry and electrochemical catalysis. Chapter 9 of this volume is devoted to SEIRAS and describes experimental aspects and many applications. Highlights are presented below, and the reader is referred to Chapter 9 for details regarding cell design, working electrode characteristics, and preparation techniques and applications. 

Another area in which SEIRAS is providing important new information is electrocatalysis [21, 137-142]. In recent studies of methanol oxidation on Pt, adsorbed formate [21] and formate-like species [142] were identified as by-products. The findings showed that, in addition to the frequently studied reaction leading to adsorbed CO, methanol oxidation can progress through a parallel pathway to formate, which avoids surface poisoning by CO and provides a po- 

In addition to electrocatalysis and double-layer phenomena, SEIRAS has proved particularly useful in the study of organic adsorption on electrodes [99, 146-149]. This is an area where SEIRAS can have an especially important impact, as traditional in-situ infrared methods are often limited by the low absorption cross-sections of organic adsorbates. Along these same lines, SEIRAS is 

In a final step, the oriented, surface-attached cytochrome c oxidase was reconstituted into a lipid environment formed at the surface by spontaneous assembly from exposure to the vesicles, in order to enhance the stability and functionality of the membrane protein. 

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Figure 6.16 Attenuated total reflection surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS) spectra for the oxidation of 0.1 M HCOOH in 0.5 M H2SO4 on a polycrystaUine electrode. The bands at 2055 -2075 and 1800-1850 cm are assigned to linear- and bridge-bonded CO, whereas the band at 1323 cm corresponds to adsorbed formate. (Reproduced from Samjeske et al. [2006].)...

Figure 9.2 SEIRAS spectra for a Pt thin film electrode in 02-saturated 0.1 M NaC104 + NaOH (pH 11). The reference spectmm at 0.4 V was taken before the potential sweep started. The scan rate was 10 mV/s. (Reproduced with permission from Shao et al. [2006a].)...

Delgado JM, Orts JM, Rodes A. 2005. ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes. Langmuir 21 8809-8816. 

Pronkin S, Wandlowski T. 2004. ATR-SEIRAS—An approach to probe the reactivity of Pd-modified quasi-single crystal gold film electrodes. Surf Sci 573 109-127. 

Support effects in electiocatalysis, 567-586 Surface diffusion, 163, 173-177 Surface Enhanced Infrared Reflection Adsorption Spectroscopy (SEIRAS), 183... 

LC-IR using surface-enhanced IR absorption spectroscopy (SEIRAS) was recently designed in order to develop a highly sensitive and rapid analysis method for polymer additives [506]. The method, which consists of spraying the LC eluents on to a metal film of Ag on a BaF2 substrate, allows an enhancement factor of about 90. 

Sudo et al. [506] have reported the detection of 10 ng of triphenylphosphate by means of LC-SEIRAS the method is used for the analysis of additives in commercial polypropylene. 

A related effect has been described for IR spectroscopy - Surface Enhanced Infrared Absorption spectroscopy (SEIRA). However, as the enhancement factors are significantly lower than for SERS and both the required metal particle size and the activation distance between the target molecule and the particle are more than one order of magnitude smaller, no practically applicable SEIRA sensors have been demonstrated up to now. 

Dovbeshko GI, Repnytska OP, Obraztsova ED, Shtogun YV (2003) DNA interaction with single-walled carbon nanotubes A SEIRA study. Chem. Phys. Lett. 372 432 437. 

CN-C6H4-NC One NC group bonded to surface in p mode the second one is free and remote from the surface 2127 2129 uncoord NC 2180 coord NC 2184 coord NC SERS SERS SEIRA [38] [48]... 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

Figure 10.5. Schematic model for electromagnetic enhancement in SEIRA.

Figure 10.6 demonstrates the SEIRA spectra of the C-H modes of a monolayer of 4-nitrobenzoic acid using ATR infrared techniques. The pres-... 

Figure 10.6. Absorption of the C-H modes of a monolayer of 4-nitrobenzoic acid using SEIRA techniques. The curves are for increasing thicknesses of a silver overlayer. The inset shows the path of the infrared beam through the silicon total-internal-reflection plate. The sample is deposited on the two sides of the plate. (With permission from Ref. 23.)...

Samples for SEIRA are typically in the form of molecular monolayers deposited on both sides of the internal reflection element or ATR plate, which is usually a silicon crystal. The silicon substrate is cut in the paral-... 

Alternatively, various analytical methods based on SPR phenomenon have been developed, including surface plasmon field-enhanced Raman scattering (SERS) [7], surface plasmon field-enhanced fluorescence spectroscopy (SPFS) [8-11], surface enhanced second harmonic generation (SHG) [12], surface enhanced infrared absorption (SEIRA) [13], surface plasmon field-enhanced diffraction spectroscopy (SPDS) [14-18], Most of these methods take advantage of the greatly enhanced electromagnetic field of surface plasmon waves, in order to excite a chromophoric molecule, e.g., a Raman molecule or a fluorescent dye. Therefore, a better sensitivity is expected. 

Fig. 1. (a) A chemical structure of a 2.5th generation carboxylic acid-terminated poly(amido amine) (PAMAM) dendrimer. (b) Transmission surface enhanced infrared absorption spectra (SEIRAS) of dendrimer adlayers prepared at 30 min adsorption from aqueous solutions (0.01 wt.%) of a dendrimer at different pHs. Numerical values are pHs of the solutions, (c) Adsorption-desorption profiles as a function of time at different pHs and adlayer thicknesses at adsorption and desorption equilibrium as a function of pH for aqueous solutions (0.1 wt.%) of the dendrimer. The symbols, j and J, in the top figure denote start of adsorption and desorption, respectively. In the bottom figure, filled circle and opened square denote adlayer thicknesses at adsorption and desorption equilibrium, respectively. The dark tie denotes the calculated dendrimer size width. A solid curve is drawn to be visual, (d) Schematic illustration of dendrimers adsorbed at different pHs. Reprinted with permission from Ref. [69], 2006, American Scientific Publishers. 

Fig. 5. (Left) SEIRAS of NaHA and DNA on PAMAM dendrimer SAMs after adsorption for 30 min from aqueous solutions. Dendrimer SAMs were prepared by the amide bond formation of dendrimers with active ester groups of 3-mercapto-propionic acid (MPA) SAMs on CaF2 substrates. Infrared absorption spectra of NaHA, DNA, and PAMAM dendrimer are also included. (Right) Schematic illustration of the interactions between polyelectrolytes and dendrimer SAMs. Reprinted from Ref. [110].

Desorption reaction in water at different pHs on polyelectrolyte-adsorbed PAMAM dendrimer SAM substrates was followed up with SEIRAS (Fig. 7) [24, 110]. The characteristic amide I and II bands of NaPGA, a C-OH band of NaHA and DNA, and a P=0 band of DNA decrease with increasing pH of immersion water. The desorption is almost done within initial 30 min but proceeds slowly with time till overnight and, in all cases, the desorption reaction runs down, when the adsorbed molecules decrease down to the amount adsorbed at each pH. Namely, it can be remarked that the adsorption/desorption processes are reversible. Moreover, the present dendrimer SAMs have an advantage to be reusable for the adsorption/desorption reactions. In the case of the desorption reaction at pH 9.08 on a DNA-adsorbed PAMAM dendrimer SAM substrates, DNA on a substrate prepared at pH 3.04 does not achieve the adsorption amount at the adsorption reaction at the same pH, owing to the... 

Fig. 7. (Top) SEIRAS after desorption process of NaHA and DNA adsorbed on PAMAM dendrimer SAMs. (Bottom) Schematic illustration of the amounts of adsorbate on the adsorption and desorption processes. Reprinted from Ref. [110].

Furthermore, it is possible to increase the sensitivity of the IR technique, and thus the probability of detecting transient surface species characterized by (very) low absorption coefficients (such as the intermediate species present during the first steps of the polymerization reaction on the Phillips catalyst) by exploiting the surface-enhanced infrared absorption (SEIRA) effect. It is known that molecules adsorbed on metal island films or particles exhibit 10-1000 times more intense infrared absorption than would be expected from conventional measurements without the metal (253-256). The possibility of performing SEIRA spectroscopy should therefore be expected to provide an opportunity to better investigate the nature of the intermediate species, not only for ethene polymerization on Cr(II)/ Si02, but for other reactions on solid catalysts. 

Recently, Shao et al. proposed superoxide (O2) formation as the first step of the ORR on Pt films in alkaline solution (NaC104 with pH=ll) by analyzing spectral data of surface-enhanced infrared reflection absorption spectroscopy with attenuated total reflection (ATR-SEIRAS). This was fuller supported by Zhang and Anderson, who performed DFT cluster calculations for the ORR on Pt(lll), Pt(lOO), and umeconstracted Pt(llO). They... 

SIERA Surface-enhanced infrared absorption As in the case of surface-enhanced Raman scattering (SERS), molecules adsorbed on metal island films or particles exhibit intense infrared absorption several folds higher than what one would expect from conventional measurements without the metal. This effect is referred to as surface-enhanced infrared absorption (SEIRA). 

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