Cylindrical internal reflectance Fourier

Characterization of Anion Binding on Goethite Using Titration Calorimetry and Cylindrical Internal Reflection-Fourier Transform Infrared Spectroscopy... 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

Cylindrical. Internal Reflection - Fourier Transform Infrared (CIR-FTIR) Spectroscopy... 

Holmen, B.A. Tejedor-Tejedor, M.S. Casey, WA. (1997) Hydroxymate complexes in solution at the goethite/water interface. A. Cylindrical internal reflectance Fourier transform infrared spectroscopic study. Langmuir 13 2197... 

Tejedor-Tejedor, M.L Yost, E.C. Anderson, M.C. (1990a) Characterization of benzoic acid and phenolic complexes at the goethite/ aqueous solution interface using cylindrical internal reflectance Fourier transform infrared spectroscopy. Part 5 Methodology. Langmuir 6 979-987... 

Holmen B. A., Tejedor-Tejedor M. I., and Casey W. H. (1997) Hydroxamate complexes in solution and at the goethite-water interface a cylindrical internal reflection Fourier transform infrared spectroscopy study. Langmuir 13, 2197-2206. 

Zeltner, W.A. et al.. Characterization of anion binding on goethite using titration calorimetry and cylindrical internal reflection-Fourier transform infrared spectroscopy, ACS Symp. Ser., 323, 142, 1986. 

Zeltner, W. A., E. C. Yost, M. L. Machesky, M. I. Tejedor-Tejedor, and M. A. Anderson (1986), Characterization of Anion Binding on Goethite Using Titration Calorimetry and Cylindrical Internal Reflection-Fourier Transform Infrared Sepectroscopy, in J. A. Davis and K. F. Hayes, Eds., Geochemical Processes at. Mineral Surfaces, American Chemical Society, Washington, PP. 142 161. 

CIR-FTIR cylindrical internal reflection Fourier transform infrared... 

Tejedor-Tejedor, M. I., Yost, E. C., and Anderson, M. A., Characterization of benzoic complexes at the goethite/aqueous solution interface using cylindrical internal reflection Fourier transform infrared spectroscopy. Part I. Methodology, Langmuir, 6, 980-987 (1990). 

Tunesi, S., Anderson, M.A. (1992). Surface effects in photochemistry an in situ cylindrical internal reflection-Fourier transform infrared investigation of the effect of ring substituents on chemisorption onto Ti02 ceramic membranes, Langmuir Vol. 8,487-495, 0743-7463. 

FIGURE 12.15 The adsorption of PO4" by monodomainic goethite used by Hiemstra and Van Riemsdijk (1996) and that of Bowden et aL (1980). The lines are calculated with the charge distribution model and are consistent with the surface species observed by cylindrical internal reflection-Fourier transform infrared spectroscopy. (Reprinted from Journal of Colloid and Interface Science, 179, Hiemstra, T. and Van Riemsdijk, W. H. 488-508. Copyright 1996, with permission from Elsevier.)... 

Final justification for using terms such as inner- or outer-sphere awaits direct spectroscopic confirmation. Electron Spin Resonance, Mossbauer, and Fourier Transform Infrared-Cylindrical Internal Reflection Spectroscopic techniques are being used to establish the structure of surface complexes (see, e.g., McBride, Ambe et al., and Zeltner et al., this volume). The potential for using EXAFS (extended x-ray absorption fine structure) to establish the type of surface complex for Pb + adsorbing onto goethite is currently being undertaken in our laboratory. 

An infrared spectrum is a plot of percent radiation absorbed versus the frequency of the incident radiation given in wavenumbers (cm ) or in wave length ( xm). A variation of this method, diffuse reflectance spectroscopy, is used for samples with poor transmittance, e.g. cubic hematite crystals. Increased resolution and sensitivity as well as more rapid collection of data is provided by Fourier-transform-IR (FTIR), which averages a large number of spectra. Another IR technique makes use of attenuated total reflectance FTIR (ATR-FTIR) often using a cylindrical internal reflectance cell (CIR) (e.g. Tejedor-Tejedor Anderson, 1986). ATR enables wet systems and adsorbing species to be studied in situ. 

A technique which has proven useful for our studies is that of cylindrical internal reflectance (CIR), coupled with a Fourier transform infrared spectrometer. In this study, an IBM-85 FTIR equipped with either a DTGS (deuterated triglycine sulfate) or MCT (mercury-cadmium-tellurium) detector was used. The infrared radiation is focused by concave mirrors onto the 45° conical ends of a transmitting crystal (Figure 1). The crystal may be made of any material which is optically transparent, has a high mechanical strength and high index of refraction, and is resistant to thermal shock and chemical attack. Suitable materials include ZnS, ZnSe,... 

The use of cylindrical internal reflectance cells for HP-IR was pioneered by Moser and further modified by others.This method involves the use of an optically transparent internal reflectance crystal (typically ZnS, ZnSe, sapphire). Due to the inherently short path length, the method is not as sensitive as transmission-based IR, and a Fourier transform infrared (FTIR) spectrometer is therefore generally required. In addition, the type of crystal may need to be changed depending on the reaction of interest, as the optics may be corroded by some reagents or catalysts. However, as the path length is fixed regardless of conditions, it is much easier to quantify catalyst species, and unlike transmission systems the cells can also be used for the study of liquid-solid and gas-liquid-solid mixtures. ... 

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