Diffuse Reflection Infrared Fourier Transform spectra

FIGURE 13. Diffuse reflectance infrared Fourier transform spectra of OOPS mullite precursor heated to selected temperatures (air/10°C/min/l h dwell)... 

A new rapid mid-infrared spectroscopic method called diffuse reflectance infrared Fourier transform spectra (DRIFTS), coupled with chemometrics, has been developed by Janik, Merry, and Skjemstad (1998) and routinely applied to rapidly screen and compare crime scene samples (Figure 1.1). Added to these rapid methods and techniques are the use of rapid mass and volume magnetic susceptibility methods, which should also always be used before moving to the more costly methods (Figure 1.1). Mineral magnetic techniques are a relatively recent development (post-1971) and have now become a very powerful and widely used research tool to characterize natural materials in landscapes (e.g., Thompson and Oldfield 1986). 

NH3-DRIFT (Diffuse Reflectance Infrared Fourier Transform) spectra were collected with a Brucker IF S88 spectrometer performing 200 scans with a resolution of 4 cm. Pure samples were placed inside a commercial controlled environmental chamber (Spectra-Tech 0030-103) attached to a diffuse reflectance accessory (Spectra-Tech collector). To investigate the stability of the adsorbed ammonia species during temperature elevation, the spectra were recorded under helium (30ml/min) at room temperature, 373, 473, and 573 K, after exposure to an ammonia flow for 30 min at room temperature. 

Adsorbent materials have been characterized and tested using a range of techniques. Characterisation of materials has focused on deteiming the physical and chemical properties of the sold sorbent materials. This has heen conducted using a range of techniques, for example, elemental analysis, power x-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectra (DRIFTS), textural properties have been determined by BET N2 adsorption analysis. Thermogravimetric analysis (TGA) has been used to determine the thermal stability of the materials as well as measure CO2 adsorption capacity and cyclic capacity [14]. 

Fig. 26.6 Diffuse reflectance infrared Fourier transform spectra for (a) freshly prepared PSi before functionalization and PSi derivatized with (b) 1-decene and (c) decylaldehyde and (d) a difference DRIFTS spectrum of (b)-(a) (Reprinted with permission from Boukherroub et al.

Figure 4. Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS) of Polymethylsilane Heated to Selected Temperatures. Data points for Ig samples heated at l°C/min in N2 to temperature and held for 0.5 h.

In the diffuse reflectance mode, samples can be measured as loose powders, with the advantages that not only is the tedious preparation of wafers unnecessary but also diffusion limitations associated with tightly pressed samples are avoided. Diffuse reflectance is also the indicated technique for strongly scattering or absorbing particles. The often-used acronyms DRIFT or DRIFTS stand for diffuse reflectance infrared Fourier transform spectroscopy. The diffusely scattered radiation is collected by an ellipsoidal mirror and focussed on the detector. The infrared absorption spectrum is described the Kubelka-Munk function ... 

Persson et al. (1991) used diffuse reflection infrared Fourier transform (DRIFT) spectroscopy to study the interactions between galena, pyrite sphalerite and ethyl xanthate. They provided the evidence that the DRIFT spectrum of oxidized galena treated with an aqueous solution of potassium ethyl xanthate is practically identical with that of solid lead (II) ethyl xanthate, which can be formed as the only detectable siuface species on oxidized galena. Dialkyl dixanthogen is formed as the only siuface species in the reaction between oxidized pyrite and aqueous solution of potassium alkyl xanthate. 

Hydrated silica gel was modified with APTS (sample 1) and studied by DRIFT (Diffuse Reflectance Infrared Fourier Transform) and CP MAS NMR. The IR spectrum of the modified silica (figure 9.4) shows silane NH, CH and Si-O-Si bands along with silica lattice and surface vibrations. Assignments of IR bands of APTS modified silica are given in table 9.2. 

For some sample types, for example a coated substrate, it is not possible to collect an infrared transmission spectrum, whereas in some cases (e.g. when there are concerns over the effects of sample preparation) it may be more desirable to collect a reflected spectrum. The most popular reflection techniques nowadays are internal reflection spectroscopy (IRS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)... 

Fieure 6 Diffuse reflectance infrared Fourier transform (DRIFT-) spectrum of the platinum based catalyst measured at 225°C in flowing 2% NO in helium (50 cm /min)... 

The primary components and the chemical structure of the raw peat and the solid product were further analyzed by Fourier transform infrared spectroscopy (FTIR) 0ASCO 670 Plus) using the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique and the JASCO IR Mentor Pro 6.5 software for spectral analysis. The cross polarization/magic angle spinning (CP/MAS) NMR spectrum of raw peat and the solid... 

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. 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

With the advent of the commercial FT-IR instruments, and computer techniques, it is now possible to record the infrared spectrum of almost any material regardless of its shape or form. A number of different sampling accessories are available for recording the infrared spectra. Some of these accessories such as AIR and specular reflectance have been used successfully with dispersive instruments, but the FT-IR instruments allow these accessories to be used more rapidly and with greater sensitivity. Most of the sample handling techniques have been reviewed in detail in the series of volumes on "Fourier Transform Infrared Spectroscopy" edited by J.R. Ferraro and J.R. Basile (1). In this paper, some of these techniques will be reviewed with particular emphasis on reflectance techniques (ATR and diffuse) and photoacoustic spectroscopy. Further applications such as far-IR, diamond cell, the absorption subtraction methodology can be found in the article by Krishnan and Ferraro (2). 

Infrared (IR) spectroscopy is most often used for qualitative identification of chemical compounds. Comprehensive works on the application of IR spectroscopy to identification of surfactants are available elsewhere. The volume of Hummel is an essential reference for experts as well as a teaching aid for novices (1). The Sadtler database is invaluable (2). A number of shorter works provide an introduction to surfactants for the beginner (3-6). With experience, the spectroscopist will find it possible to identify not only pure compounds, but also mixtures of surfactants. Modem computerized instraments aid by permitting subtraction of spectra of known compounds from the spectrum of the mixture. IR spectroscopy is widely used for detailed examination of purified fractions prepared by extraction or ion exchange chromatography. The small sample size requirement makes it possible to identify compounds collected from the eluent of a liquid chromatograph, especially if techniques like diffuse reflectance Fourier transform IR are used. 

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