IR diffuse reflectance spectra

To elucidate the nature of the bonded states of the main hydrogen mass that is retained up to high temperatures, the IR diffuse reflection spectra were measured for GNF and SWNT powders in the initial state, after the treatment under hydrogen pressure, and after the degassing annealing. Measurements were performed in the range 400-5,000 cm-1 at room temperature. The results are presented in Fig. 11.5. 

Fig. 11.5 IR diffuse reflection spectra of graphite nanofibers and single-walled carbon nanotubes in the initial state, after saturation with hydrogen at 9 GPa, after removal of about 40% of absorbed hydrogen, and after degassing annealing. T = 300 K...

A series of Diffuse Reflection measurements was performed, subsequently, on partly decomposed CPC (system B) samples to check the decomposition pattern given in Figure 6.21. Four samples were (under the same conditions) heated to different, previously selected temperatures, see Figure 6.22. The measured IR Diffuse Reflection spectra of the TGA residues of these four samples offer the possibility to monitor the changes in the molecular structure in an independent way. 

The UV-visible-near IR diffuse reflectance spectra of the en-SiOa+INi, ENien and ENien+INi samples exhibit three d-d transitions, characteristic of nickel complexes in oct edral symetry. In the following, we will only consider the Vi band due to the A2g — T2g transition, because the V2 and V3 ones are less resolved. For the samples considered, the Vi band position varies between 890 nm which is characteristic of the [Ni(en)3] complex, e.g. present in the ENien samples, and 1160 nm which is characteristic of [Ni(H20)6] complex, e.g. present in standard impregnated INi samples (Table 3) [2]. 

In a previous study [3], it was shown that the UV-visible-near IR diffuse reflectance spectra of the ENien samples calcined in air at 600°C then maintained in air at 25 C, exhibited absorption bands at 410,660 and 1160 nm attributed to isolated hexacoordinated grated nickel species, [(=Si0)2NiQ(H20)4]. An additional band at 330 nm was attributed to dimers of grafted nickel (NiP-O-NiD). The absence of bands of N-H vibrations of ethylenediamine in the near IR range, at 1530 and 2030 nm, indicates that ethylenediamine adsorbed onto silica is decomposed. An EXAFS study confirmed this interpretation [2,3]. 

The use of the Kubelka-Munk equation for quantitative analysis by diffuse reflectance spectroscopy is common for measurements in the visible, mid-IR and far-IR regions of the spectrum, but not in the near-IR region. As has been pointed out [187, 188], almost all near-IR diffuse reflectance spectra have been converted to log(l// ) R = reflectance of the sample relative to that of a non-absorbing sample). The use of log(l// ) instead of the K-M function provides a more linear relationship between reflectance and concentration. Olinger et al. [189] explain this behaviour by the effective penetration depth of the beam, which is very short, when absorption is strong. For many of the algorithms developed to achieve multicomponent determinations from the diffuse reflectance spectra of powdered samples, a linear dependence of band intensity on analyte concentration is not absolutely mandatory for an analytical result to be obtained. 

Diffuse reflectance is a technique where source radiation strikes a powdered sample and is diffusely reflected in different directions." This weak diffuse radiation is collected in a manner which minimizes the specular reflectance component and is measured by the spectrometer which is usually an FT-IR instrument. Usually the finely powdered sample is diluted to a concentration of 5 to 10% in powdered KBr or KCl for mid-IR diffuse reflectance spectra. No dilution is required in the near-IR region, where the bands are weaker. Pure powdered KBr or KCl is used as a reference against which the sample spectrum is ratioed as shown below, where is the reflectance of a thick scattering layer. 

Fig. 7.3 Left Diffuse reflectance spectra of Fe oxides in the UV-Vis-near IR range (Sherman et al., 1982, with permission). Right Median and range of the crystal field band positions determined from second-derivative minima the two...

When light is directed onto a sample it may either be transmitted or reflected. Hence, one can obtain the spectra by either transmission or reflection. Since some of the light is absorbed and the remainder is reflected, study of the diffuse reflected light can be used to measure the amount absorbed. However, the low efficiency of this diffuse reflectance process makes it extremely difficult to measure 120) and it was speculated that infrared diffuse reflection measurements would be futile 120). Initially, an integrating sphere was used to capture all of the reflected light121) but more recently improved diffuse reflectance cells have been designed which allow the measurement of diffuse reflectance spectra using FT-IR instrumentation 122). 

The absorption and emission spectra of Ru(bpy) + also showed pronounced spectral shifts (compared to that in water) upon intercalating into a sulfonated derivative of layered a-ZrP, zirconium sulfophenylphosphonate, or ZrPS [84], The XRD and the infrared (IR) spectra of the mixture, on the other hand, indicated that the chemical and structural characteristics of the complex were not significantly affected by the host matrix. The diffuse reflectance spectra, however, revealed three important differences from that observed in aqueous solution. These are that (1) the tt-tt band was strongly red-shifted to 317-320 nm from that observed at 285 nm in aqueous solution, (2) the MLCT band also red-shifted, depending on the loading, from 462 to 494 nm, and (c) the ratio of the intensity of the tt-tt band to the MLCT band decreased with loading (Fig. 40). 

EUROTS-1 was synthesized (150g) by hydrothermal treatment of a gel derived from ethyl orthosilicate and ethyl orthotitanate, in the presence of tetrapropyl-ammonium hydroxide as template [31]. Each participating laboratory performed its own calcination (3 h or 16 h at a maximum temperature of 823 K, other conditions being varible). The Ti content was 2.8%, and the calcined product consisted of a single phase of orthorhombic symmetry, with a BET surface area of 435 m2g . Its IR and diffuse reflectance spectra (DRS) have been recorded. The material had the form of small rounded cubes of about 0.15/im size. 

The high-information density of mid-infrared spectra is well-known. In comparison, the discrimination power of near-infrared spectroscopy is illustrated in (Fig. 3A) for different monosaccharides, for which diffuse reflectance spectra were recorded. (Fig. 3B) shows the near-IR spectra of two pharmaceutical substances. 

XRD measurement was carried out using TUR 62-M diffractometer with CuKa radiation. IR spectra (KBr) were recorded on Perkin-Elmer 580. The diffuse reflectance spectra were measured using self-supported wafers. The samples were evacuated at 500°C for 4 hours prior to measurement. The Perkin-Elmer 580 B and Beckman-Acta M VII Spectrometers were equipped with DR units. The details of procedure were described elsewhere [6]. Probe molecules (CO, ethylene, d4-ethylene, d3-acetonitrile) were adsorbed on the samples SnAlPO-0.1 at room temperature and their spectra were recorded. 

The obtained chitosan carriers and catalytic systems on their base were studied by transmission and diffuse-reflectance FTIR spectroscopy. IR-spectra were obtained in Nicolet Impact 410 equipment. To record the diffuse-reflectance spectra the samples were evacuated at 100°C for 2 h. The quantitatively spectrum analyses were performed using Kubelka-Munk equation according to the program OMNIC [5]. 

To gain information on metal surface compounds of both photoimmobilized and immobilized samples their diffuse reflectance spectra in IR, visible and UV region were measured using spectrophotometer "Hitachi-340". ESR spectra of catalysts iso were examined using radiospectrometer "Varian-E-9". 

Infrared spectra (i.r.) Infrared spectra of the materials II and III were obtained with a BROKER IFS48 FT-IR spectrometer purged with nitrogen gas and using a mid band mercury cadmium telluride (MCI) detector. A HARRICK Praying Mantis diffuse reflectance attachment with two ellipsoidal mirrors collected the diffuse reflectance spectra. To avoid residual radiation bands all samples were diluted with KBr powder (Uvasol quality, E. Merck) so that the sample concentration was about 10 %. 

Quantitative evaluation of diffuse reflectance spectra requires optically indefinitely thick samples (Ij = 0 cf Tab. 5.1). The reflectivity R , of such a sample (in the IR its thickness does normally not exceed a few millimeters) is ... 

Measurement of diffuse reflection spectra has a much longer tradition in UV/VIS than in IR, because (i) the scattering is much more efficient at shorter wavelengths and (ii) an ideal non-absorbing scattering substrate is missing in the MIR. 

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