PA-FTIR

Ohkoshi, M. (2002). FTIR-PAS study of light-induced changes in the surface of acetylated or polyethylene glycol-impregnated wood. Journal of Wood Science, 48(5), 394-401. 

A deuteration method for the whole silica pretreatment temperature range was developed by Vrancken et. al..53 54 Critical parameters of the above cited methods appeared to be the cyclic nature, which is labour-intensive and time-consuming, and the temperatures used during adsorption and evacuation. Using the intensity of silanol signal in FTIR-PAS as an evaluation criterion, the H/D exchange was optimized. 

Figure 3.5 FTIR-PAS spectra of silica gel pretreated at 473 K under vacuum, (a) before and (b) after deuteration at room temperature with subsequent evacuation at 473 K...

If the sample was pretreated at temperatures above 573 K, i.e. in the 673 - 1073 K range, other process parameters had to be chosen in order to obtain optimal H/D exchange. Better results are obtained with increasing temperature in the adsorption step. The choice of adsorption and evacuation temperatures was limited to 673 K, by the glass material of the experimental apparatus. Figure 3.6 shows the FTIR-PAS spectra of silica gel pretreated at 973 K, before deuteration (fig. 3.6a), after deuteration at room temperature (fig 3.6b) and at 673 K (fig 3.6c). 

I. Gillis-D Hamers, P. Van Der Voort, P. De Hulsters and E.F. Vansant, A high resolution FTIR-PAS study of the free hydroxyl group on the silica gel surface, in Proc. Int. Workshop on FTIR, ed. E.F. Vansant, U.I.A., Wilrijk, 1990. 

Inspection of the FTIR-PAS spectra of these samples (figure 9.34) indicates the presence of bridged hydroxyls (3660 cm 1) for the 473 K (figure 9.34 a) and 673 K (figure 9.34 b) sample and a small amount of free silanols (3731 cm1) for the 973 K sample (figure 9.34 c). The OHbr band may be caused by unreacted as well as amineinteracting hydroxyls. Based on these spectra no exclusion of one of both types is possible. The OHf band, present in the 973 K sample, is very weak and has its maximum at 3731 cm"1. 

Figure 9.34 FTIR PAS spectra of APTS modified silica gel with variable silica pretreatment temperature (a) 473 K, (b) 673 K, (c) 973 K.

An impression of the quantity of these surface hydroxyls can be obtained from their FTIR spectra. In figure 9.36 a the FTIR-PAS spectrum for the 973 K deuterated modified silica is displayed. In the deuteroxyl region (2800 - 2500 cm 1) no absorption band is observed. All deuteroxyl groups have reacted. 

Figure 9.36 FTIR spectra of silica gel, after pretreatment at 973 K, deuteration and modification with APTS, using (a) FTIR PAS under He, (b) DRIFT under ambient atmosphere.

Figure 10.1 FTIR-PA spectrum of the hydroxyl stretching bands of silica gel, (a) pretreated at 473 K, (b) reacted with BCl at 293 K. Spectrum (c) is the difference spectrum of (a) and (b).

The ammoniated trichlorosilylated silica gel sample was subjected to another trichlorosilylation at room temperature (cycle 2). In order to monitor the subsequent conversions, a FTIR-PA spectrum was recorded before and after the TCS treatment. These spectra are shown in figure 14.2. 

Figure 14.6 shows the FTIR-PA spectra of the precursor, treated in vacuo at 973 K and 1113 K respectively. 

Figure A.5 Detail of a FTIR-PA spectrum of ammoniated trichlorosilylated silica (a) without and (b) with apodization.

An interesting extension of this type of reaction involves the photosubstitution of the surface-confined cobalt tetracarbonyl system [S] SiCo(CO)4 (where [S] represents a high surface-area silica) and the technique of Fourier transform infrared photoacoustic spectroscopy (FTIR/PAS) has been applied for the first time (172) to study photoreactions of a species on the surface. 

Fourier Transform Infrared (FTIR) and FTIR Photoacoustic Spectroscopy (FTIR-PAS) - Initial rates of polymerization, photoinitiator effects and oxygen effects were evaluated using these techniques. 

Figure 2. Comparison of surface vs. bulk polymerization rates. Key , FTIR — PAS/air and O. FTIR.

The authors would like to thank Dr. J. F. Geibel for his input on solvent absorption studies, and R. S. Bentson and C. R. Nijander for their assistance. The authors are also indebted to Dr. Y. C. Teng for his contribution in the FTIR-PAS work. 

One of the major sample-handling problems in FTIR analysis of carbonaceous materials is that many of them are effective blackbody absorbers and thus are too opaque for direct transmission analysis in the midinfrared spectral region. Addition of KBr intensifies the signal to obtain transmission infrared spectra. It is time consuming, and grinding conditions and moisture are known to affect the spectrum of the sample [238]. Alternative techniques such as specular reflectance, diffuse reflectance (DRIFT), photoacustic spectroscopy (FTIR-PAS), and total... 

FTIR photoacoustic spectroscopy (PAS) has advantages relative to conventional IR techniques (transmission, reflection and emission) because it is non-destructive, does not involve sample preparation and can probe samples with compositional gradients and layers. The theory, instrumentation, methods and applications of FTIR-PAS are discussed and results are presented on several polymer analyses based on FTIR-PAS. 4 refs. USA... 

FIG. 2 FTIR-PA spectra of KG 60. pretreated at 973 K. (a) Reacted with SiCU in CH2CI2 and excess NEts, and afterwards reacted with NHj in the gas phase, (b. c) Same as (a) but modified with SiCU (b) in the presence of NEt, using cyclohexane, and (c) without NEt3, using cyclohexane. 

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