Diffusion spectrophotometers

Willey R R 1976 Fourier transform infrared spectrophotometer for transmittance and diffuse reflectance measurements Appl. Spectrosc. 30 593-601... 

UV diffuse reflectance spectra of the titanates were obtained with a JASCO UVIDEC-660 spectrophotometer using a sintered alumina disc as a reference. Raman spectra were recorded at room temperature on a JASCO NR-1100 spectrometer. 

The FTIR spectra of the NO molecules adsorbed on the catalyst were measured on a JEOL JIR-KX) spectrophotometer in a diffuse reflectance mode. After a back ground spectrum was measured in situ for a freshly sulfided catalyst, NO was introduced to the catalyst as 10 % NO/He pulses (5.1 cm ). The FTIR spectra were recorded after an introduction of 5 pulses. ... 

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

Stopped flow mixing of organic and aqueous phases is an excellent way to produce dispersion within a few milliseconds. The specific interfacial area of the dispersion can become as high as 700 cm and the interfacial reaction in the dispersed system can be measured by a photodiode array spectrophotometer. A drawback of this method is the limitation of a measurable time, although it depends on the viscosity. After 200 ms, the dispersion system starts to separate, even in a rather viscous solvent like a dodecane. Therefore, rather fast interfacial reactions such as diffusion-rate-limiting reactions are preferable systems to be measured. 

Samples were characterized by FTIR spectroscopy with a Perkin Elmer (Spectrum BX) spectrometer using KBr pressed disks as matrices. The DRIFT experiments were carried out with a Broker IFS 55 spectrometer equipped with a Thermo Spectra Tech reacting cell. UV-vis Diffuse Reflectance spectra were recorded on a Perkin Elmer Lambda 45 spectrophotometer equipped with a diffuse reflectance attachment. Raman spectra were collected with Perkin Elmer system 2000 NIR FT-Raman using as excitation radiation the 5th harmonic of a diode pumped Nd YAG laser (1065 nm). 

The metal content analysis of the samples was effected by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES Varian Liberty II Instrument) after microwaves assisted mineralisation in hydrofluoric/hydrochloric acid mixture. Ultraviolet and visible diffuse reflectance spectroscopy (UV-Vis DRS) was carried out in the 200-900 nm range with a Lambda 40 Perkin Elmer spectrophotometer with a BaS04 reflection sphere. HF was used as a reference. Data processing was carried out with Microcal Origin 7.1 software. 

In this paper we will first describe a fast-response infrared reactor system which is capable of operating at high temperatures and pressures. We will discuss the reactor cell, the feed system which allows concentration step changes or cycling, and the modifications necessary for converting a commercial infrared spectrophotometer to a high-speed instrument. This modified infrared spectroscopic reactor system was then used to study the dynamics of CO adsorption and desorption over a Pt-alumina catalyst at 723 K (450°C). The measured step responses were analyzed using a transient model which accounts for the kinetics of CO adsorption and desorption, extra- and intrapellet diffusion resistances, surface accumulation of CO, and the dynamics of the infrared cell. Finally, we will briefly discuss some of the transient response (i.e., step and cycled) characteristics of the catalyst under reaction conditions (i.e.,... 

XANES and EXAFS were conducted at BL-lOB in the Photon Factory of the National Laboratory for High Energy Physics (KEK-PF)[12]. s Fe Nttssbauer spectra were recorded with a Shimadzu MEG-2 spectrometer(13]. Isomer shifts were given relative to a-Fe. Infrared spectra were recorded by a Shimadzu Fourier-transform infrared spectrometer(FTIR-4100) with a resolution of 2 cm i. Diffuse reflectance UV-VIS spectra were obtained on a Hitachi 330 spectrophotometer. 

The spectrophotometer measures the transmission and, if an absorption measurement is carried out, converts the transmission into absorbance using these equations. This conversion works fine for samples where there is no reflection, either specular or diffuse, as is the case for nonturbid solutions. However, for films there is invariably some reflection, which is often quite large, particularly for films of high dielectric constant (or refractive index) materials, such as PbS and PbSe. Additionally, if the films are not completely transparent, then scattering introduces an extra element of reflection. Therefore, to measure the real absorption of a film, a reflection measurement must also be carried out and correction for this reflection made. The correction will be approximate and depends on the nature of the film itself. However, that most commonly used is... 

To collect scattered transmission and correct for diffuse reflectance, a spectrophotometer with an integrating sphere should be used. This is important if films are not very transparent. 

Franz diffusion cells apparatus (Crown Glass Company Inc., NJ), constant temperature water bath (Yamato Scientific Co. Ltd., Japan) and spectrophotometer (Shimadzu Siesakusho Ltd, Japan)... 

Differential spectra of diffused reflection around 230-700 nm were measured with a two-beam recording spectrophotometer with corrected zero line it was constructed in our laboratory to measure the spectra of adsorbed species. Spectra were recorded before and after irradiation with a PRK-2 mercury lamp for 15 minutes of the zeolite sample containing adsorbed amine. 

Raman spectra were taken on a home built system, composed of Spectra-Physics 2020 series lasers, coupled with a Dilor XY-800 triple spectrometer and a Whight Instruments nitrogen cooled CCD. All samples were measured at room temperature in a backscattering configuration, with 514.53 nm Ar+ laser excitation. The laser power was tuned between 1 mW and 30 mW. UV-VIS diffuse reflectance spectra were taken on a Varian Cary 5 spectrophotometer, equipped with a specially designed Praying Mantis diffuse reflectance attachment of Harrick. 

The X-ray diffraction (XRD) patterns of the sample were measured using Rigaku D-Max. II VC X-ray diffractometer using nickel filtered Cu Ka (X= 1.5406 A) radiation. The specific BET surface area and average pore sizes were determined by N2 adsorption-desorption isotherms at 77 K using an Omnisorp-lOO. Diffuse reflectance UV-spectra were obtained using Perkin Elmer Lambda 5 spectrophotometer using mesoporous silica MCM-41 or MCM-48 as a standard. The details are already reported earlier [27]. 

Some attention must be paid to the electrode dimensions (see Fig. 9.9). The working electrode s lower edge should be close to the bottom of the cell plates to minimize iR-drop problems. The width of the working electrode in contact with the thin layer of solution should be small to minimize edge diffusion. As noted earlier, a vertical orientation is not desirable however, it is convenient and compatible with the horizontal optical path of virtually all commercial spectrophotometers. Recommended sources of cell components (including minigrids) are listed in Table 9.1. Thin-layer cells for chromatographic detection and electron spin resonance spectroscopy are discussed in Chapters 27 and 29, and their application in optical studies is described in Chapter 3. 

The model was initially compared with LOWTRAN 7 (5) results and with Brewer spectrophotometer measurements carried out at Lisbon in 1990. LOWTRAN-MESTRad results show a reasonable good agreement over 290-400 nm range with a mean difference of about 10%. Figure 4 shows de Model/LOWTRAN ratios for direct, diffuse and global spectral irradiances computed for the same conditions of ozone (332 Dobson Units), solar zenith angle (45.2°) and aerosol optical depth (0.0). 

Other Instrumentation. Brightness of pulp handsheets was measured with a Technibrite TB-1 instrument using Tappi Standard T525 om-86 [13]. Diffuse reflectance as well as transmission FT-IR spectra were obtained on a Nicolet 6000c spectrophotometer. 

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