Diffuse-reflectance vis-NIR

The results obtained from the investigation of the crystallochemical properties of a family of mixed Li-vanadates of general formula LiCoyNi(i.y)V04 are reported. This kind of material is believed to be a valid alternative to the traditional positive electrode materials in the Li-ion cell, an electrochemical power source of outstanding importance in the portable electronics field. The powders, prepared via two different methods (a wet chemistry route and a solid state method), have been characterised by XRPD analysis, NMR and diffuse reflectance Vis-NIR spectroscopy. The findings allowed to correlate the electrochemical performance of the vanadates, which is higher for the samples prepared via wet chemistry, to the crystallinity of the powders and to the transition metal cations distribution. 

Different preparation routes lead to powders with different electrochemical performance, so, in order to investigate this aspect, we have prepared, by two different methods, series of LiCOyNi(. y)V04 (y=0, 0.2, 0.5, 0.8, 1) compounds. These powders have been characterized by X-ray powder diffraction (XRPD), diffUse reflectance Vis-NIR and NMR spectroscopies. 

Diffuse reflectance Vis-NIR spectra were obtained using a Perkin-Elmer Lambda 19 spectrophotometer equipped with an integrating sphere and using BaS04 as reference powder. 

Figure 3. Diffuse reflectance Vis-NIR spectra of LiCoV04 and LiNiV04 materials prepared via both wet chemistry (WCh) and solid state (SS) methods. Section A a) LiCoV04 WCh, b) LiCoV04 SS Section B LiNiV04 WCh, b) LiNiV04 SS.

Electrochemical Control and Reflectance, Emittance and Solar Absorptance Measurements A Princeton Applied Research (PARC) Model 263 potentiostat with PARC s 270/250 software w used for preliminary voltammetric characterization and to control devices for spectral measurements. In-situ (i.e. as a function of applied potential) Specular IR (16° incidence). Diffuse IR, and Diffuse UV-Vis-NIR (0.2 to 1.1 pm) reflectance measurements were carried out, respectively, on a Perkin-Elmer (P-E) Model 1615 FTIR, a Bio-Rad FTS 6000 FTIR and a P-E Model Lambda 12. Vendor-supplied mirrors or Au surfaces, as appropriate, were used as references. In-situ emittance and solar absorptance measurements were carried out, respectively, on an A-Z Tek Model Temp lOOOA emissometer (2.5 to 45 pm range) and a Gier-Dunkle Emissometer Solar Absorptometer (0.3 to 2.5 pm range). 

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). 

Since NIR was developed by the USDA for food products, the first (commercial) mode developed was diffuse reflection. The earliest work was performed on instruments which had, in essence, NIR as an extra. The UV/Vis hardware (e.g., Cary model 10) had an additional detector and could be used through the NIR. This one fact explains why so much literature uses nanometers for units instead of wave numbers. 

UV-VIS-NIR diffuse reflectance (DR) spectra were measured using a Perkin-Elmer UV-VIS-NIR spectrometer Lambda 19 equipped with a diffuse reflectance attachment with an integrating sphere coated by BaS04. Spectra of sample in 5 mm thick silica cell were recorded in a differential mode with the parent zeolite treated at the same conditions as a reference. For details see Ref. [5], The absorption intensity was calculated from the Schuster-Kubelka-Munk equation F(R ,) = (l-R< )2/2Roo, where R is the diffuse reflectance from a semi-infinite layer and F(R00) is proportional to the absorption coefficient. 

Optical Accessory Design for Diffuse Reflectance UV-vis-NIR Spectroscopy... 

Gao, X. and Wachs, I.E. (2000) Investigation of surface structures of supported vanadium oxide catalysts by UV-vis-NIR diffuse reflectance spectroscopy. Journal of Physical Chemistry B, 104 (6), 1261-8. 

CW-EPR X-band measurements were performed on a Bruker ESP 300E Spectrometer at a temperature of 120 K. The CuHis complexes are paramagnetic due to the S=l/2 spin of the Cu " ion. Nitrogen physisorption was performed with a Micromeritics ASAP 2400 apparatus. Measurements were done at 77 K. Prior to the measurements the zeolite samples were degassed for 24 hours at 373 K in vacuum. Micropore volumes and pore size distributions were determined with standard BET and BJH theory. Diffuse Reflectance Spectroscopy of the CuHis complex encapsulated zeolite samples were taken on a Varian Cary 5 UV-Vis-NIR spectrophotometer at room temperature. The DRS spectra were recorded against a halon white reflectance standard in... 

The diffuse reflectance UV-Vis spectra have been obtained between 190 to 900 nm using a Perkin Elmer UVA IS/NIR Spectrometer Lambda 19. 

X-Ray Diffraction (XRD) patterns were recorded on a Philips HTK-KC diffractometer with a CuKa X-ray source, linked to Philips 386 computer. Thermo-Gravimetry (TG), was recorded on a Setaram TG-DTA 92 thermobalance. Diffuse Reflectance Spectra (DRS) were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR region. Mossbauer spectra are recorded on a vertical constant acceleration drive in transmission geometry with a 28mCi Co(Rh) source. Isomer shift data are expressed relative to metallic Fe at 293 K which has an isomer shift of8 = -0.0888 mm/s relative to natural a-Fe. 

Spectroscopy. FT-IR spectra were recorded on a Nicolet F-730 spectrometer equipped with an in-situ flow-cell. Electron Paramagnetic Resonance (EPR) spectra were recorded in X-band with a Bruker ESP-300 with a fE (,4 cavity. Diffuse Reflectance Spectroscopy (DRS) spectra were recorded on a Cary-5 spectrofotometer with a BaS04 integration-sphere in the UV-VIS-NIR. Molecular graphics analysis was done with Hyperchem 3.0 for Windows (Hypercube Inc.). 

VIS-NIR diffuse reflectance spectroscopy, by which the processes taking place (decarbonylation, changes in the oxidation state, clustering of metal atoms) are monitored. 

Figure 4.23 Schematic diagram of an NIR integrating sphere for DR. The sphere is placed in the sample compartment of a Hitachi model U-3410 dispersive UV/VIS/NIR spectrophotometer. The sphere design permits only diffuse reflectance to reach the detector the specular component is reflected out through the same opening the light enters. [Courtesy of Hitachi High Technologies America, Inc.,...

Diffuse reflectance spectroscopy (DRS) has been frequently employed in UV-Vis spectroscopy of zeolites (cf. Volume 4, Chapter 4 of the present series). More recently, it became also popular in IR investigations (cf., e.g., [160, 161]). The DRIFT technique is advantageous because it is successfully applicable not only in the mid infrared but also in the near infrared (NIR) region of 4000-10,000 cm where the transmission technique usually fails because of severe scattering through the absorbent particles. The NIR range, however, is very important with respect to the study of overtone and combination modes of vibrations. Moreover, diffuse reflectance IR experiments can be carried out not only with pressed wafers as in transmission spectroscopy, but also with zeolite pow-... 

Balsam, W. L. B. C. Deaton, 1996. Determining the composition of late Quaternary marine sediments from NUV, VIS, and NIR diffuse reflectance spectra. Marine Geol. 134 31-55. 

UV/VIS and NIR diffuse reflection spectra are usually measured by an integrating sphere. The inner surface of the so-called Ulbricht sphere (Fig. 5.8) is coated by strongly scattering, non-absorbing powder. After repeated reflections at the inside of the sphere aU radiation will eventually reach the detector. 

Ground-State Diffuse Reflectance Absorption Spectra (UV-Vis-NIR)... 

Several spectroscopic and nonspectroscopic techniques may be used to study the bonding nature of the adsorbate to the surface [2a, 4]. In the first case we want to emphasize the importance of diffuse reflectance techniques for absorption and emission studies in the ultraviolet (UV), Visible (Vis), and near infrared (NIR) spectral ranges. X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. In the second group, we refer the heat adsorption and the isotherm adsorption techniques, among others. 

A model 6500 On-Line Vis-NIR spectrophotometer (NIR Systems, Inc., Silver Spring, MD) equipped with single bundle bifurcated fiber optics was used for data acquisition. An Interactance Reflectance probe was used along with a novel extruder/monitor interface design to obtain diffuse reflectance spectra of the plastic melt near the die. The visible region of the spectrum (400-700 nm) was used for analysis. Figure 2 shows a schematic of the experimental setup. 

FIGURE 2 (a) UV-vis-NIR spectrum of the as-synthesized PANI-EB solution in NMP (b) FT-IR spectrum (KBr powder diffuse reflectance) of the as-synthesized PANI-EB powder and (c) TGA of the as-synthesized PANI-EB powder under Ar flow (scan rate 20 C/min). 

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