UV-visible diffuse reflectance

The quantification of the extra-framework titanium species in titanium silicalites of MFI structure, TS-1, was performed using either XANES at the Ti K-edge or XPS Ti (2p) photolines. In addition, two different framework sites, [Ti(OH)(OSi)3] and [Ti(OSi)4], were characterized in dehydrated samples using Diffuse Reflectance UV-visible, multiple scattering analysis of EXAFS, H and Si NMR spectroscopies. 

The mere exposure of diphenyl-polyenes (DPP) to medium pore acidic ZSM-5 was found to induce spontaneous ionization with radical cation formation and subsequent charge transfer to stabilize electron-hole pair. Diffuse reflectance UV-visible absorption and EPR spectroscopies provide evidence of the sorption process and point out charge separation with ultra stable electron hole pair formation. The tight fit between DPP and zeolite pore size combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of charge separated state that hinder efficiently the charge recombination. 

HnZSM-5 were obtained by calcination procedure under 02 at 673 K during 24 h of NH4+-exchanged zeolites from VAW aluminium (Schwandorf, Germany) and from Zeolyst International (Valley Forge, USA). The chemical analysis, powder XRD patterns, 29Si, 27A1 MAS-NMR, IR, Raman, Diffuse reflectance UV-visible (DRUVv)... 

Figure 2. Diffuse reflectance UV-visible absorption spectra recorded as a function of time after the mixing of solid DPB and H0 57ZSM-5 (a) and after of solid DPB and H6 6ZSM-5 (b)...

Diffuse reflectance UV-visible data of titanosilicate samples... 

Fig. 35. Diffuse reflectance UV-visible spectra of Ti-MCM-41 (A), Ti-Si02 Davison (B), Ti-Si02 Aerosil (C), MST (D), and Ti02-Si02 Grace (E) [from Guidotti et al. (189)].

Visual appearance (color) Diffuse reflectance UV-visible Yellow A labile charge transfer band at about 385 nm (25,800 cm-1) in neutral H202 solutions and a relatively more stable band at 350 nm (28,500 cm-1) in alkaline H202 solutions... 

FIGURE 11.5. Diffuse reflectance UV-visible spectra of Ni0-Ce02-Zr02. ... 

Fig. 6 shows the diffuse reflectance UV-visible spectra of typical salen Co(IH) complexes immobilized on MCM-41, the homogeneous salen complex of the same structure, and a pure Si-MCM-41. The chiral salen ligands of Co(IU) form showed the bands at near 250 and 370 nm on the UV spectra. But the pure siliceous MCM-41 no absorption peak at all. This broad band is probably due to the charge-transfer transitions between metal and ligand. This result indicates that the successful immobilization of chiral salen ligands was achieved. 

Several authors used diffuse reflectance UV-Visible spectroscopy to probe the local environment of Ti sites [136-138,140,141,143,147]. Sayari et al. [137,141,147] found that both Ti-HMS and Ti-MCM-41 exhibit an absorption band at 220 ran with no indication of a band at 330 ran characteristic of anatase [148]. There was however a weak shoulder at 270 nm, particularly for Ti-iich samples. Conna et al. [140] also found a band at 205-220 nm and a shoulder at 270 nm. The absence of anatase was also confirmed by the absence of the characteristic 140 cm Raman band [138,149]. The band at 220 nm was attributed to isolated framework Ti species in interaction with water molecules [150]. The 270 nm band was assigned to partially condensed hexacoordinated Ti species belonging to a silicon rich amorphous phase [155]. 

TEM showed that V-MCM-41 particles have a highly ordered porous structure with some typical hexagonal crystals [38,93,173,176]. However, as other HMS materials, V-HMS consisted of globular particles of 0.1 to 0.4 pm in diameter with disordered channel packing [173,175]. Diffuse reflectance UV-visible spectra of V-HMS exhibited two bands in the range of 373-385 nm and 252-272 nm. Similar bands were observed at 384 and 265 nm for V-... 

J Schmidt and C Heimer. Use of Diffuse Reflectance UV-Visible Spectroscopy to Characterize Chromophores in Wood Fibers. In D Argyropoulos, ed. Progress in Lignocellulosics Characterization. Atlanta TAPPI Press, 1999, pp. 187-209. International Standards Organization. ISO 2470 Measurement of Diffuse Blue Reflectance Factor (ISO Brightness). 

Deposition of the redox-active polymers onto high-surface-area silica was monitored using diffuse reflectance UV-visible spectroscopy. Shown in Figure 4a are the spectra for the PS-MV /Cab-O-Sil composites, both coiled and... 

Co-containing zeolites of MFI structure were synthesized using alkaline media. The orthorhombic-monoclinic symmetry transition suggests that at least the Co(II) ions also occupy tetrahedral framework positions. The XPS data clearly show that the samples contain both framework tetrahedral and extraframework octahedral Co(II) ions at ion exchange positions. The diffuse reflectance UV-visible spectra show unambiguously the presence of tetrahedral Co(II) ions in the structure. 

We report in this study the hydrothermal synthesis of Co-silicate of MFI structure in alkaline media. The samples were characterized by XRD, chemical analysis, thermal analysis, A1-NMR, diffuse reflectance UV-visible spectroscopy and XPS spectroscopy. 

Mesoporous vanadosilicate molecular sieves with MCM-48 structure and atomic SiA ratio 30-200 have been synthesized using vanadyl sulphate as the source of vanadium. The product was characterized using X-ray diffraction (XRD), Nj adsorption analysis, transmision electron microscopy (TEM), electron spin resonance (ESR), Fourier-transform Infrared (FTIR), Diffuse reflectance UV-visible spectroscopy (UV-vis) and V solid state NMR. A noticeable decrease in unit cell parameters and main pore diameter was observed. Thus, a strong interaction between vanadium and mesoporous wall can be suggested. 

L. Jiang, Q. J. Xie, L. Yang, X. Y. Yang, S. Z. Yao, Simultaneous EQCM and diffuse reflectance UV-Visible spectroelectrochemical measurements poly(aniline-co-o-anthranilic acid) growth and property characterization, Journal of Colloid and Interface Science 2004, 274,150. 

Diffuse reflectance UV-Visible spectroscopy was carried out to further identify the transformations of the cationic species in the exchanged zeolite after reduction, at different temperatures (Figure 3). This allows a better comprehension of the silver reduetion mechanism. In freshly calcined Ag/13X(E), cationic silver (band at 235mn) and silver clusters (246-280 nm) with a slight contribution of metallic silver were detected (>290 nm) [11]. The decrease of the cationic silver band contribution when the temperature increases to 700°C, and the simultaneous increase of the metallic and clusters bands, suggest a two step formation of the silver particles in the exchanged silver zeolite as follows Ag" Agn Ag. 

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