Visible adsorption spectrum

Steady-state UV-visible absorption spectrum of the NKX-2311/ZnO film is also shown in Fig. 1. It was found that adsorption of the dye onto ZnO and TiC>2 (data not shown) leads to the spectral blue-shift of the dye absorption by 15 and 25 nm, respectively, and slight broadening compared with the spectrum in solution. When a bare ZnO film (without dye) was excited at 355 nm with the nanosecond laser, an absorption band shown by the dashed line in the same figure was observed in the near IR region. This band is assigned to intra-band transitions of electrons in the conduction band [10], Electrons in Ti02 showed weaker absorption in the near IR region. 

Self-organized materials with high surface area and pore size 3-25 nm was produced used templating and coassembly. The highly porous nature of the ordered combined with low adsorption and emission in the visible spectrum, facile diffusion makes them good candidate for optical and chemical sensor and provide new avenues for encapsulation/ immobilization processes and solve the problems mentioned above. 

Despite the relatively large band-gap energy, Ti02 is often used as a photocatalyst because of its relative inertness with regard to dissolution. In order to render such materials more suitable as photocatalysts for the visible part of the solar spectrum, the surface of the solid phase is modified by the specific adsorption of a chromophore which has a lower energy gap between the HOMO and the LUMO as compared to the band-gap of the semiconductor. The principle is shown in Fig. 10.8 for the case of a photoelectrochemical cell. 

The adsorption of the vapors of these amines in vacuo on carefully degassed silica gel, or porous glass at temperatures, ranging from 20 to 100°C does not produce any visible coloration of the adsorbent. The absorption spectrum reveals only the normal ultraviolet bands of the adsorbed molecules at 280-300 m/j,. However, the adsorption of the same vapors on carefully degassed and evacuated silica-alumina invariably produces a more or less strong coloration of this adsorbent, the spectrum of which reveals bands undoubtedly belonging to the positive ion-radicals of the adsorbed molecules (27, 77a). 

Figure 6b also reveals that the positive lobe of the bipolar band around 1280 cm decreases at potentials above 0.45 V this decline coincides with the onset of the surface oxidation in the voltammetry of Ru(OOOl) (c.f., Fig. 2). Adsorption of the OH species is followed by the desorption of bisulfate and a concurrent increase in the bisulfate species in the double layer. This effect becomes visible in the IR spectrum by the appearance of the positive-going solution-phase bands for the bisulfate anion at 1051 and 1200 cm at potentials equal to, or higher than 0.55 V. The most pronounced feature in the IR spectra above 0.55 V is the negative lobe of the bipolar band centered at 1248 cm , which represents adsorbed bisulfate at the reference potential.

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

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