Absorption band of the titanium oxid

Furthermore, as shown in Fig. 10.2, such red shifts in the absorption band of the metal ion-implanted titanium oxide photocatalysts can be observed for any kind of titanium oxide except amorphous types, the extent of the shift changing from sample to sample. It was also found that such shifts in the absorption band can be observed only after calcination of the metal ion-implanted titanium oxide samples in 02 at around 723-823 K. Therefore, calcination in 02 in combination with metal ion-implantation was found to be instrumental in the shift of the absoiption spectrum toward visible light regions. These results clearly show that shifts in the absorption band of the titanium oxides by metal ion-implantation is a general phenomenon and not a special feature of a certain kind of titanium oxide catalyst. 

The results of the IRRAS study show that the absorption bands of the interfacial oxide layer differ substantially from those of the initial oxide on a free silicon surface, depending on the substrate temperature during the titanium deposition. Specifically, the intensity of the 1240-cm (Si02) and 1160-cm (SiO) bands decreases, and the 1240-cm peak shifts to lower frequencies. The dependence of the intensities of the absorption peaks of Si02, SiO, and TiO t on the temperature of the silicon substrate during the Ti deposition is shown in Fig. 6.1. Extrapolations to absorbances of the initial oxide layer on the free silicon surface are indicated by the dashed line. 

Furthermore, as shown in Fig. 5, such red shifts in the absorption band of the metal ion-implanted titanium oxide photocatalysts can be observed for any... 

Ti ion-implanted titanium oxides exhibited no shift, showing that such a shift is not caused by the high energy implantation process itself, but to some interaction of the transition metal ions with the titanium oxide catalyst. As can be seen in Fig. 10-1 ((b)—(d)), the absorption band of the Cr ion-implanted titanium oxide shifts smoothly to visible light regions, the extent of the red shift depending on the amount and type of metal ions implanted, with the absorption maximum and... 

When the number of Ti-O layers is increased, the absorption spectrum of the anchored titanium oxide shifts to a longer wavelength region, approaching the absorption band of bulk Ti02 (anatase) at four or five Ti-0 layers. The anchored titanium oxide is X-ray amorphous up to three Ti-0 layers, whereas at higher loadings the weak diffraction lines due to anatase... 

Sometimes, optically polished materials that one obtains for the laboratory show absorption bands of an unknown origin. These bands could have been caused by impurities within the material itself or by impurities left in the surface from the grinding and polishing process. To help workers identify the source of such absorption bands, McCarthy (1968) has published the spectra of aluminum oxide, bamesite, cerium oxide, glassite, rouge, sodium thiosulfate, stannic oxide, and titanium oxide. 

The photocatal3 ic cycle on titanium dioxide commences through the absorption of a photon of sufficient energy to promote an electron from the valance band (VB) of the material to the conduction band (CB). This generates an electron in the CB and a hole in the VB. Following successful migration of the holes and electrons to the surface of the titanium dioxide particle (their recombination with the liberation of heat is always a concern) they become available for reaction. The CB electron can be donated to a substrate molecule and as such act as a reductant in a reaction, and the VB hole can accept an electron from another substrate (thereby acting as an oxidant in a reaction). 

The decrease in the intensities of the 1240- and 1160-cm absorption peaks, indicating a decrease in the oxide film thickness during the Ti deposition, is connected with the formation of titanium oxide, as evidenced by the appearance of the broad absorption band in the region of 1000-400 cm . The possibility of titanium oxide formation in these structures has been proven by theoretical and experimental investigations of the H-Si02-Si system [15, 16]. The data correlate well with the results of chemical analysis of the Ti-Si and Ti-Si02 Si interfaces by Raman spectroscopy [17], XPS, and AES [8, 16, 18]. It was shown that the formation and structural reconstruction of the TiO c (0.14 < x < 1.7), TiSi c, and SiO phases is governed by the substrate temperature. 

Of the important properties of glass, color is one of the most interesting. Color is usually achieved by the addition of various metal oxides. The strongest of these are titanium, vanadium, chromium, manganese, selenium, iron, cobalt, nickel and copper. Silver and uranium will give weak colors. Some of the rare earths are also used as colorants with sharp absorption bands in contrast to the broad bands given by most colorants. (4)... 

The activity data confirm that an IR absorption band at 960 cm" is a necessary condition for titanium silicates to be active for the selective oxidation of hydrocarbons with aqueous H2O2 as suggested by Huybrechts et al. (9). However, this band is not a sufficient condition for predicting the activity of the TS-1 catalyst. Although TS-l(B) and TS-l(C) show intensities for the 960 cm- band similar to TS-1 (A), their activities are different First of all, the reaction data reveal that TS-1 (A) is much more active than TS-l(B) for phenol hydroxylation, while both samples show similar activity for n-octane oxidation and 1-hexene epoxidation. Therefore, the presence of the IR band at 960 cm-i in TS-1 catalysts may correlate with the activities for the oxidation of n-octane and the epoxidation of 1-hexene but not for phenol hydroxylation. However, note that the amorphous Ti02-Si02 also has an IR absorption band at 960 cm- and it does not activate either substrate. 

The ESR spectra of the V-ion-implanted titanium oxide catalysts were measured before and after calcination of the samples in O2 at around 723-823 K, respectively (Fig. 11). Distinct and characteristic reticular V" ions were detected only after calcination at around 723-823 K. It was found that only when a shift in the absorption band toward visible-light regions was observed, the reticular V ions could be detected by ESR. No such reticular V ions or shift in the absorption band have ever been observed with titanium oxides chemically doped with V ions [16,18,19]. 

Figure 13 UV-vis absorption spectra (diffuse reflectance) of the Cr-ion-implanted titanium oxide photocatalyst (top) and the chemically doped Cr-ion titanium oxide photocatalyst (bottom) and their modified band-gap energy structures.

The nanocrystalline solids are metal oxides, especially titanium dioxide [54-58], Various dyes are used. Transition metal complexes such as (65) and (66) have broad absorption bands and allow the harvesting of a large fraction of sunlight [54,58], Fluorescent dyes are also used, such as Eosin-Y (67) [57], Dye-sensitized nanocrystalline solar cells are now giving efficiencies in excess of 10% [54,58], compared to just 1 % ten years ago [3],... 

---