Band gap irradiation

Band-gap irradiation of CdS, led to sacrificial 565 photoreduction of Ag+ at the outer surfaces of SUVs via electron exchange between CI6MVi + and CiSMV+i, located at the inner and at the outer surfaces of the vesicles, at the expense of benzyl alcohol as a sacrificial electron donor... 

Adsorption of substrates may also be altered by photoexcitation or by the presence of other adsorbates. That adsorption and photoadsorption are influenced by thermal removal of water and surface hydroxyl groups has been shown in detailed studies On tin oxide, preadsorption of other reagents can produce a substantial increase in oxygen photoadsorption under sub-band gap irradiation and can shift the photosensitivity threshold to longer wavelengths... 

Photocatalysis, i.e., using semiconductor particles under band gap irradiation as little micro reactors for the simultaneous reduction and oxidation of different redox systems, has been intensively studied during the last 25 years since the pioneering work of Carey et al [1]. The main focus of these studies seems to be the investigation of the principal applicability of photocatalytic systems for the efficient treatment of water and air streams polluted with toxic substances. Several review articles on this topic have recently been published [2]. In some cases, pilot-scale or even commercially available reactors have already been constructed, especially when titanium dioxide is used as the photocatalyst [3]. 

Since Bahnemann and co-workers have observed that a comparatively high amount of trapped holes are formed when partially platinized titanium dioxide particles are subjected to ultra band gap irradiation (cf. Fig. 7.6), they have chosen this system to study the dynamics of the photocatalytic oxidation of the model compounds dichloroacetate, DCA", and SCN- [7]. To explain their experimental observations these authors have used a model assuming two energetically different types of hole traps (see our detailed discussion above). 

Previous work using band gap irradiated metal loaded semiconductors has shown that hydrogen is really evolved from aqueous suspensions of these systems though 02 evolution was not observed in most cases (Duonghong et al., 1981 Mills et al., 1982). 

In distilled water, K4Nb60i7 without any modification evolves H2 and O2 under band-gap irradiation. This indicates that the photoexcited electrons and holes have enough potential to reduce and oxidize water. The rates of H2 and O2 evolution are,... 

Figure 15. Schematic representation of H 7K4Nb(,Oi7-catalyzed MV " formation using methanol as reductant under band gap irradiation. From Ref. [27].

Jaeger and Bard using a spin trapping technique (with a-phenyl N-tert-butyl nitrone, PBN, and a-(4-pyridyl N-oxide) N-tert-butyl nitrone, 4-POBN, as spin traps), have detected hydroxyl, OH, and perhydroxyl, HO2, radicals during band-gap irradiation of aqueous suspensions of Ti02 and platinised Ti02 powders. Titanium dioxide employed was a pre-reduced anatase powder and the experiments were performed in... 

Use of p-type semiconductors under band gap irradiation to directly reduce CO and its intermediates. 

Fig. 8.10. a Light and dark cycles in the UV-light induced decomposition of water. 24 ml solutions containing 400 mg l l Ti02 as well as 40 mg l-1 Pt and 0.1% Ru02 (per weight of Ti02 codeposited were irradiated with a 450 W-Xe lamp, b Band model to explain the processes induced by band gap irradiation... 

Preparation of noble metal/Cr203 (core/shell) nanostructures on GaN ZnO was conducted through a stepwise photodeposition under oxygen-free conditions [17, 18]. The scheme is shown in Fig. 10. First, noble metal nanoparticles were deposited using a proper metal salt complex under band gap irradiation of GaN ZnO (1 > 400 nm). The as-prepared noble metal/GaN ZnO sample was then treated with K2Cr04 in a similar manner. The final product was washed thoroughly with distilled water and dried overnight at 343 K. 

Probably the first reported instance of observation of an APE was in 1977 for a n-Ti02-Na0H electrolyte interface [158]. The APE was observed in the saturation region of cathodic current flow and was induced by sub-band gap irradiation of the photoanode. A peak in the spectrum of the photoresponse at 800 nm (the corresponding photon energy being lower than the 3.0 eV band gap of Ti02) was used by the authors to invoke a surface... 

Figure 24 contains a schematic representation of the nanocrystalline semiconductor film-electrolyte interface at equilibrium (Fig. 24a) and the corresponding situation under band gap irradiation of the semiconductor (Fig. 24b) [9]. Because the diffusion length of the photogenerated carriers is usually larger than the physical dimensions of the structural units, holes and electrons can reach the impregnated electrolyte phase before they are lost via bulk recombination. This contrasts the situation with the single-crystal cases discussed earlier.

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