Metal oxides, photocatalytic properties

The addition of a second species can cause a decrease in charge recombination and an increase in the TiOz photocatalytic efficiency. Such behavior was examined by loading a series of species on the surface or into the crystal lattice of photocatalysts inorganic ions [148-152], noble metals [153,154], and other semiconductor metal oxides [155], It was thus proven that modifications produced by these species can change semiconductor surface properties by altering interfacial electron-transfer events and thus the photocatalytic efficiency. 

Shchukin DC, Schattka JH, Antonietti M, Curasu RA (2003) Photocatalytic properties of porous metal oxide networks formed by nanoparticles infiltration in a polymer gel template. J Phys Chem B 107 952-957... 

We focus attention here on titania (Ti02) for the following reasons. The first is that titania is a widely used oxide support for both metal particles and metal oxides, and used in some cases also directly as catalyst (Claus reaction, for example). The second is that it possesses multifunctional properties, such as Lewis and Bronsted sites, redox centres, etc. The third is that it has several applications both as a catalyst and an advanced material for coating, sensors, functional films, etc. The fourth is its high photocatalytic activity which make titania unique materials. 

Bahnemann, D.W. (1993). Ultrasmall metal oxide particles Preparation, photophysical characterization, and photocatalytic properties. Israel Journal of Chemistry, 33, 115-136. 

Photocatalytic properties for hydrogen production were investigated [209] on layered titanium compounds intercalating CdS in the interlayer, which were prepared by direct cation exchange reactions and sulfurization processes. The photocatalytic activity of the compounds intercalating CdS was superior to those of simple CdS and the physical mixture of CdS and metal oxides. The improvement might be attributed to the formation of microheterojunctions between the CdS nanoparticles and the layers of oxides. 

The most important solid materials with photocatalytic properties, that are present in the atmosphere, are metal oxides and sulfides. Many of them are semiconductors, and some of them absorb visible and near-infrared light. 

The most common photocatalytic processes, in terms of both mechanistic analysis and practical use, involve insoluble semiconductor metal oxides or sulfides, which upon irradiation undergo dual interfacial electron transfer between the excited semiconductor surface and adsorbed donor (D) and/or acceptor (A) molecules (Scheme 6.291). Titanium dioxide (Ti02) is a particularly popular photocatalyst due to its good redox properties (see also Special Topic 6.29), high stability, low toxicity and low price. 

The Local Structures of Transition Metal Oxides Incorporated in Zeolites and their Unique Photocatalytic Properties... 

Unique and efficient photocatalytic systems incorporating transition metal oxides (Mo, Ti, V) have been designed using the cavities and frameworks of zeolites and mesoporous molecular sieves. The present results have demonstrated the unique physicochemical properties of the local stmcture of such anchored metal oxides, which were the result of the rigidity or flexibility of the zeolite framework, as well as their photocatalytic reactivities. These well-defined photocatalysts can be considered one of the most promising candidates for use in the environmentally-friendly reaction systems. 

K-01 - The local structures of transition metal oxides incorporated in zeolites and their unique photocatalytic properties... 

Other uses of nanostructured chromophores may include fluorescent nanoparticles or nanoparticle-based porous materials that change their light absorption or emission when a toxin is encountered. Some metal oxides and POMs already exhibit such properties. Likewise, electrochemical properties, including induced photocurrents, could be sensitive to encountering a toxin. Clearly, both decontamination and detection are relevant aspects here. Basic research is needed on the design and synthesis of engineered nanostructures whose electronic structures, thermal catalytic, photophysical (emission), and photocatalytic properties are strongly perturbed by the presence or absence of toxic compounds. 

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