Photocatalyst development

Several t)rpes of materials, over 130 including oxides, nitrides, sulfides, and others have been reported to act as efficient photocatalysts for hydrogen evolution via water splitting. 

Photocatalysts (reference) Band-gap energy (eV) Cocatalyst Sacrificial reagent Activity gmol h H2 g O2  

Under visible light, this Pt-modified photocatalyst evolves O2 from aqueous AgNOs as sacrificial electron acceptor and traces of H2 from aqueous solutions of methanol as sacrificial electron donor. 

Considering the importance of the structural characteristics (crystalline phase, crystalline size, and geometrical surface area) in the control of band structure and in the concentration and mobility of photocatalyst charges, studies have been conducted on the influence of preparation methods on the photophysical properties of CdS (Arora et al., 1998 Jing and Guo, 2006). Improvement in CdS photoactivity is observed from preparation methods that lead to CdS phases with good crystallinity and few crystal defects. 

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Table 2 Overview of photocatalysts developed in last years for water splitting reaction under visible light... 

To improve the efficiency of photocatalysts, developments in the future must be based on an understanding of the sophisticated factors that determine the photoactivity of the water-splitting reaction (i) molecular reaction mechanisms involved in the oxidation and reduction of water on photocatalyst surfaces, (ii) structure and defect chemistry of photocatalyst surfaces, and (iii) charge transfer mechanisms between... 

Such photocatalysis can also be induced by slight ultraviolet radiation due to fluorescent lights, etc. In 2001, the nitrogen-doped TiO photocatalyst to enable a photocatalysis under visible light was developed [2], and has attracted much attention since then. More recently C-doped photocatalysts have been developed [6]. Construction materials with TiO photocatalyst develop the major performance or functions as shown in Fig. 1.3 [16, p. 21 24, p. 12], based on both effects of strong decomposition power and high water-wettability. 

In the last two decades we have witnessed in photocatalysis, as a science, a continuous shift from phenomenological approaches to studies at the molecular level. With accumulation of information obtained in such studies, the accents in the work aimed at development of new photocatalysts and new photocatalytic reactions and technologies, are expected to more and more shift from empirical search to intentional design. 

Investigation of direct conversion of methane to transportation fiiels has been an ongoing effort at PETC for over 10 years. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using li t, water, and a semiconductor photocatalyst. Research in our laboratory is directed toward ad ting the chemistry developed for photolysis of water to that of methane conversion. The reaction sequence of interest uses visible light, a doped tungsten oxide photocatalyst and an electron transfer molecule to produce a hydroxyl i cal. Hydroxyl t cal can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional wata- molecule to produce methanol and hydrogen. 

Conventional colloid chemistry and elaitrochemistry have always been clo ly related with each other, the keywords electrophoresis, double layer theory, and specific adsorption describing typical asp ts of this relationship. In more ro nt times, new aspects have arisen which again bring colloid chemistry into contact with modem developments in electrcolloidal particles as catalysts for electron transfer reactions and as photocatalysts. In fact, the similarity between the reactions that occur on colloidal particles and on compact electrodes has often been emphasized by calling the small particles microelectrodes . 

The following two papers deal mainly with problems in energy conversion, in piarticular, the transformation of irradiation energy into electrical or chemical energy. The present status and future possible developments of photoelectrochemical energy conversion is presented. In a second paper electrochemical developments are connected to colloidal chemistry and the application of colloidal particles as catalysts for electron transfer reactions and as photocatalysts are discussed. 

Hernandez-Alonso, M.D., Fresno, F., Suarez, S., and Coronado, J.M. (2009) Development of alternative photocatalysts to Ti02 challenges and opportunities. Energy Environmental Science, 2 (12), 1231-1257. 

Yoong, L.S., Chong, F.K., and Dutta, B.K. (2009) Development of copper-doped Ti02 photocatalyst for hydrogen production under visible light. Energy,... 

Kudo, A., Development of photocatalyst materials for water splitting with the aim at photon energy conversion, ]. Ceram. Soc. Jpn., 109, S81, 2001. 

Practical application of the results of photocatalysis will depend much on the capability of the catalysts to work under visible fight conditions. Therefore, the design of new photocatalysts either by modification of the existent TiOz or by discovery of new materials will be a key step in developing... 

H. Kato, I. Tsuji, A. Kudo, Strategies for the development of visible-light-driven photocatalysts for water splitting, Chem. Lett. 33 (2004) 1534-1539. 

Scientific interest in nanocarbon hybrid materials to enhance the properties of photocatalysts and photoactive electrodes has been growing rapidly [1-8]. The worldwide effort to find new efficient and sustainable solutions to use renewable energy sources has pushed the need to develop new and/or improved materials able to capture and convert solar energy, for example in advanced dye-sensitized solar cells - DSSC (where the need to improve the photovoltaic performance has caused interest in using nanocarbons for a better cell design [9,10]) or in advanced cells for producing solar fuels [11-13]. 

The use of nanocarbon-semiconductor hybrid materials thus offers a great potential to the design and development of novel/improved photocatalysts and photoanodes, but it is necessary to have a detailed understanding of the many factors which determine the overall properties. This chapter will analyze these aspects presenting a concise analysis of the topic with selected relevant developments in the field, mainly in the last few years. 

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