Photocatalysis photocatalytic activity

Heterogeneous photocatalysis is based on the photonie exeitation of a solid, which renders it more complex. The term photocatalysis may designate several phenomena that involve photons and catalyst, while this part of the ehapter will consider only semiconductor photocatalysis. Photocatalytic activity of Ti02 is based on its semiconductor properties. Radiation by photons, whieh have higher transfer energy, of such semiconductor leads to generation of electron-hole pairs [94] ... 

A debate centers on the mechanistic details of heterogeneous photocatalysis. The goal is to improve the photocatalytic activity of Ti02, and understand the role and importance of mineralisation by (/) free versus surface bound oxidising radicals, OH, and (2) by surface OH radicals versus direct hole oxidation. 

Since BaTi40g and Na2TieOi3 have a pentagonal prism tunnel and a rectangular tunnel structure, respectively, we have paid attention to the role of the tunnel structures in photocatalysis. A barium titanate, Ba4Tii303o, in a series of Ba-Ti titanates was chosen as a representative with non-tunnel structure, and we have compared the photocatalytic activity and the ability for the production of surface radical species with uv irradiation between the tunnel and the non-tunnel titanates. 

Titania-silica aerogels possess very high surface areas (600 to 1000 m2/g) and large pore volumes (1 to 4 cm3/g), and thereby have attracted considerable interest for photocatalysis. A number of studies have shown that titania-silica intimate mixtures exhibit enhanced UV photocatalytic activity compared with pure titania [180-183],... 

In the development of meta oxiae photocata-ysts with high and stable photocatalytic activity for water decomposition, the establishment of a correlation betweer photocatalytically active sites and metal oxide structures is desirable. In particular, it is important to see how the local structures of metal oxides are associated with the essential steps such as photoexcitation, the transfei of excited charges to the surface, and reduction/oxidation of adsorbec reactants. This chapter deals with photolysis of water by titanates with tunnel structures. The roles of tunnel-related local structures ir the photocatalysis and of Ru02 promoters loaded on the titanates are presented. 

Selective photocatalysis can be achieved through the use of proper molecular sieves, such as the titanosilicate ETS-10, an alternative approach. The photocatalytic activity of ETS-10 is due to the presence of photoexcitable Ti-O-Ti chains and the three-dimensional interconnected pore system of large 12-membered ring channels in its structure, which endow the material with excellent diffusion properties [83], This regular channel system has a direct effect in determining the shape selectivity of the degradation process [84],... 

Fundamentals of heterogeneous photocatalysis have been described in Chapter 7. The photodynamic activity of Ti02 (based on its photocatalytic activity and high efficiency in ROS generation) can find applications in photodynamic therapy (PDT) and photodynamic inactivation of microorganisms (PDI), described in Chapters 17 and 18, respectively. Selected environmental aspects of heterogeneous photocatalysis are described below. 

Keywords Photocatalysis and catalysis Photocatalytic activity Band structure and excitation Energy conversion Langmuir-Hinshelwood mechanism Electron-hole recombination Quantum efficiency Physical property-activity correlation Synergetic effect. 

The term synergetic effect in photocatalysis could be defined as follows when more than two kinds of photocatalysts are used as a mixture, the overall photocatalytic activity exceeds the sum... 

Intermediate in interlayer ion density between KCa2Nb30io and K2La2Ti30io are compounds of general formula A2-,vLa2Ti3 NbxOio, where the cation density can be varied between the end members [85]. Photocatalysis of x = 0.5 members has been studied by Takata et al. [138]. Band-gaps of 3.4-3.5 eV were estimated from reflectance measurements. The photocatalytic activities for H2O decomposition under UV irradiation are also listed in Table 13. 

In order to observe the effect of the structural change of the surface on the photocatalysis, effect of excess Cd + on the photoproduction of CO was examined (Fig.l). The CO formation was increased by a factor of two when 0.2 equivalent amount of excess Cd + to the concentration of CdS-DMF was etdded into the system. Induction period of the CO formation became shorter by the addition of excess Cd +. The addition of more than 0.2 equivalent of excess Cd +, however, led to a decrease in the photocatalytic activity. During the reaction with the system containing more than 0.2 equivalent of excess Cd +, photo-darkening of the CdS-DMF solution was observed after 30 min irradiation. 

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