TiO2 particles

It appears that TiO2 particles in water are widely hydroxylated. Therefore holes escaping annihilation may migrate to the surface and oxidize adsorbed water molecules and hydroxyl ions. Oxygen adsorbed at the surface captures electrons preventing their recombination with h and therefore favouring the yield of OH radical (Fig. 5). 

The most common reaction at the anodic side of biofuel cells is the oxidation of sugars which relies on the catalytic properties of oxidases. This class of enzymes has, however, usually poor potential for direct ET. Direct ET on the anodic site was, however, described for a number of hydrogenases [235, 236] and cellobiose dehydrogenase [225, 237, 238]. Enzymatic catalysis by means of direct ET was also realized on conducting graphite or TiO2 particles [239, 240]. 

Malgat, A., Boisvert, J.P., and Daneault, C., Specific influence of univalent cations on ionization of alumina-coated TiO2 particles and on the adsorption of poly(acrylic) acid, J. Colloid Interf. Sci., 269, 320, 2004. 

Figure 13 Tunable morphology of TIO2 particles Induced by different Ti-llgand coordinations.

Thus the remarkable achievement of Kiwi et al (47), who simultaneously oxidized and reduced water with a single bifunctional catalyst (TIO2 particles treated with Pt and RUO2), stands as a milestone which will be difficult for polymeric systems to emulate. 

Fig. 14 Reaciiions taking place between an illuminated TIO2 particle in aqueous solution, based on Cai and coworkers [93].

Bondzie VA, Parker SC, Campbell CT. 1999. The kinetics of CO oxidation by adsorbed oxygen on well-defined gold particles on TiO2(110). Catal Lett 63 143. 

Okazawa T, Kohyama M, Kido Y. 2006. Electronic properties of Au nano-particles supported on stoichiometric and reduced TiO2(110) substrates. Surf Sci 600 4430-4437. 

However, under some circumstances, the rate is not only leveled but it is also inhibited as the substrate concentration increases. In a comprehensive study on 3-chloro-4-hydroxybenzoic acid and chlorophenols, Cunningham and colleagues [35] deduced that the rate can be strongly inhibited in consequence of (1) chemisorption-induced depletions of surface —OH groups, (2) adsorbate-enhanced hole-electron recombination on the TiO2 surfaces, (3) mass transport limitations within the TiOz particle aggregates. They reported that, depending on... 

Upon illumination, semiconductor particles become charged, allowing even for electrophoretic mobility under an applied electrical field When appropriately prepared, colloidal TiO2 can apparently accumulate charge to effect directly multiple quanta redox reactions The efficiency of such charge accumulation is surely related to doping level for the doping level can alter band positions and may improve the efficiency of photoinduced electron transfer. For example, the dispersal of FcjOa... 

Carefully prepared Au catalysts have a relatively narrow particle size distribution, giving mean diameters in the range 2-10 nm with a standard deviation of about 30%. A major reason why Au particles remain as NPs even after calcination 573 K is the epitaxial contact of Au NPs with the metal oxide supports. Gold particles always expose its most densely packed plane, the (111) plane, in contact with a-Fe2O3(110), Co304(lll), anatase Ti02(112), and rutile TiO2(110). 

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