Semiconductor homogenous solution catalysts

While the exploration of the implications of irradiated semiconductor surfaces for organic chemistry have only recently been attempted, there now exists a growing body of experiments illustrative of their power (283). A typical example of the contrasting oxidative reactivity observed on irradiated semiconductor surfaces can be seen in the different product distributions obtained by oxidation of 1,1-diphenylethylene photo-electrochemically on Ti02, electrochemically on Pt (an inert electrode material), and with thermal single electron transfer catalysts in homogeneous solution, eq. 89 (284) ... 

Figure 1. Basic features of sacrificial water reduction systems. (A) Homogeneous solution, with sensitizer, S, electron relay, R, sacrificial electron donor, D, and metal catalyst. (B) Catalyst-coated colloidal semiconductor dispersion, obviating the need for electron relay.

Fig. 10. Band diagram of an illuminated semiconductor particle in the electrolyte solution, a - a homogeneous particle CAT 1 and CAT 2 are catalysts for H2 and O2 evolution respectively, b - a heterojunction particle. CAT is catalyst forH2 evolution.

Another example of this method is the synthesis of dual Au/Pt composites-the aqueous solutions of polyvinyl alcohol and poly-(JV>vinyl-2-pyrollidone) have been used [39] with polymerization in the solution after colloid particle formation. The aggregation of nanoparticles in this case does not usually take place however the polymerization conditions affect the homogeneity of the composite obtained. They show some catalytic propertks, characteristic of bimetallic catalysts. There were some reports on semiconductor composites with metal coatings such as CdS/Rh 40 A composites [44] and CdSe/Ag SO A composites [45]. The former system exhibits enhanced photochemical properties, the latter was used for investigation of Raman scattering of nanocomposites. 

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