SEMICONDUCTOR PHOTOCATALYSIS - EFFECT OF LIGHT-INTENSITY ON NANOSCALE CDS-CATALYZED PHOTOLYSIS OF ORGANIC SUBSTRATES

The relationship between light intensity and Product distribution in semiconductor photocatalysis was investigated by using nanoscale CdS microcrystallites (CdS-0) as photocatalysts, triethylamine (TEA) as the electron donor, and either aromatic ketones, electron-deficient alkenes, or 1-benzylnicotinamide (BNA+) as substrates. In the case of the ketones and BNA+, the yield of their respective one-electron reduction products, Pinacols and the dimer, (BNA)2, increases with decreasing light intensity. When alkenes are employed in the CdS-0 system, cis-trans photoisomerization always occur regardless of the light intensity. The kinetics for the photocatalysis of the alkenes and the measurement of the initial formation rate of active lattice Cd atoms (Cd0) (which act as catalytic sites for two-electron-transfer reductions) reveal that Cd0 formation is proportional to the square of the relative light intensity, 1,2. The chemoselectivity in the photocatalysis using nanoscale CdS should be affected by the quantity of the Cd0, whose formation strongly depends on the light intensity.