Abstract
The electronic property and the photocatalytic activity of a semiconductor particle were determined by the electrochemical measurement and the hydrogen production experiment, respectively. The energy level of electrons at the bottom of the conduction band of the particle under irradiation was revealed to be different from that of a bulky electrode. This value involves the information on the relative position of the valence band of the semiconductor to the donor level of a reducing agent. The activity of hydrogen production from water-ethanol mixture with various platinized photocatalysts could not be explained by the property of the corresponding bulky electrode, but could be correlated with the obtained energy levels of the electrons under iradiation.
New photocatalysts, CdS1-x Sex solid solution particles, were prepared to obtain the desired energy level of the valence band, and their photocatalytic activities were examined by the hydrogen production experiment. The electronic properties of the solid solution particles were determined by the measurements of the luminescence and the photoconductivity. These experiments demonstrated that there are two determining factors for the activity of photocatalytic hydrogen production.
When the top of the valence band of the particle locates around the donor level of the reducing agent, the main determining factor is the relative position between the donor level of a reducing agent and the energy level of the valence band of a semiconductor particle. On the other hand, when the donor level is much more negative than the top of the valence band, the transport property of the carries in the particle mainly controls the reaction. With the choice of the proper composition of sulfur to selenium, the CdS1-x Sex photocatalyst can have the selectivity for the oxidation of organic compounds.
