Abstract

The effect of platinum loading on the efficiency of CdS-photocatalyzed hydrogen evolution from an aqueous solution of sodium sulfide and on the intensity of the green emission (510 nm) of CdS suspended in the same solution was studied. The Fermi level of the CdS photocatalyst at the working condition can be estimated from the intensity of the green emission of the platinum-loaded CdS powder and the luminescence-potential curve of a CdS electrode. When the amount of platinum deposited on CdS is increased, the Fermi level of CdS at the working stage is moved down toward more positive potential, leading to a stronger band bending, and the photocatalytic reaction is stimulated. Too much Pt loading, however, lowers the photocatalytic activity because of the enhanced rate of electron-hole recombination as well as light absorption by platinum. The temperature effect on the reactivity and the reason for the presence of an induction period of the reaction are also elucidated in relation with the band bending of the photocatalyst.

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