Photo-production of hydrogen over the CdS–TiO 2 nano-composite particulate films treated with TiCl 4

Abstract

Nanosize CdS and TiO 2 sol were prepared by precipitation reaction of Cd(NO 3) 2 and Na 2S aqueous solutions and by sol–gel reaction of Ti alkoxide, respectively. They were mixed together mechanically with variation of the mole ratio ( r) of TiO 2/(CdS+TiO 2). Then, the CdS−TiO 2 mixed sols were further treated with the hydrothermal processing at the temperatures of 120–240°C. CdS–TiO 2 composite particulate films were thus prepared by casting the resulting sol onto F:SnO 2 conducting glass and a subsequent heat-treatment at 400°C under air. Again, the physical properties of these films were controlled by the surface treatment with TiCl 4 aqueous solution. With the hydrothermal treatment, the crystallinity of both CdS and TiO 2 particles increased, and CdS particles were seen to be surrounded homogeneously by TiO 2 particles. Hydrogen photo-production rates measured under the present experimental conditions varied according to the mole ratio ( r) and showed the maximum value at r=0.8, which were in consistent with the photocurrent trend of the composite films, suggesting the importance of effective distribution and contacts among the particles. Also, the film surface treatment with TiCl 4 aqueous solution caused a considerable improvement in photocatalytic activity and photocurrent of the films, probably as a result of closer contacts between the primary particles by the etching effect of TiCl 4.