Photo-production of hydrogen over the CdS–TiO2 nano-composite particulate films treated with TiCl4

Nanosize CdS and TiO2 sol were prepared by precipitation reaction of Cd(NO3)2 and Na2S aqueous solutions and by sol–gel reaction of Ti alkoxide, respectively. They were mixed together mechanically with variation of the mole ratio (r) of TiO2/(CdS+TiO2). Then, the CdS−TiO2 mixed sols were further treated with the hydrothermal processing at the temperatures of 120–240°C. CdS–TiO2 composite particulate films were thus prepared by casting the resulting sol onto F:SnO2 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 TiCl4 aqueous solution. With the hydrothermal treatment, the crystallinity of both CdS and TiO2 particles increased, and CdS particles were seen to be surrounded homogeneously by TiO2 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 TiCl4 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 TiCl4.