Effects of the preparation method of the ternary CdS/TiO2/Pt hybrid photocatalysts on visible light-induced hydrogen production

A variety of combinations of US, TiO2, and Pt in preparing the hybrid catalysts were studied for hydrogen production under visible light (lambda > 420 nm) irradiation. The preparation method sensitively influenced the activity of the ternary hybrid catalysts. The formation of the potential gradient at the interface between US and TiO2 is necessary in achieving the efficient charge separation and transfer and how the platinum as a cocatalyst is loaded onto the CdS/TiO2 hybrid catalysts determines the overall hydrogen production efficiency. The common method of photoplatinization of CdS/TiO2 hybrid [Pt-(CdS/TiO2)] was much less efficient than the present method in which Pt was photodeposited on bare TiO2, which was followed by the deposition of US [CdS/(Pt-TiO2)]. The CdS/(Pt-TiO2) has the hydrogen production rate ranging (6-9) x 10(-3) mol h(-1) g(-1), which is higher by a factor of 3-30 than that of Pt-(CdS/TiO2). The photocatalytic activity of the ternary hybrid catalysts was extremely sensitive to where the platinum is loaded. The photoactivity of the hybrid catalyst was also assessed in terms of the photocurrent collected by the methyl viologen electron shuttle in the catalyst suspension. CdS/(Pt-TiO2) generated higher photocurrents than Pt-(CdS/TiO2) by a factor of 2-7. The extreme sensitivity of the preparation method to the hydrogen production activity should be taken into account when hybrid photocatalysts are designed and prepared.