Composite photocatalysts based on Cd(1−x)Zn(x)S and TiO(2) for hydrogen production under visible light: effect of platinum co-catalyst location

Ternary composite photocatalysts based on titania and solid solutions of CdS and ZnS were prepared and studied by a set of physicochemical methods including XRD, XPS, HRTEM, UV-vis spectroscopy, and electrochemical tests. Two synthetic techniques of platinization of Cd(1−x)Zn(x)S/TiO(2) were compared. In the first case, platinum was deposited on the surface of synthesized Cd(1−x)Zn(x)S (x = 0.2–0.3)/TiO(2) P25; in the second one, Cd(1−x)Zn(x)S (x = 0.2–0.3) was deposited on the surface of Pt/TiO(2) P25. The photocatalytic properties of the obtained samples were compared in the hydrogen evolution from TEOA aqueous solution under visible light (λ = 425 nm). The Cd(1−x)Zn(x)S (10–50 wt%; x = 0.2–0.3)/Pt (1 wt%)/TiO(2) photocatalysts demonstrated much higher photocatalytic activity than the Pt (1 wt%)/Cd(1−x)Zn(x)S (10–50 wt%; x = 0.2–0.3)/TiO(2) ones. It turned out that the arrangement of platinum nanoparticles precisely on the titanium dioxide surface in a composite photocatalyst makes it possible to achieve efficient charge separation according to the type II heterojunctions and, accordingly, a high rate of hydrogen formation. The highest photocatalytic activity was demonstrated by 20% Cd(0.8)Zn(0.2)S/1% Pt/TiO(2) in the amount of 26 mmol g(−1) h(−1) (apparent quantum efficiency was 7.7%) that exceeds recently published values for this class of photocatalysts.