Doped Solid Solution: (Zn0.95Cu0.05)1-xCdxS Nanocrystals with High Activity for H2 Evolution from Aqueous Solutions under Visible Light

A series of (Zn0.95Cu0.05)(1-x)CdxS solid solutions with different compositions (x = 0, 0.17, 0.27, 0.33, 0.50, 0.67, 1) were synthesized via a simple coprecipitation method at room temperature. Structural, morphological, and optical properties of the samples have been characterized by XRD, TEM, XPS, N-2 physisorption, and UV-vis DRS techniques. The solid solution samples with a cubic structure are composed of nanocrystals with their sizes in a range of 2-5 nm. A narrow band gap of ca. 2.0 eV has been observed for all the solid solution samples. High activities for H-2 evolution from aqueous solutions containing S2- and SO32- have been observed, even without a cocatalyst. The sample with x = 0.33 gives a H-2 production rate of 508 mu mol/h under the irradiation of a 300 W xenon lamp with a cutoff filter (lambda >= 420 nm), with a quantum efficiency of 15.7% at 420 nm. After the loading of 0.75 wt % Pt on the nanocrystal surface, the performance of the photocatalysts has been increased, with the highest H-2 production rate obtained at 1.09 mmol/h with a higher quantum efficiency of 31.8%. No significant decrease in the catalytic performance was observed after three consecutive runs of 12 h. The high activities of the solid solution nanocrystals have been attributed to their efficient visible light absorption due to the presence of cadmium sulfide, relatively high conduction band potentials contributed by zinc sulfide, and the accommodation sites of charge carriers provided by Cu2+ impurity levels.