Zn_1–<i>x</i>Cd_<i>x</i>S Solid Solutions with Controlled Bandgap and Enhanced Visible-Light Photocatalytic H₂-Production Activity

Abstract

Photocatalytic hydrogen (H2) production from water splitting under visible-light irradiation is considered to be an attractive way to solve the increasing global energy crises in modern life. In this study, highly efficient photocatalytic H2 production without the assistant of a cocatalyst was achieved using Zn11–xCdxS solid solutions as the visible-light-driven photocatalysts and a mixed Na2S and Na2SO3 aqueous solution as the sacrificial reagent. The Zn1–xCdxS samples were prepared by a simple zinc–cadmium–thiourea (Zn–Cd–Tu) complex thermolysis method using thiourea, zinc acetate (Zn(Ac)2), and cadmium acetate (Cd(Ac)2) as the precursors. The obtained Zn1–xCdxS solid solutions feature a small crystallite size and precisely controllable band structure, which are beneficial for the photocatalysis. When the Zn/Cd molar ratio is 1:1, the prepared Zn0.5Cd0.5S sample exhibits the highest H2-production rate of 7.42 mmol·h–1·g–1, exceeding that of the pure CdS and ZnS samples by more than 24 and 54 times, respectively, and even much higher than that of the optimal Pt-loaded CdS. This high photocatalytic H2-production activity is attributed predominantly to enough visible-light absorption capacity and suitable conduction band potential of the Zn0.5Cd0.5S solid solution, which is further evidenced from the related theory calculations on the band structures of the Zn1–xCdxS solid solutions. Moreover, the calculation on the Mulliken populations of Zn, Cd, and S atoms for the first time provides new insight into the deep understanding of the chemical shifts of element binding energies for the Zn1–xCdxS solid solutions and the designing of new ternary photocatalytic materials.