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 (H 2 ) 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 H 2 production without the assistant of a cocatalyst was achieved using Zn1 1– x Cd x S solid solutions as the visible-light-driven photocatalysts and a mixed Na 2 S and Na 2 SO 3 aqueous solution as the sacrificial reagent. The Zn 1– x Cd x S 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 Zn 1– x Cd x S 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 Zn 0.5 Cd 0.5 S sample exhibits the highest H 2 -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 H 2 -production activity is attributed predominantly to enough visible-light absorption capacity and suitable conduction band potential of the Zn 0.5 Cd 0.5 S solid solution, which is further evidenced from the related theory calculations on the band structures of the Zn 1– x Cd x S 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 Zn 1– x Cd x S solid solutions and the designing of new ternary photocatalytic materials.