Hexagonal Zn_1-xCd_xS (0.2 ≤ x ≤ 1) solid solution photocatalysts for H₂ generation from water

A series of hexagonal Zn_1-xCd_xS photocatalysts with variable composition (0.2 ≤ x ≤ 1) is synthesized by a solvothermal method. XPS spectra of Zn 2p and Cd 3d regularly shift upon changing the composition of Zn_1-xCd_xS samples, due to the difference in the Mulliken atomic charges of Zn, Cd, and S. The photocatalytic activity of the samples for H₂ evolution from water was tested under visible-light irradiation (λ ≥ 420 nm) without a cocatalyst; the Zn_0.4Cd_0.6S sample exhibited the highest photocatalytic H₂ evolution rate, which was about 81 mL h^-1 g^-1. Under irradiation with a 368 nm LED, the H₂ evolution rate decreased with increasing Cd fraction in the Zn_1-xCd_xS solid solution. By comparing the crystallinity, surface area, valence/conduction band positions, absorption spectra and fluorescence lifetimes, we conclude that the photocatalytic activity is related to the balance between the absolute positions of the valence/conduction bands and light absorption ability of the Zn_1-xCd_xS photocatalysts.