Visible-light-driven photocatalytic H2 evolution over CdZnS nanocrystal solid solutions: interplay of twin structures, sulfur vacancies and sacrificial agents

Abstract

In the perspective of visible-light-driven hydrogen evolution, photocatalysts with suitable band energy levels and wide-range responses are particularly promising. Herein, Cd_xZn_1−xS (x = 0.2, 0.4, 0.6 and 0.8) nanocrystal solid solutions (NCSSs), which integrated twinning crystal structures, rich sulfur vacancies and wurtzite-sphalerite phase-junctions all in one, were prepared via a facile hydrothermal method. With these features, the twinning Cd_0.6Zn_0.4S performed remarkable photocatalysis for H₂ evolution (42.66 mmol h⁻¹ g⁻¹) in Na₂S/Na₂SO₃ aqueous solution, the rate of which was 691 times higher than those of pristine twinning CdS nanocrystals. To the best of our knowledge, this was the highest performance of H₂ evolution among the hitherto reported one-fold sulfide photocatalysts. Density functional theory (DFT) calculations suggested the formation of twinning crystal structures improved the separation of photogenerated electron–hole pairs. Meanwhile, stability of the Cd_0.6Zn_0.4S photocatalyst was largely enhanced due to the fast hole consumption by Na₂S/Na₂SO₃ through sulfur vacancies. This work explores the interplay and mechanism of special structures, sulfur vacancies and catalytic conditions of twinning CdZnS NCSSs, and provides guidance for the design of highly efficient and stable metal-sulfide-based photocatalysts.