MOF-templated tubular Ni_1−xCo_xS₂-CdS heterojunction with intensified direct Z-scheme charge transmission for highly promoted visible-light photocatalysis

Hollow semiconductor nanostructures with direct Z-scheme heterojunction have significant advantages for photocatalytic reactions, and optimizing the interfacial charge transmission of Z-scheme heterojunction is the hinge to achieve excellent solar conversion efficiency. In this work, tubular Ni_1−xCo_xS₂-CdS heterostructures with reinforced Z-scheme charge transmission were constructed through an In-metal-organic framework (MOF) templated strategy. The Z-scheme charge transfer mechanism was sufficiently confirmed by combining density functional theory (DFT) calculation, X-ray photoelectron spectroscopy (XPS), surface photovoltage spectroscopy (SPV), and radical testing results. Crucially, the use of sodium citrate complexant contributes to the formation of intimate heterointerface, and the Fermi level gap between CdS and NiS₂ is enlarged through Co doping into NiS₂, which enhances the built-in electric field and photo-carriers transmission driving force for Ni_1−xCo_xS₂-CdS heterojunction, resulting in an evidently promoted activity toward H₂ evolution reaction (HER). Under visible-light (λ > 400 nm) irradiation, the Ni_1−xCo_xS₂-CdS composite with 10 mol% Co doping and 80 wt.% CdS (NC_0.10S-80% CdS) achieved an outstanding HER rate up to 35.94 mmol·g⁻¹·h⁻¹ (corresponding to the apparent quantum efficiency of 34.7% at 420 nm), approximately 76.4 times that of 3 wt.% Pt-loaded CdS and it is much superior to that of most CdS-based photocatalysts ever reported. Moreover, the good photocatalytic durability of Ni_1−xCo_xS₂-CdS heterostructures was validated by cycling and long-term HER tests. This work could inspire the development of high-performance Z-scheme heterojunction via optimizing the morphology and interfacial charge transmission.