Metallic MoO₂ cocatalyst significantly enhances visible-light photocatalytic hydrogen production over Mo₂/Zn₀.₅Cd₀.₅S heterojunction.

Abstract

As semiconductor-based nanoheterostructures play a decisive role in current electronics and optoelectronics, the introduction of active heterojunctions can afford new and improved capabilities that will enhance the conversion of solar energy into chemical energy. In this work, a novel metal/semiconductor MoO₂/Zn₀.₅Cd₀.₅S heterojunction has been designed and prepared to significantly enhance photocatalytic H₂ production efficiency. The photocatalytic activity of the as-prepared MoO₂/Zn₀.₅Cd₀.₅S for H₂ generation from water under visible-light irradiation (λ ≥ 420 nm) is measured. MoO₂/Zn₀.₅Cd₀.₅S hybrid nanoparticles have a higher photocatalytic activity than Zn₀.₅Cd₀.₅S even without the noble metal cocatalyst. The results show that the rate of H₂ evolution over annealed MoO₂/Zn₀.₅Cd₀.₅S is about 13 times higher than that of Zn₀.₅Cd₀.₅S alone, and 10 times higher than that of simply mixed MoO₂/Zn₀.₅Cd₀.₅S. Implying that the strong coupling at the interface of MoO₂ and Zn₀.₅Cd₀.₅S facilitates electron transfer from the conduction band of Zn₀.₅Cd₀.₅S to metallic MoO₂, thus promoting the separation of photogenerated electrons and holes. MoO₂ (2 wt%)/Zn₀.₅Cd₀.₅S heterostructured photocatalyst calcined at 673 K achieves the optimal overall activity for H₂ evolution. The introduction of metallic MoO₂ cocatalyst leads to a remarkable improvement in the photo current and photocatalytic H₂ production activity of Zn₀.₅Cd₀.₅S, and the content of MoO₂ in this catalyst has an important influence on the photocatalytic activity. It is shown that 2 wt% metallic MoO₂ loaded on Zn₀.₅Cd₀.₅S sample produces a maximum photocatalytic H₂ production rate of 252.4 μmol h(-1). The junctions formed between metallic MoO₂ and semiconductor Zn₀.₅Cd₀.₅S by calcination play a key role in high photocatalytic water splitting to produce H₂. Our study demonstrates that metallic MoO₂ is an excellent H₂ evolution cocatalyst, and could be used as a cocatalyst for other semiconductors to improve performances.