Novel dual-petal nanostructured WS2@MoS2 with enhanced photocatalytic performance and a comprehensive first-principles investigation

Abstract

For the first time, a novel dual-petal nanostructured WS₂@MoS₂ heterojunction was fabricated via a facile two-step approach and explored as a photocatalyst for the photodegradation of methylene blue (MB). In the light of the results obtained from experiments, a reasonable formation mechanism for the nanopetal (NP) structured WS₂ was proposed, in which the pretreatment of ball milling had played an important role in the formation of WS₂ NPs that subsequently acted as the base material to grow curly MoS₂ sub-NPs. Because the dual-petal nanostructured WS₂@MoS₂ possessed plenty of active sites that originated from its unique structural characteristics with densely stacked MoS₂ nanopetals and an effective separation of photoinduced carriers, it exhibited significantly enhanced photocatalytic activity and obviously exceeded the pristine MoS₂/WS₂. In order to propose a scientific explanation for the corresponding enhancement mechanism, we further conducted comprehensive first-principles calculations to investigate the corresponding structural, electronic, and optical properties of this WS₂@MoS₂ composite. The results revealed that the calculated band gap of the WS₂@MoS₂ composite was narrower than that of pristine WS₂ and MoS₂, meanwhile, it had a well-defined staggered type-II band alignment, leading to the injection of photoexcited electrons into the conduction band minimum (CBM) of MoS₂ from the CBM of WS₂. This separation of carriers can restrain the photogenerated e⁻–h⁺ pair recombination and prolong the lifetime of carriers for proper interface charge distribution. In short, the calculated results fully explained the reason why the composite presented improved photocatalysis and provide valuable references for future studies.