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

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.