Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite

The enhanced photocatalytic performance of various MoS₂-based nanomaterials has recently been observed, but the role of monolayer MoS₂ is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS₂/SnO₂ nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS₂ as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ∼0.49 eV exists between monolayer MoS₂ and SnO₂ with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO₂, thus enhancing the reduction activity of latter, indicating that the monolayer MoS₂ is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS₂, turn into catalytic active sites, making the monolayer MoS₂ to be a highly active co-catalyst in the composite. The dual role of monolayer MoS₂ is expected to arise in other MoS₂-semiconductor nanocomposites. The calculated absorption spectra can be rationalized by available experimental results. These findings provide theoretical evidence supporting the experimental reports and pave the way for developing highly efficient MoS₂-based photocatalysts.