Comparative study of the electronic and photocatalytic properties of bulk and monolayer MX2: A TB-mBJ study

Highlights: • The band edge positions of MX₂ were calculated by TB-mBJ. • MoS₂ and WS₂ monolayers have appropriate band edge positions for water splitting at pH=0. • In neutral environment MoSe₂ monolayer and bulk WS2 achieved proper band alignment for the water splitting, but WSe₂ monolayer needed basic solution. The electronic band structure and photocatalytic activity of six transition metal dichalcogenides (TMDCs) MX₂ [M = Mo and W; X = S, Se and Te] are illustrated by Tran Blaha modified Becke Johnson (TB-mBJ) potential. Interestingly, a lower recombination rate has been observed for bulk MX₂ in comparison to the monolayer. However, the calculated band edge positions indicate that only MoS₂ and WS₂ monolayers have appropriate band alignment with water redox potentials. The redox potentials are tuned by varying the pH value of the medium to verify the suitability of TMDCs as a photocatalyst. At pH = 7, MoSe₂ monolayer and bulk WS₂ exhibited proper band alignment for water splitting while WSe₂ monolayer required a basic solution (pH = 11). Our result suggests that bulk WS₂ could be a potential photocatalyst owing to its proper band alignment, lower carrier recombination rate and high absorption coefficient (10⁵ cm⁻¹) in the visible region.