Construction of a Bi₂MoO₆:Bi₂Mo₃O₁₂ heterojunction for efficient photocatalytic oxygen evolution

In this study, two different crystallographic phases of bismuth molybdate, α-Bi₂Mo₃O₁₂ and γ-Bi₂MoO₆ were synthesized hydrothermally. A series of Bi₂Mo₃O₁₂/Bi₂MoO₆ heterostructures with different phase ratios were readily prepared by tuning the concentration of the molybdenum precursor while retaining the same bismuth precursor concentration. The Bi₂Mo₃O₁₂/Bi₂MoO₆ heterojunction was found to substantially enhance the photocatalytic water oxidation capability relative to neat Bi₂Mo₃O₁₂ and Bi₂MoO₆. The Bi₂MoO₆ and Bi₂Mo₃O₁₂ were found to possess a complementary band alignment between which enabled the charge transfer process across the heterojunction interface. Ag and MnO_x photodeposition was conducted on the heterostructures to affirm the charge transfer direction between the two crystal phases. Under visible light irradiation, photogenerated holes transfer from the active Bi₂MoO₆ phase to the inactive Bi₂Mo₃O₁₂, suggesting efficient charge separation occurs between the two components, explaining the better photocatalytic performance.