Hydrothermal Synthesis, Structural Characterization and Photocatalytic Performance of Bi₂WO₆, Bi₂MoO₆ and Their Composite

Phase-pure Bi₂MoO₆, Bi₂WO₆, and their corresponding composites were successfully prepared using a one-step hydrothermal route. Crystal structures, morphologies, pore structures and surface states were characterized by XRD, SEM, BET, and XPS. Their visible-light photocatalytic performance was evaluated by methylene blue (MB) degradation.Results showed that both single samples possessed high-purity orthorhombic structures and flower-like nanosheet-assembled morphologies. The composite possessed dual phases, and structural distortion together with denser nanosheet stacking could be induced by the interaction between Mo and W. Compared with single components, the composite had smaller specific surface area (16.00 m²/g) and lower average pore diameter (25.69 nm). XPS confirmed Bi³⁺, Mo⁶⁺, W⁶⁺ and O²⁻ valence states.Photocatalytic tests revealed that both single samples achieved complete MB degradation within 120 min, with Bi₂WO₆ superior to Bi₂MoO₆. However, the composite showed significantly lower activity. This was attributed to its reduced surface area, which lowered pollutant contact probability, along with accelerated charge recombination that hindered charge transfer. This work offers insights for the design of bismuth-based layered semiconductors in environmental applications.Results indicated that both pure-phase Bi₂MoO₆ and Bi₂WO₆ exhibited high-purity orthorhombic crystal structures, while the composite retained the combined phases of the two. All samples showed a flower-like layered structure assembled by irregular nanosheets. In the composite, the mutual substitution of Mo and W atoms induces structural distortion of the octahedral units, resulting in more compact nanosheet stacking. Consequently, the composite had a smaller specific surface area (16.0028 m²/g) and a lower average pore diameter (25.6916 nm) compared to the single components. XPS analysis confirmed the valence states of Bi³⁺, Mo⁶⁺, W⁶⁺, and O²⁻in the composite.Photocatalytic tests demonstrated that both pure-phase Bi₂MoO₆ and Bi₂WO₆ achieved complete MB degradation within 120 minutes, with Bi₂WO₆ outperforming Bi₂MoO₆. However, the composite exhibited significantly inferior photocatalytic activity. This was primarily attributed to its reduced specific surface area, which not only decreased the contact probability between photogenerated electrons and target pollutant molecules but also facilitated charge carrier recombination, thereby impeding charge migration and transfer. This work provides crucial experimental insights for the rational design and structural modulation of bismuth-based layered semiconductor materials for environmental applications.