3D Hierarchical heterostructures of Bi2W1−xMoxO6 with enhanced oxygen evolution reaction from water under natural sunlight

Abstract

Self-assembled 3D hierarchical Bi₂W_1−xMo_xO₆ heterostructures with varying x (x = 0, 0.2, 0.4, 0.6, 0.8 or 1.0) with different morphologies were synthesised via a facile one-pot solvothermal method and their photocatalytic activity towards the oxygen evolution reaction (OER) from water under natural sunlight was tested. The structural properties of Bi₂W_1−xMo_xO₆ were studied by the X-ray diffraction (XRD) technique, which showed an orthorhombic Aurivillius layered crystal structure. The microstructural features were examined by FE-SEM and FE-TEM techniques which showed that the morphology of Bi₂WO₆ varies with substitution of Mo and each morphological structure grows via the assembly of tiny nanoparticles of size 50 nm. The effective substitution of Mo in Bi₂WO₆ extends the optical absorption towards the visible region. The substitution of Mo in place of W was confirmed by X-ray photoelectron spectroscopy. The photocatalytic activities were evaluated by OER under solar light irradiation. The sample Bi₂W_0.6Mo_0.4O₆ (S3) shows enhanced photocatalytic activity for OER from aqueous AgNO₃ solution (652 μmol h⁻¹ g⁻¹) which is higher than for pristine Bi₂MoO₆ or Bi₂WO₆ photocatalysts. Enhanced photocatalytic activity can be attributed to the extended absorption in the visible light region, which enhances the photocatalytic efficiency of the photocatalysts. More significantly, the 3D intrinsically layered nanosheet structure based morphology, and the unique band structure are beneficial for efficient charge transfer, which enhances the photocatalytic activity. This work demonstrates an effective strategy for developing an active photocatalyst with greater utilization of solar light.