Distinct phase formation of BiREWO₆ (RE = La–Yb) nanoparticles by a one step hydrothermal synthesis and their photocatalytic applications

Under identical hydrothermal condition, remarkably, Aurivillius BiREWO6 nanoparticles crystallize in an orthorhombic phase for RE = Ce and La, while the RE = Nd–Yb materials crystallize in the monoclinic phase. This kind of distinct phase formation in this series is not observed in solid state synthesis, where for all RE substitution, only the monoclinic phase is formed. Moreover, formation of the orthorhombic phase for BiLaWO6 and BiCeWO6 has been observed for the first time. Calcination of as-synthesized BiLaWO6 and BiCeWO6 nanomaterials results in the monoclinic phase and this indicates that the formation of the orthorhombic phase is favored only under mild reaction conditions. This could be attributed to the crucial role of the ionic radii of RE3+ and Bi3+ ions in solution. Rietveld refinement confirms the BiCeWO6 and BiGdWO6 are isostrutural to the Low Temperature (LT) orthorhombic phase and monclinic High Temperature (HT) phase of Bi2WO6, respectively. Additionally phase dependent distinct morphology and photocatalytic activity is observed. As a representative example, it is observed that needle/plate-shaped monoclinic BiGdWO6 nanoparticles show superior visible light driven photocatalytic activity for the Congo-red dye degradation over the spherically agglomerated orthorhombic BiCeWO6 nanomaterial