Bismuth vanadate hollow spheres: Bubble template synthesis and enhanced photocatalytic properties for photodegradation

Hollow sphere monoclinic scheelite BiVO₄ (m-BiVO₄) is simply synthesized via a simple hydrothermal method by using urea as guiding surfactant. The forming process is investigated to be the incorporation of bubble guiding, oriented attachment and Ostwald ripening. The heterostructured hollow spheres are built up of truncated octahedrons which are also found to be feasible based on theoretical calculation. The preferred truncated octahedron consists of {040}, {011}, and {110} crystal planes with multiplicities of 2, 2, and 4, respectively. Besides urea, different kinds of organic additives (citric acid, Vitamin C and oleic acid) are also chosen for the synthesis of m-BiVO₄ to clarify the role of urea. The photocatalytic activities with different morphologies are evaluated on the degradation of Rhodamine B. It is found out that the m-BiVO₄ with hollow structure shows the optimalizing activity and the reaction rate constant reaches up to 0.035min^-1 without adding H₂O₂ as hydroxyl radicals provider. Except for activity, the as-prepared samples have high stability and durability, after four cycling runs of photodegradation of RhB, the photocatalytic ability of as-synthesized m-BiVO₄ did not show any loss. The degradation of RhB is attributed to intrinsically strong photo-oxidation ability rather than photosensitization and the synthesized samples also shows efficient photocatalytic activity for the degradation of 2-propanol. Meanwhile, the reasons for the superior activity are also carefully investigated.