Facile synthesis of sodium bismuthate dihydrate and its efficient visible-light photocatalytic activity

A novel, green approach for the synthesis of sodium bismuthate dihydrate (NaBiO₃·2H₂O) was reported for the first time by using sodium persulfate (Na₂S₂O₈) as an oxidant. Compared with traditional synthetic approach exhausting poisonous gas inevitably, the approach in this paper is easier, safer and more expedient. The as-fabricated samples were characterized by some techniques, such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Uv–vis diffuse reflectance spectrum (DRS). The effects of reaction conditions were also investigated and discussed in detail. Under the same conditions (oil bath time and temperature), low concentrations of alkali lead to formation of cubic Bi₂O₃ and higher concentrations resulted in formation of NaBiO₃·2H₂O. Well-crystallized monophase NaBiO₃·2H₂O was obtained at 90 °C, while a mixture of NaBiO₃·xH₂O and NaBiO₃·2H₂O was obtained at 50 °C with the base concentration of 10 mol L⁻¹. In comparison with the samples containing NaBiO₃·xH₂O, monophase NaBiO₃·2H₂O with well crystallinity shows superior photocatalytic performance for the degradation of Rhodamine B under visible-light irradiation.