Structural, photophysical and photocatalytic properties of Bi₂MTaO₇ (M = La and Y)

Bi₂MTaO₇ (M = Y and La) were synthesized by solid-state reaction method and their structural and photocatalytic properties were investigated. The results indicated that these compounds crystallize in the pyrochlore-type structure, cubic system with space group Fd-3 m. In addition, the band gaps of Bi₂LaTaO₇ and Bi₂YTaO₇ were estimated to be about 2.17(3) and 2.22(7) eV, respectively. For the photocatalytic water splitting reaction, H₂ or O₂ evolution was observed from pure water respectively with Bi₂MTaO₇ (M = Y and La) as the photocatalysts under ultraviolet light irradiation. Photocatalytic degradation of aqueous methylene blue (MB) dye over these compounds was further investigated under visible light irradiation. Bi₂MTaO₇ (M = Y and La) showed markedly higher catalytic activity compared to P-25 for MB photocatalytic degradation under visible light irradiation. Complete removal of aqueous MB was observed after visible light irradiation for 190 min with Bi₂LaTaO₇ as the photocatalyst and for 200 min with Bi₂YTaO₇ as the photocatalyst. The decrease of the total organic carbon (TOC) and the formation of inorganic products, SO ₄ ²⁻ and NO ₃ ⁻ , demonstrated the continuous mineralization of aqueous MB during the photocatalytic process.