Substitution effect of Ta5+ by Nb5+ on photocatalytic, photophysical, and structural properties of BiTa1-xNbxO4(0 ≤ x ≤ 1.0)

Substitution effects of Ta5+ by Nb5+ in BiTa1-xNbxO4(0 less than or equal to x less than or equal to 1.0) on photocatalytic, photophysical, and structural properties were investigated. The powder x-ray diffraction and Rietveld structural refinement showed that the structure of BiTa1-xNbxO4 at R N-b/Bi = 0.0 and 0.5 is a triclinic system with space group P1. However, the structure at R = 0.2, 0.8, and 1.0 is an orthorhombic system with space group Pnna. Ultraviolet-visible diffuse reflectance spectroscopy measurement revealed that the band gap of orthorhombic samples is narrower than that of triclinic compounds. The H-2 evolution was obtained from an aqueous CH3OH/H2O solution and pure H2O with BiTa1-xNbxO4 under ultraviolet irradiation. The orthorhombic samples exhibit much higher activity than that of triclinic compounds. The orthorhombic compound at R = 0.2 showed the highest activity, which is higher than that of the well-known TiO2 photocatalyst.