Preparation and Characterization of Sr/TiO2 Catalysts with Different Structures and High Photocatalytic Activity under Visible Light

Sr/TiO2 catalysts with different Sr/Ti molar ratios (n(Sr)/n(Ti)) were synthesized by fractional precipitation. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectrometry, and ultraviolet-visible diffuse reflectance spectrophotometry (UV-Vis RDS). The photocatalytic activity of the samples under visible light was determined using the photocatalytic degradation of methylene blue. The photocatalytic activities and structures of the catalysts changed with n(Sr)/n(Ti) molar ratio. When n(Sr)/n(Ti)<= 3/2, the catalysts, which were composed of TiO2 and SrTiO3, showed a globular structure. When n(Sr)/n(Ti) was between 3/2 and 4/1, the catalysts had a flaky structure. As the n(Sr)/n(Ti) increased, the composition of the catalysts changed from SrTiO3 and Sr2TiO4 to Sr2TiO4 and Sr(OH)(2)center dot H2O. When the n(Sr)/n(Ti) ratio was 9/1, the catalyst mainly consisted of Sr(OH)(2)center dot H2O and exhibited an acicular structure. The sample with n(Sr)/n(Ti)=4/1 exhibited the highest photocatalytic activity; its first-order reaction rate constant was 5.0 times as high as that of the perovskite catalyst SrTiO3 and 86.7 times as high as that of the commercial Ti photocatalyst P25.