Effects of La doping on structural, optical, electronic properties of Sr2Bi2O5 photocatalyst

Single-phase Sr2Bi2O5 was obtained by calcination of the heterobimetallic complex precursor Sr [Bi(DTPA)]center dot 9H(2)O (DTPA is diethylenetriaminepentaacetic acid) at 700 degrees C for 6 h. The effect of La doping on the crystal structure, surface area, morphology, surface chemical state, and absorption properties of Sr2Bi2O5 samples prepared from Sr[Bi(DTPA)]center dot 9H(2)O were investigated. No traces of an impurity phase were detected in samples with a lower La content (3 and 5 mol%), while impurity phases such as Sr2Bi2O5 and SrCO3 were observed in Sr2Bi2O5 samples with larger La contents of 8 and 10 mol%. The Brunauer-Emmett-Teller surface area of Sr2Bi2O5 increased slightly with the content of La. High-resolution transmission electron microscopy revealed clear crystalline planes for both undoped and La-doped Sr2Bi2O5 samples without amorphous phases. Meanwhile, X-ray photoelectron spectroscopy indicated that the valence states of constituent metals were Sr2+, Bi3+, and La3+. The solubility limit of La in the Sr2Bi2O5 crystal phase was determined from Raman scattering measurements. La atoms substituted Bi sites when the doping content was low, while both Bi and Sr sites were substituted with La when the content of La was high. The electronic structure of Sr2Bi2O5 could be modified by La doping, resulting in a red shift of the absorption edge with increasing La content. The band-gap narrowing of Sr2Bi2O5 with La-doping was reproduced in energy-band calculations. The photocatalytic activity of Sr2Bi2O5 under visible-light irradiation for the oxidation of isopropanol was enhanced by doping with La. (C) 2015 Elsevier B.V. All rights reserved.