New insight for enhanced photocatalytic activity of Bi4-xLaxTi3O12 (0 ≤ x ≤ 1) solid solution: A case study on degradation of Rhodamine B under UV light irradiation

In this study, we actively investigate the structural, microstructural, vibrational and photocatalytic properties of the system Bi4-xLaxTi3O12 with x ranging between 0 and 1 (BLTx). La-doped bismuth titanate Bi4-xLaxTi3O12 powders were synthesized with conventional solid-state reaction route at 850 degrees C. The synthesized compounds were subjected to various characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman spectroscopy, diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM) coupled with energy dispersive X-rays spectroscopy (EDXS). The structural properties were determined at room temperature by X-ray diffraction using the Rietveld refinements. Scanning electron microscopy experiments showed a homogeneous evolution of the crystallite morphologies and sizes with increasing x. The vibrational modes of the Raman spectra revealed the appearance of the characteristic bands of La atom in Bi4Ti3O12, confirming the La substitution in this system. Optical measurements by DRS show a variation in the gap energy between 3.23 and 3.00 eV as a function of substitution by La. The prepared Bi4-xLaxTi3O12 (0 <= x <= 1), exhibited high photocatalytic performance when exposed to UV light in an aqueous solution containing Rhodamine B (RhB) dye. This improved photocatalytic activity can be ascribed to the particle size of the photocatalyst and/or the efficient separation of electron-hole pairs. The highest efficiency for RhB degradation is achieved by the substituted phase of composition x = 0.75 with a maximum degradation rate of 99%. The main reactive oxidative species photogenerated during the photocatalytic assays for the x = 0.75 are attributed to the superoxide radical (O-2(center dot-)). Based on the scavengers test likely degradation mechanism has been proposed.