Effect of the urea concentration on the luminescence and photocatalytic properties of Sr2CeO4 powders synthesized by a combustion method

Abstract

This work presents the effect of urea on the morphological, structural, luminescent and photocatalytic properties of Sr2CeO4 (SCO) phosphors synthesized by a combustion method. Five SCO samples were synthesized using urea concentrations from 0 to 1 mol%. The X-ray diffraction patterns revealed that all the SCO samples presented an orthorhombic phase, while the morphological studies by scanning electron microscopy (SEM) indicated that the SCO powders are formed by coalesced microparticles with irregular shape, which have sizes of 0.5–1.5 μm and are decorated by smaller nanoparticles with sizes in the range of 30−250 nm. The Photoluminescence measurements revealed that all samples presented a broad blue emission band centered at 460 nm, which is produced by the Ce4+-O−2 charge transfer transition and the emission band at 517 nm was produced by the excitation of oxygen vacancies. Moreover, the photocatalytic activity of the SCO phosphors was evaluated by monitoring the degradation of methylene blue (MB) dye under solar light and UV irradiation. We found that only the sample synthesized with 1 mol% of urea produced a complete degradation of MB after 210 min and 540 min when it is irradiated with solar and UV light, respectively. In fact, the degradation of MB was 61 % faster under solar light. Furthermore, experiments for the detection of reactive oxygen species were achieved by using as scavengers benzoquinone, isopropyl alcohol and potassium iodide. From here, we determined that O2- is the dominant oxidizing agent for the degradation of MB. Thus, the results presented here demonstrate that SCO phosphors are efficient to remove dye contaminants from water, which of environmental interest.