Using a Novel Sr 2 CeO 4 :Ni Photocatalyst for the Degradation of the Recalcitrant Congo Red Dye Under Solar Irradiation

We report the structural, morphological and photocatalytic properties of the Sr 2 CeO 4 (SCO) and Ni-doped Sr 2 CeO 4 (SCO:Ni) powders synthesized by a combustion method. The SCO was doped with Ni dopant (from 0.5 to 5 mol%) and was employed for the degradation of the recalcitrant Congo red (CR) dye. SCO powders (undoped and Ni doped) had an orthorhombic phase and they showed an irregular morphology. SCO:Ni samples presented sizes of microns (2–3.36 µm), but smaller nanoparticles were found on their surface, which had sizes of 98–106 nm. On the other hand, photocatalytic experiments were achieved and found that the SCO powder doped with 1 mol% of Ni produced 100% of CR degradation after 210 min under solar irradiation. Total organic carbon measurements were carried out and obtained TOC values of 1.81, 0.21 and 1.31 mg/L for the SCO powders doped with 0, 1 and 5 mol% of Ni, respectively, after 210 min of photocatalytic reaction. Those values indicate that the SCO powder doped with 1 mol% of Ni had the highest production of mineral (inorganic) carbon. Moreover, the absorbance spectra showed that the absorption of light in the visible region is enhanced by ≈ 45% after increasing the Ni concentration from 0 to 1 mol% in the SCO powders, but decreases ≈ 21% after increasing the Ni concentration from 3 to 5 mol%. Furthermore, scavenger experiments were carried out and found that the hydroxyl radicals ( · OH) were the main oxidizing agents produced for the photocatalytic degradation of the CR, while the super oxide radicals ( · O 2 − ) and the holes (h + ) were the secondary oxidizing agents. Thus, the results of this investigation confirmed that the SCO:Ni photocatalysts could be good candidates for the photocatalytic removal of dyes under solar light, and could find application in water treatment plants located in open areas.