Solar light sensitive samarium-doped ceria photocatalysts: microwave synthesis, characterization and photodegradation of Acid Orange 7 at atmospheric conditions and in the absence of any oxidizing agents

Abstract

Novel, high surface area, mesoporous and crystalline samarium-doped ceria (CeO₂:Sm³⁺) nanopowders were successfully synthesized by combining the excellent properties of both microwave heating and surfactants and were used as remarkably efficient new photocatalysts for the degradation of a representative azo dye, Acid Orange 7 (AO7), in an aqueous medium under natural sunlight without the addition of any external reagents like peroxide, acid or base. The synthesized nanopowders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and UV-vis diffuse reflectance spectroscopy. The effects of calcination temperature, pH of the medium, catalyst dosage and irradiation time on the decolorization of AO7 were investigated and are discussed in this paper. Sm³⁺ doping in CeO₂ narrowed the band gap and significantly enhanced the photocatalytic degradation of the azo dye. The photocatalytic degradation of AO7 was also investigated by using certain radical scavengers and the results suggest that under solar light irradiation predominantly positive holes and superoxide radicals (O₂˙⁻) act as the active species in the degradation process. Our results suggest that the materials developed here are a promising alternative solar light sensitive photocatalyst.