Main Issues in the Synthesis and Testing of Thermocatalytic Ce-Doped SrFeO3 Perovskites for Wastewater Pollutant Removal

Abstract

The effect of the synthesis and processing parameters on the thermocatalytic performance of Ce-doped SrFeO3 inorganic perovskites was investigated to improve the reproducibility and reliability of the synthetic methodology and of the testing procedure. A structural, surface and redox characterization was performed to check the extent of variability in the chemical–physical properties of the prepared materials, revealing that a strict control of the synthesis parameters is indeed crucial to optimize the thermocatalytic properties of Ce-doped SrFeO3 inorganic perovskites. The thermocatalytic tests, aimed to degrade organic pollutants in water, were performed using Orange II and Bisphenol A as target compounds, in view of a later technological application. The main issues in the synthesis and testing of Ce-doped SrFeO3 perovskite thermocatalysts are highlighted and described, giving specific instructions for the resolution of each of them. A limited number of prepared materials showed an efficient thermocatalytic effect, indicating that a full gelification of the sol, an overstoichiometric reducer-to-oxidizer ratio, a nominal cerium content of 15 mol%, slightly higher than its solubility limit (i.e., 14 mol%), a pH of 6 and a thermal treatment at 800 °C/2 h are the best synthesis conditions to obtain an effective Ce-doped SrFeO3 perovskite. Regarding the testing conditions, the best procedure is to follow the degradation reaction without any preconditioning with the pollutant at room temperature. The severe leaching of the active perovskite phase during tests conducted at acidic pH is discussed. Briefly, we suggest confining the application of these materials to a limited pH range. Variability between thermocatalysts prepared in two different laboratories was also checked. The issues discussed and the proposed solutions overcome some of the obstacles to achieving a successful scale up of the synthesis process. Our results were favorable in comparison to those in the literature, and our approach can be successfully extended to other perovskite catalysts.