Novel 3DOM CeO₂ Supported LaFeO₃ as an Effective Heterogeneous Fenton Catalyst for Degradation of Methylene Blue

Abstract

A three-dimensional ordered macroporous cerium dioxide (3DOM CeO2) was synthesized using a template method combining the sol-gel method, and LaFeO3 was synthesized and immobilized on 3DOM CeO2 via the sol-gel method combining the impregnation method. The thermogravimetric (TG), scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to characterize the samples. The catalytic performance and reaction mechanism of the catalyst were studied with methylene blue (MB) as the model pollutant. The MB catalytic behavior showed that the addition of 3DOM CeO2 increased the specific surface area of the pristine perovskite. At the same time, there was a synergistic effect between ceria support and perovskite, which significantly improved the activity and stability of the pristine perovskite catalyst. LaFeO3/3DOM CeO2 had a wider pH range and higher H2O2 utilization rate than homogeneous Fenton catalyst. At the same time, in the test range, the leaching concentration of Fe in LaFeO3/3DOM CeO2 was less than 0.2 mg·L−1, which is conducive to reducing the production of iron sludge and greatly controlling the secondary pollution. Furthermore, the LaFeO3/3DOM CeO2 catalyst also possessed superior stability of activity and structure in 10 cycles. The results of quenching tests and electron spin resonance (ESR) analyses showed that the catalytic degradation of MB was mainly completed under the action of high-activity •OH. The redox cycle between Ce4+ and Ce3+ is conducive to improving the efficiency of electron transfer, thereby increasing the production efficiency of •OH in the heterogeneous Fenton process. Catalytic degradation of MB approximately conformed to first-order kinetics. The aforementioned results indicate that the novel LaFeO3/3DOM CeO2 has great application potential in the field of heterogeneous Fenton treatment of organic pollutants. A novel ceria-perovskite composite LaFeO3/3DOM CeO2 was successfully prepared in this experiment, and the catalytic performance and reaction mechanism of the catalyst were studied with methylene blue (MB) as the model pollutant. The LaFeO3/3DOM CeO2 has higher catalytic activity and stability than LaFeO3 prepared by the sol-gel method, and it has higher pH adaptation range and hydrogen peroxide utilization than FeSO4·7H2O. At the same time, in the test range, the Fe leaching concentration in LaFeO3/3DOM CeO2 is lower than 0.2 mg·L−1, which significantly reduces the generation of metal sludge and greatly controls the secondary pollution. Furthermore, the LaFeO3/3DOM CeO2 catalyst also possessed superior stability of activity and structure in 10 cycles. During the reaction, there were Fe3+⇋Fe2+ and Ce4+⇋Ce3+ cycles on the surface of LaFeO3/3DOM CeO2 during the reaction process. The two cyclic reactions synergistically initiated the efficient Fenton reaction, resulting in a large number of highly active •OH, thereby realizing the efficient degradation of MB. In summary, LaFeO3/3DOM CeO2 can be used as an excellent heterogeneous Fenton catalyst for the treatment of organic pollutants.