Enhanced photocatalytic degradation of oxytetracycline using LaFeO₃ supported on Mullite ceramic foam

Photocatalysis is an accepted technique for persistent pollutant remediation. Compared to conventional photocatalytic systems based on a powdered catalyst, the immobilization of the catalyst on a solid support is essential for practical environmental applications. LaFeO₃ is a stable p-type oxide semiconductor with a medium bandgap of 2.48 eV. Undoped-LaFeO₃, like many ABO₃ perovskite-type oxides, presents an extensive recombination rate for photogenerated electron–hole pairs, but it is stable in acidic solutions (pH>3) and non-toxic.

Thus, we applied a thin active layer of catalyst on the surface of sintered mullite-based ceramic foam. The photocatalyst powder covering the outer surfaces was placed layer by layer through adding the alcohol slurry of LaFeO₃ powder dropwise and then thermal treatment in air at moderate temperature. With this procedure, the catalyst particles remain nanometric. Parallel tests for the photocatalytic degradation of oxytetracycline (OTC) c₀ = 5.0∙10^-6 M under visible-light irradiation in three different configurations were carried out: H₂O₂ c₀ = 3.0∙10^-3 M solution, H₂O₂ + LaFeO₃ supported on the mullite foam, and H₂O₂ + mullite foam without catalyst. In this study, the OTC solution was buffered at pH = 5.0, so OTC had a zwitterionic form. The OTC solutions were stirred in the dark for 20 minutes, and then two fluorescent lamps (daylight, 8 W each) emitting in the 380-780 nm region were turned on for 240 min.

H₂O₂ + mullite foam and H₂O₂ + LaFeO₃ supported on the mullite foam degraded 34% and 50% of OTC, respectively, after 240 min of irradiation. The small addition of H₂O₂ increases the photodegradation rate of organic pollutants by removing the surface-trapped electrons, thereby lowering the electron–hole recombination rate. The final results show that mullite foam with a thin layer of LaFeO₃ has a promising and stable photocatalytic activity for oxytetracycline degradation under visible light.