Photocatalytic degradation of tetracycline by a Fe-doped BiMnO3 catalyst with honeycomb-like microstructure

Abstract

Photocatalysis is an effective way to degrade organic pollutants. The development of catalysts with excellent activity is the basis for the practical application of photocatalysis. The activity of a catalyst is closely related to its special microstructure. Therefore, it is very important to study the effect of special microstructure on the activity of a catalyst. In this work, Fe-doped BiMnO3-based catalysts (BiMn1−xFexO3, x = 0, 0.15, 0.20, and 0.25) were synthesized by a hydrothermal method when the pH of the reaction solution was 11. The as-prepared catalysts were denoted as BMO, BMFO(015), BMFO(020), and BMFO(025), respectively. These BMFO catalysts were investigated with different characterization techniques. The photocatalytic activities of the BMFO catalysts were evaluated by degrading tetracycline (TC). Compared with the undoped BMO, the enhanced photocatalytic performance of Fe-doped BMO catalysts may be ascribed to the following factors. Doping Fe decreased the particle size of BMO and both increased the specific surface area and pore volume. Doping Fe also reduced the bandgap of BMO and improved its absorption capability in the visible region. Furthermore, Fe3+ and Fe2+ ions were introduced into the BMO lattice by doping Fe. Along with the cyclic transformation between Mn4+ and Mn3+, the cyclic transformation between Fe3+ and Fe2+ further captured photogenerated electrons (e-) to prevent carrier recombination and boost the generation of ▪O2- radicals. In particular, BMFO(020) acquired a honeycomb-like microstructure in the hydrothermal reaction. To explore the origin of forming different microstructures in BMFO(020), the other two catalysts BMFO(020)-pH= 9 and BMFO(020)-pH= 13 with different micromorphologies were prepared by adjusting the pH of the reaction solution to 9 and 13, respectively. It was found that the honeycomb-like microstructure was the most favorable to enhanced the photocatalytic performance of the BMFO(020) catalyst due to it improved light utilization, provided abundant channels for transferring and absorbing TC molecules, and decreased the recombination of carriers. Therefore, the degradation efficiency of TC solution (10 mg/L, 100 mL) reached 98.47% with 50 mg BMFO(020) after 60-min visible light irradiation. In the cyclic degradation experiment, BMFO(020) exhibited excellent stability performance, and the degradation efficiency of the TC solution was still higher than 89.55% even after 5 times recycling. Results of the trapping experiment demonstrated ▪O2- and h﹢were the main active substances. A possible mechanism for the enhancement of photocatalytic degradation to TC by the BMFO catalysts was proposed. This work highlights that doping with an adequate amount of Fe and adjusting pH of the reaction solution to form a specific microstructure is a new strategy to enhance the photocatalytic performance of BMO in degrading TC.