Stability improvement of Fe3S4 for peroxymonosulfate activation by trace Mn doping

Iron sulfide has a great prospect in the field of peroxymonosulfate (PMS) activation due to its high catalytic activity. However, the weak stability of iron sulfide has become an important disadvantage limiting its application. In this study, trace amount of Mn was doped into Fe3S4 with the purpose of reducing metal leaching and improving catalytic efficiency. It was found that trace Mn doping could increase the Fe-S bond energy, thus the structure stability was enhanced and metal leaching was decreased. Moreover, a new (2 2 0) plane (3.49 Å) was observed on the surface of trace Mn doped Fe3S4 in addition to the conventional (3 1 1) plane. Molecular modelling indicated that the (2 2 0) crystal plane was more compact than the (3 1 1) crystal plane, which was believed to play an important role in decreasing the metal leaching. Furthermore, a reduction in oxidation potential and electrochemical impedance was also observed for the trace Mn doped Fe3S4, which promoted more efficient activation of PMS to produce higher amount of reactive oxygen species (ROS). Quenching tests and EPR analysis demonstrated both sulfate radicals and singlet oxygen were generated in the PMS activation process, in which the singlet oxygen was the dominant ROS for BPA degradation. This work provides a new idea for the design of stable and efficient iron sulfide catalytic materials.