Pollutant degradation by Fenton-like system with Prussian blue analogs (PBAs) on cotton and modified oyster shell: Via re-Fenton reaction

Advanced oxidation processes extensively use Prussian blue analogs (PBAs) catalysts. However, metal-ion leaching limits their application in Fenton-like systems, causing environmental pollution and a decline in long-term performance. This study prepared a cubic iron–manganese bimetallic PBA catalyst by co-precipitation–calcination method. In the suspended flow experiment, under the optimal conditions, methylene blue (MB) was degraded by over 99.92 % within 90 min. The synergistic effect of iron–manganese bimetallic components and the degradation pathway of MB was proposed based on density functional theory (DFT) analysis and LC-MS results. In the recycling experiment, metal-ion leaching and catalyst structure damage significantly reduced the catalyst activity. To overcome the metal-leaching problem of PBA materials, a continuous-flow Fenton-like system was constructed. Cotton balls loaded with the iron–manganese bimetallic catalyst were connected to a calcined oyster shell fixed-bed reactor. In the 60 h continuous-inflow experiment, the average MB degradation rate of the effluent reached 95.81 %, which was 25.42 % higher than that of the single catalyst continuous-flow system. Experiments and characterization verified the mechanism of improving the reaction effect by using modified oyster shell. This shell can effectively adsorb the iron and manganese metal ions leached during the reaction, and these adsorbed metal ions further promoted the peroxymonosulfate (PMS) oxidation of MB through heterogeneous Fenton reaction, which was called re-Fenton reaction. This study provided a new strategy for the practical application of PBA catalysts in advanced oxidation processes.