Efficient activation of peroxymonosulfate by amorphous MnO2/α-Fe2O3 for the degradation of organic pollutants

Constructing bimetallic nanostructures with specific crystalline phases provides an attractive strategy to develop highly efficient catalysts and explore structure-dependent catalytic properties. Herein, a new iron-based bimetallic catalyst consisting of amorphous MnO2 and crystalline α-Fe2O3 was synthesized for peroxymonosulfate (PMS) activation, named as a-MnO2/α-Fe2O3. The results show that the removal efficiency of sulfamethoxazole is over 90% within 120 min by the a-MnO2/α-Fe2O3 in the presence of PMS at broad pH conditions ranging from 3 to 9. Furthermore, a complete degradation of bisphenol A (BPA) is achieved within 2 min in the a-MnO2/α-Fe2O3/PMS system under optimum conditions, and the BPA degradation rate constant of 1.67 min−1 outperforms most reported Fe- and Mn- based catalysts. The results of electron paramagnetic resonance analysis, quenching tests and Raman spectroscopy analysis show that the mechanism for the a-MnO2/α-Fe2O3-based PMS activation is dominated by the formation of activated surface-PMS complexes. ≡Mn(Ⅳ)–OH and ≡Fe(III)–OH of a-MnO2/α-Fe2O3 are active sites for PMS adsorption to form inner-sphere complexes (≡Mn(Ⅳ)-OOSO3-) through the replacement of surface hydroxyl groups. Finally, the a-MnO2/α-Fe2O3 exhibits a remarkable removal efficiency of over 99% for BPA in column-bed tests conducted over 600 cycles, demonstrating its immense potential for practical applications.