Construction Of The Heterogeneous Catalytic PMS/H₂O₂ Systems And Modification Of Performances Based On Highly Active Free Radical

In this paper, the optimization strategy of surface structure and electronic transport of bimetallic oxide catalysts (MnFe₂O₄、ZnFe₂O₄ and Co_xMn_3-xO₄) was proposed to improve the generation rate of active free radicals for the degradation of refractory organic pollutants. The new types of carbon-based catalysts (MnFe₂O_4-rGO and ZnFe₂O₄-C₃N₄) were prepared, and MnFe₂O₄/PMS （peroxymonosulfate）, MnFe₂O_4-rGO/PMS, ZnFe₂O₄-C₃N₄/H₂O₂/vis, CoMn₂O₄/PMS systems were established for the catalytic test. Through a series of studies, the growth mechanism and the structure control approach of the as-prepared catalysts were revealed. Based on the experiments, the reaction mechanism of organic pollutants mineralization and the structure activity relationship of composition-structure-catalytic performance were further verified. The major contents are described as follows:（1） Graphene oxide （GO） prepared by the modified Hummers method was used as the presoma for the fabrication process of MnFe₂O_4-rGO, which synthesized by the in-situ method. Besides, the pure MnFe₂O₄ was prepared by the same method. The characterization results showed that MnFe₂O₄ NPs was supported on graphene sheets successfully. The catalytic performance test indicated both magnetic MnFe₂O₄ nanoparticle and MnFe₂O_4-rGO hybrid can activate PMS to generate SO₄^-· efficiently for various organic pollutants degradation in water. The degradation process can be described by the pseudo-first-order kinetics, and the activation energies （Ea） of the reaction on the catalyst surface of MnFe₂O_4-rGO and MnFe₂O₄ were determined as 25.7 and 31.7 kJ/mol, respectively, suggesting that graphene plays a significant role in the enhancement of PMS catalytic degradation of dyes. In addition, the efficiency of Orange II decomposition affected by different ion species, and increased with increasing Cl-strength and reaction temperature. Based on the above study, the catalytic reaction mechanism was verified. Meantime, the activity of magnetically recovered catalyst can remained almost unchanged in five cycles, suggesting it possessed high stability.（2） Magnetic ZnFe₂O₄-C₃N₄ hybrids were successfully synthesized through a simple reflux treatment of ZnFe₂O₄ prepared by solvothermal method with graphitic C₃N₄ sheets prepared by modified heat-etching method. The characterization results showed that ZnFe₂O₄ NPs was supported on g-C₃N₄ sheets successfully. The catalytic performance test indicated ZnFe₂O₄-C₃N₄/H₂O₂/vis system can effectively degrade the organic pollutants and the degradation process can be described by the pseudo-first-order kinetics. The ZnFe₂O₄-C₃N₄ hybrid （mass ratio of ZnFe₂O₄/g-C₃N₄= 2:3） exhibited the highest degradation rate of 0.012 min-1. g-C₃N₄ acted as not only a p-conjugated material for the heterojunction formation with ZnFe₂O₄, but also a catalyst for the decomposition of H₂O₂ to·OH radicals. Meantime, the magnetically recovered catalyst exhibited stable performance without losing activity after five successive runs.（3） A series of Co_xMn_3-xO₄ （x= 0.5,1.0 and 2） particles as Fenton-like solid catalysts were synthesized, and the characterization results showed that the CoMn₂O₄ sample were rule microspheres （ca.0.25-0.35 μm） aggregated by nanoparticles （ca.70～80 nm）. The catalytic performance test of Co_xMn_3-xO₄/PMS systems indicated CoMn₂O₄/PMS systems can effectively degrade the organic pollutants, and its catalytic activity is better than other catalyst with different proportion of Co and Mn, as well as the physical mixture of Co₃O₄ and Mn2O3. The efficiency of Rhodamine B decomposition increased with increasing temperature, but decreased with the increase of fulvic acid concentration. In addition, the catalyst showed strong stability in five cycles for Rhodamine B degradation. Moreover, ·OH and SO₄^-· radicals participating in the process were evidenced using quenchingexperiments, and a rational mechanism was proposed.