Mechanistic Study On The Weak Magnetic Field Enhanced Activation Of Molecular Oxygen By CuFe₂O₄

As one of the advanced oxidation technology for water treatment,Fenton-like oxidation technology usually uses transition metals such as iron,copper and their oxides as catalytic materials.However,the application of these catalysts is always limited by low reactivity,high leaching,and narrow p H range.Consequently,the development of high-efficiency catalysts has become a hotspot in the present.Copper ferrite（CuFe₂O₄）,a catalyst with magnetic recovery performance,is able to activate molecular oxygen in situ to oxidize organic pollutants at the presenc of hydroxylamine（HA）.In this study the weak magnetic field was introduced into the CuFe₂O₄/HA system and its effect on the activation of molecular oxygen was evaluated.It was observed that the 4-CP removal was significantly enhanced while with a lower metal leaching.The main work of this study included:（i）the systematic investigation of several key parameters,（ii）the exploration in mechanism of magnetic enchanced activation of molecular oxygen,（iii）the application of CuFe₂O₄/HA system assisted by magnetic field to treating simulated 4-CP wastewater in continuous flow.The details are as follows:（1）It was observed that the magnetic field could effectively increase the removal efficiency of 4-CP in the CuFe₂O₄/HA system and inhibited the copper leaching under most of investigated conditions.In this system,HA maintained the cycles of copper and iron on CuFe₂O₄ surface and promoted the activation of molecular oxygen at Cu（Ⅰ）sites.In the meantime,the magnetic field strengthened the reduction of surface Cu（Ⅱ）by Fe（Ⅱ）,and promoted the enrichment of paramagnetic O₂ on the CuFe₂O₄ surface,accelerating the formation of adsorbed oxygen with higher reacitvity.The magnetic field did not change the free radical generation path of the system,but accelerated the conversion efficiency of O₂to·O₂^-and·O₂^-to·OH,thereby improving the efficiency of catalytic degradation.（2）The influence of Fe/Cu ratio,calcination temperature/atmosphere and pre-magnetization on the properties of CuFe₂O₄,such as crystal structure,magnetism and reactivity,was investigated.The results showed that the crystal structure,particle size and surface active sites did have significant effects on the catalytic activity of CuFe₂O₄.The copper ferrite containing more Cu（Ⅰ）or forming Cu⁰ and CuFeO₂ phases showed better catalytic activity.The impurity phase woud affect the saturation magnetization of CuFe₂O₄,and CuFe₂O₄ with lower saturation magnetization performed poorly under the weak magnetic field.The pre-magnetized CuFe₂O₄ also exhibited a magnetic synergistic effect.（3）The four common anions showed similar effects on the CuFe₂O₄/HA system regardless of magnetic field.Cl^-,SO₄^2-,NO₃^-and low concentration HCO₃^-promoted the degradation efficiency of 4-CP,and the system with weak magnetic field exhibited higher 4-CP degradation efficiency with lower copper dissolution tendency.A long-term continuous flow treatment study of 4-CP wastewater with simulated surface water background found that the magnetic field promoted CuFe₂O₄ activating molecular oxygen,increased HA utilization rate,and significantly inhibited copper dissolution.It indicated that the CuFe₂O₄ catalytic system assisted by magnetic field should be of good prospects in the application to water treatment.