Visible-light-assisted Activation Of Peroxymonsulfate Via Magnetic Hybrid CuFe₂O₄@N-rGO For Synergistic Degradation Of Sulfamethoxazole

In recent years,sulfonamide antibiotics（SAs）and their residues have been detected in river sediments,groundwater and soil in many countries due to the abuse of SAs,resulting in the production of resistance genes and super bacteria,which seriously disrupt the ecological balance and brought potential threat to humans.Advanced oxidation technology（AOP）based on sulfate radicals has considered to be a promising scheme for removing toxic and refractory SAs in environment due to its strong oxidizing force,wide p H tolerance range and high selectivity.With the development of treatment technology,a new AOP based on visible light VL coupled with persulfate driven by solar energy has been proposed.However,the synergic catalytic and degradation effect on the coupling system is not clear enough.In addition,the easy deactivation and difficult recovery of catalysts,which play an important role in the system,are also a great challenge at present stage,thus the development of new stable,efficient and recyclable"dual-acting catalysts"has become a hot topic.CuFe₂O₄was widely applied in the field of advanced oxidation of persulfate and photocatalysis due to its unique advantages of environmental compatibility,high reactivity,visible light activity and easy separation.However,it was limited by easy agglomeration,low conductivity and potential risk of metal ion leaching.Based on this,a magnetic nanocomposite CuFe@NG was prepared by loading CuFe₂O₄on N-doped graphene oxide（N-r GO）with large specific surface area and excellent electrical conductivity,which was used to calalyze and degrade SMX by two different oxidation systems CuFe@NG/PMS and CuFe@NG/PMS/VL.Combining the degradation properties of the system with the physical and chemical properties of the CuFe@NG through a series of experimental and characterization tools to illustrate comprehensively and systematically the mechanism of the systems.The main conclusions s of this thesis are as follows.（1）GO,N-r GO,CuFe₂O₄,CuFe@GO and CuFe@NG five different catalysts were prepared and further characterized comprehensively in terms of morphology,physicochemical structure and electrochemical properties.The results showed that the support of the carrier made the CuFe₂O₄metal nanoparticles well dispersed and less agglomerated,resulting in the specific surface area and total pore volume increasing by more than two times.And the two components were tightly combined through the M-O-C site which provided a channel for charge transport.The doping of N atoms made CuFe@NG add N-O,C-N and nitrogenous aromatic functional groups,rich carbon backbone defects andπelectrons,further enhancing the surface electron cloud density and reducing the charge transfer resistance.The experiments on the catalytic degradation of SMX by activating PMS revealed that the degradation rate and mineralization efficiency of the CuFe@NG/PMS system reached 93.15%and 31.96%,respectively,within 60 minutes.And the first-order rare constant k value was1.68 times that of the CuFe₂O₄/PMS system.（2）The best catalytic performance was achieved when the mass ratio of the two components(m _CuFe:m _NG)in CuFe@NG was 4:1.The most suitable reaction conditions for CuFe@NG/PMS system were explored as follows:0.25 g·L^-1CuFe@NG,0.4 m M PMS,10mg·L^-1SMX and the initial p H of the solution=6.After five cyclic degradation experiments under this condition,the peak intensity of XRD and FTIR of CuFe@NG was slightly weakened,the leaching rate of Cuions was 0.25 mg·L^-1and Fe ions were not detected.The degradation of SMX in the actual surface water of tap water,river and lake was performed,the removal rate was higher than 85%.The addition of coexisting anions NO₃^–,HPO₄^2-and HA in water had a negative effect on the removal of SMX,while the presence of Cl^-and HCO₃^–could significantly promote the degradation of SMX.The surface-bound radicals(·OH,SO₄^·–)and singlet oxygen ¹O₂played a dominant role in the CuFe@NG/PMS system.The two components of the CuFe@NG efficiently and synergically activated PMS to generate abundant active groups and sites as well as excellent electron transfer ability,promoting jointly the degradation of SMX.The degradation pathways of SMX were mainly amine group oxidation,S-N bond breakage,N-C bond cleavage and hydroxylation of isoxazole rings.（3）The CuFe@NG/PMS/VL system was constructed by introducing visible light,degraded 94.12%of SMX and achieved 0.277 min^-1of the first-order rare constant in only 10minutes,which was 1.54 times and 2.86 times that of the CuFe@NG/PMS system.What’s more,up to 51.70%mineralization rate on SMX by the coupled system.According to the calculation of synergistic index,there was a three-synergistic system:I.VL induced the CuFe@NG to generate photogenerated e^--h⁺,increasing the type of active species.And Fe³⁺/Cu²⁺effectively captured light-induced e^-and accelerated the conversion to Fe²⁺/Cu⁺,while promoting the high-speed separation of photogenerated carriers.II.The reaction of photogenerated e^-with PMS accelerated its activation,and PMS acted as an electron acceptor to promote the separation of photogenerated e^--h⁺,enhancing the rate and concentration of active substances production.III.Fe³⁺/Cu²⁺reacted with PMS to form SO₄^·-and Fe²⁺/Cu⁺,PMS accelerated the redox cycle of metal ions and generates·OH.Compared with the CuFe@NG/PMS system,h^+,1O₂and·O₂^-became the main active species,and SMX was degraded by hydroxylation,S-N bond breaking and C-S bond breaking and was better detoxified in the CuFe@NG/PMS/VL system.After 5 cycles of degradation experiments,more than 91%of SMX could still be removed,and it also has a good removal effect（>93%）for other types of antibiotics,indicating that the coupling system was reusable and suitable for a wide range of pollutants and has excellent application potential.