Enhanced Activation Of Persulfate By Spinel Composites Under Simulated Sunlight For Degradation Of Antibiotic In Water

In recent years,with the rapid expansion of heavy industry and fast growth of population as well as the increased water pollution,the water resources situation is deteriorating worldwide.The total wastewater volume all over the world increased from1500 km³ in 1995 to²212 km³ in 2010.In these wastewater,antibiotic wastewater accounted for a large proportion.Due to the irreplaceability of antibiotics in the treatment of diseases,they are increasingly used in many fields,but they cannot be completely metabolized by organisms and cannot be effectively removed from municipal wastewater treatment using conventional techniques.Persulfate based advanced oxidation processes?AOPs?have become a research hotspot due to the strong oxidizing capacity,long life and good water solubility of the sulfate radical?SO₄?^-?produced during this process.Among them,heterogeneous catalysis can effectively improve the activation capacity of persulfate due to its low cost and high catalytic activity.In addition,the northwest region has sufficient sunshine,which provides innate conditions for the large-scale application of photocatalytic technology.If these two technologies can be combined,the degradation of antibiotics will be improved.Based on these,CuFe₂O₄/Bi₂O₃,Bi₂O₃/CuNiFe LDHs,Co₃O₄/?-FeOOH and CuCo₂O₄/ZnO spinel and spinel precursor composite were designed and synthesized in this thesis to activate persulfate for antibiotics degradation in water.The specific work of this thesis is as follows:In order to improve the catalytic performance of the catalyst,CuFe₂O₄/Bi₂O₃ was synthesized by sol-gel-calcination method.The surface morphology and microstructure of CuFe₂O₄/Bi₂O₃ were characterized,and the catalytic performance of it was evaluated by activating peroxydisulfate?PDS?to degrade lomefloxacin?LOM?.The results showed that CuFe₂O₄/Bi₂O₃ had superior catalytic performance for PDS activation compared with CuFe₂O₄.When both the catalyst dosage and PDS concentration were1.0 g?L^-1,CuFe₂O₄/Bi₂O₃ could degrade 77.19%LOM within 20 min at natural pH?6.08?and room temperature.In addition,radical scavenging experiment show that SO₄?^-and hydroxyl radicals?HO??are the main active species in the reaction system.In order to further improve the catalytic effect of the catalyst,we synthesized Bi₂O₃/CuNiFe LDHs spinel precursor composite with a composition similar to that of CuFe₂O₄/Bi₂O₃ spinel composite,and apply it to activate persulfate for LOM degradation under simulated sunlight.Characterization and degradation experiment results show that combining Bi₂O₃ with CuNiFe LDHs is a good choice for PDS activation iunder simulated sunlight,in which 84.6%of LOM(10 mg?L^-1)was degraded over 40 min with 0.4 g?L^-1 of Bi₂O₃/CuNiFe LDHs composite and 0.2 g?L^-1of PDS at natural pH.Moreover,active radical scavenging experiments indicated that hydroxyl radicals?HO??,sulfate radicals?SO₄?^-?,superoxide radicals?O₂?^-?and hole?h⁺?were the main active species under LOM degradation process.The cycle test showed that both CuFe₂O₄/Bi₂O₃ and Bi₂O₃/CuNiFe LDHs composites have good reusability and stability in four cycles.In addition,the degradation mechanism and pathway for LOM degradation in CuFe₂O₄/Bi₂O₃/PDS and Bi₂O₃/CuNiFe LDHs/PDS/simulated sunlight systems were proposed based on experimental analysis and density functional theory?DFT?calculation.At the same time,the toxicities of LOM and its degradation intermediates were evaluated by quantitative structure–activity relationship?QSAR?analysis.In order to improve the PMS catalytic activity and stability of cobalt species,Co₃O₄/?-FeOOH spinel composite catalyst was synthesized to activate PMS for LOM degradation.Compared with pure Co₃O₄ and?-FeOOH,Co₃O₄/?-FeOOH composite exhibited the best efficiency towards LOM degradation,in which the removal of LOM?>82%?was achieved after 25?min reaction with 0.25?g?L^-1 Co₃O₄/?-FeOOH,0.3?g?L^-1PMS,and 10?mg?L^-1 LOM at initial pH 6.08.Moreover,the highest degradation efficiency of LOM was achieved under neutral conditions,which was due to the minimum repulsive force between the PMS and the catalyst.In addition,active radical scavenging experiment was performed and it was found that the contribution of hydroxyl radicals was greater than that of sulfate radicals.Based on the excellent catalytic performance of CuFe₂O₄/Bi₂O₃,Bi₂O₃/CuNiFe LDHs,and Co₃O₄/?-FeOOH,we speculate that cobalt-copper spinel?CuCo₂O₄?as a spinel with cobalt at its B-sites has strong PMS activation performance.Besides,the mutual effect between the carrier and active component could improve the dispersion and adhesion of transition metals,thereby enhancing the activity and stability of the active components.On this basis,a new spinel composite material of CuCo₂O₄/ZnO was prepared and applied as a catalyst for PMS activation to decompose enrofloxacin?ENR?under simulated sunlight.Compared to sole ZnO and CuCo₂O₄,the CuCo₂O₄/ZnO composite could significantly activate PMS under simulated sunlight,resulting in the generation of more active radicals for ENR degradation.89.2%of ENR could be decomposed over 10 min with0.2 g?L^-1 catalyst and 0.2 g?L^-1 PMS at natural pH.Furthermore,the influences of the experimental factors,including the catalyst dosage,PMS concentration,and initial pH,towards ENR degradation were systematically evaluated.Subsequent active radicals trapping experiments indicated that the sulfate,superoxide and hydroxyl radicals together with holes?h⁺?were involved in the degradation of ENR.It is worth noting that the CuCo₂O₄/ZnO composite exhibited good recyclability and durability during the recycling experiments.Based on the UPLC-MS/MS results and DFT theoretical calculations,the degradation pathways of pollutants in Co₃O₄/?-FeOOH/PMS and CuCo₂O₄/ZnO/PMS/simulated sunlight systems were proposed.The biological toxicity of pollutants and degradation intermediates was evaluated by QSAR analysis.In order to evaluate the feasibility of the synthesized spinel and its precursor composites in actual environmental treatment,the catalytic activity of sunlight-assisted spinel composites to activate PMS for medical wastewater degradation was investigated.The results showed that the synthesized spinel composites had a better performance for medical wastewater degradation by activating PMS under the assistance of simulated sunlight,in 60.2%of COD can be removed over 4 h with 1.0 g?L^-1 catalyst and 3.0 g?L^-1 PMS.