Regulation Of CuBi₂O₄ Surface Properties For Enhanced Peroxymonosulfate Activation To Degrade Typical Refractory Organic Pollutants

Sulfate radical(SO₄^·-)based advanced oxidation processes(SR-AOPs)are one of the most promising chemical oxidation methods to eliminate refractory organic pollutants due to the high redox potential,strong selectivity and long half-life of SO₄^·-.Among all methods of peroxymonosulfate(PMS)activation,heterogeneous metal oxide catalysts can be easily separated from water for reuse,greatly reduces the dissolved metal ions,and can work at wide range of pH(pH 2-9).However,there are lack of systematic and thorough research on the regulation of highly efficient and stable metal oxides,interfacial reaction mechanism of PMS activation and degradation mechanism of organic pollutants.Therefore,this paper focused on PMS activation with CuBi₂O₄for the construction of the relationship between the catalytic activity of CuBi₂O₄ with its size,morphology and surface properties induced by preparation methods and conditions,and the study of interface reaction mechanism of PMS activation and reactive oxygen species(ROS)generation,and the degradation mechanism of organic pollutants.Firstly,CuBi₂O₄ composites were prepared by a sol-gel method,the crystal phase composition,catalytic activity and copper ion leaching were regulated by the optimization of preparation conditions.Visible light was introduced for the construction of visible light-assisted CuBi₂O₄composites activated PMS water treatment technology to realize the efficient degradation of Rhodamine B(Rh B).99.8%of Rh B removal rate and 55.3%of mineralization rate were obtained.Under the irradiation of visible light,photo-generated e^-and h⁺on the catalyst surface could react with PMS to generate SO₄^·-and·OH.Photo-generated e^-with strong reducibility could also facilitate the cycling of Cu(I)/Cu(II),thereby accelerating the decomposition of PMS to generate SO₄^·-and·OH.The apparent formation rate of SO₄^·-and·OH was calculated by radical chemical reaction kinetics for the first time,that is(2.38-2.78)×10^-2 min^-1 and(9.44-9.96)×10^-3 min^-1,respectively.Secondly,the nucleation and growth of CuBi₂O₄ was controlled by the hydrothermal method to realize the directed regulation of size,morphology and surface properties of CuBi₂O₄,thereby improving the performance of PMS activation.It was found that CuBi₂O₄ microsphere with higher density of surface hydroxyl groups and smaller diameter showed better PMS activation performance for organic pollutants degradation.After 60 min of reaction,more than 90%of Rh B and micropollutants(bisphenol A,benzotriazole and carbamazepine)was degraded.The surface hydroxyl groups provided sites for the complexation with PMS.During the reaction the cycling of Cu(I)/Cu(II)on CuBi₂O₄ surface promoted the activation of PMS to generate SO₄^·-and·OH,which contributed to Rh B degradation through N-deethylation,the cleavage of conjugate xanthene ring structure and ring opening pathway.Thirdly,the microwave-assisted method with subsequent calcination treatment was used to well-distributed CuBi₂O₄ microspheres,which effectively solved the problem of uneven morphology and size of CuBi₂O₄ and the high copper ions leaching.The effective degradation of Rh B and micropollutants(benzophenone-4(BP-4),benzophenone-3,sulfamethoxazole and acyclovir were realized.The PMS activation performance of well-distributed CuBi₂O₄ microspheres is 2.2-6.2 times of that of hierarchical CuBi₂O₄ microspheres prepared by the hydrothermal method.The uniform exposure of active sites on the surface of CuBi₂O₄ microspheres promoted the contact between PMS and Cu(I)-OH,accelerated the cycling of Cu(I)/Cu(II)for PMS activation to generate SO₄^·-,·OH and ¹O₂.SO₄^·-and·OH are dominant ROS,which attacking BP-4 by radical addition reaction and resulted to BP-4 degradation through hydroxylation,demethylation,C-C bond cleavage and Baeyer-Villiger rearrangement pathway.The combination of high resolution mass spectrometry and theoretical chemical calculation broken through previous reports that reaction between SO₄^·-and electron-rich aromatic organics is mainly via single electron transfer.The presence of Cl^-resulted in the generation of chlorinated degradation products,but degradation products did not show high toxicity.In summary,the size,morphology and surface properties of CuBi₂O₄ were controlled by optimizing the preparation method and conditions,thereby improving its PMS activation performance.The reaction mechanism of CuBi₂O₄ activating PMS and the degradation mechanism of target organic pollutants were studied in depth.Above provide a theoretical basis for the directed regulation of metal oxide with high performance,enriches the basic principles of SR-AOPs,and provides theoretical support for the practical application of SR-AOPs.