Efficient Removal Of Bisphenol A From Water By Activated Peroxymonosulfate Using Manganese Sesquioxide Based Catalysts

With the rapid development of industrialization and urbanization,a large number of organic pollutants are discharged into water,which is difficult to degrade in the environment.Ultimately,it enters animals,plants,and humans through various environmental media,endangering human health.Developing a method for the effective removal of persistent organic pollutants from water is an important way to ensure the quality of drinking water sources.A variety of radicals(·OH、SO₄^·-、O₂^·-)and non-radicals（¹O₂）can be generated in situ by advanced oxidation process（AOPs）based on activated persulfate in water.Herein,a series of Mn₂O₃-based catalysts were prepared to explore their performance in activating PMS to degrade the organic pollutant（bisphenol A,BPA）in water.The specific research work is as follows.The complexing agents affect the surface hydroxyl concentration of Mn₂O₃ as well as the content of multivalent manganese ions.Herein,a simple and convenient method for the preparation of Mn₂O₃ was used to synthesize three catalytic materials（Mn₂O₃-S,Mn₂O₃-A and Mn₂O₃-U）by adding different complexes（sodium oxalate,ammonia and urea）.The Mn₂O₃/PMS system was investigated for its ability to remove refractory organic pollutants from water,using bisphenol A（BPA）as the target pollutant.The results show that Mn₂O₃-S had the best performance,effectively degrading 88.11%of BPA within 15 min,which was about 86%higher than that of PMS alone.In addition,the system can adapt to various water qualities.The concentration of surface hydroxyl groups plays an important role in the oxidation of PMS and the generation of reactive oxygen species.In the oxidation system,¹O₂is mainly produced.The more similar the contents of Mn⁴⁺and Mn²⁺in the Mn₂O₃ catalyst are,the more favorable the redox reaction and the oxygen conversion,thereby improving the performance of the system in activating the PMS.The presence of oxygen vacancies can facilitate the activation of PMS on the catalyst surface.Herein,Ni_xMn_2-xO₃ catalyst with oxygen vacancies was prepared by the co-precipitation method.The Ni_xMn_2-xO₃/PMS oxidation system showed excellent performance in the degradation of bisphenol A（BPA）,with 93.56%of BPA degraded in 8 min.The Ni_xMn_2-xO₃ structure has nickel-manganese double active sites,with the main active oxygen species being ¹O₂ and O₂^·-.The oxygen vacancy,as a defect site,accelerates the formation of the chemical bond between the catalyst and PMS,and promotes the migration of lattice oxygen.As the same time,oxygen vacancies and electrophilic oxygen species（O₂^-/O^-/·O）are formed,followed by conversion to ¹O₂.The ability of Ni doping to accelerate the electron transfer rate and promote the adsorption and decomposition of PMS at the active site was confirmed by DFT calculations of the catalyst d-band centres.The synergistic effect of Mn³⁺/Mn²⁺,Mn⁴⁺/Mn³⁺,and Ni³⁺/Ni²⁺redox pairs with reactive oxygen species together enhance the decomposition of PMS.Carbon nitride is a common narrow-band semiconductor with a unique structure that accelerates the transfer of electrons.Herein,CN-N_vac with porous nitrogen vacancies was first prepared by modification of carbon nitride,and x CN-N_vac/Mn₂O₃ composite catalyst was prepared by in-situ template method.In the degradation experiment with BPA as the target pollutant,a small amount of CN-N_vac（1%）showed a higher catalytic activity than Mn₂O₃alone,with 87.63%BPA removal in 8 min.The presence of anions and natural organic compounds in the water had little effect on the performance of the catalyst,making it a good environmental adaptor.The main reactive oxygen species in this oxidation system are ¹O₂、O₂^·-、·OH and SO₄^·-,and these reactive oxygen species were quantified and the main sources of ¹O₂ were identified.It was shown that the presence of nitrogen vacancies in CN-N_vacenhances the content of high-valent manganese as well as accelerates the electron transfer capacity of Mn⁴⁺/Mn³⁺/Mn²⁺,The synergistic interaction between the nitrogen vacancies and Mn₂O₃ together accelerates the activation of PMS.