Degradation Of Methylene Blue And Aniline In Water By Peroxymonosulfate Activated With Cobalt-Nickel Bimetallic Oxides

Methylene blue and aniline are organic compounds with toxicity and difficult to biodegrade,which have been widely used in dye industry,medicine and so on.In the process of production and application,once they are discharged into the environment,it not only pollutes the water environment,but also threatens aquatic organisms and human health.Today,environmental protection becomes a cardinal question with the increasingly scarce water resources.Thus,it is imperative to seek an efficient and environmentally friendly treatment method for organic pollutants.Activated persulfate technology,as one of advanced oxidation processes（AOPs）,has been widely used for the removal of refractory organic pollutants owing to its advantages of high efficiency and wide applicability.Peroxymonosulfate（PMS）has a high redox potential,but it is slowly decomposed at room temperature and atmospheric pressure,resuting in the low degradation efficiency of organic pollutants in water.Therefore,more and more people have paid attention to how to activate PMS efficiently.Among thses methods,transition metal oxides are used as catalysts for the decomposition of PMS to produce reactive oxygen species（ROS）with strong oxidation,such as sulfate radical(SO₄^?-),hydroxyl radical（^?OH）,superoxide radical(O₂^?-)and singlet oxygen（¹O₂）,which can significantly improve the removal efficiency and mineralization efficiency of organic pollutants.In this study,cobalt-nickel bimetallic oxide（Co₃O₄-Ni O）and rice straw biochar modified with cobalt-nickel bimetallic oxide（RSBC@Co₃O₄-Ni O）were synthesized by coprecipitation and calcination.The two bimetallic composite oxides were employed for PMS activation to degrade methylene blue（MB）and aniline in water.The effects of initial p H,catalyst dosage and PMS concentration on the degradation of organic pollutants in water were investigated by batch experiments.The catalysts before and after reaction were characterized by scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）.The catalytic mechanism and degradation pathway were proposed combined with electron paramagnetic resonance（EPR）technology and an high performance liquid chromatography-tandem mass spectrometry（HPLC-MS）.The main research contents are divided into two parts.Part I:Co₃O₄-Ni O was used as a catalyst to activate PMS for the degradation of MB.It was found that Co₃O₄-Ni O exhibited better catalytic role than Co₃O₄,Ni O and the mixture of Co₃O₄ and Ni O,and the removal efficiency of MB increased by over 68%,indicating a good synergy between cobalt and nickel in Co₃O₄-Ni O druring activating PMS.When the dosage of Co₃O₄-Ni O was 0.15 g/L,the concentration of PMS was 1 mmol/L,and the initial p H was 6.0,the degradation efficiency of MB and the removal efficiency of total organic carbon（TOC）were 92.2%and 31.9%,respectively,within 60 min.The concentrations of Co ions and Ni ions leaching from Co₃O₄-Ni O in the reaction system were lower than 1.0 mg/L,and the degradation efficiency of MB remained still above 92%after the fourth recycling,indicating that the material exhibited good stability and recycling performance.In the range of initial p H 5-10,the removal efficiencies of MB were more than 92%.In a certain range,the increase of catalyst amount and PMS concentration could significantly improve the degradation efficiency of MB.The coexisting anions HCO₃^-and Cl^-have a certain inhibitiory effect on MB degradation,while humic acid showed the more obvious inhibition.Radical quenching experiments and EPR technology confirmed that ¹O₂and SO₄^?-were generated in the Co₃O₄-Ni O/PMS system,which were responsible for the efficient removal of MB and final mineralization into CO₂ and H₂O.Part II:Based on the above research,cobalt-nickel bimetallic oxide was loaded on rice straw biochar（RSBC@Co₃O₄-Ni O）,which used as a catalyst to activate PMS for the degradation of aniline,an organic pollutant in water.The effects of different factors on the degradation of aniline were investigated.The results showed that aniline was almost completely removed within 60 min at the initial p H 6.0 under the condition of 0.05 g/L catalyst and 0.5 mmol/L PMS.The degradation of aniline could be accelerated by increasing the amount of catalyst and the concentration of PMS,and the degradation rate of aniline increased with the rise of initial p H in the studied range of 4-10.After the catalyst was recycled for the third time,the degradation efficiency of aniline increased from 63.7%to 87.7%by calcination,which indicated that calcination could improve the recycling performance of the catalyst.Radical quenching experiments and EPR technology proved that ¹O₂was the main ROS responsible for the removal of aniline,followed by SO₄^?-.It was concluded combined with XPS and HPLC-MS that cobat,nickel and the oxygen groups on the surface of RSBC in the catalyst had a synergistic effect on the activation of PMS to produce ¹O₂ and SO₄^?-,resulting in the effective degradation of aniline.The results obtained in this study have demonstrated that these two materials,Co₃O₄-Ni O and RSBC@Co₃O₄-Ni O,can effectively activate PMS to degrade MB and aniline in water,and have high stability and good recycling effect.These can provide an important theoretical basis and reference value for the treatment of organic pollutants in water environment.