Study On The Mechanism Of CoAl-LDH/LDO Activated Persulfate Degradation Of Aniline

In recent years,the treatment of aniline,an aromatic hydrocarbon organic pollutant that seriously endangers the environment and human life and health,has become a hot research topic in the field of water treatment.Peroxynitrite（PS）advanced oxidation technology has shown superior ability in removing organic pollutants from water due to its economic and safety advantages.However,the ability of PS alone to oxidize pollutants is weak,and the search for an efficient and practical means of activation has become the focus of research on PS advanced oxidation technology.Layered double metal hydroxide（LDH）have a relatively wide alkaline strength distribution,exchangeable interlayer anions and multiple choices of divalent and trivalent metals in the layered structure,making LDH-based catalysts with high catalytic potential.Its calcination product,layered double oxide（LDO）,can provide more active sites and also has good catalytic activity,plus Co is a metal element with great catalytic potential.Therefore,in this thesis,CoAl-LDH/LDO catalysts were optimally prepared,and morphological and structural analysis and mineralogical characterization were systematically carried out.And the catalytic efficacy of four different catalyst systems for the activated persulfate degradation of aniline pollutants was comparatively studied with aniline as the target pollutant,and the reaction mechanism of catalytic degradation of aniline was further explored.The results showed that the CoAl-LDH was prepared by reverse co-precipitation method,and the weakly basic NH₄OH buffer system was more effective than the strongly basic Na OH system.Thermodynamic experiments were conducted using CoAl-LDH prepared under the weakly basic system,and the thermal treatment process was analyzed and calculated,so that four temperature nodes were selected for calcination preparation to obtain CoAl-LDO for the subsequent degradation process.The CoAl-LDH/LDO before and after calcination at 500℃were characterized by XRD and SEM-EDS,and it was found that CoAl-LDH was a hexagonal cobalt-aluminum hydrotalcite structure,and CoAl-LDO was composed of tetragonal crystalline Co₃O₄ and CoAl₂O₄,and the percentage of cobalt-aluminum atoms were maintained at about 3:1,and the layer structure of the catalyst was unchanged.The comparative study of four catalytic systems activated with PS for the degradation of aniline found that LDO@500 had the best catalytic performance,the amount of PS also affected the aniline degradation effect,and the aniline degradation process of denitrification and decarbonization was carried out simultaneously.under the condition of LDO@500 activated with PS,AN:PS>1:50,the reaction 180 min aniline degradation rate reached 100%;when AN:PS=1:200,the aniline degradation rate of the reaction system reached 100%.When AN:PS=1:200,43%of TOC in the reaction system could be removed in 60 min;when AN:PS=1:200,the reaction could convert 83%of organic nitrogen into inorganic nitrogen in 120 min,and the inorganic nitrogen mainly existed in the form of nitrate nitrogen.Combined with Arrhenius equation equation and pseudo-first-order kinetic model,the reaction activation energy of different reaction systems is negatively correlated with its degradation effect,LDO@500 effectively reduces the reaction activation energy.The linear scanning voltammetry curve（LSV）,timing current curve（i-t curve）and electron paramagnetic resonance（EPR）were further used.It was found that LDO@500 catalyzed the degradation of aniline by PS produce free radicals SO₄^-·and·OH and non-free radical ¹O₂ catalyzed by LDO@500,and SO₄^-·played a major role in the degradation of aniline.The completion of aniline degradation contained a small amount of three-dimensional fluorescence signal of benzene ring and-NH₂ group,indicating that there were intermediate products generated from aniline degradation.Further,the intermediate products of aniline degradation were measured by gas chromatography-mass spectrometry（GC-MS）,including azo-benzene,benzoquinone and nitroso-benzene.The six degradation pathways of aniline were hypothesized and the degradation of aniline was terminated by NO₃^-,CO₂ and H₂O.