Study On The Degradation Performance And Mechanism Of 2,4-dichlorophenoxyacetic Acid In CuCoMgAl-LDH/Peroxymonosulfate /Ozone System

Permonosulfate（PMS）-based advanced oxidation process is considered to be a promising technology because it can generate sulfate radicals(SO₄^·–)with strong oxidation ability.However,PMS is biologically toxic and relatively costly.At present,there is a trend to use a combined-oxidant system,thereby reducing the toxicity and cost of the system.Catalytic ozonation technology is more and more widely used because it can generate·OH,and has fast response and no pollution.However,finding a catalyst that can activate both O₃and PMS is also a major challenge at this stage.This study chose CuCoMgAl-LDH as the catalyst and refractory organic 2,4-dichlorophenoxyacetic acid（2,4-D）as the model pollutant,and combined the two technologies,using PMS and O₃as combined oxidants to construct CuCoMgAl-LDH/PMS/O₃heterogeneous catalytic system,and its treatment effect and mechanism were studied.The main research contents and results are as follows:1)A series of Co,Cu,Fe transition metals supported on Mg Al-LDH structure catalysts were prepared by co-precipitation method.Physical properties and catalytic properties of these catalysts were compared by BET,ICP,surface hydroxyl density measurement and other experiments.CuCoMgAl-LDH catalyst could activate O₃and PMS at the same time.Under the condition of CuCoMgAl-LDH dosage of 0.15 g/L,PMS concentration of 2 m M,O₃dosage of 13 mg/L,the degradation rate of 2,4-D reached97.6%,which basically achieved complete degradation.2)The effect of external factors such as initial p H and different anions on the degradation of 2,4-D in the reaction system was studied.The result showed that the initial p H of the solution had a greater effect on the degradation of 2,4-D in CuCoMgAl-LDH/PMS/O₃three-phase catalytic system.The system had the best degradation effect under acidic p H.When the p H value was between 5～11,the degradation efficiency of 2,4-D decreased.Among common inorganic anions,NO₃^-and Cl^-had little effect on the degradation of 2,4-D in the system with a slight promotion effect;CO₃^2-,HCO₃^-and HPO₄^2-had a certain inhibition on the degradation of 2,4-D in the three-phase catalytic system.3)The activation mechanism of PMS and O₃was studied through experiments such as ozone decomposition kinetics,R_ctvalue measurement,PMS decomposition kinetics and quantive measurement of SO₄^·–concentration,etc.,and radical species were confirmed through radical quenching and EPR experiments.The XPS results deduced the possible redox pathway of the system.The results showed that the greater the density of surface hydroxyl groups was,the greater the rate constant of O₃decomposition of the catalyst and the larger the R_ctvalue was,the better the effect of the catalyst on the decomposition of O₃to produce OH was.The transition metals Cu and Co were the main catalytic components for PMS activation and improved the utilization rate of PMS.The redox reactions of Cu（Ⅰ）/Cu（Ⅱ）and Co（Ⅱ）/Co（III）were responsible for PMS activation and the generation of SO₄^·–.The presence of O₃during this period didn’t affect the decomposition of PMS.Active species such as SO₄^·–,·OH,and¹O₂existed in the system.SO₄^·–,·OH dominated the reaction,and the contribution of ¹O₂to the reaction was relatively weak.4)The lettuce seed experiment was used to study the biological toxicity before and after the reaction,and the stability of the catalyst was studied and evaluated using XRD and stability recycling experiments before and after the reaction.The results showed that the toxicity of the system was effectively reduced after the reaction.CuCoMgAl-LDH had a good activity in three recycling runs,and the structure didn’t change after the reaction,which showed that the catalyst had good stability.