Removel Of 2,4-dichlorophenoxyacetic Acid In Aqueous Systems By Photocatalytic Ozonation Compound Advanced Oxidation Process

The use of herbicides has,to a certain of degree,promoted the development of agriculture and forestry and achieved considerable economic benefits.In recent years,due to people’s requirements for production efficiency and manpower savings,the irrational use and abuse of herbicides have become increasingly serious.Excessive use herbicides not only cause the contamination of soil and water body,but also damage the ecological environment even affect human health.Therefore,it is urgent to remove herbicides efficiently in water environment.Photocatalytic technology provides a new and effective way to solve current environmental pollution with its advantages of low cost,environmental protection,and simple operation.The core of photocatalytic technology is the photocatalyst.LaFeO₃ has a narrow band gap and has a good visible light of absorption.Graphitic carbon nitride（g-C₃N₄）is a kind of non-metallic organic polymer semiconductor.Because it contains only two elements of carbon and nitrogen,its raw materials are non-toxic,cheap and abundant.LaFeO₃ and g-C₃N₄ also exhibits high thermal and chemical stability.But its photocatalytic activity remains limited by its low visible light utilization and high recombination rate of photoinduced electrons,which restricts its further application in photocatalysis.In order to resolve the problem,we use LaFeO₃ in the photocatalytic ozonation to improve photoelectric separation efficiency of LaFeO₃.For g-C₃N₄,we have modify it by constructing heterojunctions and adding auxiliary catalysts to increase the separation efficiency of electron-hole pairs.Then we use the two Composite photocatalyst in the photocatalystic ozonation to improve the degradation rate.Using 2,4-dichlorophenoxyacetic acid（2,4-D）as the target pollutant,the photocatalytic degradation of 2,4-D was carried out under simulated sunlight to investigate the photocatalytic performance of the photocatalyst that we prepared.We also use the prepared photocatalyst in photocatalytic ozonation to investigate the synergistic effect between photocatalystic and ozonation.The main contents and results of this thesis are as follows:（1）LaFeO₃ nanoparticles were used as a visible light photocatalyst for efficient removal of 2,4-dichlorophenoxyacetic acid（2,4-D）with the assist of ozone.The first-order kinetic rate constants of degrading 2,4-D removal in 60-PO/Vis in 1 h was 5.72 times as great as the sum of that when using LFO/O₂/Vis and 60-Oz/Vis at the best concentration of ozone（60 mL/min）.This improvement was attributed to the efficient synergistic effect between photocatalysis and ozonation triggered by LaFeO₃.In PO/Vis,ozone facilitates the photo-generated electrons trapping and improves separation efficiency of photo-generated charges,which enhanced the yield of hydroxyl radical,so as to the degradation efficiency of organic pollutants.In addition,the effects of ozone concentrations on the photocatalytic ozonation processes were also studied.（2）P25/g-C₃N₄ composite photocatalysts with different mass ratio of P25 were synthesized by calcination mothod.The results of SEM and TEM show that P25 particles were uniformly dispersed the surface of g-C₃N₄,and the intimate heterstructure between P25 and g-C₃N₄ were built.The best degraded activity of photocatalytstic ozonation under full light and visible light was 99%and 89%,respectively,with the ozone concentration of 30 mL/min in 60min.The synergistic factor of visible light is 9.34,which is 4.56 times greater than full light.The result shows that there is better synergy between photocatalysis and ozonation under visible light.The experiment of the effect of the initial pH on the degradation activity showed that the photocatalytic remove of 2,4-D can get the best degrade at pH=5.（3）The noble-metal-free photocalyst CoP/g-C₃N₄ were prepared with the CoP as cocatalyst and the C₃N₄ as catalyst.Within 60 min,the photocatalytic degradation rate of the0.5%-CoP/CN composite sample was 17%,which was much higher than the 4%of the pure phase g-C₃N₄.This was mainly due to the addition of CoP enhanced the separation efficiency of photogenerated carriers.The best degradation rate was 96.4%when the ozone inflow was 30mL/min and the reaction time was 60 min,which was significantly higher than the single photocatalytic（17.1%）and ozonation（27%）under the same conditions.The synergy factor between the two technologies is 3.53,which shows the synergy between photocatalytic oxidation and ozone oxidation.