Study On The Mechanism Of General Catalytic Ozonation Of Organic Compounds

The physical chemistry properties of ozone and its application in water treatment were reviewed,the research objection was proposed too. There were three parts in this paper:Mechanism of UV catalytic ozonation of organic compound in solution;Fe²⁺/Fe³⁺homogeneous catalytic ozonation of phenol;MnO₂ catalytic ozonation of Sodium Benzoate. In chapterâ…¢,the mechanism of producing of OH in O3/UV was proposed as follows:O₃ + H₂O→H₂O₂ + O₂;H₂O₂→2·OH.UV can promote the dissolved ozone to firstly produce H₂O₂,then the intermdiate H₂O₂ can react with dissolved ozone or decompose by UV to produce HO·.The experimental results also indicated that decomposition of H₂O₂ radiated by UV could be accerlated in the present of O₂.Furthermore,the characteristic of organic,which acts as promoter or inhibitor in the process of ozonation, also affects the degradation efficiency of O₃/UV directly,when glycolic acid,a promoter in ozonation,was degraded,the combination UV radiation with ozonation could remove it efficiency despite of less initiation reaction; however,when acetic acid,an inhibitor in ozonation,was degraded by O₃/UV,the removal rate of acetic acid was very low unless enough initiation of hydroxyl radical(OH^-,H₂O₂).The intermediate H₂O₂,has been proved to plays an important role in enhancement of degradation efficiency of O₃/UV.It resulted directly in the formation of two AOPs:O₃/H₂O₂å’ŒH₂O₂/UV systems,which both produce·OH efficiently.The results in chapterâ…£show that the direct reactions between phenol(or C₆H₅O^-)and ozone are the main causes for degradation of phenol.Both Fe²⁺and Fe³⁺could improve the degradation efficiency of ozonation of phenol,and Fe²⁺had higher activity in ozonation of phenol than Fe³⁺had.The possible mechanism of Fe²⁺homogeneous catalytic ozonation of phenol includes two reasons:O₃/H₂O₂ and Fenton system.In this system,the intermdiate H₂O₂ resulted in promoting the removal of phenol.The R_ctof different systems is:O₃/Fe²⁺＞O₃/Fe³⁺＞O₃,which is in accordance with their degradaton efficiencies of phenol.The results in chapterâ…¤show that the COD removal was not high in spite of the complete disappearance of Sodium Benzoate in specific time,indicating some compounds inert to ozone accumulated in solution. Addition of MnO₂ increased the degradation efficiency of COD by ozone obviously(from 79%to 94%).R_ctof different systems were calculated: O₃/MnO₂＞O₃.The mechanism of MnO₂ catalytic ozonation of Sodium Benzoate included two causes:(1)MnO₂ increased the reactive activity of organic acid with ozone;(2)adding MnO₂ cound increase the pH of solution,then high pH promoted the decomposition of ozone to produce·OH.The radical scavenger test confirmed the second cause.