Degradation Of Sulfonamide Antibiotics By Chlorine Dioxide:Reaction Kinetics And Mechanism Research

Sulfonamide antibiotics are consumed in a large amount and have been frequently detected in multi-environment media in China,which are most frequently detected in the aquatic environment.Traditional water treatment processes cannot degrade sulfonamide antibiotics effectively,which is the source of the migration and transformation of the pollutants in the environment.As a green disinfectant,chlorine dioxide is often used in the disinfection process of high-quality source water.It has the advantages of high redox potential,stable oxidation capacity,and safer disinfection products.Chlorine dioxide does not generate trihalomethanes,so it has bright application prospects.In this thesis,chlorine dioxide is used as the oxidant,and the target compounds are sulfamethoxazole,sulfadiazine,sulfaguanidine and 4-（methylsulfonyl）aniline.The reaction efficiency,kinetics and reaction mechanism have been studied in detail.The effects of the initial concentration of oxidant,reaction temperature and pH on the reaction efficiency and rate constant are discussed,and the oxidation products are inferred respectively.The product of the target compound reacts with chlorine dioxide is detected by High Performance Liquid Chromatograph Mass Spectrometer,which can measure the concentration and the charge ratio of the product.The experimental results show that chlorine dioxide is effective in removing sulfonamide antibiotics.The oxidation process follows the second-order reaction kinetic model.Chlorine dioxide and each sulfonamide antibiotic conform to the first-order reaction kinetic model respectively.4-（methylsulfonyl）aniline does not react with chlorine dioxide basically.The reaction rates of sulfamethoxazole,sulfadiazine,sulfaguanidine under the room temperature and neutral reaction system are:k=2.28×10³ M^-1·s^-1,k=2.73×10³ M^-1·s^-1 and k=5.60×10² M^-1·s^-1respectively;the activation energy of the reaction are:E_a=47.40 k J·mol^-1,E_a=44.97 k J·mol^-1 and E_a=55.01k J·mol^-1 respectively,which can reflect the difficulty of the reaction;all the above parameters proved that the reaction rate of chlorine dioxide oxidation of sulfadiazine antibiotics from fast to slow is sulfadiazine,sulfamethoxazole and sulfaamidine.The ratio reaction rate constants of anion has the deepest influence on the reaction rate constant,which are:6)_SA-=3.28×10³ M^-1·s^-1,6)_SA-=6.19×10³ M^-1·s^-1 and6)_SA-=4.46×10³ M^-1·s^-1respectively.This thesis combines the structure of the parent compound,the mass-to-charge ratio of the product,the principle of chemical reaction and related research literature,speculates the oxidation products and reaction pathways,and explores the reaction mechanism.There are more than ten kinds of oxidation products of sulfonamides antibiotics oxidized by chlorine dioxide.Four kinds of oxidation products with the same target are generated by the oxidation of sulfonyl group and aniline by chlorine dioxide,such as p-aminophenol.Different oxidation products are caused by different substituents of each target.The reaction process of the oxidation of sulfonamides by chlorine dioxide is complex,and at least three reaction pathways have been speculated in this dissertation.In the degradation process,chlorine dioxide mainly attacks the sulfonyl group of sulfonamide antibiotics,and degrades sulfonamide antibiotics by breaking the S-N and S-C bond.Another major reaction pathway is hydroxylation of amino,which is also common in the degradation of sulfonamide antibiotics by chlorine dioxide.This study provides an effective solution for the treatment of sulfonamide antibiotics in the aquatic environment.