Photo-induced Reactions Between Bisphenol A,triclosan And Acetaminophen With K₂S₂O₈ In Waters

Endocrine disruptors and Pharmaceuticals and personal care products?PPCPs?are an important new pollutants that have developed in recent decades,as well as due to their large varity and hight consumption,they are discharged into the environment through various links such as production,transportation and use,and have a persistent phenomenon caused by biodegradability in the environment.Therefore,it is important to explore the effectively methods and degradation mechanisms for degrading such pollutants.In this paper,bisphenol A?BPA?,triclosan?TCS?and acetaminophen?ACT?were selected as the research objects.Study on the degradation of BPA,TCS and ACT by 254 nm ultraviolet?UV?activated K₂S₂O₈,and the effects of initial concentration of pollutants,K₂S₂O₈ concentration,pH and the common anions on photochemical reactions were investigated.The properties and kinetics of transient intermediates induced by 266 nm laser flash photolysis were analyzed.The products of photochemical reactions were analyzed by GC-MS and the degradation mechanism of reaction was inferred.The results were shown as following:?1?The degradation efficiency of BPA was significantly affected by the initial concentration of BPA,the dose of K₂S₂O₈ and pH.Laser flash photolysis studies found that SO₄^·-as the main active species in UV/K₂S₂O₈ system,and the BPA-SO₄^·-adduct could be formed by attacting of SO₄^·-on aromatic ring of BPA with a second-order rate constant of?1.09±0.15?×10⁹ L mol^-1 s^-1.Phenoxyl radicals could be generated by the self-decay of BPA-SO₄^·-adduct.In addition,the BPA-SO₄^·-adduct also react with oxygen with rates of?1.28±0.14?×10⁸ L mol^-1 s^-1.The transformation products of bisphenol A were identified by using GC-MS including 4-isopropylphenol,4-isopropenylphenol,3,5-di-tert-butylphenol and 2,4-di-tert-butylphenol.?2?The TCS-SO₄^·-adduct was generated in the reaction of TCS with SO₄^·-by electrophilic addition reaction,and the second-order rate constant was determined as?2.78±0.24?×10⁹ L mol^-1 s^-1.The TCS-SO₄^·-adduct was unstable and could also react with S₂O₈^2-and oxygen with rates of?8.26±0.26?×10⁶ L mol^-1 s^-1,?1.32±0.15?×10⁸L mol^-1 s^-11 respectively.In addition,SO₄^·-could directly attack the ether bond in TCS into a monocyclic substance and further oxidation to some substance with a smaller molecular weight.?3?The experimental results showed that the photoreaction of SO₄^·-induced the degradation of ACT mainly through electrophilic addition and attacking of the side chain.The bimolecular rate constant of ACT with SO₄^·-by addition reaction was calculated as?3.58±0.16?×10⁹ L mol^-1 s^-1.The steady-state experimental study found that the degradation of ACT according with quasi-first-order decay kinetics,and its degradation efficiency is obviously affected by the initial concentration of ACT,the initial concentration of K₂S₂O₈,the initial pH of the solution and HCO₃^-,but is weakly affected by Cl^-.The results of this study indicate that SO₄^·-induced photochemical reactions based on UV-activated K₂S₂O₈ can effectively remove contaminants and provide important ideas for the photochemical conversion of BPA,triclosan and ACT in wastewaters.