Chlorination And Photochemical Behavior Of Paraben In Aqueous Solutions

Paraben are widely used in food, drug and personal care products industry. The municipal wastewater treatment plants are the main route of these compounds into aquatic environment. Water treatment not only can't remove paraben completely but also form chloro-paraben with higher toxic and stability than parent compounds. It has been found that the UV-Vis absorption of chlorinated paraben shifts to longer wavelength and partially overlaps with the solar spectrum. Therefore, direct photodegradation become a critical factor in the fate of chloro-parabens in water. However, so far, few researches study kinetics of chlorinated paraben photochemical behavior of chlorinated paraben in natural water.The paraben were choosed as target subjects react with NaClO, a common used oxidant in chlorination. The effect of initial substrates concentration, NaCl O concentration and pH on removal efficiency was investigated. The reaction mechanism and main degradation products were analysed. This experiment also study the photodgradation kinetics and degradation mechanism of chlorinated paraben, understanding the environmental fate of chloro-parabens.Paraben removed by NaClO were investigated. Results suggested:(1) The reaction between NaClO and paraben followed the first-order kinetic equation.(2) The removal rate of paraben in solution increased with the concentration of NaClO. The optimal dosage of NaClO is 0.42 mM.(3) Higher initial concentration inhibit the removal rate of paraben. When the concentration of paraben were 20 ?M, the removal rates of MeP, EtP, PrP and BuP were highest.(4) The degradation rates of paraben in chlorination at different pH followed the order: pH = 8.0 > pH = 10.0 > pH = 4.0 > pH = 6.0.(5) Paraben cannot minerlization in chlorination.(6) According to LC-MS, The NaClO can remove paraben efficiency through ortho-chloro substituted paraben. The main chlorinated products are 3,5-2Cl-MeP and 3-Cl-MeP. The concentration of 3-Cl-MeP increased first and then decreased. The concentration of 3,5-2Cl-MeP kept increasing with reaction time.Under stimulated sunlight, the photochemical behavior of chlorinated paraben is invesgited. Results were as following:(1) During the reaction of paraben and NaClO, UV-Vis absorption of the chlorinated paraben kept moving to longer wavelength. The absorbance also increases. After interact in 30 mins, the absorbance wavelength corresponded to absorption peak is 300 nm.(2) Chlorinated paraben do not undergo degradation in the dark, but degradation under stimulated solar irradiation. The photodegradation of chlorinated paraben followed the first-order kinetic equation. The photodgradation kinetic constant of chlorinated methyparaben, ethylparaben, propylparaben and butylparaben were 0.0104 min-1, 0.0102 min-1, 0.0083 min-1 and 0.0076 min-1.(3) The increase of chlorinated paraben concetration was unfavorable to the photodegradation.(4) The degradation rates of chlorinated paraben followed the order: p H = 8.0 ? p H = 10.0 > p H = 6.0 > p H = 4.0.(5) The photolysis of chlorinated paraben was via the direct photodecomposition of the triplet excited-state chlorinated paraben accompanied by few 1O2.(6) 4 photodegradation products were detected. Photooxidation and photodechlorination were main photodegradation pathways.