| The parabens have been widely used and defected in natural waters. As parabenscannot be completely eliminated by conventional wastewater treatment plants, they havebeen widely detected in surface waters. The occurrence of parabens in the aquaticenvironment has raised public concern over the potential suspected adverse ecological orhuman health effects. It has been reported that these compounds have weakly oestrogenicactivity and reproductive toxicity. It is essential to develop effective techniques to removethese compounds. As Fe（Ⅲ）、citric acid and humic substances are widely distributed innature, this study is based on these two sysetms.The main content and results obtainedwere as following:The photodegradation of four parabens by Fe（Ⅲ）-citrate system from aqueoussolution was studied. Besides, the impact of pH value, various aqueous media andlow-molecular-weight acid on the photosensitization of parabens were investigated.Results suggested:(1) the formation of HO at different Fe（Ⅲ）-to-cit molar ratios wasanalysed. The optimal Fe（Ⅲ）-to-cit ratio was chosen for the elimination of parabens byFe（Ⅲ）-cit complexes. Fe（Ⅲ）-cit-induced HO formation rate increased with decreasingpH at the Fe（Ⅲ）-to-cit ratio of10:50(106M). Lower ratio such as10:150and10:500ledto different order for HO formation.(2) the pH-dependent HO production are governedby the stability of Fe(II)/Fe(II)-cit and amount of O2.(3) The photodegradationefficiency decreased with increasing pH within the range of5.0-8.0at fixedFe（Ⅲ）-to-citrate ratio of10:150M and follow the order of pH5.0>6.0>6.5>7.0>8.0.(4) The photodegradation of parabens have been investigated in different types of aqueoussolutions. Both waste water and lake water exhibit inhibition effect compared to purifiedwater.(5)The addition of low-molecular-weight acid showed diversely effect on thephotodegradation of methylparaben. In general, formic and acetic acids had inhibitioneffect and followed the order of formic acid> acetic acid. In contrast oxalic acid exhibitedpromotion effect. Moreover, the optimal promotion effect did not as higher concentrationof low molecular weight acid.(6) by GC-MS analyses, the photoproducts ofmethyl-paraben were identified and the degradation pathway was proposed.In the simulated sunlight, the relationship between humus and parabens were studied,besides, the impact of the initial concentration of parabens, pH value, various aqueous media, different molecular weight about and halide ions including Cl, Br, and Ion thephotosensitization of parabens were investigated. Results suggested:(1) with theincreasing of initial concentration about parabens, the reaction rate constants decreased.(2)the removal rate of parabens increased in the order of pH6.07.08.09.010.0.(3)the lower molecular weight fractions possesss more aromatic C=C content,oxygen-containing functional groups and fluorescent chromophores, which can greatlyinfluence on the fate of parabens pollutants in natural waters. And the fraction of (3-10k)and (30-100k) has the largest the rate constants of the reaction because of the morearomaticity and oxygen content.(4) mechanism between humic substances and parabensphoto-sensitized degradation was investigated by various quenching reactions. The resultdisplayed that3HS*was the main ROS for the degradation of parabens under thesimulated sunlight. The occurrence of the degradation of parabens depended on anon-bonding electron transferring from the parabens to triplet3HS*. |
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