不同形态无机氮对水环境中双酚A光降解的影响

The effect of different forms of inorganic nitrogen on photodegradation of bisphenol A in water environment

在紫外光照射条件下,研究了水溶液中不同形态无机氮(NO_(3)^(-)、NO_(2)^(-)和NH_(4)^(+))对双酚A(BPA)光解的影响和机制.结果表明,BPA在纯水中的光解包括直接光解和·OH、^(1)O_(2)、O_(2)^(-)等ROS(活性氧物种)参与的自敏化光解反应,其反应均符合准一级动力学模型特征,·OH、^(1)O_(2)、O_(2)^(-)、BPA*相对应的贡献率分别为13.4%、7.7%、22.9%、47.9%,以直接光解途径为主.分别添加的不同形态的无机氮显示出不同的效应,NO_(3)^(-)、NO_(2)^(-)表现出抑制效应,NH_(4)^(+)则没有影响.当不同形态无机氮共存时,若pE值<5,此时无机氮以NH_(4)^(+)为主,故对BPA光解基本没有影响;随着pE值的增大(4.82~8.15),NH_(4)^(+)逐渐转化为NO_(2)^(-)和/或NO_(3)^(-),光解速率常数减小,且NO_(3)^(-)和NO_(2)^(-)共存时表现出比NH_(4)^(+)和NO_(2)^(-)之间更强的拮抗作用.最后利用GC-MS法鉴定了BPA可能的光解产物,发现NO_(3)^(-)/NO_(2)^(-)单独或共存时均能引发硝代反应.

The impact and mechanism of inorganic nitrogen(NO_(3)^(-),NO_(2)^(-),and NH_(4)^(+))on the photodegradation of bisphenol A(BPA)was investigated in aqueous media under UV light irradiation.Results suggested that BPA photodegradation in pure water was associated with direct photodegradation and self-sensitized photodegradation involving reactive oxygen species(ROS),such as·OH,^(1)O_(2),and O_(2)^(-).It was found that BPA photodegradation conformed to pseudo first-order kinetics in all cases and the corresponding contributions of·OH,^(1)O_(2),O_(2)^(-),and BPA*to BPA photodegradation were 13.4%,7.7%,22.9%,and 47.9%,respectively,indicating that the direct photodegradation was the main reaction pathway.Furthermore,the presence of different forms of inorganic nitrogen(NO_(3)^(-),NO_(2)^(-)and NH_(4)^(+))showed different effects on BPA photodegradation.NO_(3)^(-)and NO_(2)^(-)showed inhibitory effects,whereas NH_(4)^(+)had no impact.When different forms of inorganic nitrogen coexisted,NH_(4)^(+)was a dominating inorganic nitrogen at low pE value(<5)and therefore showed little effect on BPA photodegradation.With the increase of pE value from 4.82 to 8.15,NH_(4)^(+)gradually transformed to NO_(2)^(-)and/or NO_(3)^(-),slowing down the photolysis.Additionally,an antagonistic action between NO_(2)^(-)and NO_(3)^(-)was stronger than that between NH_(4)^(+)and NO_(2)^(-).Finally,the possible photodegradation products of BPA were identified by GC-MS and it was considered that NO_(3)^(-)and NO_(2)^(-)could initiate nitration reaction either alone or coexisting.