节点文献
部分典型有机污染物在环境界面的光化学行为
Photolytic Behavior of Selected Organic Pollutants at Some Interfacial Environment
【作者】 牛军峰;
【作者基本信息】 大连理工大学 , 环境工程, 2002, 博士
【摘要】 光解是有机污染物在环境中的重要转化过程。由于持久性有机污染物(POP)在环境中难以被生物降解,因此研究POP的光化学行为对于POP的环境行为评价有重要的意义。前人对于POP的光化学行为研究主要集中于水相和大气相中,本研究则主要研究POP在环境界面上的光化学行为。 本研究首次通过将云杉(Picea abies(L.)Karst.)针叶暴露在燃烧炉中燃烧聚氯乙烯(PVC)、木材、高密度聚乙烯(HDPE)和苯乙烯产生含多氯代二苯并二噁(口英)(PCDD)和多氯代二苯并呋喃(PCDF)及多环芳烃(PAH)的废气中,经过一段时间,云杉针叶表面富集了一定浓度的燃烧所产生的PCDD/F和PAH,然后研究了太阳光和模拟太阳光照射下,吸附到云杉针叶表面的PCDD/F和PAH的光化学行为。 太阳光照射下,吸附到云杉针叶表面的70个不同PCDD/F分子和18个不同PAH分子的光解符合一级动力学方程,PCDD/F的光解半衰期约为20~50h;PAH的光解半衰期约为15.8~75.3 h;实验结果表明,在野外环境条件下,光解对于吸附到云杉针叶表面的PCDD/F和PAH的归宿起着重要的作用。 燃烧实验结果表明,云杉针叶表面富集的PCDF的浓度约为PCDD浓度的5倍;三年生长的云杉针叶吸附的PCDD/F的浓度略高于一年生长和二年生长的云杉针叶。太阳光的照射下,在具有相同氯代原子数目的条件下,PCDF的光解速率高于PCDD的光解速率,高氯代PCDD/F的光解半衰期大于低氯代PCDD/F的光解半衰期。PCDD/F分子中C-Cl的断裂可产生芳基自由基,这种自由基能从云杉针叶表面的质子供体如饱和链烃快速吸收氢原子,光还原脱氯可能是云杉针叶表面的PCDD/F的重要降解途径。云杉针叶表面可能产生过氧化基(O2-)、羟基(-OH)、过氧化氢(H2O2)或纯态氧(1O2)等活性氧基团或分子,通过这些物质进攻PAH分子可能是PAH的一种重要的降解途径。 在模拟太阳光中的UV-B部分的照射下,吸附到云杉针叶表面的75个不同的PCDD/F分子在光照第一阶段(0~48 h)和光照第二阶段(48~528 h)的光解分别符合一级动力学方程,第一阶段的光解速率远大于第二阶段的光解速率;云杉针叶的生长时间对于PCDD/F的光解有影响,随着生长时间的增加,光解速率略有提高, 大连理工大学博士学位论文三年生长的云杉针叶表面的 PCDD/F的光解速率略高于一年生长和二年生长的云杉针叶表面上PCDD/F的光解速率。 燃烧过程中产生的烟灰中含有一定浓度的PCDD/F,在模拟太阳光中的UV-B部分的照射下,烟灰表面的PCDD/F的光解符合一级动力学方程,而烟灰内部的PCDD/F比较稳定,难以光解;沉积到云杉针叶表面上的烟灰能使PCDD/F在云杉针叶表面的光解速率减小。研究表明,在野外环境条件下,太阳光中的UV-B部分对于吸附到云杉针叶表面的PCDD/F的归宿起着主要的作用。 在含UVE部分的模拟太阳光和不含UV卫部分的模拟太阳光的照射下,吸附到当年生的云杉针叶表面的PAH分于的光解符合一级动力学方程,含UVE部分的模拟太阳光照射下PAH的光解速率大于不含UVI部分的模拟太阳光照射下PAH的光解速率。 燃烧过程中产生的烟灰中含有一定浓度的PAH,在模拟太阳光中的UV*部分的照射下,烟灰表面的PAH的光解符合一级动力学方程,而烟灰内部的PAH比较稳定,难以光解。沉积到云杉针叶表面上的烟灰表面的PAH的光化学降解速率与云杉针叶表面卜PAH的光解速率差别不大,PAH在云杉针叶表面与烟灰表面的迁移对云杉针叶表面PA H的光解速率影响不大,而PA H在烟灰内部和表面之间的迁移速率对PAH的光解有较大的影响。 从辽河新民段采集了 14种具有不同含量的 FeZOs的天然沉积物,为了探讨沉积物中 Fe。O。和其它具有光诱导和光催化能力的物质如 TIO。和有机质成分对沉积物表面上的林丹O-HCH)的光解的影响,研究了Y-HCH在这些沉积物表面上的光解动力学。研究发现,Y爿CH在辽河新民段沉积物表面上的光化学降解符合准一级动力学。采用逐步口归分析、因子分析和偏最小二乘oLS)算法建立了沉积物组成与Y-HCH光解速率常数之间的定量关系模型,得到的模型表明,沉积物中有机碳和无机碳含量的增多抑制Y-HCH的光解,而 Fe。O。和 TIO。等金属氧化物含量的增多对Y-HCH的光解有促进作用。应用所得的模型可以预测Y-HCH在不同沉积物表面上的光解速率常数。光解实验中,检测到了有光解中间产物a-HCH的生成,这可能是出于沉积物中的Y-HCH在紫外光的照射下,发生了异构化现象。 通过对另一种典型有机氯污染物六氯苯(HCB)在高岭土和不同Fe。O。含量的沉积 二I 摘要物中的光解也证实了随着样品中Fe。Os含量的增大,HCB的光解半衰期减少。因此,本项研究结果为强化有机氯农药污染沉积物或土壤的自然光化学修复过程提供了理论依据。
【Abstract】 Persistent organic pollutants (POP) are highly lipophilic and chemically stable. Photodegradation may be one of the dominant abiotic transformations of the chemicals. Therefore, it is of great importance to investigate the photolytic behavior of POP in the environment. Previous studies focus on the photodegradation of POP in aqueous phase and in atmosphere. The photolytic behavior of POP at the interfacial environment is investigated in this study.Spruce (Picea abies (L.) Karst.) needles were exposed exhaust gas containing polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polycyclic aromatic hydrocarbons (PAH) generated by combustion of polyvinyl chloride (PVC), wood, high-density polyethylene (HOPE), and styrene. Photodegradation of PCDD/F and PAH adsorbed on spruce needles under sunlight irradiation was studied. The factors of sunlight irradiation on the surfaces of spruce needles were taken into consideration when investigating the kinetic parameters.The photodegradation of the 70 PCDD/F and the 18 PAH follows pseudo-first-order reaction kinetics. The photodegradation half-lives range between 20 h and 50 h for PCDD/F and between 15.8 h and 75.3 h for PAH. Thus in the field conditions, photodegradation plays a major role on the fate of PCDD/F and PAH adsorbed on spruce needle surfaces.The photodegradation rates of PCDF congeners are faster than PCDD congeners with the same chlorinated substitutions. Higher chlorinated PCDD/F tend to photolyze slowly. The wax components in spruce needles may act as proton donors and accelerate the photodegradation rate. C-C1 cleavage through the addition of protons to PCDD/F molecules may be an important route for PCDD/F photodegradation. Photooxidation mediated by reactive oxygen species may be an important photodegradation mechanism for PAH on spruce needle surfaces.With the radiation of UV-B part of simulated sunlight, the photodegradation of the 75 PCDD/F absorbed to spruce needle follows pseudo-first-order reaction kinetics for the initial phase (0-48 h) and the second phase (48-528 h), respectively. The photodegradation rate constants for the initial phase are far greater than for the secondIVphase. The degradation rates increase with the age of spruce needles. The photodegradation rate constants of PCDD/F absorbed to 3-year-old spruce needles are greater than that of PCDD/F absorbed to 1 -year-old spruce needles and 2-year-old spruce needles.The photodegradation of PCDD/F on fly ash surfaces follows pseudo first-order kinetics under the irradiation of simulated sunlight with UV-B, whereas inner PCDD/F of fly ash is photostable. The fly ash deposited on spruce needle surfaces can decrease the degradation rates of PCDD/F on spruce needle surfaces. In the field conditions, UV-B radiation plays a major role on the fate of PCDD/F and PAH adsorbed on spruce needle surfaces.The photodegradation of the 16 PAH absorbed to one-year-old spruce needle follows pseudo-first-order reaction kinetics with or without the radiation of UV-B part of simulated sunlight. The photodegradation rates for the PAH with the radiation of UV-B part are greater than for the PAH without the radiation of UV-B part of simulated sunlight.The photodegradation of PAH on fly ash surfaces follows pseudo first-order kinetics under the irradiation of simulated sunlight with UV-B, whereas inner PAH of fly ash is photostable. The transfer of PAH between fly ash surfaces and needle surfaces has little effect on the decrease of PAH on spruce needle surfaces, whereas the transfer of PAH from the exterior to the interior of fly ash can decrease the degradation rates of PAH on spruce needle surfaces.Fourteen sediment samples with different content of Fe2C>3 were collected from lower reach of the Liao River in China. The photodegradation of y-hexachlorocyclohexane (y-HCH) on the sediment surfaces was investigated to observe the effects of Fe2Os and other photoinducable substances, such as TiO2 and organic substances, on photodegradation of y-HCH. The stepwise analysis, fac
【Key words】 Photodegradation; PCDD/F; PAH; Spruce needles; Sunlight irradiation; Simulated sunlight; γ-HCH; Metal oxides;