【作者】 张亚；

【导师】 杨曦；

【作者基本信息】 南京大学 ， 环境工程（专业学位）， 2014， 硕士

【摘要】 碳基纳米材料是指至少在一个维度上其结构单元的尺寸在1-100nm范围内的材料,包括富勒烯、碳纳米管及二者衍生物。因为优良的物理、化学和电学特性,碳基纳米材料被广泛应用于医疗、交通运输、环境保护等领域。随着碳基纳米材料的商业化,世界各地大量生产和使用增加了碳基纳米材料的环境暴露风险。相对于碳基纳米材料的合成和应用研究,碳基纳米材料的环境暴露和风险评价投入仍处于起步阶段,其环境归趋和生态风险数据仍极度缺乏。水体分散的部分碳基纳米材料(富勒烯、羧基化碳纳米管等)在UVA和可见光的辐照下可以生成活性氧物质(ROS),如羟基(·OH)、单重态氧(1O2)、氧负离子(O2-)等；这些具有较强反应活性的活性氧物质不仅影响天然水体成分和外源有机污染物的环境行为,除此之外还可以通过脂质过氧化等过程产生生物毒性,使得活性氧机制成为碳基纳米材料环境化学、生态毒理学研究的核心内容之一。由于碳基纳米材料在天然水体中的分散行为极为复杂,其水体分散以及与水体成分的相互作用受其本身粒径、结构、官能团以及水环境因子的显著影响,造成他们的环境光化学研究工作极具挑战性。深入探讨碳基纳米材料的水化学行为、光化学活性以及其对水体有机污染物环境光化学归趋影响,是综合评价其环境归趋和生态风险的重要过程。本文以典型的一类碳基纳米材料官能化多壁碳纳米管(FMWNTs)为研究对象,以模拟自然光辐射下的天然水体为研究介质,综合定量分析、动力学实验设计和分子模拟等研究手段,探讨水体稳定分散的官能化多壁碳纳米管光化学活性和其对水体典型有机污染物环境归趋影响。文章选择心血管药物阿替洛尔(ATL)和兽药氟苯尼考(FLO)作为研究官能化多壁碳纳米管光化学活性对水体有机物环境归趋的模式化合物,对其环境光化学行为进行深入研究。主要的研究内容如下：(1) FMWNTs水体分散和光化学活性研究使用细胞破碎仪在70-80W功率下间歇性超声可以获得水体稳定分散的羟基化多壁碳纳米管(MWNT-OH)和羧基化多壁碳纳米管(MWNT-COOH)悬浮液,该悬浮液浓度(以总有机碳计,mgC L-1)与吸光度存在良好的线性关系。实验室静置处理该悬浮液,30d内吸光度变化小于5%,100d后无相分离。利用竞争动力学方法,分别以呋喃醇(FFA)和对氯苯甲酸(PCBA)为分子探针,测定8mgCL-1的MWNT-OH和MWNT-COOH悬浮液模拟自然光(氙灯光源)辐射下活性氧物质1O2和·OH的生成,并计算出稳态浓度分别在10-14mol L-1和10-15mol L-1数量级。其中MWNT-OH和MWNT-COOH生成单重态氧能力相当,但MWNT-OH光致产生羟基能力高于MWNT-COOH。在一定范围内增加碳纳米管浓度(0.8-8mgC L-1)可以提高光致活性氧的稳态浓度。对比分析天然水体中羟基和单重态氧含量,证实了进入水体中的FMWNTs是102和·OH的重要来源,从而会改变水体的氧化能力,进而可能会影响污染物的环境归趋。(2) MWNT-OH对阿替洛尔光解影响模拟自然光照下,去离子水中阿替洛尔即不会水解也难以发生直接光解,但在天然有机质(NOMs)、NO3-、Fe3+存在下发生间接光解。模拟自然光照下,MWNT-OH也会造成ATL的间接光解,光解符合准一级动力学,且淬灭实验证实光解过程中羟基自由基是涉及的主要活性物质。当MWNT-OH和天然水体成分NOMs、NO3和Fe3+同时存在时,N03-和Fe3+可促进ATL在MWNT-OH悬浮液中的光解；Suwannee河富里酸(SRFA)和Suwannee河腐植酸(SRHA)具有光屏蔽效应和羟基淬灭效应,而Nordic河富里酸(NOFA)、Nordic河腐植酸只具有光屏蔽效应。与ATL在天然水体成分NOMs、NO3-和Fe3+中光解途径相比,在MWNT-OH中ATL降解过程中除共同的羟基化、醚键侧链断裂、乙酰胺基氧化光解途径外,出现了中间产物聚合现象。(3) MWNT-OH对氟苯尼考光解影响太阳辐射和氙灯辐射下,氟苯尼考直接光解符合一级动力学,半衰期分别为187.3h和22.4h。通过计算发现,除光屏蔽作用外,MWNT-OH与硝酸根、天然有机质一样可以促进氟苯尼考的光解,该光解过程涉及羟基和单重态氧自由基。在MWNT-OH悬浮液中,氟苯尼考的光解受pH影响,且偏酸或碱时,光解加快；硝酸根和天然有机质因光屏蔽作用和自由基淬灭作用抑制氟苯尼考在MWNT-OH中的光解。对光解产物分析发现,氟苯尼考在MWNT-OH中的光解过程涉及苯环的羟基取代反应；光致水解过程；F被羟基取代；溶解氧存在下,侧链末端脱氯氧化途径,生成更具有光化学活性的醛基化合物；侧键断裂反应这四类反应途径。以MWNT-OH光解氟苯尼考为例,不仅为评价MWNT-OH光化学特性对水体有机污染物归趋影响提供了可靠依据,同时也开拓了碳纳米管光化学研究的新方向。更多还原

【Abstract】 Carbon-based nanomaterials (CNM) include fullerenes, carbon nanotubes and their derivatives with at least one dimension in the structure is less than100nm. Owing to their unique physical, chemical and electrical properties, CNM are widely used in medical, transportation and environmental protection. The huge production of commercial CNM and extensive application raise concerns about their environmental occurrence and risk. Although the synthesis and application of CNM have been frequently studied, their environmental fate and ecological risk are still largely unknown, especially for those water-dispersible CNM. Colloidal dispersible CNM could photochemically produce reactive oxygen species (ROS), such as hydroxyl radical (·OH) and singlet oxygen CO2), under UVA or solar irradiation, and promote the degradation of organic pollutants. Since ROS could damage the lipid chain, many studies in environmental chemistry and ecotoxicology focused on the mechanisms of ROS formation by CNM. Environmental behavior of CNM in natural waters is extremely complex because their dispersion and interaction with natural water constituents may be significantly affected by particle, structure and functional groups. Thus, there is a huge challenge for studing the environmental photochemistry of CNM.In the present study, the photoreactivity of functional multi-walled carbon nanotubes (FMWNTs) and their effects on the photochemical transformation of organic pollutant under simulated sunlight irradiation were investigated. In order to investigate the possible effects of hydroxylated multi-walled carbon nanotubes (MWNT-OH) on the transformation of organic pollutants upon irradiation, two emerging organic contaminants, atenolol (ATL) and florfenicol (FLO), were chosen as model compounds due to their widespread occurrence and relatively high level in natural aquatic environment. The main results are as follows:(1) Dispersion and photoreactivity of FMWNTsAqueous suspensions of the MWNT-OH and carboxylic multi-walled carbon nanotubes (MWNT-COOH) were prepared in DI water via intermittent and ice-bath sonication. There were good linear relationships between the concentrations and absorbances of the suspensions. The FMWNTs suspensions were stable since the absorbances remained unchanged (<5%) within30d and no phase separation was observed after100d.Furfuryl alcohol (FFA) and p-chlorobenzoic acid (PCBA) as molecular probes were used to identify the possible production of different ROS species, i.e.,1O2and·OH. The steady-state concentrations of ROS were measured to be10"14and10-15mol L-1level in8mgC L"1MWNT-OH and MWNT-COOH suspensions, respectively, under simulated sunlight source. The ability to generate1O2by MWNT-OH and MWNT-COOH was comparable, however, photoinduced generation of·OH by MWNT-OH was stronger than MWNT-COOH. The steady-state concentration of ROS increased with increasing concentration of carbon nanotubes (0.8-8mgC L"1). Compared with the naturally occurring1O2and·OH, the presence of FMWNTs in natural waters may provide addtional source of1O2and·OH, which would change the oxidative capability of water bodies and affect the environmental fate of many contaminants.(2) Photodegradation of atenolol in MWNT-OH suspensions Atenolol in DI water was photostable and hydrolysis resistant, but could be degradated in aqueous solution in the presence of NOMs, NO3-, Fe3+and MWNT-OH under simulated sunlight irradiation. The presence of natural water constituents, such as NOMs, NO3-and Fe3+, affected the photolysis rate constant of atenolol in MWNT-OH solution. Hydroxyl radical was identified as the predonminant reactive species in the photolysis process. SRFA and SRHA had both light screening and OH scavenging effect on atenolol photolysis, while NOFA and NOHA only showed light screening effect. NO3-and Fe(III) could promote the decay of atenolol in MWNT-OH solution. The photochemical transformation pathways of atenolol in MWNT-OH suspension involved hydroxylation, acetamide group oxidation, ether side chain cleavage and di-pohymerization of the intermediates.(3) Photodegradation of florfenicol in MWNT-OH suspensionsUnder solar and xenon lamp irradiation, direct photolysis contributed to the degradation of florfenicol in DI water, with a half-life of187.29h and22.4h, respectively. The photolysis for florfenicol in pure water and MWNT-OH suspensions under two irradiation sources follow pseudo-first-order kinetics. Hydroxyl radical (·OH) and singlet oxygen (1O2) were found to be involved in the photolysis process. The decays of florfenicol in MWNT-OH suspension were pH-dependent. The presence of MWNT-OH affected the photolysis of florfenicol in NO3-and NOMs solutions though light screening and radical quenching effect as well as photoinduced oxidization process. Under simulated solar irradiation, thiamphenicol was determined as the photohydrolysis product of florfenicol in MWNT-OH suspension. Others pathways included the electrophilic attacking of·OH at the aromatic ring, dechlorination, oxidation and cleavage of the side chain. The results of this study are not only important for better understanding the environmental fate of florfenicol and assessing the environmental risk of MWNT-OH, but also useful for further photochemical studies on carbon nanotubes.更多还原