【作者】 于春艳；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境科学， 2009， 博士

【摘要】 腐殖酸（humic acids,HA）是天然水体中溶解性有机质（dissolved organic matter,DOM）的主要组成部分,也是最重要的天然吸光物质之一,腐殖酸吸收太阳光后能够对水体中持久性有毒物质（persistent toxic substances,PTS）的迁移转化起到重要作用。铁是地球中最丰富的过渡金属元素,其离子形态广泛存在于天然水体中。当腐殖酸和铁离子共存时,通过配位键作用结合成稳定的络合物,对共存体系中PTS的光解过程产生重要影响,而腐殖酸组成非常复杂,其中具有特殊活性的物质其结构与光化学作用之间的关系并不清楚,因此建立新颖有效的腐殖酸分离方法,将腐殖酸按结构和官能团进行分离尤为关键。本论文研究了腐殖酸的分离及其组分对水体中微量PTS的光解作用,选择了全世界范围内广泛使用的氯代苯氧羧酸类除草剂2,4-二氯苯氧乙酸（2,4-dichlorolphenoxyacetic acid,2,4-D）作为目标污染物,获得了如下主要研究结果:（1）利用红外光谱、紫外/可见吸收光谱和荧光光谱等分析结果表明腐殖酸和Fe（Ⅲ）共存时形成稳定的络合物;电子顺磁共振图谱表明,水溶液中HA、Fe（Ⅲ）以及HA-Fe（Ⅲ）络合物在λ=355 nm光照下均能产生·OH。在模拟太阳光照射下（500 W氙灯,λ＞290nm）考察了腐殖酸和Fe（Ⅲ）的存在对2,4-D光解速率的作用,反应动力学分析表明2,4-D的光降解遵循准一级动力学过程,单纯2,4-D（2 mg/L）溶液的光解速率常数为0.007 h^-1,而含有HA（5 mg/L）、Fe（Ⅲ）（0.2 mmol/L）或二者络合物的2,4-D溶液的光解速率常数分别是0.004、0.034和0.046 h^-1,结果显示HA-Fe（Ⅲ）络合物显著提高2,4-D的光解速率,具有较强的光催化活性。（2）采用硅胶层析的方法,以不同比例的乙醇和水混合溶剂作为流动相对腐殖酸进行淋洗,按极性从弱到强将其分成F_A、F_B、F_C和F_D不同级分。元素分析、紫外/可见吸收光谱和红外光谱分析表明,强极性级分F_C和F_D含有较多的芳香成分,在500 W氙灯的照射下,腐殖酸及其四个级分均减慢了2,4-D的光解速率,且强极性级分F_C和F_D对2,4-D的光解抑制作用比弱极性级分F_A和F_B更明显,说明腐殖酸的光化学活性与其结构和官能团有关。（3）采用分子印迹的方法,利用酞菁铜分子印迹聚合物有效地分离了腐殖酸中类酞菁结构的物质,电子顺磁共振图谱表明,在λ=355 nm脉冲激光的照射下,腐殖酸溶液中含有类酞菁结构的级分(F_mip-b)产生较多的·OH,且在模拟太阳光照射下（氙灯耐气候试验箱,λ＞290 nm）,F_mip-b具有较好的光化学活性,促进了2,4-D的光降解,2,4-D的准一级降解动力学常数是在流出液级分(F_eff)存在时的2.5倍。（4）利用叶绿素、卟啉铁和内消旋-四苯基卟啉分子印迹聚合物选择性地分离了腐殖酸中与各自结构类似的光敏性物质;同时,利用叶绿素、卟啉铁和内消旋-四苯基卟啉三种分子印迹聚合物的混合物将腐殖酸中具有外伸π-共轭大环结构的类卟啉物质分离出来,在模拟太阳光照射下（氙灯耐气候试验箱,λ＞290 nm）,腐殖酸中类卟啉的级分(F_mip-b)比流出液级分(F_eff)具有更好的光化学活性。上述研究结果表明,采用硅胶层析方法和分子印迹方法能够有效地分离腐殖酸中具有光化学活性的组分,腐殖酸中各种不同组分的确对污染物的地球化学过程产生重要影响,这个结果对认识自然界中腐殖酸对微量有机污染物的光解历程具有重要价值。更多还原

【Abstract】 Humic acids（HA）,the major components of dissolved organic matter（DOM）,are widely distributed in aquatic environment,and play an important role in photochemistry because they are one of the most important natural sunlight-absorbing components.HA can affect the transfer and transformation of persistent toxic substances（PTS） in natural water under sunlight irradiation.Iron,a ubiquitous element in natural water,can complex with HA to form HA-Fe（Ⅲ） complex which could affect the photodegradation of PTS.However,the relationship between photochemical activity and HA’s structure hasn’t been well established due to HA’s complexity.Therefore,it is important to separate HA according to structure and functional group using novel and effective methods,and to study photolysis pathway of PTS in solutions containing HA fractions and Fe（Ⅲ）.In this dissertation,the separation of HA and the effects of their fractions on the photodegradation of 2,4-dichlorophenoxyacetic acid （2,4-D） under simulated sunlight were investigated,and the main results are as following:（1） The interactions of HA with Fe（Ⅲ） were characterized by Fourier transform infrared spectroscopy（FTIR） spectra,ultraviolet-visible（UV-vis） absorption spectra and fluorescence spectra,indicating the formation of HA-Fe（Ⅲ） complex.Electron paramagnetic resonance （EPR） spectra show·OH radicals are generated with pulsed laser illumination atλ=355 nm in solutions containing HA,Fe（Ⅲ） and HA-Fe（Ⅲ） complex.Under the simulated sunlight irradiation（500 W Xe lamp,λ＞290 nm）,the photodegradation of 2,4-D followed the pseudo-first-order reaction kinetics.The pseudo-first-order rate constant of 2,4-D photodegradation with the presence of only 2,4-D（2 mg/L） was 0.007 h^-1.In the presence of HA（5 mg/L）,Fe（Ⅲ）（0.2 mmol/L） and HA-Fe（Ⅲ） complex,the rate constants of 2,4-D degradation were 0.004,0.034,and 0.046 h^-1,respectively.The results indicated that in the coexistence of HA and Fe（Ⅲ）,the formed HA-Fe（Ⅲ） complex showed better increased effect on the photodegradation of 2,4-D and had better photo-catalytic activity.（2） Based on the different polarity,HA was separated into four fractions（F_A,F_B,F_C,and F_D） from weak to strong by silica gel chromatogram using different volume proportions of ethanol and water as the mobile phase.Elemental analysis,UV-vis absorption spectra and FTIR spectra showed that the fractions F_C and F_D possessed more aromatic C=C content.The influences of HA and its fractions on the photolysis were investigated by the photodegradation of 2,4-D solutions under 500 W Xe lamp irradiation.All the bulk HA and its fractions decreased the degradation rates of 2,4-D.The fractions of strong polarity F_C and F_D retarded the degradation rate more than the fractions of weak polarity F_A and F_B,indicating the photochemical activity of HA depended on its structure and functional group.（3） Copper phthalocyanine（CuPc） imprinted polymers（MIP） were synthesized successfully and employed to separate phthalocyanine-like（Pc-like） substances from HA using MIP technique effectively.EPR spectra indicated that more·OH radicals were generated in solution of the Pc-like fraction(F_mip-b) under light irradiation（λ=355 nm）.F_mip-b presented better photochemical activity for degradation of 2,4-D when irradiated by simulated sunlight（Xe lamp phytotron,λ＞290 nm）.The pseudo-first-order rate constant of 2,4-D photodegradation in the presence of F_mip-b was 2.5 times as high as that the presence of effluent fraction(F_eff).（4） Chlorophyll-MIP,hemin-MIP,and meso-tetraphenylporphine-MIP（TPP-MIP） were employed to separate structure-like substances from HA,respectively.Furthermore,the integration of chlorophyll-MIP,hemin-MIP,and TPP-MIP was used to separate extendedπ-conjugated porphyrin-like substances from HA.Under the simulated sunlight irradiation （Xe lamp phytotron,λ＞290 nm）,the porphyrin-like fraction(F_mip-b) in HA presented better photochemical activity for degradation of 2,4-D than effluent fraction(F_eff).According to these results,separating HA using silica gel chromatogram or MIP technique was feasibile,and the fractions with better photochemical activity were separated from HA effectively.Our results also indicated the different fractions of HA affected geochemistry process of other coexisting organic compounds evidently.These works are helpful for understanding the mechanism of PTS photodegradation in the presence of HA in nature.更多还原