【作者】 方国东；

【导师】 司友斌；

【作者基本信息】 安徽农业大学 ， 环境科学， 2010， 硕士

【摘要】 2,4-D和阿特拉津是广泛使用的有机氯类除草剂,其在环境中残留期长、难以降解,传统的处理技术存在降解不完全、效率低等缺点。纳米技术的发展给污染物的处理带来了一种新的颇具潜力的方法,纳米材料具有比表面积大、高化学反应活性等特点。本文采用纳米四氧化三铁（Fe₃O₄）降解2,4-D和阿特拉津,将分子结构中吸电子基团—氯原子通过还原的方式脱去,虽然不能彻底达到矿化2,4-D和阿特拉津的目的,但脱氯增加了2,4-D和阿特拉津的可生化性。主要的研究内容和结果如下;1采用Fe₃O₄降解水溶液中2,4-D和阿特拉津,结果表明:Fe₃O₄对水溶液中2,4-D和阿特拉津有明显的降解作用,且纳米Fe₃O₄的降解效果优于微米Fe₃O₄。农药初始浓度为10 mg/L、溶液pH 3.0、纳米Fe₃O₄投加量300 mg/L,反应48 h内2,4-D和阿特拉津的浓度分别降为5.2 mg/L、6.2 mg/L;氯离子浓度分别升高到85μmol/L、34μmol/L,2,4-D和阿特拉津的降解是一个脱氯的过程。溶液中2,4-D和阿特拉津的降解符合准一级反应动力学。利用LC-MS和化学动力学模型确定了2,4-D降解的主要产物是苯酚,其它中间产物是2,4-DCP、4-CP、2-CP。2考察了不同因素对2,4-D和阿特拉津降解的影响。2,4-D和阿特拉津初始浓度在0～10 mg/L、纳米Fe₃O₄投加量0～300 mg/L范围内,2,4-D和阿特拉津的降解率随初始浓度和纳米Fe₃O₄投加量的增加而增大;添加H2O2构成类Feton试剂和升高温度可以提高降解率;阴离子对2,4-D和阿特拉津的降解存在抑制作用。溶液pH对2,4-D和阿特拉津的降解有显著影响,pH为3.0～3.5时,纳米Fe₃O₄对2,4-D和阿特拉津的降解效果最好。同时,反应过程中溶液pH逐渐升高,至反应结束,2,4-D和阿特拉津降解体系中pH分别升高至4.9和3.9。纳米Fe₃O₄对2,4-D和阿特拉津的降解是一个耗氢过程,酸性条件有利于降解反应的进行。3采用纳米Fe₃O₄降解土壤中的2,4-D和阿特拉津。纳米Fe₃O₄对不同性质土壤中的2,4-D和阿特拉津都有显著的降解效果。纳米Fe₃O₄投加量为1%、2,4-D和阿特拉津初始浓度为100 mg/kg,反应7 d后,2,4-D在红壤、黄褐土、砂姜黑土中的残留率分别为18%、33%、42%,一级动力学拟合出2,4-D在3种土壤上的降解半衰期分别为2.8 d、5.2 d、7.1 d。阿特拉津降解实验中能得到类似的结果。4从生物效应的角度考察了纳米Fe₃O₄对土壤微生物和酶活性的影响。纳米Fe₃O₄对细菌和放线菌具有激活效应,且随着纳米Fe₃O₄投加量的增加,激活效应逐渐增强,纳米Fe₃O₄投加量为8%时激活效应最显著,对细菌和放线菌的激活率分别为50%和20%;纳米Fe₃O₄对真菌存在抑制作用,投加量为8%,抑制率为48%。纳米Fe₃O₄对淀粉酶、脲酶、中性磷酸酶、过氧化氢酶具有激活效应,纳米Fe₃O₄投加量为2%时,对淀粉酶的激活效应最强,淀粉酶活性从0.075 mg/g增加到0.12 mg/g;投加量从1%～8%时,脲酶、过氧化氢酶的活性分别从0.065 mg/g、0.065 mg/g增加到0.092 mg/g和0.081 mg/g;中性磷酸酶在纳米Fe₃O₄投加量为4%时活性最强,从0.102 mg/g增加到0.15 mg/g。更多还原

【Abstract】 The 2,4-Dichlorophenoxyacetic acid （2,4-D） and atrazine are most commonly used organochlorine pesticides, which are of strong toxicity and difficult to biodegraded. Traditional technologies have some disadvantages such as incomplete degradation, low efficiency and so on. Nanoscale particles represent a new generation of environmental remediation technologies that provide cost-effective solutions to some of most challenging environmental cleanup problems. Nanoscale particles have large surface areas and high surface reactivity. Degradation of 2,4-D and atrazine by Fe₃O₄ nanoparticles were investigated, and Fe₃O₄ can reductively transform the electron-withdrawing chlorine groups to chlorine ion. Even though the further mineralization of the 2,4-D and atrazine could not achieve, the biodegradation of its intermediates and products would become quick and easy because of the reductive dechlorination. The concrete research contents and results were as follows:1. Degradation of 2,4-D and atrazine by nanoscale and microscale Fe₃O₄ were studied. The results showed that 2,4-D and atrazine could be degraded by Fe₃O₄ particles very well, and the removal efficiency by Fe₃O₄ nanoparticles was prior to Fe₃O₄ microparticles. The concentration of 2,4-D and atrazine decreased from 10 mg/L to 5.2 and 6.2 mg/L respectively within 48 h in the presence of 300 mg/L Fe₃O₄ nanoparticles. Meanwhile, the concentration of chloride ion was increased to 85 and 34μmol/L, and the degradation of 2,4-D and atrazine were the reductive dechlorination process. Disappearance of the parent species and formation of reaction intermediates and products were analyzed by LC/MS. The transformation of 2,4-D followed a primary pathway of its complete reduction to phenol and a secondary pathway of sequential reductive hydrogenolysis to 2,4-dichlorophenol （2,4-DCP）, 4-chlorophenol （4-CP） or 2-chlorophenol （2-CP） and phenol. The degradation equations of 2,4-D and atrazine by Fe₃O₄ nanoparticles conformed to pseudo- first-order kinetics.2. The effects of 2,4-D and atrazine initial concentration, the dosage of Fe₃O₄ nanoparticles, pH and temperature on degradation rate of 2,4-D were investigated, respectively. The degradation rate increased with the increase in the initial concentration of 2,4-D from 0 mg/L to 10 mg/L, and increasing the dosage of nanoscale Fe₃O₄ from 0 mg/L to 300 mg/L. Adding H2O2 and raising the reaction temperature will increasing the degradation of 2,4-D and atrazine. The reaction will be hindered in the presence of different anion. The pH of reaction solution significantly influenced on the degradation of 2,4-D and atrazine, and the optimum pH value was 3.0～3.5. Besides, the solution pH increased from 3.0 to 4.9 and 3.9 respectively during the whole experiments.3. The Fe₃O₄ nanoparticles were used to degraded the 2,4-D and atrazine in different soils. The results indicated that 2,4-D and atrazine could be effectively removed by Fe₃O₄ nanoparticles. The residual rate of 2,4-D decreased from 100% to18%, 33% and 42% respectively within 7 d in the presence of 1% Fe₃O₄ nanoparticles in red soil, vertisol and alfisol. The 2,4-D degradation in soils could be described by first-order kinetic equation. The half-lives （t1/2） of 2,4-D were 7.1 d, 5.2 d and 2.8 d for red soil, vertisol, and alfisol, respectively. The degradation of atrazine in soils had the same results as the 2,4-D.4. The magnetic effect of Fe₃O₄ nanoparticles on the activity of the microorganism and enzyme were investigated. The bacteria and antinomies were stimulated by the magnetite treatment, and the stimulation increased along with the percentage of the Fe₃O₄ nanoparticles. The activation rates of bacteria and antinomy were 50% and 20% at the Fe₃O₄ nanoparticles percentage of 8%. However, the fungi was restrained by the magnetite treatment. The Fe₃O₄ nanoparticles could improve the activities of amylase, urease and catalase, and the higher the dosage of Fe₃O₄ nanoparticles the stronger the stimulation. The activity of amylase increased from 0.075 mg/g to 0.12 mg/g, which 2% Fe₃O₄ nanoparticles was added to soil. The activity of urease and catalse increased from 0.065 mg/g to 0.092 mg/g, 0.65 mg/g to 0.81 mg/g in the presence of Fe₃O₄ nanoparticles from 1% to 8%.更多还原