【作者】 房晓红；

【导师】 王栋；

【作者基本信息】 大连理工大学 ， 环境工程， 2013， 博士

【摘要】 重金属离子广泛存在于各种水体中,具有痕量致毒、生物放大及在生物体内难以降解等特点,对人体健康危害明显,因而重金属污染控制研究已经成为环境保护研究中的重要课题。目前,治理有害重金属污染、净化水质的方法很多,其中,吸附法具有净化效果好、可回收资源、操作简单、实用有效的特点,已得到广泛的应用。吸附法的关键是选择吸附速率快、吸附容量大、再生容易的优良吸附剂。聚苯胺(PANI)是一种新型导电功能聚合物,其分子中含有大量的氨基和亚胺基功能基团,它们对重金属离子具有良好的络合作用,能够对金属离子形成有效络合。这些氨基及亚胺基还具有还原性,可以与一些氧化电位较高的重金属离子发生氧化还原反应吸附。聚苯胺作为重金属吸附剂的这些独特吸附性能,引起了人们的极大兴趣,已经成为国内外研究热点。本论文针对PANI不溶于一般有机溶剂、机械强度差、难以加工的缺陷,利用具有大比表面积的碳材料作为载体,制备聚苯胺／碳复合材料,开展了聚苯胺／椰壳活性炭(PANI/GAC)复合材料和聚苯胺／光谱纯石墨(PANI/SPG)复合膜修饰电极的制备及去除污水中重金属的性能研究。采用原位化学聚合的方法制备了PANI/GAC复合材料,通过正交实验考察了过硫酸铵/苯胺摩尔比、硫酸浓度、反应温度、反应时间等因素对PANI产率的影响,优化了复合材料的制备条件,利用SEM、FT-IR、XRD和XPS等表征测试手段对PANI/GAC复合材料的形貌结构进行了分析。结果表明,过硫酸铵/苯胺摩尔比是影响PANI产率的首要因素,降低温度,延长反应时间有利于提高产率。PANI/GAC复合材料制备的最优条件为,过硫酸铵/苯胺摩尔比为1：1、硫酸浓度为1.0M、反应温度0℃、反应时间12h。冠状堆积的PANI颗粒均匀分布在GAC的表面,表明PANI/GAC复合材料的成功制备。研究了PANI/GAC复合材料对水溶液中Cu2+的吸附性能,考察了pH值,吸附剂用量,吸附时间、金属离子初始浓度和温度等因素对吸附过程的影响以及材料的再生性,对吸附过程进行了动力学和热力学的模拟研究,通过对吸附前后PANI/GAC复合材料进行SEM、EDS、FT-IR、XRD和XPS等表征分析,进行了吸附机理探讨,并与其他常用吸附剂进行了对比。实验结果表明,PANI/GAC复合材料对水中Cu2+的吸附最佳pH为5.5；吸附剂用量2.0g/L；吸附动力学符合二级动力学方程；吸附等温线结果表明,PANI/GAC复合材料对Cu2+的吸附基本符合Langmuir等温吸附方程,根据Langmuir方程计算的饱和吸附量为38.97mg/g与实验得到的数据结果相一致；吸附过程为吸热过程,在15～50℃范围自发进行,并且随着温度的增加,吸附量增大,吸附速率加快；Cu2+是通过化学作用吸附在PANI/GAC复合材料上；吸附了Cu2+的PANI/GAC复合材料可以通过O.lmol/L HCl溶液解吸再生,经过6次循环使用吸附能力降低较少。综上所述,PANI/GAC复合材料充分发挥有机和无机吸附材料的协同作用,具有吸附速率高,成本较低,再生性能良好的特点,是一种高效低成本的吸附剂。同时,采用两步电化学氧化法制备了硫酸(H2SO4)和对甲苯磺酸(p-toluenesulfonic acid, pTSA)掺杂的PANI/SPG复合膜修饰电极, SEM表明H2SO4/PANI复合膜具有多孔的形貌和三维网状结构。整个膜由均匀的一维纳米线构成,纤维直径100-200nnm。pTSA/PANI复合膜的形貌相对松散,纤维短而粗,纤维直径300-400nm。电化学降解表明,与H2SO4掺杂的聚合膜相比,pTSA作为大分子酸掺杂的PANI在较低的电极电位(0.2-0.6V)下稳定性并未提高。但在较高的电极电位范围内(0.7-1.0V),pTSA/PANI复合膜表现出了更加优良的稳定性。发生降解后,pTSA/PANI和H2SO4/PANI复合膜的FT-IR谱带发生蓝移,强度降低,EIS结果表明两复合膜的电荷传递电阻均变大,导电性降低。利用PANI的电化学氧化还原特性,以H2SO4掺杂的PANI/SPG复合膜修饰电极为阴极,通过电化学还原作用处理水中Cr(VI)。结果表明,与裸SPG电极相比,PANI/SPG复合膜修饰电极对Cr(Ⅵ)的电化学还原去除具有优良的催化性能,PANI的部分氧化态,EM2+是Cr(Ⅵ)与PANI主链之间发生电子转移反应的催化媒介；较负的阴极电位、低电解液pH值、适宜的PANI膜厚和电解液温度可促进Cr(VI)的电还原去除；PANI/SPG复合膜修饰电极上Cr(VI)的还原遵循准一级动力学(k°=2.57×10-2min-1);循环伏安和FT-IR技术表明,电催化还原Cr(Ⅵ)后, PANI/SPG复合膜只发生微小的结构变化,与新制备的复合膜相比,使用后的PANI/SPG复合膜修饰电极仍具有优良的电化学活性。更多还原

【Abstract】 Heavy metal ions, which are toxic and non-biodegradable, exist in various kinds of aquatic systems. They are stable and can be accumulated into the human body through the food chain, causing a serious threat to human health. Thus, how to control and manage heavy metal pollution has become a great issue in the environmental protection field.At present, there are lots of treatment methods for heavy metal removal from water. Among these technologies, adsorption has been widely used because of its high efficiency and simplicity to operate. The excellent adsorbent not only should have fast adsorption rate and high adsorption capacity but also it should be low-cost and easy to regenerate. Polyaniline (PANI) is a new conductive polymer and it contains lots of imine and amine groups, which can react with heavy metal ions to form metal complex. In addition, the imine and amine groups of PANI also have the ability to reduce some heavy metal ions with high oxidation potential. Due to these advantages, PANI has attracted great attention and become a hot topic in the field of waste purification.Aiming at the shortcomings of PANI, such as insoluble in common organic solvents, poor mechanical strength and hard to process, granular activated carbon (GAC) with high specific surface area was used to support PANI in this work, and the performance of PANI/GAC composites in heavy metal ions removal was investigated. In addition, doped PANI modified spectroscopically pure graphite (SPG) electrode was prepared and its electro-catalytic properties for heavy metal ions removal were also examined.The main research works and conclusions are as follows:The PANI/GAC composites were prepared by in situ chemical polymerization. The effect of molar ratio of ammonium persulfate (APS) relative to aniline (AN), sulfuric acid concentration, reaction temperature and reaction time were investigated by orthogonal experiment to optimize the preparation condition. The surface morphology and micro-structure of the PANI/GAC composites were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Results indicated that the optimal preparation condition were1:1of APS/AN molar ratio,1.0M of sulfuric acid concentration,0℃and12h of reaction. Among these conditions, APS/AN molar ratio was the most primary factor. Meanwhile, the yield of PANI/GAC could be enhanced by lowering the reaction temperature and prolonged the reaction time. The cauliflower-like PANI particles were uniformly attached to the surface of GAC, indicative of the successful preparation of the PANI/GAC composites.The adsorption performance of the PANI/GAC composites in Cu(II) ions removal from aqueous solutions was evaluated, and the effects of pH, contact time, dosage of adsorbent, the initial concentration of Cu(II) ions and the reaction temperature on adsorption kinetics and material regeneration performance were investigated. Thermodynamic parameters were also calculated. Various techniques, such as SEM, energy dispersive spectrometer (EDS), FT-IR, XRD and XPS, were used to characterize the PANI/GAC composites before and after adsorption, and the adsorption mechanism was proposed. Experimental results showed that the best pH for Cu(II) ions removal was at around5.5and the dosage of the PANI/GAC composites was2.0g/L corresponding to Cu(II) concentration at400mg/L. The adsorption process followed pseudo second-order kinetics and fitted the Langmuir isotherm excellently. According to the Langmuir equation, the saturated adsorbing capacity of Cu(II) ions on the PANI/GAC composites was calculated as38.97mg/g, which was consistent with experimental data. Thermodynamic results indicated that the adsorption processes was endothermic and could happen spontaneously. Thus, higher temperature favors the adsorption of heavy metal ions. The PANI/GAC composites could be regenerated using0.1M HC1as desorption solution because Cu2+ions were adsorbed on the PANI/GAC composites by chemical reaction. The adsorption capacity of the PANI/GAC composites was with little loss after reused for6times. In summary, the PANI/GAC composites can make full use of the synergistic effect of organic and inorganic materials and have the advantages of high adsorption rate, low cost and good regeneration performance, making it an excellent adsorbent.PANI film was also synthesized on SPG surface by a two-step electrochemical polymerization method from sulfonic acid solution and p-toluenesulfonic acid (pTSA) solution. The SEM characterization showed that the morphology of H2SO4/PANI film had porous morphology and three-dimensional textured structure and was composed of uniform ID nanowires with an average diameter of about100-200nm, while pTSA/PANI film was relatively loose and had short and thick fibers with an average diameter of about300-400nm. Electrochemical experiments indicated that the pTSA/PANI film exhibited a better stability than the H2SO4/PANI film at relatively high electrode potential (0.7-1.0V). After degradation, the FT-IR bands of the pTSA/PANI and H2SO4/PANI film were both blue-shift and with a lower intensity. The results of electrochemical impedance spectroscopy (EIS) illustrated that the ion transfer impedances of two modified electrodes were increased and their conductivities were also significantly reduced. The electro-reduction of Cr(VI) to much less toxic trivalent state (Cr(III)) was subsequently studied on the H2SO4/PANI modified SPG (PANI/SPG) electrode. Compared to the bare SPG, the PANI/SPG electrode exhibited better electro-catalytic performance in Cr(VI) reduction. The partial oxidation state of PANI, EM2+, could act as the catalytic medium for electron transfer between Cr(VI) and the backbone of PANI. It was found that more negative electrode potential, low electrolyte pH, appropriate thickness of PANI film and suitable temperature were beneficial for the removal of Cr(VI). The reduction of Cr(VI) on the PANI/SPG electrode followed pseudo-first-order kinetics (k°=2.57×10-2min-1). The results of cyclic voltammetry and FT-IR illustrated that the H2SO4/PANI film still possessed excellent electrochemical activity and its structure had little changed after electro-catalytic reduction of Cr(VI).更多还原