【作者】 陈勇；

【导师】 孙国新；

【作者基本信息】 济南大学 ， 化学工程（专业学位）， 2021， 硕士

【摘要】 日趋加剧的水污染,已经对人类的生存安全构成了重大威胁。铬化合物是一种典型的水污染源,因为它是许多工业废料的基本成分。铬离子常以Cr（III）和Cr（Ⅵ）形式存在于水相中,浓度在5000 mg/L以下的Cr（Ⅵ）通常以氧阴离子形式(HCrO₄^-,Cr₂O₇^2-或CrO₄^2-)出现,其存在形式受到pH值的影响,pH<2.0时,H₂CrO₄占主导地位,2<pH<6.5时,主要以HCrO₄^-的形式存在,而当pH>6.5时,CrO₄^2-占主导地位。Cr（Ⅵ）具有很高的毒性且易被人体吸收,引发各种癌症,甚至造成遗传性基因缺陷。因此,从水体中去除Cr（Ⅵ）对生态系统和公共健康至关重要。吸附法由于在吸附过程中不产生任何有毒的副产物,可以进行再生,被认为是最经济有效的水体重金属污染处理方法。近年来,许多材料已被用来制备吸附剂以去除水中的Cr（Ⅵ）,例如活性炭,沸石,生物质和聚合物等,但它们存在颗粒小回收难、成本高和重复利用性差等缺点。因此,制备出高再生性和对Cr（Ⅵ）具有优异吸附效果的吸附剂十分迫切。季铵盐衍生物功能化的吸附剂由于含有N⁺离子,可以与水相中的Cr（Ⅵ）氧阴离子形成离子键,表现出良好的吸附性能,被广泛应用于Cr（Ⅵ）吸附。然而,此类吸附剂的功能基团通常只含有单个N⁺,和HCrO₄^-的一个负电荷相匹配,更适合在酸性条件下工作,具有很大的局限性,尤其是应用到中、碱性水体以及污染的土壤时。为了提高吸附剂对Cr（Ⅵ）的捕获效率,吸附剂需要在宽的pH范围内工作。因此,我们根据CrO₄^2-的电荷和构型特点设计了一种预组织双季铵阳离子结构（N⁺-C-C-N⁺）,与中、碱性条件下铬酸根带有的两个负电荷正好匹配,大大提高离子缔合的能力,实现中、碱性条件下Cr（Ⅵ）的高效吸附去除。通过密度泛函理论（DFT）计算了该活性结构和Cr（Ⅵ）的结合能,证实了该结构的有效性。通过将N⁺-C-C-N⁺结构固定在氯甲基化交联聚苯乙烯微球（CMCPS）和线性对氯甲基聚苯乙烯纳米纤维（PVBCl）载体上得到带有特定双季铵结构的ETMEDA-CMCPS和QPVBCl吸附剂,这两种吸附剂都具有许多微孔结构和相互作用位点,能有效提高Cr（Ⅵ）的吸附量与吸附速率,且吸附后的吸附剂与废水溶液通过简单的过滤即可快速分离。本文的具体研究内容如下:（1）中间体（ETMEDA）结构的设计与合成:根据CrO₄^2-的电荷和构型特点,设计出双季铵阳离子结构（N⁺-C-C-N⁺）,其中两个N⁺作为活性位点。通过DFT计算了此结构与HCrO₄^-和CrO₄^2-的结合自由能,发现此结构对CrO₄^2-有更好的选择性,随后通过四甲基乙二胺和溴乙烷反应合成了该中间体。（2）ETMEDA-CMCPS微球的合成:由于中间体季铵盐易潮解且易溶于水,限制了它在吸附中的应用。氯甲基化交联聚苯乙烯微球（CMCPS）具有比表面积大、粒径分布均匀、易回收等优点。将ETMEDA固定在CMCPS载体上,制得了具有特定双季铵盐结构的ETMEDA-CMCPS吸附剂。通过FTIR、EDS、XPS、BET等表征方法,证实成功合成了预期的吸附剂。（3）ETMEDA-CMCPS微球对Cr（Ⅵ）的吸附性能研究:为了评价ETMEDA-CMCPS的吸附性能,探究吸附机理,通过批量吸附实验考察了ETMEDA-CMCPS微球对Cr（Ⅵ）的吸附行为,包括pH值,竞争离子,吸附动力学,吸附等温线和吸附热力学参数的影响。研究发现ETMEDA-CMCPS微球对Cr（Ⅵ）具有良好的吸附能力和选择性。在pH=2.0-12.0范围内对Cr（Ⅵ）吸附效果几乎不受pH值的影响,这与理论结果相一致,且该吸附剂循环使用5次后,对Cr（Ⅵ）移除率仍保持在90%以上。为进一步模拟该吸附剂在实际工业应用中的情况,进行了柱吸附实验,探究了初始浓度对吸附性能的影响。（4）QPVBCl纳米纤维的合成:为了得到比表面积更大的吸附剂,通过静电纺丝法制备了PVBCl纳米纤维,并通过季铵化反应将ETMEDA负载到PVBCl纤维上。通过FTIR、SEM表征方法,证明得到了目标吸附剂。（5）QPVBCl纳米纤维对Cr（Ⅵ）的吸附性能研究:通过批量吸附实验考察了Cr（Ⅵ）在QPVBCl纤维上的吸附行为,包括pH值,实际废水,吸附动力学,吸附等温线和吸附热力学参数的影响。发现该吸附剂吸附Cr（Ⅵ）时受pH值的影响同样很小,对Cr（Ⅵ）的去除率始终保持在80%以上。实验结果表明该纤维吸附剂能广泛的适用于不同酸碱条件下废水中Cr（Ⅵ）的去除,且具有较好的循环再生性能。更多还原

【Abstract】 Increasing water pollution has considered a serious threat to the development of human health,economy,and society.Chromium compounds are typical sources of water pollution because they are basic component of many industrial wastes.Chromium ions often exist in the aqueous phase in the form of Cr（III）and Cr（Ⅵ）.The Cr（Ⅵ）at low concentrations usually appears in the form of oxygen anions(HCrO₄^-,Cr₂O₇^2-,or CrO₄^2-).The existence form is affected by the pH value.When pH<2.0,H₂CrO₄ dominates,when 2<pH<6.5,Cr（Ⅵ）mainly exists in the form of HCrO₄^-,and when pH>6.5,CrO₄^2-dominates.The Cr（Ⅵ）is highly toxic and easily absorbed by the human body,which may cause various cancers and even genetic disorders.Therefore,the removal of Cr（Ⅵ）from water bodies is vital to the ecosystem and public health.Adsorption is considered to be the most efficient method.Toxic contaminants can be completely removed without any toxic by-products.The adsorbent used can be easily regenerated.Different types of adsorbents have been used,such as activated carbon,zeolite,biomass and polymers,etc.However,disadvantages arise due to small particle size,difficult recovery,high cost,and poor reusability.Therefore,developing new adsorbents with high regeneration ability and excellent adsorption performance for Cr（Ⅵ）is a current challenge.The adsorbents functionalized with quaternary ammonium salt derivatives contain N⁺ions,which can form ionic bonds with the oxygen of Cr（Ⅵ）in the aqueous phase,are widely studied.However,such types of adsorbents usually contain a single N⁺,they are more suitable for working under acidic conditions to match HCrO₄^-with one negative charge,which has great limitations when applied to neutral and alkaline water.Therefore,to improve the capture efficiency of adsorbents toward Cr（Ⅵ）,working in a wide range of pH is extremely desired.In this dissertation,we designed a pre-organized diquaternary ammonium cation structure（N⁺-C-C-N⁺）based on the charge and structural configuration properties of CrO₄^2-,which exactly matches the two negative charges of Cr（Ⅵ）under neutral and alkaline conditions.Thus,the ability of ion-association,and the efficient adsorption of Cr（Ⅵ）under neutral and alkaline conditions is improved.The binding energy of the activated structure and Cr（Ⅵ）was calculated by density functional theory（DFT）,which confirmed the validity and effectiveness of the structure.By fixing the diquaternary ammonium cation structure（ETMEDA）on the chloromethylated cross-linked polystyrene microspheres and linear p-chloromethyl polystyrene nanofiber supports,the ETMEDA-CMCPS and QPVBCl with a specific diquaternary ammonium structure are obtained.Both of them are microporous structures and have enormous interaction sites,which can effectively increase the adsorption capacity and adsorption rate of Cr（Ⅵ）.After the adsorption experiments,the adsorbent and wastewater solution is quickly filtered through simple filtration process.The main results and finding in this research content are given as follows:（1）Design and synthesis of intermediate（ETMEDA）structure:Firstly,according to the charge and structural configuration of CrO₄^2-,a diquaternary ammonium salt with a structure（N⁺-C-C-N⁺）having two N⁺as active sites was designed.Then the binding free energy between the two structures,such as HCrO₄^-and CrO₄^2-was further analalzed by DFT calculations.It was found that the designed and fabricated diquaternary ammonium structure has excellent selectivity to CrO₄^2-.The intermediate was synthesized by the reaction of tetramethylethylenediamine and bromoethane.（2）Synthesis of ETMEDA-CMCPS microspheres:The intermediate quaternary ammonium salt is deliquescent and easily soluble in water,which limits its application in adsorption.Chloromethylated cross-linked polystyrene microspheres（CMCPS）have the advantages of large specific surface area,uniform particle size distribution,and easy recovery.ETMEDA was immobilized on the CMCPS carrier to prepare an ETMEDA-CMCPS adsorbent with a specific diquaternary ammonium salt structure.Through FTIR,EDS,XPS,BET characterization methods,it was confirmed that the expected adsorbent was successfully synthesized.（3）Study on the adsorption performance of ETMEDA-CMCPS microspheres of Cr（Ⅵ）:In order to evaluate the adsorption performance of ETMEDA-CMCPS and explore the adsorption mechanism,the adsorption behavior of Cr（Ⅵ）on ETMEDA-CMCPS microspheres was investigated through batch adsorption experiments,including the influence of pH value,competing ions,adsorption kinetics,adsorption isotherms and adsorption thermodynamic parameters.It was found that ETMEDA-CMCPS microspheres have good adsorption capacity and selectivity for Cr（Ⅵ）.In the solution pH=2.0-12.0,the adsorption effect of Cr（Ⅵ）is almost not affected by the pH value,which is consistent with the theoretical results,and the adsorbent can be recycled for many times.In order to further simulate the actual industrial application of the adsorbent,we conducted column adsorption experiments to study the effect of the initial concentration on the adsorption performance.（4）Synthesis of QPVBCl nanofibers:In order to obtain an adsorbent with a larger specific surface area,linear p-chloromethyl polystyrene nanofibers（PVBCl）were prepared by electrospinning,and the ETMEDA was loaded onto PVBCl fiber by quaternization reaction.The FTIR and SEM characterization methods proved that the target adsorbent was successfully obtained.（5）Study on the adsorption performance of QPVBCl nanofibers of Cr（Ⅵ）:The adsorption behavior of Cr（Ⅵ）on QPVBCl fibers was investigated through batch adsorption experiments,including the influence of pH values,actual wastewater,adsorption kinetics,adsorption isotherms and adsorption thermodynamic.The results show that the adsorbent is also affected little by pH variations when adsorbing Cr（Ⅵ）in a wide pH range,and the removal efficiency of Cr（Ⅵ）is always maintained above 80%.The fiber adsorbent can be widely used in the removal of Cr（Ⅵ）in wastewater under different acid-base conditions,and has good recycling performance.更多还原