【作者】 夏至；

【导师】 刘惠玲；

【作者基本信息】 哈尔滨工业大学 ， 环境科学与工程， 2013， 博士

【摘要】 氯代有机物作为一种重要的化工原料，在被广泛应用于工业生产的各个领域的时候，也同时通过各种途径进入环境，成为危害人类健康和生态环境的难降解污染物。以零价铁为代表的高级还原技术的出现和发展，为氯代有机物脱氯去毒性提供了新的视角。相比其他的脱氯方法，零价铁廉价、无毒、无害，还原脱氯反应在常温常压下就可以进行，同时又是零碳排放的环保技术。金属钯催化剂和纳米材料技术引入都使零价铁还原体系的脱氯效率有了质的飞跃，将纳米催化还原剂固定化已经是零价铁高级还原法未来发展的主要趋势。目前膜载纳米双金属颗粒还存在很多问题：现有的PVDF载体膜改性技术有很多缺陷；对小分子含氯少的氯代有机物的去除效果不理想；对膜载双金属催化还原体系还没有系统的机理研究。本文主要研究了通过化学改性法制备新型改性PVDF膜，并用其负载纳米钯/铁双金属颗粒对氯代有机物进行脱氯。首先采用了“碱洗脱氟”、“亲核加成”和“接枝丙烯酸”三步法对PVDF膜进行了亲水化改性，制备出PVDF-g-AA膜。通过正交试验优化了“碱洗脱氟”步骤的反应参数：KOH浓度为0.5mol/L，KMnO4质量浓度为2wt.%，温度为40oC，反应时间为15min；并通过对载铁量和一氯乙酸脱氯实验确定了接枝丙烯酸的最佳浸渍浓度为20wt.%。然后，以“碱洗脱氟”为基础，分别通过接枝法和原位聚合法，制备出两种接枝聚丙烯酸的改性膜，PVDF-g-PAA-1和PVDF-g-PAA-2。通过对载铁量和一氯乙酸脱氯实验确定了接枝聚丙烯酸制备PVDF-g-PAA-1膜的最佳浸渍浓度为30wt.%；通过正交试验优化了“原位聚合法”的反应条件：丙烯酸溶液浓度为30wt.%，BPO投加量为50mg，温度为80oC，反应时间为3h。通过扫描电镜（SEM）、能谱分析（EDS）、X射线光电子能谱（XPS）、红外光谱（FT-IR）、X-射线衍射图谱（XRD）、比表面积（BET）和亲水角的测定来表征和分析了基体改性过程中的PVDF膜、PVDF-g-AA膜、PVDF-g-PAA-1膜、PVDF-g-PAA-2膜以及三种改性膜负载的钯/铁双金属颗粒的表面形态、表面元素及价态分布、表面基团、比表面积和亲水性进行了表征。结果表明，通过接枝改性，三种改性膜均具备了亲水性，且亲水性的大小依次为PVDF-g-PAA-2膜> PVDF-g-PAA-1膜> PVDF-g-AA膜；钯/铁双金属颗粒负载到了改性膜上后，分散性很好，不易团聚，粒径较均匀，大约50nm。考察了三种改性PVDF膜负载纳米钯/铁双金属颗粒的钯化率、投加量、目标污染物初始浓度、反应体系初始pH值和温度对一氯乙酸和2,4-二氯苯酚的脱氯率的影响。对于一氯乙酸的脱氯体系， Pd-Fe/PVDF-g-AA、Pd-Fe/PVDF-g-PAA-1和Pd-Fe/PVDF-g-PAA-2三种膜载催化还原剂的最佳钯化率分别为1.202wt.%、1.197wt.%和1.213wt.%；对于2,4-二氯苯酚的脱氯体系，三种膜载催化还原剂的最佳钯化率分别为0.505wt.%、0.513wt.%和0.576wt.%；当催化还原剂的钯化率小于最佳钯化率时一氯乙酸的脱氯率随着钯化率的增高而增加，钯化率大于最佳钯化率时一氯乙酸脱氯率随着钯化率的增高而减小。增加膜载还原剂的投加量可以促进脱氯反应的进行，增加目标污染物的初始浓度会降低反应体系的脱氯率，增加反应体系的温度可以提高反应体系的脱氯率和速率，与未固定的纳米钯/铁双金属颗粒相比膜载催化还原剂对氯代有机物的催化还原脱氯有较大的pH适用范围。膜载纳米钯/铁双金属颗粒催化还原一氯乙酸和2,4-二氯苯酚的脱氯速率要远高于膜载零价铁纳米颗粒和非固定纳米钯/铁双金属颗粒。通过计算脱氯反应的活化能验证了金属钯的催化性能，零价铁腐蚀产生的氢气在金属钯的表面解离成高还原性的氢原子促进了间接还原反应的进行。同时，载体膜在反应体系中不仅仅起到了负载纳米颗粒的作用，同时通过扩大了钯/铁纳米双金属颗粒的分散度、减少了催化还原反应中纳米双金属颗粒表面的氢气过量累积等方面促进了脱氯反应的进行。三种膜载纳米钯/铁双金属颗粒中，由原位聚合法制备的PVDF-g-PAA-2膜负载纳米钯/铁双金属颗粒的催化还原效果是最好的，而且Pd-Fe/PVDF-g-PAA-2连续7次重复使用，对一氯乙酸去除率可以一直保持在90%以上。接枝聚丙烯酸的PVDF膜上的PAA对Fe2+的具有螯合作用，这既可避免铁流失对水体的二次污染，又能防止铁在水相中被氧化产生钝化层，从而降低膜载纳米钯/铁双金属颗粒失活的几率。更多还原

【Abstract】 Chlorinated organic compounds (COCs) have been introduced into environmentthrough various channels and become persistent organic pollutant (POPs) which areendangering human health and ecological environment, while been used in every area ofindusty as very important chemical materials. Advanced reduction technology, such aszero-valent iron (ZVI) technology, provides a new way for dechlorination anddetoxification of COCs. ZVI is a cheap, non-toxic and harmless technology, which canreduce and dechlorinate COCs at room temperature and atmospheric pressure, and isalso promising zero carbon emissions. After the introduction of Pd the catalyst andNano-materials technology, the ZVI reduction system appears much betterdechlorination efficiency, and now to be supported as nano-scale catalytic reducingagent is the main trend of the future development of ZVI. The film-supported bimetallicNPs technology is still having several problems to deal with: the modification methodsof PVDF films are defective; the catalytic reductive system is not very effective todechlorinate COCs with smaller molecular and less chlorines; and there aren’t anysystematic studies about the mechanism of dechlorination by film-supported Pd/Fe NPs.In this study, Pd/Fe bimetallic nano-particles were supported by noble modifiedpoly(vinylidene fluoride)(PVDF) films, which were prepared by three-step hydrophilicmodification, and used to dechlorinate COCs.First of all, PVDF films were modified to have hydrophilicity and PVDF-g-AAfilms were produced by three modification steps:(1) alkaline treatment to defluorinatethe original PVDF film;(2) nucleophilic addition to hydrophilize the PVDF film; and (3)grafting acrylic acid to change the hydrophilization extent of the modified support film.The reaction parameters of the “alkaline treatment” step were optimized by using anorthogonal test, and the results were: the concentration of KOH was0.5mol/L, theconcentration of KMnO4was2wt.%, reaction temperature was40oC, and reaction timewas15min. The optimal concentration of acrylic acid was experimentally testified as20wt.%by testing Fe loading content of films and dechlorination of monochloroaceticacid (MCAA). Secondly, based on the “alkaline treatment” step, PVDF films weremodified by grafting polyacrylic acid (PAA), and PVDF-g-PAA-1films andPVDF-g-PAA-2films were prepared by grafting method and in situ polymerizationmethod, respectively. The optimal PAA concentration for PVDF-g-PAA-1preparationwas30wt.%, which was testified by testing Fe loading content of films and MCAAdechlorination; and the reaction parameters of the in situ polymerization method wereoptimized by orthogonal experiment, and the results were: the concentration of acrylicacid was30wt.%, the dosage of benzoyl peroxide (BPO) was50mg, reactiontemperature was80oC, and reaction time was3h. PVDF films, PVDF-g-AA films, PVDF-g-PAA-1films, PVDF-g-PAA-2films, andPd/Fe nano-particles (NPs) supported by three kinds of modified PVDF films werecharacterized by SEM, EDS, XPS, XRD, FT-IR, BET, and contact angle analysis toidentify morphology, the composition and valence of surface elements, surface groups,the specific surface area, and hydrophilicity. The results suggest that these three kinds ofmodified films had been hydrophilised (PVDF-g-PAA-2> PVDF-g-PAA-1>PVDF-g-AA); and Pd/Fe bimetallic NPs were immobilized in the support films with adiameter about50nm, which had better dispersion and smaller aggregation tendency.Effects of Pd loading, NPs addition, initial concentration of the contaminant, initialpH value of reaction system, and reaction temperature on dechlorination efficiency ofMCAA and2,4-dichlorophenol (DCP) were investigated. In the MCAA dechlorinationsystem, the optimal Pd loading contents of Pd-Fe/PVDF-g-AA, Pd-Fe/PVDF-g-PAA-1,and Pd-Fe/PVDF-g-PAA-2were1.202wt.%,1.197wt.%, and1.213wt.%, respectively;and in the DCP dechlorination system, the optimal Pd loading contents were0.505wt.%,0.513wt.%, and0.576wt.%, respectively. Dechlorination efficiency of both MCAA andDCP increased with the increase of Pd loading content when Pd loading was below theoptimal content, while decreased when Pd loading was beyond the optimal content.Increasing NPs addition or reaction temperature resulted in the increase ofdechlorination efficiency, whereas increasing initial concentration of MCAA or DCPcaused the decrease of dechlorination efficiency. The dechlorination system byfilm-supported Pd/Fe NPs were more tolerant in pH change than the system by freesuspended Pd/Fe NPs.Film-supported Pd/Fe NPs had better dechlorination efficiency of MCAA or DCPthan both film-supported ZVI NPs and free suspended Pd/Fe NPs. The catalysis of Pdwas testified by calculating the activation energy of the dechlorination reaction. Thehydrogen produced by the ZVI corrosion could dissociate into highly reducinghydrogen atoms on the surface of Pd NPs, which promotes the indirect reductionreaction. On the other side, the support film doesn’t only play the role of loading NPs,but also could promote the dechlorination by increasing the dispersion of Pd/Fe NPs anddecreasing the excessive accumulation of hydrogen on the surface of Pd/Fe NPs.Among three kinds of film-supported Pd/Fe NPs, Pd-Fe/PVDF-g-PAA-2appeared thebest catalytic reductive efficiency. Moreover, The stability of Pd-Fe/PVDF-g-PAA-2were preliminarily studied by a reusing batch experiment where above90%dechlorination efficiency of MCAA was accomplished for7times. The good chelationfor Fe2+of PAA on the PVDF-g-PAA-2would avoid the secondary pollution caused bythe dissolved iron and prevent the formation of iron oxide passivation layer, whichcould avoid the deactivation of immobilized Pd/Fe NPs.更多还原