【作者】 孟昭虹；

【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， 2011， 博士

【摘要】 氯化消毒水中检出的氯乙酸是一类难挥发的氯代有机物。零价铁能够促进氯代有机物还原脱氯,而在零价铁表面加入催化剂钯可以极大地促进氯代有机物的脱氯速率。由于纳米Pd/Fe催化还原剂具有较高的比表面积和表面反应活性,比普通金属铁脱氯速率快。为了有利于Pd/Fe催化还原剂的回收和提高脱氯效率,需要将纳米Pd/Fe催化还原剂固定在载体上。本研究主要对PVDF载体进行表面改性和基体改性,制备负载型的纳米Pd/Fe催化还原剂用于脱除水中氯乙酸。PVDF载体表面改性,采用对PVDF载体亲水化改性、原位聚合改性和直接涂覆法,制备不同改性法负载的纳米Pd/Fe/PVDF催化还原剂,分析不同表面改性方法在载铁量和脱氯率上的差异,发现亲水化改性和原位聚合改性在载铁量和脱氯率上没有明显的区别,但是都远大于直接涂覆法。研究PVDF基体改性,利用相转化法制备了纳米PVDF·Al₂O₃载体,添加不同量（0%⁴%）的Al₂O₃于PVDF溶液中,制备PVDF·Al₂O₃有机-无机改性载体。通过对PVDF·Al₂O₃载体的机械强度、接触角、和比面积的筛选,确定Al₂O₃添加量为2%时,PVDF·Al₂O₃作为载体效果最佳。将2%的PVDF·Al₂O₃改性载体浸泡在不同浓度的交联液中,交联液的主要组分是聚丙烯酸、乙二醇和FeSO₄·7H₂O,通过对改性载体上载铁量分析和对一氯乙酸脱氯率的实验,确定交联时间15分钟,交联液中FeSO₄·7H₂O的浓度为2.9%时,改性载体上纳米Pd/Fe催化还原剂的负载量最大,颗粒分散效果最好,计算单位面积的载铁量为0.52 mg/cm2。对基体改性的PVDF载体、PVDF·Al₂O₃改性载体、纳米Pd/Fe/PVDF·Al₂O₃催化还原剂进行扫描电镜（SEM）、能谱分析（EDS）、透射电镜（TEM）、原子力显微镜（AFM）、X射线衍射光谱（XRD）表征和分析载体的表面形态、内部形态和结构,纳米Pd/Fe/PVDF·Al₂O₃催化还原剂的形状和粒径、晶体结构、钯化率和Pd/Fe负载均匀度。结果表明,制备的纳米Pd/Fe催化还原剂负载在PVDF·Al₂O₃载体上时,颗粒不易团聚,分散效果好,粒径较均匀,载体表面的Pd/Fe催化还原剂直径在50¹50nm之间。负载的纳米铁主要以? -Fe0形式存在,进一步证明了PVDF·Al₂O₃具有良好的负载性能。考察了钯化率、Pd/Fe催化还原剂投加量、初始浓度、Pd/Fe颗粒保存时间、PVDF·Al₂O₃载体的使用寿命等因素对氯乙酸（一氯乙酸、二氯乙酸、三氯乙酸）脱氯率的影响。研究发现,当钯化率小于0.511%时,随着钯化率的增高,纳米Pd/Fe/PVDF催化还原剂对一氯乙酸的脱氯率会增大,钯化率大于0.511%时,随着钯化率的增高,纳米Pd/Fe/PVDF催化还原剂对一氯乙酸脱氯率会减小。增加Pd/Fe颗粒投加量可以促进脱氯反应的进行,不同初始浓度下,Pd/Fe催化还原脱氯效果会随初始浓度增加而下降。研究中将纳米Pd/Fe/PVDF·Al₂O₃催化还原剂长期保存于无水乙醇中,其载铁量和脱氯率都没有明显变化,纳米Pd/Fe/PVDF·Al₂O₃催化还原剂具有较好的稳定性和使用效果。分析了PVDF·Al₂O₃基体改性机制,研究纳米Pd/Fe/PVDF·Al₂O₃催化还原剂对不同浓度目标污染物氯乙酸（一氯乙酸、二氯乙酸、三氯乙酸）脱氯反应机理。研究表明纳米Pd/Fe/PVDF·Al₂O₃催化还原剂对氯乙酸脱氯满足假一级反应动力学。一氯乙酸、二氯乙酸、三氯乙酸的表观反应速率常数分别为0.0969min^-1, 0.1254 min^-1,0.2859 min^-1。更多还原

【Abstract】 Chloroacetic acid detected in chlorinated wate is a kind of less volatile halogenated organics. Zero-valent iron（ZVI） can catalytic dechlorinate chlorinated organic compounds （COCs）, the dechlorination reaction rate can be increased with palladium coated on ZVI surface. Because of high surface area and reaction activity, Pd/Fe bimetallic system has higher dechlorination efficiency than iron. Pd/Fe bimetallic system was immobilized in carrier to retrieve Pd/Fe bimetallic nanoparticles and improve the dechlorination efficiency. The PVDF carrier surface modification and the self-made PVDF matrix modification was aim to immobilize Pd/Fe nanoparticles system for the dechlorination of chloroacetic acid in this study.Three kinds of surface modified PVDF carrier-immobilized Pd/Fe nanoparticles by hydrophilization method, in situ method and direct dip-coating method were studied. The result showed that: hydrophilization method and in situ method have no obvious difference in Fe loading and dechlorination efficiency, but was higher than direct dip-coating method.Adding different quantity （0%⁴%） nano Al₂O₃ particles into PVDF solution to prepare PVDF·Al₂O₃ organic-inorganic modified carrier. The best effect of PVDF·Al₂O₃ carrier is 2% Al₂O₃ adding, which studied by mechanical strength, contact angle and specific surface area. 2% PVDF·Al₂O₃ carrier dipped into different concentration cross-linking solution constituted with PAA, EG and FeSO₄·7H₂O to confirm the FeSO₄·7H₂O quantity in cross-linking solution. When cross-linking time is 15 minutes and FeSO₄·7H₂O content is 2.9%, Pd/Fe catalytic reductant in the PVDF·Al₂O₃ carrier have maximum loading and better disperse and Fe loading is 0.52 mg/cm2 by analyzing Fe loading and MCAA dechlorination efficiency.PVDF carrier, PVDF·Al₂O₃ modified carrier and Pd/Fe/PVDF·Al₂O₃ catalytic reductant were extensively characterized according to SEM, EDS, TEM, AFM and XRD to explicit the morphology and construct of modified PVDF matrix and identify the Pd/Fe particle shape and diameter, crystal structure, Pd content, and Pd/Fe loading evenness. The characterization showed that Pd/Fe/PVDF·Al₂O₃ catalytic reductant had smaller aggregation with good scattered tendency and were more evenly sized with a diameter in the range of 50^-150 nm, the crystal structure of iron was a regular -Fe0. The results show that PVDF·Al₂O₃ carrier has benign properties.Discussion the factor of chloroacetic acid dechlorination including Pd loading, Pd/Fe catalytic reductant quantity, initial concentration, Pd/Fe in different conservervation time, PVDF·Al₂O₃ using time. The results indicated that the dechlorination rate of chloroacetic acid by Pd/Fe/PVDF·Al₂O₃ increased with Pd loading increasing when Pd loading less than 0.511% and dechlorination rate decreased with Pd loading increasing when Pd loading more than 0.511%. Increasing Pd/Fe nanoparticles addition resulted in the increase of dechlorination efficiency. The dechlorination rate of chloroacetic acid decreased with high initial concentration. Fe loading and dechlorination rate of chloroacetic acid have no obvious change when Pd/Fe/PVDF·Al₂O₃ catalytic reductant long-term conserved in alcohol solution, which showed Pd/Fe/PVDF·Al₂O₃ catalytic reductant has good stabilization.Analysed the mechanism of PVDF·Al₂O₃ matrix modification and research the dechlorination kinetics of Pd/Fe/PVDF·Al₂O₃ catalytic dechloriantion of MCAA, DCAA, and TCAA. The results indicated that the chloroacetic acid dechlorination accorded with pseudo-first-order kinetics. Reaction rate constants of MCAA, DCAA, and TCAA were 0.0969min^-1, 0.1254 min^-1, 0.2859 min^-1, respectively.更多还原