纳米钯/铁双金属体系对氯乙酸还原脱氯研究
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摘要
零价铁作为一种廉价、简单有效的脱氯还原剂,其在处理氯代有机物方面的作用已经得到了普遍肯定。为了提高铁催化还原的效率,人们采用纳米钯/铁双金属颗粒,膜载纳米钯/铁双金属颗粒对氯代有机物进行还原脱氯研究。
     本文采用化学沉淀法制备了纳米钯/体双金属颗粒,采用交联浸涂法制备了载有纳米钯/铁双金属颗粒的催化还原膜,并对纳米钯/铁双金属颗粒和载有纳米钯/铁双金属颗粒的催化还原膜进行了系统研究。
     通过透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X-射线衍射光谱(XRD)、X射线荧光光谱(XRF)、能谱分析(EDS)、BET-N2比表面积等分析检测手段,表征了纳米级Pd/Fe双金属颗粒的形状、大小、晶体结构、钯化率及其比表面积。本研究制备的纳米钯/铁双金属颗粒中Fe主要以α-Fe0形式存在。纳米钯/铁双金属颗粒的直径约为30-50nm,比表面积约51m2/g。
     采用纳米钯/铁双金属颗粒对一氯乙酸进行还原脱氯研究。比较不同还原剂对一氯乙酸还原脱氯效果,考察了纳米钯/铁双金属颗粒投加量、纳米钯/铁双金属颗粒钯化率对一氯乙酸还原脱氯效果影响。结果表明纳米钯/铁双金属颗粒对一氯乙酸还原脱氯的脱氯率是还原铁粉和纳米铁粉对一氯乙酸还原脱氯的脱氯率的7.9倍和1.7倍。在实验条件下纳米钯/铁双金属颗粒投加量为10g/L,钯化率为0.083%时,纳米钯/铁双金属颗粒对一氯乙酸还原脱氯效果最好。
     采用纳米钯/铁双金属颗粒对三氯乙酸进行还原脱氯研究,发现在反应1min内90%以上的三氯乙酸被还原脱氯为二氯乙酸,二氯乙酸在反应30min后基本全部被还原脱氯,产物为一氯乙酸,一氯乙酸随着反应时间的进行浓度先升高后下降。
     采用等离子发射光谱和扫描电子显微镜对催化还原膜的钯化率和膜表面形貌进行了分析。发现实验制备的催化还原膜上纳米钯/铁双金属颗粒实测钯化率低于理论钯化率。HCPF催化还原膜上纳米钯/铁双金属颗粒分散效果效果好于HPF催化还原膜、CPF催化还原膜、PF催化还原膜。
     采用四种工艺制备的催化还原膜对三氯乙酸进行还原脱氯研究。实验结果表明HCPF催化还原膜对三氯乙酸还原脱氯的修正反应速率常数是HPF催化还原膜、CPF催化还原膜、PF催化还原膜的2.1、4.2、7.8倍。
     采用HCPF催化还原膜对三氯乙酸进行还原脱氯研究。考察了钯/铁双金属体系钯化率、催化还原膜投加量、催化还原膜稳定性、溶液水含量和溶液初始浓度对HCPF催化还原膜对三氯乙酸还原脱氯效果的影响。实验结果表明钯化率为0.534%,催化还原膜上纳米钯/铁双金属颗粒投加量多于5.08mg时,三氯乙酸的还原脱氯效果最好。催化还原膜稳定性实验结果表明本研究制备的HCPF催化还原膜可以连续使用四次而不影响三氯乙酸去除效果。水对三氯乙酸的还原脱氯起重要作用,在没有水存在的溶液中,三氯乙酸与载有纳米钯/铁双金属颗粒的催化还原膜不反应。随着三氯乙酸初始浓度的增加,催化还原膜对三氯乙酸的还原脱氯效果下降。
Iron plays an important role in reducing chlorinated organics for its efficiency and convenience. Nanoscale Pd/Fe bimetallic particles and membrane stabilized nanoscale Pd/Fe bimetallic particles were used to enhance dechlorination efficiency of iron.
     Nanoscale Pd/Fe bimetallic particles were prepared by chemical deposition method. Membrane stabilized Pd/Fe bimetallic particles(hybrid membrane) were prepared by dip-coating method. Systematic work on nanoscale Pd/Fe bimetallic particles and membrane stabilized Pd/Fe bimetallic particles were conducted in this study.
     Particle shape, size, crystal structure, Pd to Fe ratio(PFR) and specific surface area of nanoscale Pd/Fe bimetallic particles were studied by transmission electronic microscopy(TEM), scanning electron microscope(SEM), X-ray diffraction(XRD), X-ray fluorescence(XRF), enengy distribution spectra(EDS) and Brunauer-Emmett-Teller-nitrogen(BET) method. Iron element in nanoscale Pd/Fe bimetallic particles prepared in this study existed mainly asα-Fe0. The diameter and specific surface area of nanoscale Pd/Fe bimetallic particles were 30-50 nm and 51m2/g, respectively.
     Nanoscale Pd/Fe bimetallic particles were used to dechlorinate monochloroacetic acid(MCAA). Dechlorination of MCAA with different reducts was studied. Effect of dose and PFR of nanoscale Pd/Fe bimetallic particles on dechlorination of MCAA was detected. Data showed that dechlorination efficiency(DE) of MCAA with nanoscale Pd/Fe bimetallic particles were 6.9 times and 0.7 times larger than that with reductive Fe and nanoscale Fe, respectively. When the amount of nanoscale Pd/Fe bimetallic particles were 10 g/L and PFR was 0.083%, DE of MCAA was the best.
     Nanoscale Pd/Fe bimetallic particles were used to dechlorinate trichloroacetic acid(TCAA). More than 90% of TCAA were dechlorinated to dichloroacetic acid(DCAA) during the first 1 min of reaction. DCAA were dechlorinated completely to MCAA after 30 min and the concentration of MCAA in solution appeared a decrease trend after the increase.
     Surface morphology and PFR of hybrid membrane were studied by inductively coupled plasma atomic emission spectrometer(ICP-AES) and SEM. It was found that metrical PFR of hybrid membrane was lower than theoretical PFR. Nanoscale Pd/Fe bimetallic particles stabilized in HCPF hybrid membrane congregated less than that in HPF, CPF and PF hybrid membranes.
     Four kinds of hybrid membranes were used to dechlorinate TCAA. It was found that modified reaction rate constant of HCPF hybrid membrane was 2.1, 4.2 and 7.8 times as large as that of HPF hybrid membrane, CPF hybrid membrane and PF hybrid membrane, respectively.
     HCPF hybrid membrane was used to dechlorinate TCAA. Effect of PFR of nanoscale Pd/Fe bimetallic particles stabilized in the hybrid membrane, dose of hybrid membrane, stability of hybrid membrane, H2O amount in solution and initial TCAA concentration on dechlorination of TCAA were detected. Data showed that dechlorination efficiency of TCAA could be the best when PFR was 0.534% and dose of nanoscale bimetallic particles stabilized in hybrid membrane was more than 5.08 mg. HCPF hybrid membrane could dechlorinate TCAA with the same dechlorination efficiency during the fist 4 repetition times. H2O plays an important role in dechlorination, and dechlorination of TCAA did not occur without H2O. Dechlorination effect of TCAA decreased as the initial concentration increased.
引文
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