Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solid electrode

Electroreductive dechlorination of chlorophenols with Pd catalyst supported on solidelectrode was studied. As solid electrodes, carbon cloth (CC), carbon felt (CF) and titanium mesh were used, and palladium was plated on solid electrodes by either electrolytic or electroless method. On each electrode with Pd, chlorophenols were qualitatively dechlorinated to phenol, while they were entirely intact on electrodes without Pd. Moreover, neither base electrode nor plating method significantly affected the activity of Pd as far as it was sufficiently loaded on the electrode. Based on the results in the experiments using one electrode repeatedly, Pd catalyst proved to possess a satisfactory duarability under the present condition. It was suggested that the reactive species responsinble for the dechlorination of chlorophenols could be formed during preliminary electrolysis. Thus, (Pd)_x-H resulting from the adsorption of electrogenerated hydrogen on metallic Pd might be assumed most probable.     

Pd/Fe及纳米Pd/Fe对氯酚的脱氯研究

采用化学沉淀法制备得到了纳米Fe和纳米Pd/Fe(20～100nm),利用制备的纳米催化剂对氯酚进行了催化脱氯研究,并与常规的零价铁和Pd/Fe进行了对比分析.结果表明,纳米颗粒具有较高的比表面积和表面反应活性,所制备的纳米Pd/Fe双金属BET比表面积达到12.4m²/g,而商用铁颗粒(<10m)的比表面积只有0.49m²/g;当钯化率为0.0666%,纳米Pd/Fe用量在6g/L时,氯酚脱氯率达到90%以上,在相同的处理效果下,常规Pd/Fe的使用量为纳米Pd/Fe的20倍左右,纳米Pd/Fe催化氯酚的脱氯降解遵循一级反应动力学.     

Pd/Ti电极上2,4,6-三氯酚还原脱氯:条件优化及降解途径

利用电沉积法制备了Pd/Ti电极,用于2,4,6-三氯酚(2,4,6-TCP)的电还原脱氯.采用单因素实验和响应面分析法,探讨了2,4,6-TCP脱氯试验条件;根据实验结果,拟合出了脱氯中各步骤的反应速率常数.结果表明,2,4,6-TCP初始浓度为80mg/L时,优化的脱氯参数为电流为5mA,支持电解质Na2SO4浓度为0.05mol/L,阴极电解液初始pH值为2.40.在优化条件下, 2,4,6-TCP在80min内完全脱氯; 2,4,6-TCP的还原脱氯符合准一级反应动力学,主要脱氯途径为2,4,6-TCP→2,6-DCP→2-CP→苯酚.     

Catalytic dechlorination of o-cllorophenol by nanoscale Pd/Fe

Transformation of chlorophenols by nanoscale bimetallic particles represents one of the latest innovative technologies for environmental remediation. Nanoscale Pd/Fe bimetallic particles were synthesized in the laboratory for treatment of o-chlorophenol. Most of the nanoscale particles are in the size range of 20-100 nm. BET specific surface area of the nanoscale Pd/Fe particles is 12.4 m2/g. In comparison, a commercially available Fe powder( ＜100 mesh) has a specific surface area of just 0.49 m2/g. Batch experiments demonstrated that the nanoscale Pd/Fe bimetallic particles can effectively dechlorinate o-chlorophenol. Dechlorination efficiency is affected by the mass fraction of Pd in the bimetal, nanoscale Pd/Fe mass concentration and mixing intensity.     

Catalytic dechlorination of o-chlorophenol by nanoscale Pd/Fe

IntroductionTheuseofzerovalentironforthetreatmentofchlorinatedorganiccompounds (COCs )inwaterandgroundwaterhasbeenthefocusofmuchrecentresearch .Thestudieswereconcernedwithcompoundssuchascarbontetrachloride(Bradley ,1995 ) ,trichloroethene(Orth ,1996 ;Chen ,2 0 0 1)andpesticidesandrelatedcompounds(Sayles,1997;Monson ,1998;Eykholt,2 0 0 1;Dombek ,2 0 0 1) .Whenironisincontactwithalessreductivemetal,themetalcouplecanformgalvaniccells.ThishasledtothediscoveryofPd Febimetalliccomplexinwhichpal…     

EDTA优化纳米Pd/Fe对2,4-D的催化脱氯研究

采用EDTA优化纳米Pd/Fe催化脱氯水中2,4-二氯苯氧乙酸(2,4-D),并考察了EDTA投加浓度、pH、钯化率、温度等因素对2,4-D还原的影响.结果表明,EDTA的加入络合了纳米Pd/Fe在催化脱氯过程中生成的铁离子,抑制纳米Pd/Fe颗粒表面钝化层的形成,提高了体系的反应活性.适宜的EDTA浓度、低pH、高钯化率、低温等有利于2,4-D的还原脱氯.当EDTA浓度为25.0 mmol·L-1,纳米铁含量为1.0 g·L-1,初始pH=4.3、钯化率为0.5%,温度为25.0℃,搅拌速率为200 r·min~(-1)时,反应50 min,10.0 mg·L-1的2,4-D去除率及苯氧乙酸(PA)生成率均达到100%.     

CeO2负载型双金属Pd/Fe催化还原四氯化碳的实验研究

实验采用共沉淀法制得CeO_2负载型双金属Pd/Fe催化剂,并对催化剂的结构特征进行了X射线衍射(XRD)和扫描电子显微镜(SEM)分析.使用负载型双金属催化剂对四氯化碳进行还原脱氯研究,探究了温度、溶液初始pH值、催化剂投加量及不同钯载率对四氯化碳脱氯的影响;对比了不同催化剂包括纳米零价铁、纳米钯铁双金属和CeO_2负载型双金属Pd/Fe对四氯化碳的脱氯效果.实验结果表明负载型双金属催化剂在温度为40℃,溶液初始pH为6.5,催化剂投加量为0.4 g·L-1,钯载率为0.5%的条件下,对初始浓度为5 mg·L-1的四氯化碳的去除率高达99.88%.在相同的反应条件下,纳米零价铁和纳米钯铁双金属对四氯化碳的脱氯率分别为58.25%、87.94%.此外,对四氯化碳的脱氯机制进行了探讨.     

纳米级Pd/Fe@SiO2复合颗粒对2,4-DCP的还原脱氯研究

为有效抑制纳米级Pd/Fe颗粒的团聚和钝化及改善其表面特性,将纳米SiO_2包覆在Pd/Fe颗粒表面,超声波辐照下液相还原法制备纳米级Pd/Fe@SiO_2复合颗粒,采用TEM、SEM、XRD、EDX及BET表征其物性,以2,4-二氯苯酚(2,4-DCP)为目标污染物,探究其对2,4-DCP的还原脱氯影响因素、降解机理和动力学,结果表明:制备的纳米级颗粒粒径均匀、分散性好,比表面积大;体系中纳米级Pd/Fe投加量、钯化率、TEOS投加量、反应温度及溶液初始pH均会对2,4-DCP的降解效果产生明显影响;并推测出纳米级Pd/Fe@SiO_2复合颗粒对2,4-DCP的降解机理即快速吸附—逐步脱氯—最终脱附释放,其降解符合拟一级动力学关系.     

碳毡阴极电还原降解氯霉素效能与机制研究

为实现氯霉素（CAP）的稳定高效去除,通过阴极材料筛选优化,构建了以碳毡为阴极的电化学还原体系.实验分别考察了阴极材料、阴极电位、pH、电解质种类和CAP初始浓度对CAP降解效果的影响.结果表明：以碳毡为阴极,电流密度为2.5 mA·cm^-2时,反应30 min后初始浓度为10 mg·L^-1的CAP去除率达到了94.9%,60 min内CAP得以完全去除;CAP中氯的脱除是其降解的重要途径,60 min内氯离子的转化率可达60.5%;碳毡阴极电位降低至-1.4 V （vs.SCE）利于还原降解过程;硝酸根的存在对CAP还原有一定的抑制作用;重复降解实验和扫描电镜（SEM）实验证明了碳毡阴极降解CAP效能的稳定性;通过电子自旋共振（ESR）自由基捕获和猝灭实验初步探讨了CAP的脱氯还原机制,发现原子H^*的生成和电子还原作用是CAP快速降解的主要机制.     

In situ adsorption-catalysis system for the removal of o-xylene over an activated carbon supported Pd catalyst

An activated carbon (AC) supported Pd catalyst was used to develop a highly efficient in situ adsorption-catalysis system for the removal of low concentrations of o-xylene. In this study, three kinds of Pd/AC catalysts were prepared and tested to investigate the synergistic efficiency between adsorption and catalysis for o-xylene removal. The Pd/AC catalyst was first used as an adsorbent to concentrate dilute o-xylene at low temperature. After saturated adsorption, the adsorbed o-xylene was oxidized to CO2 and H2O by raising the temperature of the catalyst bed. The results showed that more than 99% of the adsorbed o-xylene was completely oxidized to CO2 over a 5% Pd/AC catalyst at 140℃. Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), and temperature-programmed oxidation (TPO) were applied to investigate the physical properties of o-xylene adsorption-desorption and the in situ adsorption-catalysis activity of the AC support and Pd/AC catalyst. A synergistic relationship between the AC support and the active Pd species for the removal of low concentrations of o-xylene was established.     

Electrochemical dechlorination of chloroform in neutral aqueous solution on palladium/foam-nickel and palladium/polymeric pyrrole film/foam-nickel electrodes

Electrochemical dechlorination of chloroform in neutral aqueous solution was investigated using palladium-loaded electrodes at ambient temperature. Palladium/foam-nickel （Pd/foam-Ni） and palladium/polymeric pyrrole film/foam-nickel （Pd/PPy/foam-Ni） composite electrodes which provided catalytic surface for reductive dechlorination of chloroform in aqueous solution were prepared using an electrodepositing method. Scanning electron microscope （SEM） micrographs showed that polymeric pyrrole film modified the electrode-surface characteristics and resulted in the uniform dispersion of needle-shaped palladium particles on foam-Ni supporting electrode. The experimental results of dechlorination indicated that the removal efficiency of chloroform and current efficiency in neutral aqueous solution on Pd/PPy/foam-Ni electrode could be up to 36.8% and 33.0% at dechlorination current of 0.1 mA and dechlorination time of 180 min, which is much higher than that of Pd/foam-Ni electrode.     

EDTA对Pd/Fe体系还原脱氯2,4-D的影响

针对Pd/Fe体系对含氯有机物催化还原脱氯过程中,零价铁易腐蚀并在颗粒表面形成钝化层,阻碍目标污染物的进一步脱氯去除,本研究利用乙二胺四乙酸(EDTA)与Fe2+和Fe3+的络合作用,消除Pd/Fe颗粒表面的钝化层,使还原脱氯过程得到持续进行.实验考察了EDTA的投加方式和投加量、p H、钯负载率、温度等因素对2,4-二氯苯氧乙酸(2,4-D)还原脱氯的影响.结果表明:1EDTA浓度为25.0 mmol·L-1、投加速率为20 m L·h-1时,苯氧乙酸(PA)生成率在20 min达到了90.7%.而未加EDTA的反应体系,反应210 min后,PA的生成率仅为74.5%;2EDTA可以络合Pd/Fe体系在催化脱氯过程中生成的Fe2+和Fe3+,防止或减缓了Pd/Fe颗粒表面钝化层的形成,提高了反应活性;3适宜的2,4-D催化脱氯条件为:浓度25.0mmol·L-1的EDTA溶液,投加速率20 m L·h-1、初始p H为4.2、钯负载率0.050%、温度30.0℃、搅拌速率200 r·min-1,反应210 min,20.0 mg·L-1的2,4-D几乎可完全转化为PA;42,4-D催化脱氯的中间产物主要是2-氯苯氧乙酸及微量的4-氯苯氧乙酸,最终产物为苯氧乙酸.     

短链脂肪酸对太湖底泥多氯联苯微生物厌氧脱氯的影响

选取二氯联苯PCB5和PCB12、四氯联苯PCB64和PCB71、类二噁英五氯联苯PCB105和PCB114、六氯联苯PCB149和PCB153、七氯联苯PCB170,考察了添加7.5mmol/L乙酸和7.5mmol/L混合酸（乙酸：丙酸：丁酸=1：1：1）条件下,9种典型商业多氯联苯单体在太湖底泥厌氧微环境中24周内的脱氯降解情况.结果表明：乙酸和混合酸的添加均在一定程度上强化了多氯联苯的降解,多氯联苯总浓度降低速率由（0.276±0.023） mg/（kg·week）分别加快至（0.383±0.033）和（0.410±0.036） mg/（kg·week）;提高了部分脱氯路径的相对反应速率,特别是单侧氯取代的对位脱氯,但未改变脱氯微生物对多氯联苯降解底物的选择性及主要脱氯路径;进一步降低了体系类二噁英多氯联苯总毒性当量（TEQ）,24周降幅均在95%以上;乙酸和混合酸所起到的促进效果并无显著性差异.     

Pd/C气体扩散电极用于电化学降解五氯酚钠的研究

采用氢气还原法制备出Pd/C催化剂,利用循环伏安曲线（CV）对氧在Pd/C催化剂上的电化学还原行为进行了分析,并由催化剂制备成Pd/C气体扩散阴极,采用先通H₂后通空气的方式在隔膜电解体系中对五氯酚钠进行降解,比较了不同电极体系下五氯酚钠的去除效果.结果表明,在阴极室,Pd/C气体扩散电极通过外界曝气提供的O₂在阴极还原产生H₂O₂,电解100 min后H₂O₂的稳定浓度达到9.8 mg/L.实验制备的Pd/C气体扩散阴极既对五氯酚钠具有还原脱氯作用（通入H₂时）,又促进O₂还原生成H₂O₂（通入O₂时）,它对五氯酚钠的去除效果要好于不掺杂Pd的气体扩散阴极.反应120 min后,五氯酚钠平均转化率和脱氯率均超过80%,反应200 min后TOC平均去除率分别超过75%.采用高效液相色谱（HPLC）等手段分析出五氯酚钠在阴极室还原脱氯的中间产物主要是苯酚,Pd/C气体扩散阴极利用电化学还原脱氯和阴阳极同时氧化相结合对氯酚类有机物的降解是可行的.     

Pd/C气体扩散电极用于电生成H2O2降解苯酚的研究

采用自制的Pd/C气体扩散阴极和Ti/IrO2/RuO2阳极,在无隔膜电解槽中对苯酚模拟废水降解效果及机制进行了研究,采用电子自旋共振法(ESR)对电解体系中产生的羟自由基(·OH)进行了检测.结果表明,在Pd/C气体扩散体系中掺杂Pd催化剂可以促进H2 O2的生成(H2 O2的稳定浓度是7.5 mg/L),有利于·OH的产生.经电化学氧化处理120 min后,苯酚和COD的去除率分别达到97.2%和50%,表明在电催化氧化过程中苯酚被氧化生成了大量低分子量中间产物.废水的BOD5/COD值达到0.73是处理前的9.1倍,苯酚废水的可生化降解性通过电化学氧化处理后显著提高.在该电化学体系中苯酚的降解是在阳极直接、间接氧化及阴极产生的H2 O2、·OH的氧化共同作用下完成的.通过对紫外扫描光谱图的分析推断出苯酚在电解过程中有醌类物质生成;由GC-MS检测到了邻苯二酚、对苯二酚、苯醌等芳香族化合物和己二酸、顺丁烯二酸、反丁烯二酸、丁二酸、丙二酸、乙二酸等短链羧酸,据此提出了苯酚降解的可能历程.     

多金属氧酸盐电催化降解染料废水的研究

采用IR和XRD等手段对磷钼酸(PMo12)和3,3',5,5'-四甲基联苯胺(TMB)形成的电荷转移配合物(TMB)3PMo12进行表征,结果表明配合物中的杂多阴离子仍保留着Keggin结构.将配合物负载于γ-Al2O3上制备(TMB)3PMo12/γ-Al2O3负载型催化剂填充于电化学反应器中,考察电催化氧化体系降解酸性大红3R染料废水的效果.研究表明,(TMB)3PMo12/γ-Al2O3催化剂对酸性大红3R废水显示了良好的电催化活性,催化剂填充量为50g,负载量为0.6%时,在pH值为4,槽电压15.0V,曝气量0.14m3/h,极板间距3.0cm反应条件下,60min后,色度去除率达到79.7%,去除效果较传统二维平板和三维电解槽更高.     

Pd/CeO2催化水中溴酸盐的加氢还原研究

采用溶胶-凝胶法制备了CeO2载体,以浸渍法和沉积沉淀法制备了负载型催化剂Pd/CeO2.使用透射电镜(TEM)和Zeta电位仪对催化剂进行了表征.结果表明两种材料的等电点都在5.0左右; Pd颗粒在载体表面具有良好的分散性,且Pd负载量越高,Pd颗粒的粒径越大.采用Pd/CeO2催化剂催化溴酸盐加氢还原,发现在溴酸盐初始浓度为0.39mmol/L时,采用沉积沉淀法和浸渍法合成的Pd/CeO2催化剂反应50min后对溴酸盐的去除率分别为100%和71%,表明使用沉积沉淀法合成的催化剂具有较高的催化活性.改变催化剂用量,溴酸盐的催化还原速率不受传质阻力的影响,反应过程符合Langmuir–Hinshelwood模型,即催化还原反应由溴酸盐在催化剂表面的吸附控制.增加Pd的负载量,溴酸盐的还原速率增大.溶液pH值较低时,有利于对溴酸盐的催化还原.     

利用活性碳毡构建流通式电容去离子器件及其电容脱盐性能研究

采用活性碳毡(ACF)作为电吸附材料,构建流通式(Flow-through)电容去离子(CDI)装置,以模拟盐水为对象,考察了电压、通量、进水初始浓度及盐离子种类等条件对ACF电吸附容量的影响,并与平板式(Flow-by)电容去离子装置对比.结果表明,在流通式运行模式下,ACF电吸附容量随着电压、进水盐浓度的增大而增大,吸盐量最终会达到极值(最大吸附量).ACF电吸附容量会随着进水通量的增大先增大后减小.在电压1.2 V、通量0.053 m L·min~(-1)·cm~(-2)、进水初始浓度1000 mg·L~(-1)的条件下,流通式CDI中ACF对硫酸钠的电吸附容量达到7.73 mg·g~(-1),而平板式CDI中ACF电吸附容量为5.42 mg·g~(-1).此外,还考察了在不同盐离子类型条件下的流通式CDI脱盐效果,结果表明,ACF电极对阳离子电吸附强弱顺序依次为K~+Na~+Ca~(2+),对阴离子电吸附强弱顺序为Cl~-NO_3~-SO_4~(2-).流通式CDI装置在12个周期内脱盐效果并无明显衰减,表明CDI具有较好的稳定性.     

Activated carbon supported TiO2-photocatalysis doped with Fe ions for continuous treatment of dye wastewater in a dynamic reactor

Fe-doped TiO2 coated on activated carbon (Fe-TiO2/AC, FTA) composites were prepared by an improved sol-gel method and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray di ractometry, inductively coupled plasma mass spectrometry and BET surface area analysis. Obtained FTA composites were applied to the continuous treatment of dye wastewater in a dynamic reactor. The e ects of Fe ion content, catalyst content, UV-lamp power and flowrate of the continuous treatment of dye wastewater on degradation e ciency were analyzed to determine the optimum operating conditions of dye wastewater degradation. Continuous photocatalytic experiments provided interesting results that FTA had a high chemical oxygen demand (COD) removal rate compared with TiO2, Fe doped TiO2 (FT) and TiO2 coated on activated carbon (TA). In particular, when using the FTA catalyst with a Fe ion content of 0.33%, the kinetic content (k = 0.0376) of COD removal was more than the sum of both TA (0.0205) and 0.33% FT (0.0166). FTA showed a high photoactivity because of a synergistic e ect between Fe ions and AC on TiO2, which is higher than the individual e ects of AC or Fe ions on TiO2. Additionally, for the photocatalytic degradation of dye wastewater, the optimum Fe ion content, catalyst content, UV-lamp power and flowrate were 0.33%, 6 g/L, 60 W (two lamps) and 300 mL/hr, respectively. An investigation of catalyst reuse revealed that the 0.33% FTA showed almost no deactivation in photocatalytic degradation of naturally treated wastewater.