Hydrodechlorination of 2,4,6-trichlorophenol for a permeable reactive barrier using zero-valent iron and catalyzed iron

Dehalogenation of toxic organic compounds has been intensively studied during the last decade by using zero-valent iron (ZVI). However, the reactivity of iron is compound specific and very low reactivities were reported for aromatic compounds including chlorophenols. In this study, hydrodechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) was conducted in a batch system by using ZVI and catalyzed iron. No degradation was observed with ZVI over the 40 days experiments. Catalyzed ZVIs removed 2,4,6-TCP and palladium-coated iron (Pd/Fe) and nickel-coated iron (Ni/Fe) showed relatively enhanced reactivity while copper-coated iron (Cu/Fe) and platinum-coated iron (Pt/Fe) showed lower reactivities. The surface area normalized kinetic constants (k _SA ) of Pd/Fe, Ni/Fe, Cu/Fe, Pt/Fe are 2.54×10⁻⁴, 1.01 × 10⁻⁴, 2.24×10⁻⁵, 2.56×10⁻⁵ L m⁻² h⁻¹, respectively. The identification of less chlorinated phenols and phenol confirmed that the removal is dechlorination. Pd/Fe system exerts relatively low pH compared with the ZVI system, and the low pH is favorable for the dechlorination. The reactivity enhancement of catalyzed iron was discussed in terms of catalytic effects and the corrosion potential by the bimetal coupling. Variable Pd content on the Pd/Fe was tested, and the degradation rate of 2,4,6-TCP increased in proportion to the increase of Pd content.     

2,4,6-TCP removal mechanism in the process of leaching manganese

ABSTRACT

2,4,6-trichlorophenol (2,4,6-TCP) was used in the leaching system of manganese/pyrite to achieve the simultaneous utilization and removal of 2,4,6-TCP. When the initial concentration of 2,4,6-TCP was 300 mgL^?1 and the weight percentage of pyrite was 12.8%, the removal of 2,4,6-TCP was 83.3%, meanwhile, the leaching efficiency of manganese was 97.6%. Fourier Transform Infrared Spectroscopy (FTIR) showed that the removal of 2,4,6-TCP mainly relied on the chemical oxidative degradation by Mn (IV) and the surface adsorption by leaching residue, including physical adsorption and chemical adsorption. Gas Chromatography–Mass Spectrometry analysis and Chemical Oxygen Demand (COD) indicated that 2,4,6-TCP was degraded to inorganic substances eventually.     

Degradation of carbon tetrachloride in modified Fenton reaction

We showed that the dechlorination of carbon tetrachloride (CT) can be significantly enhanced at nearneutral pH by modified Fenton reaction in the presence of Fe(II) chelated by cross-linked chitosan (CS) with glutaraldehyde (GLA). CT dechlorination was verified by monitoring the release of chloride and detection of intermediates such as trichloromethane and dichloromethane in the modified Fenton system with Fe(II) chelated by cross-linked CS with GLA (Fe(II)-CS/GLA). Measured chlorine mass balance of each sample was greater than 91% of total chlorine mass corresponding to initial CT concentration throughout the reaction. Addition of hydroxyl radical scavenger (2-propanol) enhanced the CT degradation in 5 h at near-neutral pH (removal efficiency from 57.2% to 92.4%), while the addition significantly inhibited trichloroethylene (TCE) degradation at the same condition (74.7% to 19.9%). This implies that, in contrast to the dechlorination of TCE, that of CT did not follow an oxidative dechlorination pathway but a reductive dechlorination pathway in the modified Fenton system with Fe(II)-CS/GLA. Dechlorination kinetics of CT in the modified Fenton system was affected by the concentrations of H₂O₂, Fe(II), and CT. The formation of surface Fe(II)-CS/GLA complex and its valence change from Fe(II) to Fe(III) observed during the modified Fenton reaction gave a clue to identify the proposed reaction mechanism properly.     

Structural and Catalytic Differences between Two FADH(2)-Dependent Monooxygenases: 2,4,5-TCP 4-Monooxygenase (TftD) from Burkholderia cepacia AC1100 and 2,4,6-TCP 4-Monooxygenase (TcpA) from Cupriavidus necator JMP134

2,4,5-TCP 4-monooxygenase (TftD) and 2,4,6-TCP 4-monooxygenase (TcpA) have been discovered in the biodegradation of 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4,6-trichlorophenol (2,4,6-TCP). TcpA and TftD belong to the reduced flavin adenine dinucleotide (FADH(2))-dependent monooxygenases and both use 2,4,6-TCP as a substrate; however, the two enzymes produce different end products. TftD catalyzes a typical monooxygenase reaction, while TcpA catalyzes a typical monooxygenase reaction followed by a hydrolytic dechlorination. We have previously reported the 3D structure of TftD and confirmed the catalytic residue, His289. Here we have determined the crystal structure of TcpA and investigated the apparent differences in specificity and catalysis between these two closely related monooxygenases through structural comparison. Our computational docking results suggest that Ala293 in TcpA (Ile292 in TftD) is possibly responsible for the differences in substrate specificity between the two monooxygenases. We have also identified that Arg101 in TcpA could provide inductive effects/charge stabilization during hydrolytic dechlorination. The collective information provides a fundamental understanding of the catalytic reaction mechanism and the parameters for substrate specificity. The information may provide guidance for designing bioremediation strategies for polychlorophenols, a major group of environmental pollutants.     

纳米钯金铁三金属催化剂的制备及其对三氯乙烯的降解

在乙醇-水体系中利用硼氢化物液相还原法合成纳米铁颗粒,通过化学沉淀法将钯金粒子负载于纳米铁表面,得到纳米钯金铁(Pd-Au@Fe)三金属催化剂复合材料,采用TEM, EDS和XPS对其进行表征. 结果表明,与纳米单金属Fe0及双金属Pd@Fe相比,三金属催化剂对三氯乙烯(TCE)具有更高的降解能力. 保持催化剂加量1.4 g/L, Pd/Fe为0.35%(w), Au/Fe为1.0%(w)时,其降解15 mg/L TCE的速度最快,5 min时去除率为88.21%,表观速率常数为0.311 min-1,是相同Pd含量下Pd@Fe双金属催化剂的3.6倍. 随降解反应持续,Pd-Au@Fe的乙烯乙烷生成率及乙烯加氢转换乙烷速率均远高于双金属Pd@Fe.     

Pd/Fe双金属对水中m-二氯苯的催化脱氯

引　言氯代芳烃及其衍生物化学性质稳定 ,易在生物体内累积 ,大多被列为美国EPA环境优先控制污染物 ,一旦进入环境将对人类及其生态环境造成长期威胁 .因此 ,氯代芳烃的治理技术日益引起全球的关注[1] .自 2 0世纪 80年代末提出金属铁屑用于地下水的原位修复以来[2 ,3] ,用Fe0 还原脱氯已成为一个非常活跃的研究领域 ,特别是应用于地下水修复方面的研究 .Fernando等[4～ 7] 将双金属催化剂用于有机氯的催化还原脱氯 ,Fe0 表面的Pd或Ni等金属加速了还原脱氯反应 ,脱氯速率比Fe0 体系快得多 .本研究利用Pd/Fe双金属对m DCB进行了催化还…     

Electrooxidation of 2-chlorophenol and 2,4,6-chlorophenol on glassy carbon electrodes modified with graphite–zeolite mixtures

This work reports the behavior of zeolite–graphite electrodes for the oxidation of 2,4,6-trichlorophenol (2,4,6-TCP) and 2-chlorophenol (2-CP) in a pH 3, 0.5 M Na₂SO₄ electrolyte using cyclic voltammetry, chronoamperometry, electrochemical impedance and galvanostatic electrolysis. Three zeolites with different hydrophobic/hydrophilic balance were used, in order to determine the possible effect of this parameter. On glassy carbon (GC) modified with 80–20 % graphite–zeolite mixtures the voltammetric peak charge of 2-CP oxidation was higher than that on GC modified with graphite alone, clearly showing a catalytic effect of the zeolites. ZSM-5 was the more active zeolite, probably due to its hydrophobic character, which should favor its interaction with the also hydrophobic 2-CP. In agreement with this, the charge-transfer resistance of GC modified with a graphite-ZSM-5 mixture was about half that of GC modified with graphite alone, and its double-layer capacity about 50 % higher, indicating a modification of the interface which favours the reaction. On the contrary, for 2,4,6-TCP both the oxidation peak charge, and the charge-transfer resistance, for GC electrodes modified with graphite–zeolite mixtures was about the same as that of GC modified with graphite alone. This lack of catalytic action could be due to the fact that the oxidation of 2,4,6-TCP requires the release of at least one chlorine atom, this release being so difficult that it cannot be promoted by any of the zeolites studied. However, in prolonged galvanostatic electrolysis practically all the current went to the oxidation of 2,4,6-TCP, while in the case of 2-CP only a small fraction was oxidized. Probably with 2-CP at long times surface poisoning blocked the reaction, as reflected by the fact that the electrolysis potential rose to a value 0.2 V higher than that reached by TCP, and so high that most of the current went to oxygen evolution. The zeolites ZA and ZY decreased the mineralization of 2,4,6-TCP, since they promoted a one-electron oxidation reaction, so that its concentration at 80 min was about 80 % of that observed with graphite alone. The oxidation of 2-CP was not significantly affected by any zeolite as compared with that on graphite.     

IMPREGNATED RESINS CONTAINING DI-(2-ETHYLHEXYL) THIOPHOSPHORIC ACID FOR THE EXTRACTION OF PALLADIUM(H). II. SELECTIVE PALLADIUM(II) RECOVERY FROM HYDROCHLORIC ACID SOLUTIONS

ABSTRACT

The extraction of Pd(II) from HC1 solutions by impregnated resins containing di-(2-ethylhexyl) thiophosphoric acid (DEHTPA or HL) on the Amberlite XAD2 polymeric support has been studied. Graphical and computer analysis with the program LETAGROP-DISTR demonstrated that the Pd(II) extraction can be explained by the formation of metal complexes in the resin phase having the composition PdL₂(HL)₂. DEHTPA/XAD2 resins extracted Pd(II) in the presence of other metals: Pt(IV), Rh(III), Cu(II), Fe(III) as well as Zn(II). The stripping of Pd(II) loaded on the organic phase and the lifetime of the resins were also investigated.     

高分散型纳米级Pd/Fe对4-氯苯酚的还原脱氯

引言氯酚类化合物在医药、农药、塑料、抗氧剂、涂料、制革和造纸等生产过程中有着广泛的应用,是首批列入斯德哥尔摩国际公约的12类持久性有机污染物(POPs)之一,属于典型的环境雌激素[1]。因此,如何修复氯酚类化合物对环境的污染已成为当今环境科学界迫切需要解决的问题。在众多氯酚类化合物的治理方法中,利用廉价的金属铁(Fe0,zero-valent iron,ZVI)及其化合物脱氯为含氯有机物的处理提供了一种具有前景的途径,该法具有简单实用和操作费用低等特点[2-5]。     

Removal of heavy metals from municipal solid waste incineration (MSWI) fly ash by traditional and microwave acid extraction

BACKGROUND: Municipal solid waste incinerator (MSWI) fly ash is regarded as hazardous waste because it contains various toxic metals. A previous study has shown that fly ash can be detoxified by removal of heavy metals. In this work, the extractability of heavy metals from MSWI fly ash by traditional and microwave acid extraction were compared. RESULTS: A 2^{4 ? 1} fractional factorial experimental design was adopted using acid concentration, extraction time, temperature, and liquid/solid (L/S) ratio as the experimental factors for traditional extraction, and acid concentration, extraction time, liquid/solid (L/S) ratio and microwave power as the experimental factors for microwave extraction. The traditional extraction results show that L/S played an important role in Zn, Cd extraction while L/S ratio and extractant concentration were important for Pb extraction. However, no controlling parameter was determined for Cu and Cr extraction. For the microwave extraction, it was shown that L/S was important for Pb and Zn and extractant concentration was important for Pb, Zn and Cd. The time and the power were not significant for the extractability of heavy metals. CONCLUSION: Hydrochloric acid was an effective extractant. Microwave heating promoted extraction and shortened extraction time. Microwave acid extraction treatment is a potentially feasible method for the removal of heavy metals from MSWI fly ash. Copyright © 2010 Society of Chemical Industry     

零价铁对土壤中六氯乙烷还原脱氯研究

本文研究了常温常压下Fe^0及其负载贵金属的多组分体系及其他反应条件对土壤中六氯乙烷还原脱氯效率的影响。实验证明：Fe^0及其负载Pd、Pt、Rh多组分金属体系对六氯乙烷都有还原脱氯作用,Pd、Pt、Rh之间不存在协同催化还原脱氯效应;反应初始pH呈酸性时有利于脱氯反应进行;加入甲醇能够提高六氯乙烷在土壤溶液中的溶解度,但不能有效提高其在土壤中的还原脱氯率;甲酸铵是Fe^0体系对六氯乙烷还原脱氯的良好助剂,当甲酸铵加入量为400mg时,用Fe^0还原六氯乙烷脱氯率可以提高59％左右;相同实验条件下,用Pd／Fe还原六氯乙烷的脱氯率可以提高77％左右。文中对零价铁还原脱氯反应机理和助剂甲酸铵的作用机理作了初步探讨。     

Pd/Fe双金属对1,2,4-三氯苯的催化脱氯

采用Pd/Fe双金属体系对1,2,4-三氯苯（1,2,4-TCB）进行了快速催化还原脱氯的研究.结果表明,在钯的催化作用下,零价铁对1,2,4-TCB有较好的还原脱氯效率.当Pd/Fe双金属的钯化氯为0.06%时,催化剂用量为1g/40mL,反应1h后TCB的脱氯率可达99%.反应速率随钯化氯的提高而增加.反应在Pd/Fe表面进行,符合准一级反应,反应速率常数为0.0837min-1.TCB在催化脱氯的过程中先脱氯成为DCB,再依次脱氯为氯苯和苯.     

Treatment of chlorinated organic contaminants with nanoscale bimetallic particles

Nanoscale bimetallic particles (Pd/Fe, Pd/Zn, Pt/Fe, Ni/Fe) have been synthesized in the laboratory for treatment of chlorinated organic pollutants. Specific surface areas of the nanoscale particles are tens of times larger than those of commercially available microscale metal particles. Rapid and complete dechlorination of several chlorinated organic solvents and chlorinated aromatic compounds was achieved by using the nanoscale bimetallic particles. Evidence observed suggests that within the bimetallic complex, one metal (Fe, Zn) serves primarily as electron donor while the other as catalyst (Pd, Pt). Surface-area-normalized reactivity constants are about 100 times higher than those of microscale iron particles. Production of chlorinated byproducts, frequently reported in studies with iron particles, is notably reduced due to the presence of catalyst. The nano-particle technology offers great opportunities for both fundamental research and technological applications in environmental engineering and science.     

零价金属对土壤中五氯苯酚的脱氯研究

五氯苯酚（PCP）目前仍为国内外普遍而大量采用的防腐剂、杀虫剂和除莠剂，由于它的化学稳定性致使残留不易消失，给环境造成严重污染。本文以恒温培养为方法，气相色谱-质谱联用仪（GC—MS）为检测手段．研究了三种零价金属对在不同土壤中五氯苯酚的脱氯规律。结果表明，五氯苯酚可被Fe、zn、sn还原降解成四氯苯酚．产物为1，2，3，4-四氯苯酚和1，2，4，5-四氯苯酚；在相同土壤中，脱氯性能与零价金属的还原性成正比关系，Fe-Zn混合物的不同质量比对PCP的降解没有协同催化的作用；不同理化性质的土壤，其脱氯效果存在一定的差异．主要讨论了土壤酸度和有机质含量的影响。     

Ba修饰的Pd/C催化剂催化2,6-二氯吡啶加氢脱氯性能

采用浸渍法制备系列不同助剂修饰的Pd/C催化剂,并考察不同助剂对2,6-二氯吡啶加氢脱氯性能的影响。结果表明,助剂Sn使催化剂活性明显下降,Fe、Mg对催化剂活性影响不大,少量Ba的修饰可以提高Pd/C催化剂活性。Ba质量分数为1.0%时,2,6-二氯吡啶完全转化,催化剂可多次重复使用。     

Pd/Fe对-二氯苯的催化脱氯及其动力学

o-Dichlorobenzene (o-DCB) was dechlorinated by Pd/Fe powder in water through catalytic reduction. The dechlorination reaction is believed to take place on the surface site of the catalyst via a pseudo-first-order reaction. The final reduction product of o-DCB is benzene. The dechlorination rate increases with the increase of bulk loading of palladium due to the increase of both the surface loading of palladium and the total surface area. Dechlorination efficiency accounts for 90% at Pd/Fe mass ratio 0.02% and metal to solution ratio about 53.3g-L-1 in 120 minutes. Dechlorination is affected by the reaction temperature, pH, Pd/Fe ratio and the addition of Pd/Fe. Ea is found to be 102.5kJ.mol-1 in the temperature ra,nge of 287-313K.     

锌催化电还原脱氯合成2,3,5,6-四氯吡啶:反应机理和工艺优化

采用循环伏安法和恒电位电解法,探讨了含有ZnCl₂的乙睛水混合溶液中五氯吡啶(PCP)在不锈钢阴极表面电还原脱氯生成2,3,5,6-四氯吡啶(2,3,5,6-TCP)的反应机理;采用恒电流电解法对该电还原脱氯过程的各种工艺条件进行了优化。结果表明:该体系中PCP电还原脱氯生成2,3,5,6-TCP主要遵循以Zn/Zn²⁺为氧化还原媒介的间接电还原机理;优化工艺条件下(阴极液含0.025mol·L^-1HCl+15%(体积分数)水+0.2mol·L^-1苯磺酸钠+0.16mol·L^-1ZnCl₂的乙腈溶液;电流密度为1.25A·dm^-2),0.08mol·L^-1PCP能高选择性地脱氯生成2,3,5,6-TCP,2,3,5,6-TCP的收率和电解电流效率分别可达88.7%和59.1%。     

Palladium Isolation and Purification from Nitrate Media: Efficient Process Based on Malonamides

ABSTRACT

Solvents based on malonamides have been described to be very efficient and selective for liquid-liquid extraction of Pd(II) from nitrate media. The present study details the possibility to selectively extract Pd(II) over common metallic cations, Cu(II), Ni(II), Co(II), Zn(II), Nd(III), Fe(III) and Al(III) using N,N’-dimethyl,N,N’-dibutyltetradecylmalonamide (DMDBTDMA) in toluene. The lowest selectivity was obtained considering Fe(III) and Nd(III), the extraction of all other cations being negligible. Pd(II) distribution and selectivity regarding Fe(III) have been fine-tuned using the aqueous HNO₃ concentration as the sole parameter, so that extraction, scrubbing and stripping steps can be simply designed without the need for other specific metal chelating reagents and/or aqueous media and without the extensive generation of aqueous effluents. DMDBTDMA was also benchmarked with other classical Pd(II) extractants such as tributylphosphate (TBP), dihexylsulfide (DHS), tetraoctyl diglycolamide (TODGA) and bis(2-ethylhexyl)sulfoxide (BESO) in toluene and in n-heptane. Overall, this study reveals that malonamides are very well positioned and should be considered for further processing of aqueous nitrate wastes containing Pd contaminated with common base metals.     

Continuous-mode photocatalytic degradation of chlorinated phenols and pesticides in water using a bench-scale TiO2 rotating disk reactor

Photocatalytic degradation of phenol, chlorinated phenols, and lindane was evaluated in a continuous flow TiO₂ rotating disk photocatalytic reactor (RDPR). The RDPR operated at a hydraulic residence time of 0.25 day and at a disk angular velocity of 12 rpm. At low molar feed concentrations (0.038 mmol/l), the removal efficiencies for phenol and chlorinated phenols were in the order of 86% or higher, whereas the removal efficiency for lindane at a feed concentration of 0.016 mmol/l was in the order of 63%.

For 2,4,6-trichlorophenol (TCP), an increase in the molar influent concentration resulted in a decrease in removal efficiency but in an increase in removal rate. The degradation rate of 2,4,6-TCP followed a saturation type dependancy with the effluent concentration, suggesting a Langmuir–Hinshelwood (L–H) reaction rate equation. A L–H equation was employed to determine the reaction rate constant and the adsorption coefficient for 2,4,6-TCP. The photonic efficiency increased from 0.68% at an influent concentration of 0.13 mmol/l to 2.06% at an influent concentration of 1.0 mmol/l.     

Carbide and Nitride Supported Methanol Steam Reforming Catalysts: Parallel Synthesis and High Throughput Screening

A series of Mo₂C and Mo₂N supported catalysts have been synthesized using a parallel synthesis and high throughput screening approach. The high surface area Mo₂C and Mo₂N supports were prepared using temperature programmed reaction methods. Metals including Co, Cu, Fe, Ni, Pd, Pt, Ru, and Sn were impregnated onto these supports using a synthesis system. Methanol steam reforming (MSR) activities and selectivities for these materials were evaluated using a high throughput-screening reactor. The support type, metal type and concentration, and metal precursor type influenced the activity and selectivity patterns. Of more than 400 materials that were synthesized and evaluated, the Pt/Mo₂N, Pt–Ni/Mo₂N, Pt–Fe/Mo₂N, and Pd–Fe/Mo₂C catalysts possessed the highest activities. Some of these formulations were more active than a commercial Cu/Zn/Al₂O₃ catalyst, however, the CO₂ selectivities were typically lower. At similar conversions, materials that were highly active were not selective while the less active materials were very selective. Many of the highly active catalysts included noble metals while the highly selective catalysts included base metals.