纳米钯?铝双金属对水中3-氯酚的脱氯降解研究

采用置换沉积法制备了纳米钯/铝双金属催化剂,氢解还原去除水相中难降解有毒有机物3-氯酚(3-CP),考察了溶液pH、钯负载量、纳米钯/铝双金属投加量、反应温度对脱氯效果的影响并解析相关反应机制。结果表明:(1)初始pH 3.0时,沉积液中93.25%(质量分数,下同)～96.67%的钯可有效负载于铝材上。(2)在pH为3.0、纳米钯/铝双金属投加量为2g/L、钯负载量为1.16%(质量分数)、反应温度为25℃下降解初始摩尔浓度为0.389mmol/L的3-CP,反应终了时脱氯率在99%以上。利用纳米钯/铝双金属降解氯代有机污染物具有高效低耗的优势,在实际应用上具有较好的前景。     

纳米Pd／Fe双金属颗粒对单氯酚及二氯酚的还原脱氯

采用改进液相化学还原法制备纳米Pd／Fe双金属颗粒，研究其钯化率为0．045％和0．135％的条件下分别对3种单氯酚（2-CP、3-CP和4-CP）和3种二氯酚（2，3-DCP、2，4-DCP和2，6-DCP）的脱氯反应。结果表明，合成的纳米Pd／Fe颗粒分散性良好，粒径分布介于25～40nm。纳米Pd／Fe双金属颗粒对单氯酚及二氯酚具有良好的去除效果，3种单氯酚和3种二氯酚的脱氯难易程度分别为2-CP〉4-CP〉3-CP和2，6-DCP〉2，4-DCP〉2，3-DCP，脱氯反应均符合拟一级反应动力学方程。通过还原脱氯实验揭示了分子中氯原子的化学环境对还原脱氯过程具有明显影响。     

Pd/Fe催化脱氯水中PCE的动力学研究

以GC-MS为分析方法，采用Pd／Fe双金属对水溶液中四氯乙烯（PCE）进行了催化还原脱氯处理，考察了PCE初始浓度、钯含量、Pd／Fe用量和溶液初始pH值等各因素对脱氯效果影响及还原动力学规律。结果表明，Pd／Fe双金属对PCE有较好的还原脱氯效率，反应遵循准一级反应动力学规律，以反应物PCE浓度为参照的反应速率常数K变化范围为0．019min^-1～0．16min^-1，对应的PCE半衰期从6min到36min，揭示反应有可能是在过量的Pd／Fe双金属表面进行。当PCE溶液初始浓度为1mmol／L，投加1．2g钯含量为0．03％的Pd／Fe双金属，在25℃下反应60min，PCE的脱氯率达到95％以上。增大钯含量和Pd／Fe用量可有效提高脱氯率，在初始pH值为弱酸性条件下有利于还原脱氯反应进行。     

超声波和零价铁联用对氯代苯酚脱氯降解作用的研究

采用超声波和零价铁联用对氯代有机物3氯苯酚(CP)、2,4-二氯苯酚(DCP)和2,4,6-三氯苯酚(TCP)模拟废水进行了脱氯处理研究。以单因素法, 考察了铁粉初始投加量、溶液的初始浓度、超声波功率和溶液的pH值等因素对氯代酚降解的影响，并探讨了降解反应动力学。结果表明，超声波和零价铁联用对氯酚具有显著的降解效果，当水样初始浓度为25 mg/L，溶液pH呈弱酸性，超声波功率为200 W时，氯代酚的脱氯效率达到最大值。降解反应符合准一级反应，CP、DCP和TCP的反应速率常数分别0.0613 h^-1、0.374 h^-1和0.197 h^-1。     

维生素B_(12)协同纳米Fe/Cu双金属对五氯酚的催化降解与机理

针对水中含氯有机物的脱氯降解,制备了Fe/Cu双金属纳米颗粒,并引入维生素B12,研究铜负载率和维生素B12的剂量对以五氯酚为典型污染物的脱氯效果。结果表明:维生素B12和纳米零价铜能够有效提升五氯酚的脱氯速率及脱氯程度,脱氯率从4.52%增加到78.55%,降解产物从四氯酚进一步降解为苯酚。实验发现增加铜负载率可使双金属比表面积增大,催化活性位增多;增加维生素B12浓度可促进体系电子传递,使体系还原反应活性提升。铜负载率和维生素B12浓度过大均会使体系反应速率减缓甚至抑制。实验优化铜负载率为10%(质量分数),维生素B12浓度为20 mg·L~(-1)。探讨纳米零价铜和维生素B12的催化机理,以期对降解含氯有机物提供可操作性的参考。     

2-氯酚在超临界水-NaOH体系中的脱氯特性

研究了2-氯酚在超临界水-NaOH体系中的脱氯特性,考察了NaOH添加对2-氯酚转化率、Cl-生成率、脱氯选择性等的影响。实验结果表明,NaOH的添加能够显著提高2-氯酚的转化率、Cl-的生成率和脱氯选择性。2-氯酚的转化率随着NaOH添加量的增大而增大,460℃、25 MPa条件下,NaOH添加量与2-氯酚的摩尔比为1∶1时,停留时间27 s时可实现2-氯酚的完全转化。     

Ni/Fe双金属降解四氯化碳和四氯乙烯的对比试验

以四氯化碳(CT)和四氯乙烯(PCE)为目标污染物,以批试验方法研究Ni/Fe双金属对CT和PCE的还原性脱氯.结果表明:Ni/Fe双金属可有效去除水中的CT和PCE;Ni/Fe双金属对CT和PCE的降解反应均符合准一级反应动力学方程;在相似的反应条件下,Ni/Fe双金属对CT和PCE脱氯的反应速率常数(kobs)之比为1.48和1.67,说明Ni/Fe双金属对CT的脱氯速率要快于对PCE的脱氯速率;Ni/Fe双金属可对PCE完全脱氯,但对CT脱氯过程中产生少量三氯甲烷(TCM).     

PCBs污染土壤的CaO诱导低温热处理脱氯研究

研究了低温热处理脱氯技术对废弃电容器封存点附近污染土壤中多氯联苯脱氯的效果,考察反应温度、反应时间及CaO添加比例对PCBs去除率、脱氯率的影响以及反应前后土壤中污染物的组分变化。实验土样中PCBs浓度为107.7 mg/g,属于罕见高浓度PCBs污染土壤。当反应温度为400℃、停留时间4h、CaO添加比例为10%,PCBs的去除率为87.7%,脱氯率为85.3%。土壤样品中五氯联苯和四氯联苯反应后含量降低或未检出,部分反应后样品检出一氯联苯和联苯,说明在CaO诱导PCBs低温热处理脱氯反应中存在逐步脱氯/加氢反应途径。     

土壤中零价铁还原3-氯硝基苯的作用

利用零价铁在常温常压下对土壤中的3-氯硝基苯的还原，对反应物和产物随时间的变化及反应的各个影响因素进行了研究。实验结果表明，零价铁能够有效地将3-氯硝基苯还原为3-氯苯胺，反应过程中没有检测到脱氯产物。其反应速率随铁粉用量、反应体系含水量的增加以及反应温度的升高而升高，随土壤初始pH值的升高而降低。在土壤中3-氯硝基苯含量约为2.5×10^-6 mol/g，铁粉使用量为25 mg/g，反应体系中含水量为0.75 mL/g，pH值为6.8时，在恒温生化培养箱(25±1)℃反应5 h后，3-氯硝基苯的还原率达到92.75％。     

Ni/Fe/Al2O3·PVDF催化还原剂的表征及制备过程优化

在PVDF基体改性的基础上,采用浸渍法制备出Ni/Fe/Al₂O₃·PVDF催化还原剂。通过对一氯乙酸的脱氯效果研究,对交联液配比及交联时间、不同浓度硫酸镍浸渍时间、镍铁比等因素进行优化,实验优化结果表明,Ni/Fe/Al₂O₃·PVDF催化还原剂对一氯乙酸脱氯60 min脱氯率达到64%。经SEM表征,制备出的双金属在膜载体表面及断面分布均匀,呈球状和片状结构且双金属未发生团聚。     

Catalytic dechlorination kinetics of p-dichlorobenzene over Pd/Fe catalysts

p-Dichlorobenzene (p-DCB) was dechlorinated using Pd/Fe bimetallic catalytic reductants synthesized by chemical deposition. Batch experiments demonstrated that the Pd/Fe bimetallic particles could effectively dechlorinate p-DCB, p-DCB and its intermediate chlorobenzene were removed completely at a Pd loading of 0.02% (weight ratio of Pd to Fe) and Pd/Fe power to solution ratio about 4g 75 ml-1 in 90 min. Dechlorination was affected by various factors such as the reaction temperature, pH, Pd loading percentage over Fe and the introduction of Pd/Fe catalysts et al. Chlorobenzene represents partially stable dechlorinated intermediates in the generation of benzene and part of p-DCB was dechlorinated to benzene indirectly on the surface of Pd/Fe. The dechlorination of p-DCB took place on the surface of the Pd/Fe bimetallic particles in a pseudo-first-order reaction, the activation energy of the dechlorination reaction was determined to be 80.0 kJ mol-1 at the temperature range of 287-313 K.     

Catalytic amination and dechlorination of para-nitrochlorobenzene (p-NCB) in water over palladium-iron bimetallic catalyst

Chemical treatment of para-nitrochlorobenzene (p-NCB) by palladium/iron (Pd/Fe) bimetallic particles represents one of the latest innovative technologies for the remediation of contaminated soil and groundwater. The amination and dechlorination reaction is believed to take place predominantly on the surface site of the Pd/Fe catalysts. The p-NCB was first transformed to p-chloroaniline (p-CAN) then quickly reduced to aniline. 100% of p-NCB was removed in 30 min when bimetallic Pd/Fe particles with 0.03% Pd at the Pd/Fe mass concentration of 3g 75 ml(-1) were used. The p-NCB removal efficiency and the subsequent dechlorination rate increased with the increase of bulk loading of palladium and Pd/Fe. As expected, p-NCB removal efficiency increased with temperature as well. In particular, the removal efficiency of p-NCB was measured to be 67%, 79%, 80%, 90% and 100% for reaction temperature 20, 25, 30, 35 and 40 degrees C, respectively. Our results show that no other intermediates were generated besides Cl(-), p-CAN and aniline during the catalytic amination and dechlorination of p-NCB.     

Bimetallic iron-aluminum particles for dechlorination of carbon tetrachloride

Bimetallic iron-aluminum (Fe/Al) particles were synthesized and tested for their reactivity toward carbon tetrachloride using batch reactors and a flow-through column at near neutral pH. Preparation of bimetallic Fe/Al particles was conducted under acidic conditions under which iron was readily deposited onto the aluminum surface. The SEM image showed clusters of iron on the aluminum surface at the measured Fe:Al molar ratio of about 2:3. Results showed that the presence of zero-valent aluminum successfully prevented the formation of a passive layer at the iron surface and maintained the reactivity of iron. The dechlorination of carbon tetrachloride by bimetallic Fe/Al particles produced chloroform (9%), dichloromethane (17%) and methane (38%). Kinetic analysis suggests that bimetallic Fe/Al particles increased the reactivity toward carbon tetrachloride degradation by a factor of 10 compared to zero-valent iron and possessed a comparable reactivity with nano-sized Fe. The effectiveness of bimetallic Fe/Al particles was further confirmed by the continuous flow column study from which an ageing of bimetallic particles was also observed.     

Rapid and complete dechlorination of PCP in aqueous solution using Ni-Fe nanoparticles under assistance of ultrasound

The Ni-Fe bimetallic particles have been laboratory prepared using sodium borohydride (NaBH4) as the reductant to reduce Ni2+ and Fe2+ in aqueous solution simultaneously, and characterized by TEM, XRD, BET and XPS. The particles were proved to be nanoscale amorphous alloy with an average diameter of about 30 nm and a BET surface area of 20.9 m2 g(-1). Experiments for dechlorination of pentachlorophenol (PCP) by the Ni-Fe bimetallic nanoscale particles in aqueous solutions were carried out under the enhancement of ultrasound. Major factors that influence the dechlorination efficiency, such as initial pH value, Ni content in the Ni-Fe particles, and output power of ultrasonic irradiation, were investigated. The results indicated that Ni-Fe nanoscale bimetallic particles were very effective for the dechlorination of PCP. Dechlorination efficiency was 46% in 30 min under the optimal condition without assistance of ultrasound, whereas it increased to 96% when ultrasonic irradiation was present. Initial pH value showed apparent effect on the dechlorination. As the pH varied from acidic condition to neutral condition, the dechlorination efficiency decreased dramatically. In addition, the dechlorination efficiency was improved with increased Ni/Fe ratio and ultrasonic output power. Less chlorinated phenols including tetrachlorophenol, trichlorophenol, dichlorophenol, monochlorophenol were formed during the initial reaction, and phenol was determined by GC-MS as sole product in the end of reaction.     

Catalytic degradation of chlorothalonil in water using bimetallic iron-based systems

Modified zero valent iron (MZVI) was used to study the transformation of a chlorothalonil (CLT) solution and the variation of the observed degradation rate of the reduction reactions. This was carried out when transition metals e.g. Pd, Cu and Co plated on the surface of micrometric iron particles (< 150 microm) were used as reducing catalytic agents for pesticide removal. Reactions were undertaken under both oxic and anoxic conditions in the presence and the absence of a phosphate buffer solution (PBS). Results of batch studies in nitrogen sparged solutions revealed that incomplete slow dechlorination merely occurred with zero valent iron (ZVI), however, complete rapid dechlorination reactions took place with MZVI especially Fe/Pd. Dechlorination was depicted by studying UV absorbance and MS spectra of CLT and all corresponding by-products. Typical blue shifts (deltalambda = 4-6 nm/chlorine atom) were observed at the same time as chlorine cluster isotopes disappeared. After the plating process, metal loading was controlled by analyzing the remaining metal in the solution by atomic absorption spectroscopy. Experiments showed that CLT degradation mechanism is faster in nitrogen sparged solutions in the absence of PBS. Time needed for complete removal of 2.08 +/- 0.19 microM CLT solution was about 2 h when experiments were conducted with ZVI (t1/2 = 15.0 min) and about 10 min when the reaction was carried out under the same conditions with Fe/Pd 1% (t1/2 = 1.0 min). Degradation rates for all bimetallic systems were determined showing that Pd is the more exciting catalytic transition metal followed by Cu and Co. Furthermore, MZVI method showed obvious advantage to traditional CLT treatment methods.     

Degradation of 2-chlorophenol via a hydrogenotrophic biofilm under different reductive conditions

This research studies the 2-chlorophenol (2-CP) degradation by the hydrogenotrophic biofilm cultivated in three silicone-tube membrane bioreactors under the conditions of denitrification (DN), sulfate-reduction (DS) and dechlorination (DC). Experimental results showed that after acclimation for more than four months with 2-CP, the respective 2-CP removal efficiency was 95% in DN, 94% in DS and 95% in DC reactors, under the condition of influent 2-CP 25 mg/l with hydraulic retention time (HRT) of 15 h. The metabolic pathway of 2-CP was different in different reactors. The 2-CP was thought to be utilized as carbon and energy source in DN and DS reactors, while the dechlorination occurred in the DC reactor in lack of nitrate and sulfate. The pH dramatically affected the 2-CP degradation in all reactors. Experimental results showed that the optimal pH range was around 6+/-0.2 in DN, 7+/-0.2 in DS, and 5.8-7.2 in DC reactors. Both nitrate and sulfate inhibited the 2-CP dechlorination, but the inhibition levels were different. Nitrate completely inhibited the dechlorination at once, while sulfate took a longer time to reach complete inhibition, only after the bacteria were adapted to the sulfate-reducing condition. Both inhibitions were accomplished by taking the place of 2-CP as electron acceptors. H2 served as an electron donor for dechlorination of 2-CP. The dechlorination was apparently stopped when lacking H2 and another pathway was responsible for the 2-CP degradation.     

Electrospun and functionalized PVDF/PAN nanocatalyst-loaded composite for dechlorination and photodegradation of pesticides in contaminated water

A novel approach for the electrospinning and functionalization of nanocatalyst-loaded polyvinylidene fluoride/polyacrylonitrile (PVDF/PAN) composite grafted with acrylic acid (AA; which form polyacrylic acid (PAA) brush) and decorated with silver (Ag/PAN/PVDF-g-PAA-TiO₂/Fe–Pd) designed for the dechlorination and photodegradation of pesticides was carried out. PAN was used both as a nitrogen dopant as well as a co-polymer. Smooth nanofibers were obtained by electrospinning a solution of 12:2 wt.% PVDF/PAN blend using dimethylformamide (DMF) as solvent. The nanofibers were grafted with AA by free-radical polymerization using 2,2′azobis(2-methylpropionitrile) (AIBN) as initiator. Both bimetallic iron–palladium (Fe–Pd) and titania (TiO₂) nanoparticles (NP) were anchored on the grafted nanofibers via the carboxylate groups by in situ and ex situ synthesis. The Fe–Pd and nitrogen-doped TiO₂ nanoparticles were subsequently used for dechlorination and oxidation of target pollutants (dieldrin, chlorpyrifos, diuron, and fipronil) to benign products. Structural and chemical characterizations of the composites were done using various techniques. These include surface area and porosity analyzer (ASAP) using the technique by Brunner Emmett Teller (BET), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM) analyses were done. After dechlorination, the transformation products (TPs) for dieldrin, chlorpyrifos, diuron, and fipronil were obtained and identified using two-dimensional gas chromatography (time-of-flight) with a mass spectrometer detector (GCxGC-TOFMS). Analysis of total organic carbon (TOC) was carried out and used to extrapolate percentage mineralization. Experimental results showed that dechlorination efficiencies of 96, 93, 96, and 90 % for 1, 2, 2, and 3 h treatment period were respectively achieved for 5 ppm solutions of dieldrin, chlorpyrifos, diuron, and fipronil. The dechlorination of dieldrin, diuron, and fipronil follows first-order kinetics while that of chlorpyrifos followed pseudo-first order. Mineralization performance of 34 to 45 % were recorded when Fe–Pd was used, however upon electrospinning, doping, and grafting (Ag/PAN/PVDF-g-PAA-TiO₂/Fe–Pd composite); it significantly increased to 99.9999 %. This composite reveals great potential for dechlorination and mineralization of pesticides in contaminated water.     

Catalytic dechlorination of monochlorobenzene with a new type of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant

A unique type of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant was prepared and used for dechlorination of monochlorobenzene (MCB). The sample Ni(B)/Fe(B) was synthesized by an electroless plating method, in which nanoscale Ni(B) was deposited on the surface of nanoscale Fe(B) synthesized by chemical reduction. The results suggest that the nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant has higher dechlorination efficiency than Ni/Fe(B) catalytic reductant prepared by replacing Fe(B) with Ni(2+) in aqueous solution. The Ni content was found to be an important factor in catalytic dechlorination, with the dechlorination rate increasing with Ni content. The electroless plating method improve the efficiency of the Ni(2+) in the solution. Dechlorination takes place with the existence of nanoscale Ni(B)/Fe(B) bimetallic catalytic reductant via a pseudo-first-order reaction.     

Hydrogenolysis of chlorobenzene,dichlorobenzenes and chlorotoluenes by in situ generated and gaseous hydrogen in alkaline media and the presence of Pd/C catalyst

A method for dechlorination of chloroaromatic compounds at room temperature and atmospheric pressure by an in situ generated––in reaction of Al particles with water––or gaseous hydrogen in alkaline media and the presence of Pd/C catalyst was thoroughly investigated, having in mind its possible application in utilization of organochlorine waste. Conversion degree to dechlorinated compounds depended on the constitution of substrates and ranged between 88% and 96% when in situ hydrogen was used (at substrate (chlorine) to catalyst molar ratio 550:1 and over twofold stoichiometric excess of Al relative to substrate (chlorine); the process lasted ca. 26 h until all Al was consumed), or 90–97% if gaseous hydrogen was purged. Effectiveness of dechlorination was markedly affected by stirring, i.e. size of the stirrer and speed of revolution. Prospects for application of the method described were briefly outlined.