Dechlorination of hexachlorobenzene using ultrafine Ca-Fe composite oxides

Ca-Fe composite oxides with different Ca/Fe atomic ratios were synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy with elemental X-ray analysis (SEM-EDX) and inductively coupled plasma optical emission spectrometer (ICP-OES). Their dechlorination activities were evaluated using hexachlorobenzene (HCB) as a model compound. The results indicate that the dechlorination activity is related to the composition of metal oxides. Different compositions lead to the formation of different phases of Ca-Fe composite oxides. When Ca/Fe atomic ratio was 3.4, the dechlorination activity reached 97%, which was the highest in the dechlorination of HCB at 300 degrees C for 0.5 h. This may be related to the formation of Ca(2)Fe(2)O(5) phase and small agglomerate size of oxide crystal of about 1 microm. The effect of reaction time on HCB dechlorination and the pathway of dechlorination were investigated using the Ca-Fe composite oxide with the highest activity. It was found that hydrodechlorination took place in the destruction of HCB, the dechlorination efficiency is almost 100% after 2 h reaction. After reaction, quantitative measurement of chloride ion and qualitative analysis of CaCO(3) indicate besides hydrodechlorination, other degradation routes may be present. The mechanism of synergic dechlorination using Ca-Fe composite oxides was discussed.     

Dechlorination of chlorinated methanes by Pd/Fe bimetallic nanoparticles

This paper examined the potential of using Pd/Fe bimetallic nanoparticles to dechlorinate chlorinated methanes including dichloromethane (DCM), chloroform (CF) and carbon tetrachloride (CT). Pd/Fe bimetallic nanoparticles were prepared by chemical precipitation method in liquid phase and characterized in terms of specific surface area (BET), size (TEM), morphology (SEM), and structural feature (XRD). With diameters on the order of 30-50 nm, the Pd/Fe bimetallic nanoparticles presented obvious activity, and were suited to efficient catalytic dechlorination of chlorinated methanes. The effects of some important reaction parameters, such as Pd loading (weight ratio of Pd to Fe), Pd/Fe addition (Pd/Fe bimetallic nanoparticles to solution ratio) and initial pH value, on dechlorination efficiency were sequentially studied. It was found that the maximum dechlorination efficiency was obtained for 0.2 wt% Pd loading. The dechlorination efficiency was observed to increase with increasing Pd/Fe addition. The optimal pH value for dechlorination reaction of chlorinated methanes was about 7. Kinetics of chlorinated methane dechlorination in the catalytic reductive system of Pd/Fe bimetallic particles were investigated. The dechlorination reaction complied with pseudo-first-order kinetics.     

Influence of surfactants on the structure of the adsorption layer in the system: Carboxymethylcellulose/alumina

The influence of surfactants: anionic SDS, nonionic Triton-100 and their mixture (SDS/TX-100) on the structure of the adsorption layer in the system: carboxymethylcellulose (CMC)/alumina (Al₂O₃) was measured. The surface charge density of alumina and its zeta potential were determined in the presence of the CMC macromolecules and the surfactant particles. In order to gain more information about the structure of adsorption layer the amount of CMC adsorption in the presence of surfactants as well as the thickness of the CMC adsorption layer were determined. It was proved that in the presence of surfactants mixture (SDS/TX-100) the amount of adsorption of CMC is the highest and the obtained adsorption layer is the thickest. On the other hand, when Triton X-100 is added to the measured system the polysaccharide conformation is closely packed. The amount of adsorption is large but the thickness of the adsorption layer is relatively low. In the presence of SDS macromolecules of CMC form conformation expanded towards the bulk solution. Such a conformation is characterized by the smaller amount of adsorption of polymer but the larger thickness of the adsorption layer.     

Modeling the effects of methanol on iron dechlorination of a complex chlorinated NAPL

Research was conducted to examine the effects of various fractions of cosolvent solutions on dechlorination of toxaphene by zero-valent iron (Fe(0)). Experimental results showed that toxaphene degradation in solution was found to be the result of dechlorination at the Fe(0) surface. The rate of toxaphene dechlorination was also found to reduce with the increase of cosolvent in solution, as the cosolvent presence caused a reduction in toxaphene adsorption to Fe(0) surfaces. Toxaphene sorption to Fe(0) was found to correspond to a Freundlich nonlinear sorption equation and indicated that the linearity of this isotherm in the presence of cosolvent was related to the saturation of solution, which was the ratio of aqueous concentration to the solubility (C(a)/S(c)). When C(a)/S(c)>0.2, the sorption isotherm was almost linear and the concept of cosolvency power can be applied mathematically to describe this process. A mathematical model detailing the sorption and dechlorination of toxaphene by Fe(0) was developed, and showed that experimental data agreed with the theoretically derived data. Overall, results indicated that dechlorination of complex chlorinated substances, such as toxaphene, by Fe(0) can be greatly dependent upon adsorption to the iron surface.     

Effects of transition metal and sulfide on the reductive dechlorination of carbon tetrachloride and 1,1,1-trichloroethane by FeS

Reductive dechlorination of carbon tetrachloride (CT) and 1,1,1-trichloroethane (1,1,1-TCA) by FeS with transition metals (Cu(II), Co(II), and Ni(II)) and hydrosulfide was characterized in this study. The batch kinetic experiments were conducted by spiking each stock solution of CT and 1,1,1-TCA into 33 g/L of FeS suspensions with and without transition metals at pH 7.5. No significant enhancement was observed in the reductive dechlorination of target compounds by FeS with 1mM transition metals. However, except the addition of Cu(II), the reduction rate of 1,1,1-TCA increased with increasing the concentration of transition metals. The rate constants with 10mM Co(II) and Ni(II) were 0.06 and 0.11h(-1), approximately 1.3 and 3.0 times greater than those by FeS alone. The addition of 20mM HS(-) also increased the rate constants of 1,1,1-TCA by FeS by one order of magnitude. SEM analysis showed that the addition of transition metal (Ni(II)) and HS(-) caused a noticeable morphologic change of FeS surface. The transition metal added was substituted by the structural iron resulting in the decrease of iron content of FeS (52.6-46.9%). One third of the transition metal in FeS suspension existed as zero-valent form playing a catalyst role to accelerate the reaction kinetics.     

Direct measurement of interaction force between hydrophilic silica surfaces in triblock copolymer solutions with salt by atomic force microscopy

Triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) are used in various fields as nonionic surfactants. In this study, we measured interaction forces between untreated hydrophilic silica surfaces in solutions with two typical triblock copolymers, Pluronic P123 (PEO₂₀PPO₇₀PEO₂₀) and F127 (PEO₉₉PPO₆₅PEO₉₉), in the presence of 1 mM and 500 mM NaCl using atomic force microscopy (AFM). In solutions at the copolymer concentration of 1 µM, which is below the critical micelle concentration (CMC), the measured interaction forces were monotonically repulsive in the presence of 1 mM NaCl, which suggested the brush-like conformation of copolymers on the surfaces. When the concentration of NaCl was increased to 500 mM, interaction forces became attractive, which indicated the bridging of adsorbed polymers onto surfaces, the strength of which varied depending on the affinity and adsorption density of copolymers. The interactions at the copolymer concentration of 1 mM, which were above the CMC of both copolymers, were steric repulsions between adsorbed micelles on the surfaces with 1 mM of NaCl. For 500 mM of NaCl, an attractive jump after a steric repulsion was observed only in the force curve for P123, which inferred that the displacement of micelles from the surfaces was presumably due to a decrease in the strength of adsorption caused by the dehydration of EO groups. These results indicated that the length of the EO group considerably affected the interactions.     

Interaction of 2,4,6-trichlorophenol with high carbon iron filings: Reaction and sorption mechanisms

Reductive dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) by two types of high carbon iron filings (HCIF), HCIF-1 and HCIF-2 was studied in batch reactors. While the iron, copper, manganese and carbon content of the two types of HCIF was similar, the specific surface area of HCIF-1 and HCIF-2 were 1.944 and 3.418m(2)g(-1), respectively. During interaction with HCIF-1, 2,4,6-TCP adsorbed on HCIF-1 surface resulting in rapid reduction of aqueous phase 2,4,6-TCP concentration. However, reductive dehalogenation of 2,4,6-TCP was negligible. During interaction between 2,4,6-TCP and HCIF-2, both 2,4,6-TCP adsorption on HCIF-2, and 2,4,6,-TCP dechlorination was observed. 2,4,6-TCP partitioning between solid and aqueous phase could be described by a Freundlich isotherm, while 2,4,6-TCP dechlorination could be described by an appropriate rate expression. A mathematical model was developed for describing the overall interaction of 2,4,6-TCP with HCIF-2, incorporating simultaneous adsorption/desorption and dechlorination reactions of 2,4,6-TCP with the HCIF surface. 2,4-Dichlorophenol (2,4-DCP), 2-chlorophenol (2-CP) and minor amounts of 4-chlorophenol (4-CP) evolved as 2,4,6-TCP dechlorination by-products. The evolved 2,4-DCP partitioned strongly to the HCIF surface. 4-CP and 2-CP accumulated in the aqueous phase. No transformation of 2-CP or 4-CP to phenol was observed.     

Reductive dechlorination of 3,3',4,4'-tetrachlorobiphenyl (PCB77) using palladium or palladium/iron nanoparticles and assessment of the reduction in toxic potency in vascular endothelial cells

Palladium-based nanoparticles immobilized in polymeric matrices were applied to the reductive dechlorination of 3,3',4,4'-tetrachlorobiphenyl (PCB77) at room temperature. Two different dechlorination platforms were evaluated using (1) Pd nanoparticles within conductive polypyrrole films; or (2) immobilized Fe/Pd nanoparticles within polyvinylidene fluoride microfiltration membranes. For the first approach, the polypyrrole film was electrochemically formed in the presence of perchlorate ions that were incorporated into the film to counter-balance the positive charges of the polypyrrole chain. The film was then incubated in a solution containing tetrachloropalladate ions, which were exchanged with the perchlorate ions within the film. During this exchange, reduction of tetrachloropalladate by polypyrrole occurred, which led to the formation of palladium nanoparticles within the film. For the second approach, the membrane-supported Fe/Pd nanoparticles were prepared in three steps: polymerization of acrylic acid in polyvinylidene fluoride microfiltration membrane pores was followed by ion exchange of Fe(2+), and then chemical reduction of the ferrous ions bound to the carboxylate groups. The membrane-supported iron nanoparticles were then soaked in a solution of tetrachloropalladate resulting in the deposition of Pd on the Fe surface. The nanoparticles prepared by both approaches were employed in the dechlorination of PCB77. The presence of hydrogen was required when the monometallic Pd nanoparticles were employed. The results indicate the removal of chlorine atoms from PCB77, which led to the formation of lower chlorinated intermediates and ultimately biphenyl. Toxicity associated with vascular dysfunction by PCB77 and biphenyl was compared using cultured endothelial cells. The data strongly suggest that the dechlorination system used in this study markedly reduced the proinflammatory activity of PCB77, a persistent organic pollutant.     

非离子表面活性剂对石墨-H_2O分散液稳定性的影响

选用非离子表面活性剂(TX-100)作为分散剂,制备了稳定性较好的石墨-H2O分散液.通过测定石墨-H2O分散液的吸光度和Zeta电位,探讨了不同TX-100添加量、pH值、电解质对石墨-H2O分散液稳定性的影响,并分析了作用机理.结果表明,TX-100的添加量存在一个最佳值,以石墨质量为基准,TX-100用量为25%时,分散液稳定性最好;分散液受pH值影响较小,在较宽的pH值范围内都能达到稳定,在pH=3的强酸性环境下,由于电荷中和及分散剂吸附状态的变化导致分散液稳定性下降;电解质的加入严重破坏了体系稳定性;该体系中,主要通过空间斥力使石墨粒子稳定,同时静电斥力也是不可忽略的因素;石墨-H2O分散液的粒径分布及粘度曲线表明,石墨粒子在水中达到良好的分散.     

Effect of nonionic surfactants on the solubilization of alachlor

The ability of nonionic surfactants to solubilize the pesticide alachlor was studied. Two homologue series, octylphenol ethoxylates (Triton X-114, Triton X-100 and Triton X-102) and ethoxylated decyl alcohols (Neodol 91-5E, Neodol 91-6E and Neodol 91-8E) were used at concentrations 3 critical micelle concentration (CMC) and 6 CMC. The rate of solubilization of a sufficient quantity of alachlor (for saturation) in aqueous solution containing the micelles of nonionic surfactant was recorded. The experimental data were fitted to a first-order kinetic model. The rate constant, saturation concentration and enhancement factor were estimated for each surfactant system. The effect of surfactant structure, CMC concentration, pesticide structure and its physicochemical properties on the effectiveness of solubilization was determined. In terms of solubilization capability, the nonionic surfactants of each homologue series can be ranked as follows: Neodol 91-8E>Neodol 91-6E>Neodol 91-5E and Triton X-102>Triton X-100>Triton X-114. The more hydrophilic Neodol series was proved more efficient in alachlor solubilization than Triton series. The enhancement factor values ranged from 1.064 to 1.995 at 3 CMC and 1.320 to 2.919 at 6 CMC. The results will be used mainly for micellar-enhanced ultrafiltration since the extent of solubilization is a critical factor.