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.     

Dechlorination of atrazine using zero-valent iron (Fe0) under neutral pH conditions

Zero-valent iron (Fe0) is frequently used for the dechlorination of pesticides, because it is economical, easily acquired and stable. The kinetics of dechlorination by Fe0 are improved at low pH, but this requires additional acid addition, while dechlorination hardly occurs under basic conditions. Due to the buffer capacity of geological materials such as clay and sediment, however, the addition of acid to obtain a low pH may not be effective. In this research, the dechlorination constants of atrazine by Fe0 were measured with the addition of buffer solution to simulate the buffer capacity of sediment. In the presence of the buffer solution, the pH values remained neutral, while dechlorination occurred more slowly than that observed under acid additions but faster than that without any buffer. When the initial concentrations of atrazine were 10mg/L, 30 mg/L, and 50mg/L, its dechlorination was explained using pseudo-first order reaction kinetics. The pseudo-first order constants were 3.01 x 10(-2)d(-1) at 10 mg/L, 3.23 x 10(-2)d(-1) at 30 mg/L and 3.38 x 10(-2)d(-1) at 50mg/L. In addition, the half-lives of atrazine were 8.91 d at 10mg/L, 9.32 d at 30 mg/L, and 10.00 d at 50mg/L. Acid addition may not be omitted to obtain acidic pH conditions when dechlorination is necessary in geologic materials.     

Chemical reduction of an unbuffered nitrate solution using catalyzed and uncatalyzed nanoscale iron particles

Uncatalyzed and catalyzed nanoscale Fe(0) systems were employed for the denitrification of unbuffered 40 mgN L(-1) nitrate solutions at initial neutral pH. Compared to microscale Fe(0) (<100 mesh), the efficiency and rate of nitrate removal using uncatalyzed and catalyzed nano-Fe(0) were highly promoted, in which the maximum promoted rate was obtained using copper-catalyzed nano-Fe(0) (nano-Cu/Fe). Nitrate first-order degradation rate constants (k(obs)) decreased significantly (>70%) with aged nano-Fe(0) and aged nano-Cu/Fe, and were recovered with NaBH(4) as reductants at levels of about 85 and 75%, respectively. Activation energies (E(a)) of nitrate reduction over the temperature range of 10-60 degrees C were 42.5 kJ mol(-1) for microscale Fe(0), 25.8 kJ mol(-1) for nano-Fe(0) and 16.8 kJ mol(-1) for nano-Cu/Fe. Unlike microscale Fe(0), the kinetics of denitrification by nano-Fe(0) and nano-Cu/Fe began to show characteristics of mass transport in addition to chemical reaction control. Ammonium was the predominant end product in all the systems. However, as for nitrite, 40% of the degraded nitrate persisted in the nano-Cu/Fe system. Thus, relative to nano-Cu/Fe, nano-Fe(0) is a potential reductant for denitrification of groundwater as far as toxic nitrite generation is concern.     

纳米钯/铁双金属颗粒对一氯乙酸的脱氯

为了提高零价铁对氯代有机物还原脱氯的性能,采用还原沉淀法制备了纳米钯/铁双金属颗粒.利用X射线衍射(XRD)、X射线荧光光谱(XRF)、扫描电子显微镜(SEM)、透射电镜(TEM)、以及BET-N2比表面积法对纳米钯/铁双金属颗粒进行了表征.结果表明,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.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.     

Creep of (Mg,Fe)O single crystals

The creep behaviour of (Mg, Fe)O single crystals compressed along 1 0 0 has been investigated over the temperature range 1300 to 1500° C, at stresses between 20 and 70 MPa, for oxygen partial pressures between 10^–4 and 10² Pa, and with iron concentrations between 70 and 11 900 p.p.m. Under these conditions, the dependence of the steady-state strain rate on stress, temperature, oxygen partial pressure, and iron concentration can be summarized by the flow law, exp (–445 kJ mol^–1/RT. These results suggest that the steadystate strain rate is controlled by dislocation climb with a jog velocity which is limited by lattice diffusion of oxygen by a vacancy pair mechanism. The activation energy for creep, 445 kJ mol^–1 is larger than that reported for self-diffusion of oxygen, 330 kJ mol^–1, because the formation energy for jogs is relatively large, 115 kJ mol^–1.     

Photodegradation mechanism and kinetics of methyl orange catalyzed by Fe(III) and citric acid

In this study, the photodegradation process of methyl orange (MO) catalyzed by Fe(III) and citric acid and the reaction kinetics were investigated in detail at pHs from 2 to 8. The results show that the photodegradation of MO is slow in the presence of Fe(III) or citric acid alone. However, it is markedly enhanced when Fe(III) and citric acid coexist. High initial citric acid or initial Fe(III) concentrations lead to increased photodegradation of MO. And Fe(III) citrate mediated photodegradation of MO is optimized at pH 6. The photoproduction of hydroxyl radicals (·OH) in different catalytic systems was determined by HPLC. And the concentrations of Fe(II) and citric acid concentration in the process of the reaction were analyzed. The photodegradation of MO obeys to pseudo-zero order kinetics with respect to MO and the degradation reaction occurs in two phases. At the initial initiation stage, degradation rate is relatively slow, and significantly increases at a later acceleration stage.     

Temperature-dependent magnetic behavior of the Fe (1 0 0) surface

We present a theoretical study of the magnetic properties at finite temperature of the ideal (1 0 0) surface of iron. The spin-polarized electronic structure at a given temperature is determined with a self-consistent d-band model Hamiltonian in which correlation effects are included in a temperature-dependent splitting parameter. The demagnetization process is analyzed and compared with previous results and experimental trends, which will serve us as a test. The applicability of the model to the study of other complex systems like supported clusters or surfaces with defects is discussed.     

Adsorptive removal of phenols by Fe(III)/Cr(III) hydroxide,an industrial solid waste

Phenolics have recently been of great concern because of the extreme toxicity and persistency in the environment. Laboratory investigations of the potential use of Fe(III)/Cr(III) hydroxide as an adsorbent for the removal of bisphenol A and 2-aminophenol from aqueous solution were conducted. The operating variables studied are agitation time, initial concentration, adsorbent dose, pH and temperature. Equilibrium data follow Langmuir, Freundlich and Dubinin–Radushkevich isotherms. The Langmuir adsorption capacity of untreated and pretreated adsorbent was found to be 3.47 and 3.67 mg g⁻¹, respectively, for bisphenol A; and 2.94 and 6.03 mg g⁻¹ for 2-aminophenol. Adsorption was analyzed using first order, second order and Elovich kinetic models and the data were found to follow second order and Elovich kinetic models for the adsorption of bisphenol A by untreated adsorbent and first order and Elovich kinetic models for the adsorption of 2-aminophenol by untreated adsorbent. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰ and ΔS ⁰ for the adsorption were evaluated.     

90°coupling in (Fe/Cr/Fe)AFM/Cr/Fe system epitaxially grown on GaAs(0 0 1)

Single-crystalline (Fe/Cr/Fe)_AFM/Cr/Fe structures were epitaxially grown on atomically flat GaAs(0 0 1). Choosing the same thickness of the antiferromagnetically (AFM) coupled Fe layers in the bottom (Fe/Cr/Fe)_AFM structure, their net magnetization is balanced to zero, in particular up to a spin-flop transition when the field is applied along the [1 1 0] direction. For the Cr thicknesses at which the top Fe layer is weakly magnetically coupled to the bottom (Fe/Cr/Fe)_AFM structure, at low fields, the magneto-optical Kerr effect and/or SQUID signal from the sample corresponds to the top Fe layer only. An influence of the Cr spin structure on the magnetization reversal in the Fe layer is reported. In particular, a strong increase of coercivity (by a factor of 12) is found at low temperatures. A 90° coupling is detected which affects the minor loops measured along the [−1 1 0] and [1 0 0] directions.     

Hg(0) oxidative absorption by K(2)S(2)O(8) solution catalyzed by Ag(+) and Cu(2+)

The aqueous phase oxidation of gaseous elemental mercury (Hg(0)) by potassium persulfate (K(2)S(2)O(8), KPS) catalyzed by Ag(+) and Cu(2+) was investigated using a glass bubble column reactor. Concentrations of gaseous Hg(0) and aqueous Hg(2+) were measured by cold vapor generation atomic absorption spectrometry (CVAAS). The effects of several experimental parameters on the oxidation were studied; these include different types of catalysts, pHs and concentrations of potassium persulfate, temperatures, Hg(0) inlet concentrations and tertiary butanol (TBA). The results showed that the removal efficiency of Hg(0) increased with increasing concentration of potassium persulfate and catalysts Ag(+), Cu(2+) and Ag(+) provided better catalytic effect than Cu(2+). For example, in the presence of 5.0mmoll(-1) KPS, the mercury removal efficiency could reach 75.4 and 97.0% for an Ag(+) concentration of 0.1 and 0.3mmoll(-1), respectively, and 69.8 and 81.9% for 0.1 and 0.3mmoll(-1) Cu(2+). On the other hand, high temperature and the introduction of TBA negatively affect the oxidation. Furthermore, the removal efficiency of Hg(0) was much greater in neutral solution than in either acidic or alkaline solution. But the influence of pH was almost eliminated upon the addition of Ag(+) and Cu(2+), and high Hg(0) inlet concentration also has positive impact on the removal efficiency of Hg(0). The possible catalytic oxidation mechanism of gaseous mercury by KPS was also proposed.     

Magneto-transport Properties and Thermally Activated Flux Flow in Ba(Fe 0 . 9 1 Co 0 . 0 9 ) 2 As 2 Superconductor

Thermally assisted flux flow (TAFF) based on magneto-resistivity and ac susceptibility measurements is studied in a Ba(Fe_0.91Co_0.09)₂As₂(T _c=25.3 K) sample in magnetic fields up to 18 T. In addition to the upper critical field μ ₀ H _c2 and the coherence length ξ(0), the flux flow activation energy U(T,H) has also been determined. The resistive transition width is proportional to μ ₀ H, in contrast to Tinkham’s theoretical prediction. By applying Fisher’s model, the glass melting transition temperature T _g, which occurs in the upper TAFF state and not in the zero resistivity vortex solid regime, is calculated. The onset of TAFF temperature and the crossover temperature T _x from TAFF to flux flow are determined. By contrasting the ac susceptibility data with the resistivity data, considerable flux penetration appears even in the zero resistivity state, in addition to ac losses. The H-T phase diagram is drawn and shows weak pinning regime as the field approaches μ ₀ H _c2, and the strength of the weak pinning decreases to 0 with increasing magnetic field from 0 to 18 T.     

Synthesis of polyynes (and ene-ynes) segments by dechlorination reactions of chlorinated polyethylene wax and chlorinated docosane

High density polyethylene oligomers and docosane (C₂₂H₄₆) were subjected to a photochlorination reaction to a chlorine content above 70% as checked by thermogravimetry. The resulting chlorinated materials were dehydrohalogenated by potassium hydroxide in different conditions with simple reaction routes. It is shown by FT-IR, C₁₃-NMR and electronic spectroscopy that soluble low molecular weight polymers were formed having polyyne-ene and polyene-yne segments. These new soluble polymeric materials are of potential interest both in the field of optics and electronics as well as in the understanding the cosmochemical problem of the molecules in interstellar space.     

Mg/Al水滑石催化合成聚碳酸酯二醇的研究

制备了Mg-Al水滑石,并将其进行了焙烧和再水合的处理,运用XRD,IR和BET对3种催化剂进行了表征,并对其应用于催化合成聚碳酸酯二醇(PCDL)的反应进行了研究.     

Reactivity of Fe(II)/cement systems in dechlorinating chlorinated ethylenes

Ferrous iron (Fe(II)) in combination with Portland cement is effective in reductively dechlorinating chlorinated organics and can be used to achieve immobilization and degradation of contaminants simultaneously. Reactivities of chlorinated ethylenes (perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC)) in Fe(II)/cement systems were characterized using batch slurry reactors. Reduction kinetics of the chlorinated ethylenes were sufficiently fast to be utilized for the proposed treatment scheme, and were described by a pseudo-first-order rate law. The order of reactivity of the chlorinated ethylenes was TCE>1,1-DCE>PCE>VC. Reduction of TCE and PCE mainly yielded acetylene, implying that the transformation of the two compounds occurred principally via reductive beta-elimination pathways. Transformation of 1,1-DCE and VC gave rise to primarily ethylene, implying that major degradation pathways were a reductive alpha-elimination for the former and a hydrogenolysis for the latter. The reactivity of the Fe(II)/cement systems in dechlorinating TCE was proportional to Fe(II) dose when the Fe(II)/cement mass ratio varied between 5.6 and 22.3%. The Fe(II)/cement systems with a higher Fe(II) loading were less extensively affected by pH in reductive reactions for TCE than in the previous experiments with PCE or chlorinated methanes. Amendment of Fe(II)/cement systems with Fe(III) addition was found effective in increasing the reactivity in the previous study, but the current findings indicated that the extent to which the reaction rate increased by the amendment might be dependent on the source of the cement and/or the compounds tested.