| There has been a growing interest in the use of zero-valent iron for the treatment of chlorinated organic compounds (COCs) in water and groundwater. The studies have been focused on such compounds as carbon tetrachloride, trichloroethene and pesticides and related compounds. When iron is in contact with a less reductive metal such as palladium, the metal couple can form galvanic cells. This led to the discovery of Pd/Fe bimetallic complex in which palladium serves as a catalyst and iron as an electron donor. Pd/Fe bimetallic particles can effectively dechlorinate many COCs (e.g., chlorinated ethenes, chlorophenols, pentachlorophenol and PCBs).Nanoscale zero-valent metal particles, compared to the conventional large particles, have some more advantages, including a high specific surface area, a high surface reactivity and flexibility in deployment. Nanoscale bimetallic particles (Pd/Fe, Pt/Fe, Ni/Fe, Ag/Fe) have been used to dechlorinate chlorinated ethenes, a mixture of chlorinated aromatic compounds, PCBs and hexachlorobenzene. The results show that the chlorinated ethenes are all transformed to ethane or ethane containing a small amount of ethene without generating any chlorinated intermediates or final products. More than 90% of the mixture of the selected chlorinated aromatic compounds was fully dechlonnated within 24h. The PCB congeners of Aroclor 1254 were completely dechlorinated within 17h. Hexachlorobenzene was transformed to a mixture of pentachlorobenzene, tetrachlorobenzenes, trichlorobenzenes and dichlorobenzenes within 400h over a subcolloidal Ag/Fe complex.However, no study in the dechlorination of chlorophenols over a nanoscale Pd/Fe bimetallic complex has been reported yet. Chlorophenols are usually used as the intermediates to synthesize medicines, dyes, pesticides and herbicides or used as bactericides and preservatives. They are carcinogenic and stable in water. In the present paper is reported an efficient method of synthesizing nanoscale Pd/Fe bimetallic particles. BET specific surface area of the nanoscale particles was determined using nitrogen adsorption method. They were observed by transmission electronic microscopy (TEM) to determine the size. The mass fraction of Pd in the bimetal was measured using atomic absorption spectrometry (AAS). And the nanoscale particles were characterized by X ray diffraction (XRD). The results of using the synthesized nanoscale Pd/Fe particles for the treatment of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol are showed. And the mechanism of catalytic reductive dechlorination is elucidated. The results are as following:1. Most of the nanoscale Fe and nanoscale Pd/Fe particles have sizes less than 100nm. BET specific surface area of the nanoscale Pd/Fe particles is 12.4m2/g. Actual mass fractions of Pd in the bimetal are less than the theoretical values. The difference results from the loss of Pd during the rinsing. XRD patterns of the nanoscale Pd/Fe particles indicate that Fe is crystalline.2. The nanoscale Pd/Fe particles exhibited high reactivity. Dechlorination efficiency of 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol amounted to above 90% in 5h at relatively low metal to solution ratio (3g/500ml) and the three chlorophenols were removed almost completely. However, only less than 25% of them were dechlorinated in the same period over microscale Fe, microscale Pd/Fe and nanoscale Fe.3. The effect of dechlorination reaction and reaction rate of 2-chlorophenol over nanoscale Pd/Fe were dominated by the mass fraction of Pd in the bimetal (w(Pd)), the mass concentration of nanoscale Pd/Fe particles in the reaction mixture (p(Pd/Fe)), reaction temperature and initial pH value. Higher (0 (Pd), higher p (Pd/Fe), higher reaction temperature and near neutral condition favored the dechlorination reaction. Reaction rate increased as w (Pd), p (Pd/Fe) and reaction temperature increased. Reaction rate under pH=5.4 was higher than other pH conditions. No dependence-was found between reaction rate and initial concentration of 2-chl...
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