| The small size, large specific surface area and strong reducibility make nanoscale zero-valent iron particles (NZVI) attractive for treament of chlorinated hydrocarbons in underground water remediation. And bimetallic nanoparticles which are obtained by introducing and plating a second metal as a catalyst onto the surface of nanoscale iron have accelerated the dechlorination reaction of chlorinated aliphatic hydrocarbons.In this study, nanoscale iron was prepared by using the method of sodium borohydride (NaBH4) reduction; and nanoscale Cu/Fe was prepared by precipitating copper on the surface of nanoscale iron. The nanoscale Cu/Fe was characterized by applying X-ray diffraction (XRD), transmission electron microscope (TEM), N2adsorption BET specific surface area analysis, scanning electron microscopy energy dispersive spectrum (SEM-EDS) to determine the morphology and structure of nanoscale Cu/Fe before and after reaction. The effects of some main parameters, such as copper loading ratio, nanoscale Cu/Fe addition, initial trichloroethylene concentration, pH and rotational speed of shaking incubator, on trichloroethene dechlorination were investigated successively. The results are as follows:(1) The crystal stucture of iron of nanoscale Cu/Fe was body-centered cubic lattice a-Fe, and the crystal stucture of copper was face-centered cubic lattice. The particles exhibited a multilayer net structure in the form of bean-chain and branch. The iron was corroded and forms iron oxides after reaction with nanoscale Cu/Fe; and iron deposition of oxygen and carbon was also appeared. The specific surface area of nanoscale Cu/Fe increased along with the Cu loading ratio increasing. And the specific surface area of nanoscale iron and nanoscale Cu/Fe was15.215m2/g and30.922m2/g, respectively.(2) The mechanism and pathway of trichloroethylene dechlorination with nanoscale Cu/Fe were analysed. The ability of nanoscale iron to dechlorinate trichloroethylene was extremely low, and the dechlorination efficience was only0.3%. Cu could not react with trichloroethylene; while, it was able to catalyze and accelerate the reaction between nanoscale iron and trichloroethylene. Under galvanic effect, the ability and extent of trichloroethylene dechlorination with nanoscale Cu/Fe was greater than with the mixture of nanoscale iron and nanoscale copper particles. In addition, trichloroethylene was degraded by adsorption and dechlorination; and the main dechlorination products were ethane and ethylene. The iron provided electrons and transfered them to the copper; then reductive atomic hydrogen was formed by proton reduction on copper catalytic active site; under catalytic hydrogenolysis and hydrogenation, trichloroethylene adsorbed on the surface of copper was dechlorinated to ethane and ethylene.(3) The production of reductive atomic hydrogen and catalytic dechlorination occured synergistically when the copper loading ratio was5wt%, and the optimal dechlorination efficience was obtained. It was observed that trichloroethylene dechlorination efficience and product saturation increased along with the copper loading ratio when it was less than5wt%. When the copper loading ratios were0,0.1,0.51.02.55.0wt%, the dechlorination efficience were0%,0.5%,19%,22%,30%,38%, respectively; the ethane production rate were0%,0.01%,7.4%,11%,15%,27%, respectively. While, when the copper loading ratio was10wt%, the dechlorination efficience and ethane production were30%and14%, which were both lower than it was5wt%, suggesting that too much iron surface was covered by the copper and the production of reductive atomic hydrogen was hindered. The increase of nanoscale Cu/Fe addition (0.04～2.0g/L) leaded more iron reactive sites and copper catalytic active site, thus benefited the dechlorination efficience and product saturation. When the nanoscale Cu/Fe addition were0.04,0.2,0.4,1.2,2.0g/L, the dechlorination efficience were0%,1.9%,12%,21%,24%, respectively; the ethane production rate were0%,1.4%,7.1%,13%,16%, respectively. That the increase of trichloroethylene concentration (4.7-236mg/L) resulted in the decrease of dechlorination efficience. When trichloroethylene concentration were4.7,23.6mg/L,236mg/L, the dechlorination efficience were44%,24%,20%, respectively. The augment of pH value (7.0-10.5) leaded to product saturation decreasing. When pH were7.0,8.0,10.5, the dechlorination efficience were30%,28%,10%, respectively; the ethane production rate were26%,20%,1.6%, respectively. The optimal pH for trichloroethylene dechlorination was7.0. While, trichloroethylene dechlorination efficience and product saturation increased with rotational speed of shaking incubator ranging from50to100rpm; and then decreased when it was130rpm. |
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