| Recently, with the development of industry and agriculture, nitrate pollution in ground water has been an importantly environmental problem and with the tendency of gradually deterioration. Nowadays, it has been prevalently considered by people. Using nanotechnology to remediate environmental pollution is a new direction of environmental remediation in the world. Nanoscale materials have the characteristic of small diameter, high specific surface area to mass ratios and great surface reactivity. In addition, nanoparticles could be injected directly to contaminated field and realize in situ remediation of ground water. So synthesizing new and high efficiency nanoscale materials to reduce nitrate has become the focus of water research.Technologies applied to remove nitrate in ground water include biological denitrification, ion exchange, membrane separation and chemical reduction. Nitrate removal with biological approach may obtain high efficiency and low cost, but it may lead to the existence of bacteria and organic compounds in water, it request further treatment. For physico-chemical approaches, nitrate is only shift to another form, and not removed completely, on the other hand, it may bring large volumes of waste solution with high concentration which also needs to be treated. Application of loading catalyst could transform mostly nitrate to N2, but during the catalytic process, H2 is used as reductant which is easy to blast and difficult to construction. Nitrate could be rapidly reduced by nanoscale Fe0 particles, but the main product is NH4+-N, only a little nitrate may be transformed to N2.To overcome these drawbacks, liquid-phase synthesized method was applied to prepare nanoscale Fe/Ni,Fe/Cu,Fe/Pd and Fe/Pd/Cu compound materials. In the nanoscale materials, nano-Fe/Ni and nano-Fe/Pd/Cu particles were firstly used to reduce nitrate contamination in groundwater. Nanoparticles were characterized by TEM-EDS, SEM, XRD and BET techniques. Nitrate reduction with different nanoscale materials was investigated systemically. At the same time, the reduction mechanism with nanoparticle was discussed in our work. Nanosized Fe0 behaved high reactivity during the denitrification of nitrate compared with common iron powder. The introduction of Ni, Cu and Pd further enhance the removal rate, and different catalyst makes differently degree effects on reduction rate and product.For iron powder, solution pH is an important parameter influencing nitrate reduction and low pH is favorable for the denitrification of nitrate. Different from iron powder, nanosized Fe0 performed large reaction rate even under the condition of neutral solution pH. Using iron powder and nano-Fe0 to treat in-situ uranium leaching groundwater, under laboratory conditions, nitrate removal rate was 93% in 5 h by iron powder but nitrate was removed completely by nanosized Fe0 within 15 min. About 96% nitrate was reduced to NH4+-N.In nano-Fe/Ni reaction system, when Ni loading was 5.0%, nanoparticles showed the highest reactivity under neutral initial solution pH. After slowly ageing 22 h, the reactivity of freshly prepared nanoscale Fe/Ni particles decreased about 10 times, but with the followed 44 h ageing, little decreasing of reactivity was observed which is equivalent to freshly synthesized nano-Fe0. Nitrite was detected as the intermediate product during the reduce process and disappeared companied with nitrate vanishing. NH4+-N transformation rate was at the range of 84.6%~90.6%. Little improve of selectivity to N2 was obtained through changing Ni contents, initial solution pH and nitrate concentration et al. experimental conditions. According to the analysis of product, it was considered that nitrate reduction by Ni/Fe nanoparticles undergo two steps: (1) NO3- was reduced to NO2- with the tendency of increasing at first and disappeared from solution at last; (2) NO2- was then reduced to NH4+. The first transformation process was the control step.Using Cu as catalyst catalytic reduce nitrate contaminant, when Cu content was 5.0% nano-Fe/Cu bimetallic particles showed the rapidest removal rate, and nitrate was removed entirely within 30 min. During the process of nitrate reduction, about 30% nitrate was transformed to intermediate product NO2-. Increasing the reactivity of nanoscale Fe/Cu particles was favorable to the accumulation of NO2- in the solution. At the end of reaction, NO2- was reduced to NH4- N or N2 and NH4- N transformation rate was at the range of 79.4%~82.8%. For nano-Fe/Cu bimetallic material, the reaction course of nitrate reduction was similar to nano-Fe/Ni system, and it also suffers two steps. But the difference between Fe/Ni and Fe/Cu nano-material was that metallic catalyst Cu has better selectivity to NO2- than Ni. Further more, the transformation process from NO3- to NO2- was quick, reversely, the transformation from NO2- to NH4+ was slow.Nano-Fe/Pd and nanoscale Fe/Pd/Cu compound materials were also synthesized in our work, the denitrification of nitrate with these nanosized particles were discussed preliminarily. The results showed that using Fe0 as reductant, different reduction results could be obtained with the different catalyst Ni,Cu and Pd. For Fe0 systemic nanoscale particles prepared in our laboratory, nano-Fe/Cu has the highest reactivity and selectivity to NO2-, but the lowest selectivity to NH4+. So it is a promising remediation technology for nitrate contamination.
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