Dissertation > Environmental science, safety science > Environmental pollution and its prevention > General issues

Research on Polychlorinated Biphenyls Dechlorination by CMC-Ni-Fe Bimetallic Nanoparticles System

Author LiuChangGuang
Tutor ZhaoLin; ZuoHouKai
School Tianjin University
Course Chemical Engineering
Keywords PCB77 CMC bimetallic nanoparticles modified by doped PVDF multiple emulsion
Type Master's thesis
Year 2012
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In this paper, the CMC-Ni-Fe bimetallic nanoparticles were successfulsynthesized, with the monodispersed carboxymethyl cellulose (CMC) as a stabilizer.The various reaction parameters were optimized. Nanoparticles, prepared withCMC/Fe=5and NI/Fe=0.03at25℃, showed the best degradation effect of PCB77.Near94%of reduction efficiency was achieved by CMC-Ni/Fe bimetallic nanopar-ticles for48h treatment, while only about71%PCB77was degraded by Ni/Febimetallic nanoparticles. The resultsof XRD showed that the CMC-Ni/Febimetallicnanoparticles exhibited thecharacteristic peaks of elemental ironandthe characteristicpeaks of iron oxides were not detected. It was indicated thatthe elemental ironofCMC-Ni/Febimetallic nanoparticleswas not oxidized in preparationprocess. Theresultsof particle size analysis were demonstrated that the average diameter ofCMC-stabilized Ni-Fe bimetallic nanoparticles was about23.94nm, smaller than theparticle size of Ni/Febimetallic nanoparticles(100nm).This indicated that theCMC-Ni/Fe bimetallic nanoparticleshada very high activity. The BET specific area ofthe CMC-stabilizer Ni-Fe bimetallic nanoparticles were52.74093(m2/g). The resultsof the Infrared indicated that CMC and the Ni-Fe bimetallic particles interacted bybridge chelate.The nanoparticle iron is easily oxidized because of exposed to the air withoutany protection. And the nanoparticles were prone to reunite because of its smallparticle size. As a result, the dechlorination efficiency of PCB77is drastically reduced.Meanwhile, the nanoparticles were difficult to be recycled, resulting in secondarypollution. So in this paper, PVDF load film doped with CMC-stabilizer Ni-Fenanoparticles was prepared.0.25g of the PVDF membrane that the doping rate was10%was used to reduce the5mg/L PCB77solution. The removal rate of PCB77was about73%after48hours of degradation. And the degradation of PCB77was in accordancewith the pseudo-first-order kinetic model too. The kinetic constant was0.0256h-1.The concentrations of PCBs in the environment are relatively low and it isdifficult to reduce by nanoparticle iron. In this paper, by reference to the multipleemulsion prepared methods, the lipid-coated catalytic system was prepared. The outerlayer of lipid enriched PCB77and the internal catalytic reduce the PCB77. The enrichment and degradation of PCB77were carried out at the same time. By analysisthe degradation datas, it showed that adsorption equilibrium was achieved within4h.As time goes on, the concentration of PCB77was reduced between24h and48h. Itindicated that the PCB77enriched by the outer layer lipid was reduced.

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