The application of nanosized zero-valent iron (nZVI) to the degradation of various contaminants has been extensively researched over the last decade; however, few studies have focused on the application in seawater and benthic sediments. In this study, the reactivity of bimetallic palladium/nZVI (Pd/nZVI) towards the degradation of polychlorinated biphenyl (PCB) was examined in seawater and the effectiveness of using carboxymethyl cellulose (CMC) and ethylenediaminetetraacetic acid (EDTA) for further improvement was investigated. The results suggest that the CMC-coated Pd/nZVI particles exhibit a slower degradation rate than the bare assemblages. These impeding effects are possibly attributed to the reduction of Pd on CMC-stabilized particles and the mitigation of stabilizing effects of CMC due to double layer compression, charge neutralization and/or ion bridging in the seawater environment. As for the effects of EDTA, this ligand is capable of increasing the reactivity of Pd/nZVI particles via removal of the passivating layer confirmed by the appearance of dissolved Fe(II) following the exposure of Pd/nZVI to EDTA. Additionally, the removal of the passivating layer depends on the concentration of EDTA, demonstrating that insufficient EDTA is unable to 'dissolve' the growing passivated layer, whereas excess EDTA may result in enhanced aggregation due to magnetic attraction from the exposed magnetic nZVI core, thereby limiting the reactivity of Pd/nZVI particles. An optimum molar ratio of EDTA to Pd/nZVI dosage was determined as 0.6 in this study. Meanwhile, EDTA did not enhance the reactivity of CMC-coated particles, presumably as a result of the significant loss of Pd during the reaction. As the presence of the CMC layer may inhibit the reduction of Pd(II) to Pd(0) on the surface of nZVI, the introduction of EDTA would result in the rapid release of Pd(II) ions via complexing processes.

Application of CMC and EDTA to improve the reactivity of bimetallic palladium/zero-valent iron nanoparticles in seawater

248th National Meeting (2014)

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