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Reductive Degradation of Chlorinated Organics by Membrane-Supported Nanoparticles: Synthesis, Characterization and Modeling Study

Jian Xu and D. Bhattacharyya. Chemical and Materials Engineering, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506-0046

Chemical degradation of chlorinated organics using bimetallic nanoparticles (Fe/Ni or Fe/Pd) has been extensively studied. In the presence of the secondary metal, contaminants were dehalogenated by catalytic hydrodechlorination, which can greatly enhance the reaction rate as well as inhibit toxic intermediates formation. In this study, nanosized Fe/Pd particles were synthesized in polyacrylic acid (PAA) functionalized polyvinylidene fluoride (PVDF) MF membranes. The membranes and Fe/Pd nanoparticles were characterized by several electron microscopy techniques: SEM, TEM, and X-ray Mapping. Special emphasis has been given to examine the distribution of PAA inside the PVDF support membranes and the chelation of ferrous ions and carboxylic acid by high resolution X-ray mapping. 2,3,2',5'-Tetrachlorobiphenyl (TeCB) was used as a model compound to examine the reactivity of Fe/Pd nanoparticles and study the catalytic hydrodechlorination reaction pathway. The result shows that nonortho chlorines (para or meta) are preferentially removed over chlorines in the orthoposition. This is due to the higher static hindrance from coplanar aromatic rings for nonortho chlorines. For Fe/Pd nanoparticles with various Pd coating, although the observed reaction rate constant was different, the normalized reaction rate constant in terms of reactive surface sites (Pd atom) was same. Batch reactions were also performed at various temperatures to find the reaction activation energy and understand the catalytic property of palladium. A Langmuir-Hinshelwood kinetic model including mass transfer, diffusion, and membrane partition is formulated to obtain intrinsic reaction rate. This research is supported by the NIEHS-SBRP program.