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Title of Talk:
Membrane-Based Nanostructured Metals for Reductive Degradation of Hazardous Organics at Room Temperature

Abstract of Talk:
Membrane-Based Nanostructured Metals for Reductive Degradation of Hazardous Organics at Room Temperature

D. Bhattacharyya*, L. Bachas, D. Meyer, and J. Xu, Dept. of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, and S. Ritchie, L. Wu, Dept. of Chemical Engineering, University of Alabama
Project Officer: Dr. Nora Savage, U.S. EPA
* Corresponding author email address: db@engr.uky.edu

The use of nanosized metals is emerging as an important technology for the detoxification of organics and for green synthesis. Studies involving these particles have shown increased reaction rates by several orders of magnitude. To obtain isolated nanoparticles with narrow size distributions, it is necessary to reduce the metal ions in the presence of polymers or surfactants. Our present work addresses the reduction of chlorinated organics by bimetallic nanosystems comprised of nanoscale Fe/Ni particles confined within various polymeric membrane matrices. The following synthesis techniques have been developed in support of this work: (1) direct membrane-phase metal particle formation based on the classic phase-inversion method for membrane preparation, (2) use of metal chelating polymers on membrane supports, (3) external particle synthesis in solution followed by membrane incorporation. Using these methods we have obtained highly exciting results both in terms of synthesis of nanoparticles in membrane domain and resulting organic dechlorination. For the 2nd method controlled separation of background toxic metals along with organic reduction is also possible.

We have quantified (following EPA quality assurance guidelines) TCE degradation behavior resulting in ethane and Cl- formation using these nanocomposite membranes. Regardless of the method employed, test membranes contained only milligram levels (rather than grams) of reactive metal particles. A comparison of both surface-area normalized rate constants and metal loadings with literature values indicates significant enhancement to the traditional application of zero-valent metal nanoparticle technology. Using in-situ techniques to immobilize nanoparticles, one can reduce particle loss, prevent particle agglomeration, and provide a means to recapture (and feasibly recycle) metal ions, which can form non-reactive hydroxide coatings on the surfaces of particles. When ex-situ particle synthesis is employed, the Fe/Ni particles agglomerate during incorporation into the membrane phase. The agglomerates possess less available reactive surface area (Fe/Ni/H20 interface), based on electron-microscopic characterization and comparison of dechlorination rates. In addition, the use of membrane immobilization (as opposed to beads and direct ground injection) allows for the potential application of this technology to novel hybridized separation/recycle processes in the areas of industrial and municipal water treatment. Considering the performance of the bimetallic systems, the incorporation of a second metal with a high affinity for hydrogenolysis has the greatest impact on reaction rates for the given set of variables investigated.

To date, we have successfully demonstrated: (a) formation of nanoscale particles directly in cellulose acetate membranes in the 20-30 nm range, (b) cross-linking of polyacids (poly-acrylic acid) on conventional microfiltration membrane supports to entrap metals and to form (after reduction) ~30 nm metal particles, (c) the ability to synthesize immobilized Fe/Ni nanoparticles with a more uniform elemental distribution for superior dechlorination performance using a 2-step deposition process (reduction of Fe followed by electroless plating and reduction of Ni) as opposed to the simultaneous reduction of Fe and Ni (d) large conversions for TCE using a very small quantity of bimetallic (Fe/Ni ratio 4:1) nanoparticles in 60 min, (e) Production of ethane (identified in the headspace) with only trace levels (if any) of other chlorinated intermediate byproducts found in both the aqueous and headspace phases, (f) development of a novel method for preparation of Fe nanoparticles and recovery as stable slurry using anaerobic synthesis conditions, and (g) immobilization of Fe nanoparticles prepared in solution within a cellulose acetate matrix (as one example) while avoiding metal oxidation, Preliminary results with membrane immobilized Fe/Pd nanoparticles showed highly effective dechlorination of selected aromatics.

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