Degradation of chlorinated organics by membrane-immobilized nanosized metals

The use of electronegative metals, such as Fe, has been extensively studied for the treatment of groundwater containing toxic chlorinated organics. Much of the recent work has been focused on the use of nanoscale particles with diameters from 2 to 100 nm. This work examines the use of bimetallic (Fe/Ni) nanoscale particles immobilized in a cellulose acetate domain for the destruction of trichloroethylene (TCE). The organic/inorganic hybrid film is synthesized using phase inversion with sodium borohydride reduction. The resulting nanoparlicles have an average diameter of 24 nm. Using a small quantity of membrane-immobilized metal (31 mg total, Fe:Ni = 4:1), it was possible to achieve over a 75% reduction in TCE levels in 4.25 h, with ethane as the only observable product. For shorter reaction times (<2 h), traces of cis- and trans-DCE could be extracted from the baseline of the MS chromatogram. For longer reaction times, products of coupling reactions (butane and hexane) were observed. This corresponds to a surface-area-normalized pseudo-first-order rate constant, k(SA), for the immobilized system of 3.7 x 10(-2) L m(-2) h(-1). Analysis of the aqueous phase for metal content showed minimal leaching of the metals into the surrounding solution during treatment. Because various combinations of membranes containing immobilized metal nanoparticles can be achieved using the synthesis techniques presented, a more versatile platform for the application of zero-valent treatment is possible. (C) 2004 American Institute of Chemical Engineers.