Superfund Research Program
Chloro-Organic Degradation by Polymer Membrane Immobilized Iron-Based Particle Systems
Project Leader: Dibakar Bhattacharyya
Grant Number: P42ES007380
Funding Period: 2000-2019
Chloro-organic contaminations in groundwater are of immense concern due to their high toxicity and environmental persistence. Dr. Bhattacharyya’s research group has made substantial contributions in the remediation of these compounds (Such as, TCE, PCBs) via both reductive and oxidative pathways. Both approaches use non-toxic iron-based systems as a common platform. The platform for the reductive pathway included membrane and hydrogel- immobilized Fe and bimetallic Fe/Pd nanoparticles (NPs). The reducing agents used were the well-established sodium borohydride as well as the non-toxic, "green chemicals", tea extract and vitamin C.
The researchers have successfully synthesized both Pd and Fe/Pd bimetallic particles using ascorbic acid as a "green" reducing agent. By varying the ratio of ascorbic acid to metal(s), they are able to control the particle size hydrodynamic radius from ~400 nm to ~100 nm. The newest approach to minimize the Fe NP oxidation is to use an alternative "green" reducing agent, tea extract as a replacement to the well-established sodium borohydride. Tea extract contains a number of polyphenols (such as epicatechine) which have antioxidant properties; these not only reduce iron (II) to Fe NP, but also act as capping agents that protect the NP surface from oxidation. Indeed, the Fe NP prepared (in membrane domain) using this approach (~30 nm diameter) showed a remarkable stability and retained their original reactivity for at least 3 months. For membrane-immobilized systems they have found that the adsorption of iron (II) ions on the membrane (after NP formation), can substantially increase NP longevity for PCB dechlorination; thus after 4 cycles the reactivity was still ~ 80% of the original one (J. Membrane Science, 2010). The same membrane platform was also used for toxic organics destruction via oxidative pathway. Highly porous (253 m2/g) core shell Fe/Fe2O3 NPs were immobilized on a membrane and reacted with hydrogen peroxide to generate hydroxyl radicals, used for TCE dechlorination. Complete dechlorination of TCE was obtained within 24 h reaction time (91% chloride yield). Similarly, these free radical reactions can be conducted using iron ions and H2O2.
Another innovation included the incorporation of Fe NPs (~50-70 nm) in a temperature responsive hydrogel network (poly-N-isopropylacrylamide) similar to those used in drug delivery area. In addition to preventing aggregation, this polymer network has tunable properties and it was found that reactivity toward TCE dechlorination increased 3-fold with a temperature change of only 40 C. The researchers have continued their development of both oxidative and reductive platforms for the remediation of the Paducah Gaseous Diffusion Plant Superfund site in Paducah, KY. They are currently in the process of developing a treatability study work plan required by the DOE in order to implement these technologies on-site. Based on EPA regulations, they have chosen to investigate the use of nanoparticle aggregates for in situ remediation of contaminated groundwater. The reductive pathway will utilize Fe/Pd nanoparticle aggregates and the oxidative pathway will utilize Fe/Fe2O3 nanoparticle aggregates with added H2O2. The researchers are also investigating the efficiency of Fe0 nanoparticles (no Pd) synthesized using green chemistry as a potential alternative to the Fe/Pd nanoparticles. They will be utilizing on-site pump-and-treat facilities in order to test these and membrane-immobilized oxidative and reductive platforms before injection.