Mechanistic and lifetime investigation of zero valent nanoparticles for the remediation of chlorinated hydrocarbons

Zerovalent nanoscale particles were developed for the in-situ and ex-situ reduction of contaminants, specifically for the remediation of suspect carcinogenic chlorinated hydrocarbons, e.g., trichloroethylene (TCE). Due to the nanometals' higher surface/volume ratio, a bipolar redox process, and a change in reaction mechanism, the remediation rate was improved from 0.0078 to 2.2/hr when comparing iron filings to nano Ni-Fe particles. The properties of an ideal material for long term burial for the in-situ contaminant remediation would require a fast dechlorination rate, as well as a long lifetime or slow corrosion rate. Kinetic and isotope labeling studies of the nano-Ni-Fe particles showed that the dehalogenation mechanism involved the galvanic corrosion of the iron to protect the nickel, which reduced water to adsorbed and free hydrogen and hydroxide ion. To obtain fast dehalogenation, the Ni and Fe particles needed to be in electronic contact. The nickel chemisorbed the hydrogen and hydrogenated TCE to nontoxic hydrocarbons, such as ethylene, ethane, butane, and hexane. Monitoring the progress of the dehalogenation reaction showed hydrogenolysis products, e.g., propane, propylene, and other branched and straight C1-C6 hydrocarbons. There was an optimum ratio of nickel/iron to obtain a long lifetime without sacrificing a fast dechlorination rate. As long as the mechanism of TCE dehalogenation using the optimized ratio of Ni/Fe occurs via dechloro-hydrogenation rather than via reductive dehalogenation as was observed with Fe fillings, the dehalogenation rate should be fast without producing toxic reduction products, and an improved remediation material for direct injection into halocarbon plumes or in-situ burial would be obtained.