Preparation and characterization of a new class of starch-stabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons in water.

Dechlorination of TCE and PCBs using bimetallic nanoparticles has received increasing interest in recent years. However, due to the extremely high reactivity, nanoparticles prepared using current methods tend to either react with surrounding media or agglomerate, resulting in the formation of much larger flocs and significant loss in reactivity. To overcome these drawbacks, we developed a simple and green approach for synthesizing palladized iron (Fe-Pd) nanoparticles. We modified the conventional methods by applying a water-soluble starch as a stabilizer. The starched nanoparticles displayed much less agglomeration but greater dechlorination power than those prepared without a stabilizer. TEM analyses indicated that the starched nanoparticles were present as discrete particles as opposed to dendritic flocs for nonstarched particles. The mean particle size was estimated to be 14.1 nm with a standard deviation of 11.7 nm, which translated to a surface area of approximately 55 m2 g(-1). While starched nanoparticles remained suspended in water for days, nonstarched particles agglomerated and precipitated within minutes. The starched nanoparticles exhibited markedly greater reactivity when used for dechlorination of TCE or PCBs in water. At a dose of 0.1 g L(-1), the starched particles were able to destroy 98% of TCE (C0 = 25 mg L(-1)) within 1 h. While trace amounts (<25 microg L(-1)) of 1,1-DCE were detected in the initial stage (<20 min) of degradation, no other intermediate byproducts such as vinyl chloride, cis-, or trans-dichloroethene were detected. The starched nanoparticles at approximately 1 g L(-1) were able to transform over 80% of PCBs (C0 = 2.5 mg L(-1)) in less than 100 h, as compared to only 24% with nonstarched Fe-Pd nanoparticles. The application of an innocuous stabilizer may substantially enhance the performances of palladized iron nanoparticles for environmental applications.