(24a) Reduction of Immobilized Metal Ions to Zero-Valent Nanoparticles On Functionalized Silica for Dechlorination

Zero-valent iron nanoparticles (or bi-metallic iron/palladium particles) used for the dechlorination of hazardous organic groundwater pollutants are produced by reduction of iron ions immobilized on nanoscale platforms. These platforms include silica nanoparticles functionalized with sulfonate or poly(aspartic acid), as well as functionalized silica with both hydrophobic and hydrophilic functional groups. The latter platform is useful for creating hydrophobic nanodomains near the active site of dechlorination reaction. Extent of silylation for the various platforms is determined by IR, thermogravimetric analysis, total organic carbon analysis, total organic sulfur analysis, and calcium sorption. Extent of functionalization for sulfonate is about 1 molecule per square nm of surface area. The functionalized silica platforms are then used to immobilize ferrous ions. Sulfonate functionalized particles have the advantage of being useful at lower pH, and about 0.1 mmol ferrous ions are immobilized on these particles at pH = 3.5. Reducing agents (including borohydride and ascorbic acid) are used to form zero-valent iron from the immobilized ions. These particles are found (by SEM and TEM) to have possibly experienced directed growth as many of the particles are rod-shaped; the particle length is about 50 nm, and particles are also characterized by X-ray diffraction and other techniques. Palladium is preferentially deposited on these iron particles over their functionalized silica platforms, and these bi-metallic particles are characterized through electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The bi-metallic nanoparticles are shown to be reactive for the dechlorination of trichloroethylene and other chlorinated organic pollutants. This research is supported by the NIEHS-SBRP program.