The Synthesis of Zero Valent Iron Nanoparticles with Various Stabilizing Agents

Zero valent iron nanoparticles (particles between 1 and 100 nanometers) have many promising uses in groundwater remediation.  They effectively combat chlorine, pesticides, certain metals, and other pollutants underground without removing the soil, or in situ. However, due to their highly reactive and magnetic properties, zero valent iron nanoparticles have a strong tendency to clump together to form larger particles, or agglomerate. This is undesirable, as larger particles have a lower surface area to volume ratio, which decreases their reactivity and reduces their effectiveness. To minimize agglomeration, the nanoparticles can be synthesized in the presence of a stabilizer. This investigation was designed to test and compare sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), gum arabic (GA), and tannic acid (TA) as stabilizers for zero valent iron nanoparticles. The nanoparticles were synthesized with ferrous sulfate, sodium borohydride, and each stabilizer in triplicate. They were then characterized using the NanoSight NS500 which measures mean hydrodynamic diameter, and the Brookhaven ZetaPals instrument which measures both mean hydrodynamic diameter and zeta potential of the particles as indicators of overall stability. Each synthesis produced a significant number of particles with a hydrodynamic diameter of less than 100 nanometers, but the CMC and GA were found to produce the smallest average particle sizes and size distributions, while the result of using PVP was very similar to using no stabilizer. Unstabilized particles formed large agglomerates during synthesis and had a wide distribution range. The TA produced an extremely dark purple solution and at a concentration of 0.0006 M produced particles without the use of sodium borohydride, but they were difficult to characterize. At a concentration of 0.01 M, the TA produced somewhat more measureable particles that had about the same average size as the unstabilized particles, and there were a significant number of particles under 100 nm. In addition, a visual comparison was performed over time between unstabilized particles and CMC supported particles to investigate the effect of a stabilizer qualitatively. During the visual comparison, the unsupported particles formed large agglomerates immediately following synthesis which sunk to the bottom of the container while those synthesized with sodium carboxymethyl cellulose formed only very small visible particles and stayed well dispersed throughout the solution over the 24 hour period.