Dispersion of nanoscale iron particles

The technology of nanoscale zero-valent iron particles for site remediation was first developed at Lehigh University in 1996. Laboratory studies have demonstrated that iron nanoparticles have enhanced reactivity toward chlorinated organic compounds in comparison with conventional microscale or granular iron materials. In addition, a potentially significant advantage of iron nanoparticles is the possibility of direct injection into groundwater. However, increasing evidence indicates that iron nanoparticles have strong tendency to aggregate. The rapid settling of iron nanoparticle aggregates severely limits their transport in groundwater. Therefore, a challenge for field application of the iron nanoparticle technology is to overcome the rapid agglomeration and enhance their mobility in groundwater.;Commonly used methods to establish dispersion of small particles include: electrostatic, steric (polymeric), or combination (electro-steric) of the two. In this work, the steric stabilization approach was employed. A copolymer, poly(vinyl alcohol-co-vinyl acetate-co-itaconic acid) (PV3A), was used as a dispersant and found to be more effective than other commonly-used dispersants (e.g., polyacrylic acid). The PV3A-stabilized iron nanoparticles form a highly stable suspension. Sizing analysis indicated that the bare iron had a median size of 59.4 rim in diameter while the PV3A-stabilized iron nanoparticles were much smaller with median size of just 8 nm. This result was further confirmed with the TEM observations. Moreover, the particle size distribution of the PV3A-iron particles was entirely in the nano domain (<100 nm) and remained stable for a long period of time (>6 months), suggesting a very stable dispersion of iron nanoparticles.;Zeta potential (zeta) of iron nanoparticles as a function of solution pH was measured by the electro-acoustic method. Experimental results indicated that isoelectric point (IEP) of the bare iron particles was in the range of pHiep ≈ 8.1-8.3. Due to the surface modification of PV3A, IEP of the PV3A-stabilized iron particles shifted to pHiep ≈ 4.5, suggesting that the PV3A-iron particles have universal negative surface charges in groundwater. This is a very favorable condition for nanoparticle transport as aquifer materials mostly have universal negative surface charge. The increased surface charge (i.e., >-80mv, pH>8.0) not only promotes the stability of iron suspension, but also enhances the mobility of iron nanoparticles in groundwater.;Batch experiments for the nanoparticle reactivity indicated that the bare- and PV3A-iron nanoparticles with the same loading of 10 g/L had similar reaction rates for the degradation of WE and TCA, suggesting that the two types of iron nanoparticles may have similar reactive specific surface area (SSA). The breakthrough curves of column experiments demonstrated the PV3A-stabilized iron nanoparticles had high mobility, likely attributed to the high surface charge and the small and stable particle size.