Formulation design for target delivery of iron nanoparticles to TCE zones

• Target delivery of NZVI to reduce DNAPLs is a desirable but elusive goal.
• Calcium, H+, and benzethonium chloride (BC) used to modify oleate (OL) coatings
• OL + BC coatings produced stable suspensions that selectively partitioned into TCE.
• OL + BC coatings improved the nanoparticle retention in TCE-contaminated columns.
• OL + BC could improve the efficiency of NZVI without the risk of DNAPL mobilization.

Nanoparticles of zero-valent iron (NZVI) are effective reducing agents for some dense non-aqueous phase liquid (DNAPL) contaminants such as trichloroethylene (TCE). However, target delivery of iron nanoparticles to DNAPL zones in the aquifer remains an elusive feature for NZVI technologies. This work discusses three strategies to deliver iron nanoparticles to DNAPL zones. To this end, iron oxide nanoparticles coated with oleate (OL) ions were used as stable analogs for NZVI. The OL-coated iron oxide nanoparticles are rendered lipophilic via (a) the addition of CaCl2, (b) acidification, or (c) the addition of a cationic surfactant, benzethonium chloride (BC). Mixtures of OL and BC show promise as a target delivery strategy due to the high stability of the nanoparticles in water, and their preferential partition into TCE in batch experiments. Column tests show that while the OL–BC coated iron oxide nanoparticles remain largely mobile in TCE-free columns, a large fraction of these particles are retained in TCE-contaminated columns, confirming the effectiveness of this target delivery strategy.