Enhancement of dispersibility of zero-valent iron nanoparticles for environmental remediation: Entrapment and surface modification with polymers

Nanoscale zero-valent iron (NZVI) particles have been surface modified and used for contaminant remediation. NZVI tend to agglomerate due to magnetic and van der Waals forces and form larger particles that settle down in aqeous media. Agglomerated particles increase in size and have decreased specific surface area and that lead to decrease in their reactivity. In this research, polymer-based surface modifiers were used to increase dispersibility of NZVI for environmental remediation applications. Ca-alginate was selected to entrap NZVI in beads and used to remove aqueous nitrate. The two-way ANOVA test indicates that there was no significant difference between reactivities (towards nitrate) of entrapped NZVI and bare NZVI. While the reactivity of entrapped NZVI was comparable to bare NZVI, the NZVI particles were found to remain agglomerated or clustered together within the alginate beads.;A novel amphiphilic polysiloxane graft copolymers (APGC) was designed, synthesized and used to coat NZVI in an attempt to overcome the agglomeration problem. APGC was composed of hydrophobic polysilosin, hydrophilic polyethylene glycol (PEG), and carboxylic acid. The APGC was successfully adsorbed onto the NZVI surfaces via the carboxylic acid anchoring groups and PEG grafts provided dispersibility in water. Coating of NZVI particles with APGC was found to enhance their colloidal stability in water. The APGC possessing the highest concentration of carboxylic acid anchoring group (AA) provided the highest colloidal stability. It was also found that the colloidal stability of the APGC coated NZVI remained effectively unchanged up to 12 months. The sedimentation characteristics of APGC coated NZVI (CNZVI) under different ionic strength conditions (0-10 mM NaCl and CaCl2) did not change significantly. Degradation studies were conducted with trichloroethylene (TCE) and arsenic (V) [As(V)] as the model contaminants. TCE degradation rates with CNZVI were determined to be higher as compared to bare NZVI. Shelf-life studies indicated no change on TCE degradation by CNZVI over a 6-month period. As(V) removal batch studies with CNZVI were conducted to in both aerobic and anaerobic conditions. Increase in arsenic removal efficiency was observed with CNZVI as compare to bare NZVI in both aerobic and anaerobic conditions. Ionic strengths showed minimal inhibiting effect on arsenic removal by CNZVI.