Investigation of Some Factors Affecting the Stability of Zero Valent Iron Nanoparticles in Aqueous Environments

Considering high potential of zero-valent iron nanoparticles (NZVI) for contaminants remediation in surface and groundwater, it is important to investigate factors affecting their stability in aquatic environments. In this study, the effects of surface coating and background solution characteristics including nanoparticle concentration, ionic strength, electrolyte type and dissolved organic matter content on the stability of NZVI in aqueous suspensions were investigated. A number of four two-way factorial experiments based on completely randomized design with three replications were conducted to explore the effects of surface coating and each of four background solution characteristics on the stability of NZVI suspension. Initially, bare NZVI (B-NZVI) and Carboxymethyl cellulose coated NZVI (CMC-NZVI) were synthesized and characterized. Thereafter NZVI suspensions were prepared in distilled water at different levels of selected characteristics. The hydrodynamic diameter and zeta potential were then measured in each of prepared suspension. Results indicated CMC-NZVI suspensions were more stable rather than B-NZVI in all tested solutions. Increase in nanoparticle concentration, ionic strength and cation valence of background solution, increased hydrodynamic diameter and decreased zeta potential of NZVI which lead to more aggregation of NZNI and less stability of suspension. On the contrary, increase in dissolved organic matter content resulted in more stability of NZNI suspension. Results also showed that there are significant interactions between nanoparticle type and solution characteristics; as B-NZVI is more sensitive to change in solution chemistry than CMC-NZVI.