Highly concentrated, reactive and stable dispersion of zero-valent iron nanoparticles: Direct surface modification and site application

Abstract

Nanoscale zerovalent iron (nZVI) particles with a narrow size distribution (40–80nm) were modified with an environmentally acceptable non-ionic surfactant, Tween 80, with the aim to produce a highly concentrated aqueous dispersion (20% (w/w)) exhibiting temporal stability against aggregation and therefore retaining its mobility and extreme reactivity with pollutants. Powdered nZVI particles, prepared via a large-scale thermally induced process, were directly transferred into the 5% (w/w) aqueous solution of the Tween 80, which has not been performed before. Due to the nature of the surfactant molecules, they adsorb immediately at the new phase interface, which results in the formation of a thin, compact but pollutant permeable surface layer on nZVI particles (confirmed by TEM analysis). The temporal stability against aggregation and oxidation of the Tween 80 modified nZVI particles was monitored by XRD, Mössbauer spectroscopy, and DLS during its two-month storage. These analyses revealed an extraordinarily low degree of oxidation of the nZVI surface (estimated to represent less than 15%) and a high stability against aggregation even after two-month storage. The batch experiments with solutions contaminated by a mixture of chlorinated ethenes confirmed excellent reactivity of the Tween 80 stabilized nZVI particles with all studied pollutants (i.e., PCE, TCE, cis-DCE, trans-DCE). The decomposition rates achieved with Tween 80 modified nZVI particles were significantly higher compared to the non-stabilized nZVI particles prepared via the borohydride reduction method.