Comparative studies on montmorillonite-supported zero-valent iron nanoparticles produced by different methods: reactivity and stability

To mitigate the aggregation and enhance the reactivity of nanosized zero-valent iron (nZVI), montmorillonite is employed as a template-supporting matrix to prepare nZVI through two different pathways: heterogeneous nucleation and homogeneous nucleation processes. Dispersed sub-nanosized ZVI clusters with an average size around 0.5 nm (perpendicular to the clay layers) are intercalated in clay interlayers when using montmorillonite as a template in preparation via heterogeneous nucleation process. However, the particle sizes spanned from 0.62 nm (perpendicular to the clay layers) for the ZVI intercalated in montmorillonite interlayers to 150 nm for the ZVI residing on an external surface when using montmorillonite as a dispersion agent in the preparation via homogeneous nucleation. Furthermore, parallel batch experiments have been conducted with nZVIs synthesized by the two different methods in solutions of nitrobenzene and their reactivity is evaluated via response of nZVI to nitrobenzene remediation. As a result, the reactivity of ZVI synthesized by heterogeneous nucleation is greater than that by homogeneous nucleation, which is inversely correlated to the size of ZVI supported by montmorillonite clay. Evaluation of the stability of montmorillonite-supported ZVI showed that ZVI intercalated in the interlayers of montmorillonite is more stable than that located on the external surface, which can be attributed to the protective effect of montmorillonite layers on ZVI from oxidation. These results suggest that the great reactivity and high stability of montmorillonite-intercalated ZVI synthesized through heterogeneous nucleation process warrants its significant potential in developing in situ remediation and treatment technologies for organic contaminants.