Comparison of Reactivity of Nanoscaled Zero-Valent Iron Formed on Clay Surfaces

Clay minerals were used as template-supporting matrices to synthesize nanoscaled zero-valent iron (ZVI). The size and distribution of the synthesized ZVI particles were related to clay structure, origin of negative charges, and surface charge density. The average particle size ranged from 0.5 nm (perpendicular to the clay layers) for the ZVI intercalated in smectite interlayers, to I to 2 fun for the ZVI residing on kaolinite and pyrophyllite surfaces, and 5 nm for the ZVI formed on illite and smectite external surfaces. The reactivity of the ZVI was evaluated based on the rate and extent of reduction of nitrobenzene to aniline. The results revealed that the reactivity of ZVI decreased with increasing particle size, and the ZVI intercalated in smectite clay manifested the highest reactivity. The reaction efficiency of the ZVI associated with smectite clay was estimated to be as high as 90% based on the equivalency of electron transfer from ZVI to nitrobenzene. The great reactivity and high efficiency of smectite-intercalated ZVI, along with many other advantageous properties of smectite (e.g., a layer structure that protects ZVI from aggregation and oxidation), warrants its potential utilization in the development of in situ remediation and treatment technologies for inorganic and organic contaminants.