Smectite Clays Used as Templates to Synthesize Subnano-Sized Zero-Valent Iron for Reduction of Organic Contaminants.

In this study, a novel method was developed to synthesize clay-based subnano-sized zero-valent iron (ZVI).  Exchangeable Fe(III) cations were used to compensate the discrete negatively charged sites on smectite surfaces, followed by a reduction to ZVI by NaBH₄. X-ray photoelectron spectroscopy confirmed the formation of ZVI. Clay interlayers were collapsed upon the Fe(III) reduction by NaBH₄. These synthesized subnano-sized ZVI showed superior reactivity and efficiency to reduce organic contaminants, e. g. nitrobenzene. Over 90% of nitrobenzene (0.65 mM) was degraded within one minute, with the major intermediate of phenylhydroxylamine. Aniline was the final product accounting for about 94% of nitrobenzene after three-hour reaction. Smectite is a type of widely distributed clay in the environment, which can be constructed as a reactive domains for in situ remediation of many persistent contaminants in groundwater and subsurface soil.