Highly reactive subnano-sized zero-valent iron synthesized on smectite clay templates

Abstract

A novel method was developed for synthesizing subnano-sized zero-valent iron (ZVI) using smectite clay layers as templates. Exchangeable Fe(III) cations compensating the structural negative charges of smectites were reduced with NaBH4, resulting in the formation of ZVI. The unique structure of smectite clay, in which isolated exchangeable Fe(III) cations reside at the sites of structural negative charges, inhibited the agglomeration of ZVI resulting in the formation of discrete regions of subnanoscale ZVI particles in the smectite interlayer regions. X-ray diffraction revealed an interlayer spacing of -5 Å. The clay-templated ZVI showed superior reactivity and efficiency compared to other previously reported forms of ZVI as indicated by the reduction of nitrobenzene. These results confirm that nonstructural Fe from Fe(III)-smectites was reduced predominantly to ZVI which was responsible for the reduction of nitrobenzene to aniline. This new form of subnanoscale ZVI may find its utility in the development of remediation technologies for persistent environmental contaminants.