Effects of ionic liquids on the characteristics of synthesized nano Fe(0) particles

In this paper, high specific surface area zerovalent Fe(0) nanoparticles with unusual morphology and high reductive activity were prepared using a chemical reductive reaction of iron chloride hydrate with sodium borohydride in an aqueous solution of ionic liquids (ILs). The ionic liquids, [C(4)mim]X (X = Cl(-), Br(-), BF(4)(-), PF(6)(-)) and [C(n)mim][BF(4)] (n = 4, 6, 8), were used for this purpose. Transmission electron microscopy, X-ray diffraction, and Brunauer-Emmett-Teller surface area measurements were used to characterize the morphology, structure, and physical properties of the as-prepared Fe(0). The results suggest that the nucleation and growth of the Fe(0) were governed by an IL-controlled reductive reaction mechanism. The effects of ionic liquids (cations, anions, and concentration) on the morphology of the Fe(0) were examined. It was shown that anions of the ILs played a key role in the morphology and size of Fe(0), and the nanoparticle size of the Fe(0) prepared in the presence of different ionic liquids follows the trend: [C(4)mim]Cl > [C(4)mim]Br > [C(4)mim][BF(4)] > [C(4)mim][PF(6)] and [C(4)mim][BF(4)] > [C(6)mim][BF(4)] > [C(8)mim][BF(4)]. The reductive activity of the iron nanoparticles was studied by the denitrification experiment of sodium nitrite. The removal rate of nitrite by the IL-capped Fe(0) was found to be much faster than that by the noncapped Fe(0). This indicates that the IL-capped Fe(0) particles are better candidates for the reductive degradation. The high reductive activity of the Fe(0) nanoparticles was attributed to their high surface area and more active sites.