Solvent effect on zero-valent iron nanoparticles (nZVI) preparation and its thermal oxidation characteristic

Abstract

Zero-valent iron (ZVI) nanoparticle exists a nanoscale (1-100 nm) of the iron particle with zero oxidation number. It has acquired considerable attention for its potential to capture the free-electron moieties. The production and storage of ZVI material, however, is challenging because it is relatively unstable. In this research, we aim to study of solvent effects on ZVI preparation and its characterization. The nano-scaled ZVI was synthesized by a chemical reduction method. Iron (III) chloride hexahydrate (FeCl3·6H2O) was used as a chemical precursor and sodium borohydride solution (NaBH4) as a reducing agent. Two parameters used in this study were: i) solvent types (ethanol, diethyl ether, and acetone) ii) proportion of solvent and deionized water (4:0, 4:1, and 4:2 by volume). We characterized the physical and chemical properties of the synthesized samples (e.g. particle size and distribution, morphology, and the chemical composition) using various techniques, for example, TEM, UV-Vis spectrophotometer, and XRD. Moreover, we performed a thermal oxidation reaction of synthesized powder samples using DSC and TGA tools. The results show that the nZVI particle formed a spherical shape with the smallest particle size of ∼39 nm. The solvent type was the key parameter protecting the oxidation reaction during the synthesis process. According to the spherical shape of the synthesized nZVI samples, an estimated specific surface area was also reported. The cubic structure of nZVI particles was estimated at 79-81 wt.%, and almost 20 wt.% was attributed to iron oxide (Fe2O3) cubic phase. The oxidation reaction occurred above 400ºC. The minimum enthalpy of thermal oxidation was approximately 1600 J/g. Furthermore, the relation between thermal oxidation enthalpy and nZVI particle sizes were revealed and predicted by the Boltzmann equation.