금속황화물을 이용한 나노영가철의 표면 개질: 합성, 특성, 환경정화에의 응용 연구

Abstract

This study investigated a surface modification method (metal sulfide coating) for enhancing the reactivity of nano-Fe0. Various metal sulfides, known as either semiconductors or metallic conductors, were introduced on Fe0 surface to facilitate electron transfer reactions. The metal sulfides-coated nano-Fe0 showed markedly enhanced reactivity toward chlorinated organic pollutants and reduced bacterial toxicity. We examined and compared the impact of metal additives on reactivity and electrochemical corrosion behavior of nano-Fe0. Based on correlations between experimental rate constants and electrochemical variables, insights into the possible roles of each metal additive in reaction mechanism were obtained.1. We have developed a new one-pot method to prepare iron/iron sulfide nanoparticles (Fe/FeS) using dithionite at room temperature. The FeS precipitates on the Fe surface are formed by the interaction between dissolved iron species and hydrogen sulfide, one of the decomposition products of dithionite in solution. The resulting Fe/FeS nanoparticles have high surface area, good electrical conductivity, and strong magnetic responsivity. In addition, the Fe/FeS shows a much higher reactivity towards contaminants than the pure Fe nanoparticles. The above synthesized nanoparticles are successfully applied for the rapid removal of trichloroethylene (TCE) from water. The study reveals that Fe/FeS nanoparticles are a promising candidate for the efficient removal of pollutants. 2. The reactivity of freshly-synthesized FeS-coated iron nanoparticles (nFe/FeS) toward trichloroethylene (TCE) reduction was examined under various solution conditions in order to evaluate the potential advantages of nFe/FeS in field treatment. The reduction rate of TCE increased with increasing pH, which is consistent with the pH effect reported previously of iron sulfide systems, but opposite that which has been observed for (nonsulfidic) Fe0 systems. Ionic strength, hardness (Ca2+/Mg2+), and humic acid imposed significantly different effects on the reactivity of nFe/FeS. The kinetics of TCE reduction were unaffected by ionic strength over the range of 0.1–10 mM NaCl. The reaction rates were enhanced by increasing Ca2+ or Mg2+ concentrations, and Mg2+ had a greater effect than Ca2+. In contrast, the rates of TCE disappearance were somewhat inhibited by humic acid. However, the negative effect of humic acid on the reactivity of nFe/FeS was largely alleviated when humic acid was combined with Ca2+, presumably due to a change in their conformation upon adsorption to nFe/FeS surface. The relatively high rates of TCE reduction in simulated and real groundwater suggest that nFe/FeS could be a promising alternative to iron nanoparticles (nFe) for groundwater remediation.3. We synthesized different metal sulfide-coated iron nanoparticles (Fe/MeS) and systematically investigated their surface reactivity and bactericidal properties. The particles showed greatly higher reduction efficiency for trichloroethylene and lower bacterial toxicity compared to bare nanoscale iron.4. Considering the frequent occurrence of inorganic metal ions with chlorinated organic pollutants, the examination of their impacts on reductive dechlorination is necessary for a better understanding of the fate of chlorinated organic compounds. In this study, we investigated and compared the reactivity and electrochemical behavior of fresh and aged metal-amended FeS-coated iron nanoparticles (Fe/FeS). Batch studies showed that certain metal ions (Pd, Ni, and Co) enhanced rates of trichloroethylene (TCE) reduction while others (Cu and Mn) retarded the reaction rates. Pseudo-first-order rate constants (kobs values) of fresh particles did correlate well with the exchange current density for hydrogen evolution, and those of aged particles revealed strong relationships with the electrochemical parameters (corrosion potential, corrosion current, and polarization resistance). This proposes that at the early stage, the metal additive itself plays a direct role in TCE reduction by mediating hydrogenation. Then, after aging proceeds, the electronic properties of NPs and oxide would be more important because the oxide films obstructing the metal additives make their effect less direct.