Application of nano‐scale zero‐valent iron adsorbed on magnetite nanoparticles for removal of carbon tetrachloride: Products and degradation pathway

Abstract

Nano‐scale zero‐valent iron (nZVI) attached to Fe3O4 nanoparticles (Fe0@Fe3O4), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe0@Fe3O4 composites with different ratios of the two components were compared. Under optimum conditions, when the Fe0/Fe3O4 ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe0/Fe3O4 ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe3O4 alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe0@Fe3O4 system: both Fe2+ and Fe3+ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe2+ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe0 to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe2+ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe0@Fe3O4 nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds.

Remediation of chloroform in fine‐textured soil using zero‐valent iron

“…Although most studies reported in the literature did not use soil as a matrix, different bimetallic particles or modifications of reactive material, such as iron and nickel particles, sufidized iron, palladium (Pd) iron nanoparticles, zinc (Zn) or iron with nickel or palladium particles, and Fe 0 coated magnetite, were used as a sole solid phase for reductive dechlorination of carbon tetrachloride and chloroform and other chlorinated compounds such as trichloroethylene. Results revealed these modifications enhanced or catalyzed the efficiency of Fe 0 for the transformation of these chlorinated compounds (Feng & Lim, 2005; Jin et al, 2018; Lv et al, 2020). Oxidation of Fe 0 (electron donor) produces Fe 2+ by donating two electrons (oxidation half reaction).…”

“…Potential production of Fe oxide minerals (Fe III ) in Equation () and magnetite (Equation ) under anaerobic conditions can catalyze chloroform reduction by Fe 0 (Lv et al, 2020; Rodríguez‐Fernández et al, 2018). …”

“…Historically, most studies focused on carbon tetrachloride, a precursor of chloroform in the reductive transformation pathway where chloroform can potentially further dechlorinate to dichloromethane, chloromethane, or finally to methane (Supporting Information: Figure ). Those studies exhibited accumulation of chloroform and/or dichloromethane during reductive dechlorination of carbon tetrachloride (Jin et al, 2018; Lv et al, 2020; Rodríguez‐Fernández et al, 2018; Zhu et al, 2021). However, in our study, the transformation of chloroform proceeded mainly to the production of dichloromethane and chloromethane or to a small extent to methane (greater extent of dechlorination).…”

“…However, halorespiration is mostly carried out by specialized bacteria not common in the environment (Wang et al, 2022). Application of nanoscale zero‐valent iron (Fe 0 ) has been used in soil and groundwater remediation (Jin et al, 2018; Lv et al, 2020; Zhu et al, 2021), where it acts as a reducing agent donating electrons to transform halogenated contaminants into less toxic forms. The size and high reactivity of Fe 0 nanoparticles make them favorable for the remediation of water and soils as nanoparticles can infiltrate into very small soil pores and persist suspended in groundwater, allowing movement away from the injection point (Chapman et al, 2020; Galdames et al, 2020).…”

“…Most research focused on the reductive chlorination of chlorinated ethenes, such as perchloroethylene and trichloroethylene by Fe 0 . A few studies showed the application of Fe 0 for the dechlorination of chlorinated methanes and were generally related to carbon tetrachloride (Jin et al, 2018; Lv et al, 2020; Zhu et al, 2021). Most of these studies showed transformation to dichloromethane only and none showed long‐term observations for natural attenuation.…”