Abstract
Zero-valent iron nanoparticles (nZVI) treated by reduced sulfur compounds (i.e., sulfidated nZVI, S-nZVI) have attracted increased attention as promising materials for environmental remediation. While the preparation of S-nZVI and its reactions with various groundwater contaminants such as trichloroethylene (TCE) were already a subject of several studies, nanoparticle synthesis procedures investigated so far were suited mainly for laboratory-scale preparation with only a limited possibility of easy and cost-effective large-scale production and FeS shell property control. This study presents a novel approach for synthesizing S-nZVI using commercially available nZVI particles that are treated with sodium sulfide in a concentrated slurry. This leads to S-nZVI particles that do not contain hazardous boron residues and can be easily prepared off-site. The resulting S-nZVI exhibits a core–shell structure where zero-valent iron is the dominant phase in the core, while the shell contains mostly amorphous iron sulfides. The average FeS shell thickness can be controlled by the applied sulfide concentration. Up to a 12-fold increase in the TCE removal and a 7-fold increase in the electron efficiency were observed upon amending nZVI with sulfide. Although the FeS shell thickness correlated with surface-area-normalized TCE removal rates, sulfidation negatively impacted the particle surface area, resulting in an optimal FeS shell thickness of approximately 7.3 nm. This corresponded to a particle S/Fe mass ratio of 0.0195. At all sulfide doses, the TCE degradation products were only fully dechlorinated hydrocarbons. Moreover, a nearly 100% chlorine balance was found at the end of the experiments, further confirming complete TCE degradation and the absence of chlorinated transformation products. The newly synthesized S-nZVI particles thus represent a promising remedial agent applicable at sites contaminated with TCE.
Highlights
Nanoscale zero-valent iron presents an attractive and, according to current knowledge, environmentally benign reduction agent for the treatment of contaminated groundwater.[1]
This study investigates a new synthesis approach to produce sulfidated Nanoscale zero-valent iron (nZVI) particles with controlled reactivity and selectivity toward TCE removal
Available nZVI prepared by the thermal reduction of iron
Summary
Nanoscale zero-valent iron (nZVI) presents an attractive and, according to current knowledge, environmentally benign reduction agent for the treatment of contaminated groundwater.[1]. NZVI has been immobilized onto various solid porous materials[6−9] and coated with organic polymers[10−12] to limit particle exposure to water These materials, exhibited a lowered reduction capacity and/or increased contaminant sorption to the detriment of chemical reduction that could possibly result in a decreased rate of contaminant (bio)degradation and contaminant transport to other locations, causing secondary contamination.[1] The doping of nZVI with a catalytic noble metal (e.g., Pd, Pt, or Ni) to increase the particle reactivity has been widely studied.[13−15] the superior reactivity of these materials has been found to be rapidly inhibited by natural water constituents, such as humic acids, and fast iron corrosion.[16,17] Another problem of bimetallic systems can be the leaching of hazardous catalytic metals, which may generate a secondary pollution to the treated water.[17]
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