Structural transformation of sulfidized zerovalent iron and its impact on long-term reactivity

Mangayayam, Marco C.; Perez, Jeffrey Paulo H.; Dideriksen, Knud; Freeman, Helen M.; Bovet, N.; Benning, Liane G.; Tobler, Dominique J.

doi:10.1039/c9en00876d

Cited by 30 publications

(40 citation statements)

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“…The XPS S 2p spectra show only a slight shift toward more oxidized forms between freshly synthesized and reacted particles (i.e., a decrease in the S 2– and an increase in the S 0 content) ( Figure 5 B). This agrees with a recent study where the FeS shell remained intact even after 180 days of particle aging in artificial groundwater, 49 while partial disruption of FeS shell after 60 days of aging was observed in our previous study. 48 Apparently, FeS shell is resistant to chemical oxidation but is prone to mechanical damage.…”

Section: Resultssupporting

confidence: 93%

“…While the formation of fresh crystalline mackinawite is favored over amorphous FeS (ppt) thermodynamically (i.e., mackinawite has a higher saturation index), available laboratory data from FeS precipitation experiments and field data from a reducing lake and estuarine and marine sediments indicate that the formation of crystalline mackinawite is inhibited, and it is formed only later by the recrystallization of amorphous and poorly crystalline FeS phases. 49 , 55 , 56 , 60 , 61 In this study, crystalline mackinawite has been observed in the XRD patterns of S-nZVI particles with high sulfur doses after the reactivity experiments (see section 3.4 ), corroborating the gradual crystallization of iron sulfides in time.…”

Section: Resultssupporting

confidence: 74%

“…This is comparable with a previous study where S-nZVI particles with a theoretical S/Fe mass ratio 0.13 developed a 5 nm thick FeS shell. 49 Although the shell thickness was not perfectly uniform for all particles of the same type, its mean value was associated with an increasing sulfide dose.…”

Section: Resultsmentioning

confidence: 97%

“…The existence of an optimal S/Fe ratio for TCE removal was previously observed. 22 , 49 The kinetics of TCE reduction was well described by a first-order rate law. 20 The observed pseudo-first-order rate constant ( k obs ) of the best performing S-nZVI was approximately 12-fold higher than for the untreated nZVI.…”

Section: Resultsmentioning

confidence: 99%

“…The characteristics of the sulfide shell agree with previous studies that identified amorphous iron sulfide sheets with a mackinawite-like structure as the primary FeS precipitates. 27 , 49 , 55 , 56 …”

Section: Resultsmentioning

confidence: 99%

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Core–Shell Fe/FeS Nanoparticles with Controlled Shell Thickness for Enhanced Trichloroethylene Removal

Brumovský

Filip

Malina

et al. 2020

ACS Appl. Mater. Interfaces

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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.

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Section: Resultssupporting

confidence: 93%