Optimal Design of Sulfidated Nanoscale Zerovalent Iron for Enhanced Trichloroethene Degradation

Abstract

Sulfidated nanoscale zerovalent iron (S-nZVI) has the potential to be a cost-effective remediation agent for a wide range of environmental pollutants, including chlorinated solvents. Various synthesis approaches have yielded S-nZVI consisting of a Fe (or Fe/S) core and FeS shell, which are significantly more reactive to trichloroethene (TCE) than nZVI. However, their reactivity is not as high as palladium-doped nZVI (Pd-nZVI). We synthesized S-nZVI by the co-precipitation of FeS and Fe by using NaS during the borohydride reduction of FeSO (S-nZVI). This resulted in FeS structures bridging the nZVI core and the surface, as confirmed by electron microscopy and X-ray analyses. The TCE degradation capacity of up to 0.46 mol TCE/mol Fe was obtained for S-nZVI at a high S loading and was comparable to Pd-nZVI but 60% higher than the currently most reactive S-nZVI, in which FeS only coats the nZVI (S-nZVI). The high TCE degradation was due to complete utilization of Fe (2 e/mol Fe) toward the formation of acetylene. Although Pd-nZVI yielded 3 e/mol Fe, TCE degradation was comparable because it reduced acetylene further to ethene and ethane. Under Fe-limited conditions, the S-nZVI TCE degradation rate was 16 times higher than that of Pd-nZVI (0.5 wt % Pd) and 90 times higher than that of S-nZVI.

Sulfur Loading and Speciation Control the Hydrophobicity, Electron Transfer, Reactivity, and Selectivity of Sulfidized Nanoscale Zerovalent Iron

“…Recently, it was shown by us and others that the sulfidation of NZVI lowers its reactivity with water and other non‐target hydrophilic contaminants (e.g., NO 3 − ), while increasing its reactivity with target contaminants like chlorinated solvents and antibiotics. [ 25–31 ] Several mechanisms have been hypothesized for the enhanced reactivity and selectivity of sulfidized nanoscale zerovalent iron (SNZVI) compared to NZVI. First, SNZVI is more hydrophobic than NZVI, resulting in lower interaction with water and charged solutes, and greater interaction with hydrophobic contaminants.…”

Complex-conductivity monitoring to delineate aquifer pore clogging during nanoparticles injection

“…Given their relatively low costs, zero-valent iron (ZVI) and iron-oxide NP have become popular due to their ability to promote the degradation of a variety of pollutants (e.g. Grieger et al 2010;Tosco et al 2014;Velimirovic et al 2014;Chen et al 2015;Schmid et al 2015;Bhattacharjee & Ghoshal 2018). Iron-oxide particles are of special interest due to their nontoxicity, adsorption capacity and ability to stimulate bioremediation (Hua et al 2012;Xu et al 2012;Braunschweig et al 2013;Lei et al 2018).…”

Quantifying the efficiency and selectivity of organohalide dechlorination by zerovalent iron

“…The apparent decoupling of Fe(0) corrosion by water and dechlorination for S-ZVI indicate that the dechlorination by S-ZVI does not depend on the corrosion of Fe(0) by water. 19,39,68 The current consensus is that the FeS x layer formed on the ZVI surface inhibits the corrosion of ZVI in water by blocking access to Fe(0), thus preserving the electron donating capacity for reductive dechlorination. Dechlorination mediated by direct electron transfer does not require excess TCE to maintain high 3 e as with conventional or bimetallically modied nZVI because there is no need to outcompete water for reaction sites and electrons.…”

“…[13][14][15][16][17][18] Because the science and engineering of contaminant degradation, especially dechlorination, in the Fe-water system are relatively mature, most current research is now focused on higher-level issues like the optimization of the process to maximize its efficiency for contaminant degradation (e.g., electron efficiency). [19][20][21] Throughout this manuscript, the term "efficiency" is used in a precise technical sense (i.e., the relative quantity of inputs to outputs in a process 22 ), rather than the common but casual and not entirely accurate use of the term as a synonym for the rate of contaminant removal (e.g., "removal efficiency" 5 and "degradation efficiency" 23 ). Given the focus of this work on organohalide reduction by ZVI, the general denition of efficiency we use here is the relative quantity of electrons transferred from ZVI to each of the competing product formation reactions.…”