In water treatment processes that involve contaminant reduction by zerovalent iron (ZVI), reduction of water to dihydrogen is a competing reaction that must be minimized to maximize the efficiency of electron utilization from the ZVI. Sulfidation has recently been shown to decrease H formation significantly, such that the overall electron efficiency of (or selectivity for) contaminant reduction can be greatly increased. To date, this work has focused on nanoscale ZVI (nZVI) and solution-phase sulfidation agents (e.g., bisulfide, dithionite or thiosulfate), both of which pose challenges for up-scaling the production of sulfidated ZVI for field applications. To overcome these challenges, we developed a process for sulfidation of microscale ZVI by ball milling ZVI with elemental sulfur. The resulting material (S-mZVI) exhibits reduced aggregation, relatively homogeneous distribution of Fe and S throughout the particle (not core-shell structure), enhanced reactivity with trichloroethylene (TCE), less H formation, and therefore greatly improved electron efficiency of TCE dechlorination (ε). Under ZVI-limited conditions (initial Fe/TCE = 1.6 mol/mol), S-mZVI gave surface-area normalized reduction rate constants (k') and ε that were ∼2- and 10-fold greater than the unsulfidated ball-milled control (mZVI). Under TCE-limited conditions (initial Fe/TCE = 2000 mol/mol), sulfidation increased k and ε ≈ 5- and 50-fold, respectively. The major products from TCE degradation by S-mZVI were acetylene, ethene, and ethane, which is consistent with dechlorination by β-elimination, as is typical of ZVI, iron oxides, and/or sulfides. However, electrochemical characterization shows that the sulfidated material has redox properties intermediate between ZVI and FeO, mostly likely significant coverage of the surface with FeS.

Nanoscale zerovalent iron (nZVI) likely finds its application in source zone remediation. Two approaches to modify nZVI have been reported: bimetal (Fe-Me) and sulfidated nZVI (S-nZVI). However, previous research has primarily focused on enhancing particle reactivity with these two modifications under more plume-like conditions. In this study, we systematically compared the trichloroethene (TCE) dechlorination pathway, rate, and electron selectivity of Fe-Me (Me: Pd, Ni, Cu, and Ag), S-nZVI, and nZVI with excess TCE simulating source zone conditions. TCE dechlorination on Fe-Me was primarily via hydrogenolysis while that on S-nZVI and nZVI was mainly via β-elimination. The surface-area normalized TCE reduction rate ( k) of Fe-Pd, S-nZVI, Fe-Ni, Fe-Cu, and Fe-Ag were ∼6800-, 190-, 130-, 20-, and 8-fold greater than nZVI. All bimetallic modification enhanced the competing hydrogen evolution reaction (HER) while sulfidation inhibited HER. Fe-Cu and Fe-Ag negligibly enhanced electron utilization efficiency (ε) while Fe-Pd, Fe-Ni, and S-nZVI dramatically increased ε from 2% to ∼100%, 69%, and 72%, respectively. Adsorbed atomic hydrogen was identified to be responsible for the TCE dechlorination on Fe-Me but not on S-nZVI. The enhanced dechlorination rate along with the reduced HER of S-nZVI can be explained by that FeS conducting major electrons mediated TCE dechlorination while Fe oxides conducting minor electrons mediated HER.

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Clay-based aerogel is a promising material in the field of thermal insulation and flame retardant, but obtaining claybased aerogel with high fire resistance, low thermal conductivity, hydrophobicity, and mechanical robustness remains a challenge. In this work, palygorskite-based aerogel was successfully fabricated via combining with a very small proportion of alginate to form a distinctive hierarchically meso−microporous structure. By employing ethanol solution (EA) replacement method and freeze-drying process, the resultant aerogel exhibited ultralow density (0.035−0.052 g/cm 3 ), practical mechanical strengths (0.7−2.1 MPa), and low thermal conductivity of 0.0332−0.165 W/mK (25−1000 °C). The hydrophobicity of aerogel was achieved by simple chemical vapor deposition of methyltrimethoxysilane (MTMS). The Pal-based aerogel showed good performance in both fire resistance with high limiting oxygen index up to 90%, and heat resistance with tolerance of flame up to 1000 °C for 10 min. This renewable Palbased aerogel with a 3D framework is a promising material to be applied in fields of construction and aerospace for thermal insulation and high fire resistance.