Integrated effect of bulk cations on nano-confined reactivity of clay-intercalated subnanoscale zero-valent iron in water-tetrahydrofuran mixtures

Smectite clay-intercalated subnanoscale zero-valent iron (CSZVI) exhibits superior reactivity toward contaminants due to the small iron clusters (similar to 0.5 nm) under nano-confinement, which however is significantly influenced by the solution chemistry e.g., various cations, of polluted soil and water. This work was undertaken to elucidate the mechanisms of solution chemistry effects on dehalogenation ability of CSZVI in watertetrahydrofuran solution using decabromodiphenyl ether as a model contaminant. By combined spectroscopic characterization and molecular dynamics simulation, it was revealed that bulk cations, i.e., Na+, K+, Mg2+ and Ca2+ collectively affected the interlayer distance, water content and Bronsted acidity of CSZVI and thus its degradation efficiency. Although causing inter-particle aggregation, Mg2+ induced optimal nano-confined interlayers at concentration of 20 mM, exhibiting a superior debromination efficiency with rate constant 9.84 times larger than that by the common nano-sized ZVI. Conversely, K+ rendered the interlayers less reactive, but protected CSZVI from corrosion loss with higher electron utilization efficiency, which was 1.7 times higher than CSZVI in presence of Mg2+. The findings provide new strategies to manipulate the reactivity of nano-confined CSZVI for effective wastewater and contaminated soil remediation.

Automated summary

By spectroscopic characterization and molecular dynamics simulation, this study reveals the mechanisms of solution chemistry effects on the dehalogenation ability of CSZVI in water-tetrahydrofuran solution. It was found that bulk cations influenced the interlayer distance, water content, and acidity of CSZVI, thus affecting its degradation efficiency. Mg2+ at a concentration of 20 mM induced optimal nano-confined interlayers and exhibited a debromination efficiency 9.84 times larger than common nano-sized ZVI. On the other hand, K+ rendered the interlayers less reactive but protected CSZVI from corrosion loss with higher electron utilization efficiency, 1.7 times higher than in the presence of Mg2+. These findings provide new strategies for effective wastewater and contaminated soil remediation.