Assessing the Impacts of Dynamic Soft-Template Innate to Switchable Ionic Liquids on Nanoparticulate Green Rust Crystalline Structures

Journal Article · Wed Sep 25 04:00:00 EDT 2019 · Chemical Communications

DOI:https://doi.org/10.1039/C9CC04581C· OSTI ID:1576771

Zheng, Jian ^[1]; Yu, Xiao-Ying ^[1]; Nguyen, Manh Thuong ^[1]; Lao, David B. ^[1]; Zhu, Yifeng ^[1]; Wang, Feng ^[2]; Heldebrant, David J. ^[1]

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1. BATTELLE (PACIFIC NW LAB)
2. Brookhaven National Laboratory

Switchable ionic liquids (SWILs) are promising solvents for many green chemistry applications, notably the capture and (or) subsequent catalytic hydrogenation of CO2 in addition to solvents with an inherent nm-sized “soft template” that can be used for the synthesis of nanoparticles. Despite intense studies, the structural details of how soft templates form within the solvent, and how such environments solvate catalysts or chemical precursors within SWILs remains elusive. Similarly, little is known about reaction intermediates for nanoparticle synthesis, more specifically how solvent composition and speciation influence the speciation, solvation, dispersion and nucleation of nanoparticles within. Here we report a new strategy to study the dynamic solvation environments within SWILs using nanoparticulate green rust as a model system, using combined study of X-ray absorption (XAS) spectroscopy coupled with density functional theory (DFT) calculations. In situ XAS allows direct measurements of the solvent structure, and determining the speciation of reaction intermediates, offering undisturbed measurements of air-sensitive nanocrystalline green rust within liquid environments. We present here, a study showing how solvation environments change in the SWIL and how the speciation of green rust chemical precursors change as a function of the varying solvent environment. In this in situ analysis, we newly identified structural progression from linear, square planar, then ultimately octahedral iron (Fe) complexes as reaction intermediates predicted on integrative XAS measurements and DFT calculations. This study identifies a solvated octahedral Fe hydroxide complex which we propose as the critical intermediate for nucleation and growth of nanoparticulate green rust upon removal of CO2 from the SWIL. This combined experimental and computational approach enabled by the use of a novel microfluidic device offers new insights into how dynamic solvent environment (i.e., soft template) that leads to the formation of nanoparticles such as green rust in the SWILs. In this in situ analysis, we newly identified structural progression from linear, square planar, then ultimately octahedral iron (Fe) complexes as reaction intermediates predicted on integrative XAS measurements and DFT calculations. This study identifies a solvated octahedral Fe hydroxide complex which we propose as the critical intermediate for nucleation and growth of nanoparticulate green rust upon removal of CO2 from the SWIL. This combined experimental and computational approach enabled by the use of a novel microfluidic device offers new insights into how dynamic solvent environment (i.e., soft template) that leads to the formation of nanoparticles such as green rust in the SWILs.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1576771
• Report Number(s): PNNL-SA-144215
• Journal Information: Chemical Communications, Journal Name: Chemical Communications Journal Issue: 75 Vol. 55
• Country of Publication: United States
• Language: English