PNNL

Abstract

Ionic liquids are green solvents that have wide applications in material synthesis, catalysis, and separation. A model switchable ionic liquid (SWIL) consisting of 1,8-diazabicycloundec-7-ene (DBU) and 1-hexanol with carbon dioxide (CO2) as the trigger gas was chosen to synthesize nanocrystalline green rust. Under anoxic conditions, by adding iron (II) acetate (Fe(C2H3O2)2) and methanol to the degassed SWIL, a nanoparticulate green rust with carbonate (nano GR) was synthesized. The structure and oxidation state of nanocrystalline green rust has been confirmed using SEM, TEM, and Mössbauer spectroscopy in a previous publication. More importantly, the evolving material interface leading to green rust formation hase been first studied using in situ molecular imaging in this work. Specifically, the molecular structural change of the ionic liquid leading to green rust formation was characterized using in situ liquid using time-of-flight secondary ion mass spectrometry (ToF-SIMS) coupled with the System for Analysis at the Liquid Vacuum Interface (SALVI), a vacuum compatible microfluidic reactor. Dimers and ionic clusters have been identified in liquid ToF-SIMS spectra. We used spectral principal component analysis (PCA) to confirm that ion pairs including dimers and cluster ions differentiate from non-ionic liquids. Our results show that liquid ToF-SIMS can be a useful tool to study complex liquids at the molecular level providing insights into predicative synthesis of nanomaterials using environmentally friendly green solvents.