Revealing the Structural Evolution of Green Rust Synthesized in Ionic Liquids by In Situ Molecular Imaging

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 (CO 2 ) as the trigger gas was chosen to synthesize nanocrystalline green rust. Under anoxic conditions, by adding iron (II) acetate (Fe(C 2 H 3 O 2 ) 2 ) and methanol to the degassed SWIL, a nanoparticulate green rust with carbonate (nano GR) was synthesized. More importantly, the molecular structural change of the ionic liquid resulting in green rust crystallines has been first 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 in this work. Dimers and ionic clusters consisting ferric and ferrous ions have been identified in liquid ToF-SIMS spectra. We used spectral principal component analysis to confirm that these ion pairs including dimers and cluster ions are different 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 and giving unique visualization of the evolving material interface due to nucleation.

ToF-SIMS evaluation of PEG-related mass peaks and applications in PEG detection in cosmetic products

“…PCA, a widely used multivariate analysis technique, was employed to discern differences among the samples in ToF-SIMS analysis 24 , 27 , 28 , 33 . The scores plots and loadings plots are typically presented together to analyze the variances within the samples.…”

Secondary Ion Mass Spectral Imaging of Metals and Alloys

“…The ability to perform SIMS under these controlled conditions is crucial for understanding how surface composition evolves during different processes. Microfluidic liquid cells, such as vacuum-compatible microfluidic reactor systems for analysis at the liquid vacuum interface (SALVI), were developed to be applied in in situ, in vivo, and in operando imaging of liquid surface as well as the air-liquid, liquid-liquid, and solid-liquid interfaces in the past decade [53][54][55]. SALVI is one of the first microfluidics-based reactors that enabled direct analysis of real-time changes in the material's surface by combining ToF-SIMS [56].…”

“…Typically, when conducting PCA, the analyzed dataset is pre-segmented into several a priori-defined subgroups, often stemming from the experimental study design, such as control groups and treatment-specific sample groups. The data are usually subjected to normalization based on the total ion intensities of selected peaks, square-root transformation, and mean centering before PCA is executed [6,53,[177][178][179][180][181]. When evaluating the PCA results, scores plots and loadings plots are commonly presented together.…”

“…Score plots illustrate the similarity and dissimilarity among samples while loading plots reveal the contributions of components corresponding to scores in the principal component (PC). Peaks with high loadings contribute more significantly to the observed clustering of peaks in the scores plot [53,180]. The first principal component (PC1) represents the maximum possible variation in the dataset, with the second principal component (PC2) accounting for the maximum variation in uncorrelated data with PC1.…”

Detecting PEGs in real-world cosmetic products using ToF-SIMS

“…Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool in applied surface analysis. It provides detailed elemental, molecular, and isotopic mass spectra, and two-dimensional/three dimensional (2D/3D) mapping of solid surfaces, thin films, or gas-solid interfaces [24][25][26][27][28][29][30][31][32][33][34] . Although ToF-SIMS has been used more often in biological applications and the semiconductor industry in past decades, its applications are not limited to these well-known fields.…”