AVS 72 Session CA2-FrM: Chemical Analysis and Imaging at Interfaces Oral Session II

Water-lean solvents are a promising technology for capturing acid gases like carbon dioxide (CO₂).In situ liquid time-of-flight secondary ionization mass spectroscopy (ToF-SIMS) is used to study a representative solvent N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA) with different CO₂ loadings to reveal the complex solvent structure upon CO₂ capture.Characteristic peaks of 2-EEMPA, such as m/z^- 215 C₁₁H₂₃N₂O₂^- (deprotonated 2-EEMPA) and m/z⁺ 217 C₁₁H₂₅N₂O₂⁺ (protonated 2-EEMPA), are detected due to acid gas uptake.Also, solvent molecules and carboxylate ion pairs, such as m/z^- 259 C₁₂H₂₃N₂O₄^- [(deprotonated 2-EEMPA∙∙∙CO₂)] and m/z⁺ 261 C₁₂H₂₅N₂O₄⁺ (protonated 2-EEMPA∙∙∙CO₂), are observed.Interestingly, more than one CO₂ molecule can be captured per each solvent molecule as evidenced in SIMS mass spectra, for example, m/z^- 321 C₁₃H₂₅N₂O₇ [(deprotonated 2-EEMPA)∙∙∙2CO₂∙∙∙H₂O], m/z⁺ 305 C₁₃H₂₅N₂O₄⁺ [(protonated 2-EEMPA)∙∙∙2CO₂], m/z^- 389 C₁₇H₂₉N₂O₈ [(deprotonated 2-EEMPA)∙∙∙3CO₂∙∙∙3CH₂], and m/z⁺ 373 C₁₆H₂₅N₂O₈⁺ [(protonated 2-EEMPA)∙∙∙3CO₂∙∙∙2C].However, the monomer of 2-EEMPA and CO₂ seems to be most prevalent.Furthermore, solvent clusters are detected in loaded solvents, for instance m/z⁺ 433 C₂₂H₄₉N₄O₄⁺ [(2-EEMPA)₂∙∙∙H] and m/z⁺ 646 [(2-EEMPA)₃-2H], while capturing CO₂ at different amounts.Relative abundance of cluster ions provides a semi-qualitative venue to assess the free energies gas capture energetics, indicating the relative stability trend within the same solvent system, previously impossible.These observed ion clusters are verified with molecular modeling, where dimer, trimer, and cluster ions are validated for their presence either due to weak molecular interactions or hydrogen bonds.In situ molecular imaging of ionic liquids and molecular modeling reveals that the acid gas capture mechanism by ionic liquids includes both physical adsorption and chemical bonding with multiple reaction pathways, engaging cluster formation and alteration of solvent structures.

The nuclear waste stored at the US Department of Energy’s Hanford Site as an environmental remediation facility presents many major challenges. Mainly, the remediation of aluminum-containing tank waste generated from the separation of aluminum cladding of spent fuel rods requires processing and its complex dissolution chemistry is still not well understood. These wastes typically consist of three aluminum oxide/oxy-hydroxide species, namely gibbsite (γ-Al(OH)₃),^[1] boehmite (α-AlOOH),^[2] and bayerite (α-Al(OH)₃).^[3] Targeted remediation of these solids is complicated by their dissolution and stability in solution as well as a wide range of particle sizes. Physical property information on the tank waste is scarce due to computational simulation limits and the radioactivity of the waste preventing laboratory handling. Herein we report a versatile hydrothermal synthesis technique enabling tunable and scalable production of gibbsite, boehmite, and bayerite in submicrometer for use as simulant materials for in situ analysis and related experimental investigations. Synthesized samples were characterized ex situ using X-ray Diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and physisorption to verify structural and chemical properties. In situ particle analysis and imaging were subsequently investigated using the System for Analysis at the Liquid-Vacuum Interface (SALVI) microfluidic platform, which enabled probing of the vacuum-liquid interface with SEM and ToF-SIMS.^[4] The insights gained from this work are expected to inform the development of remediation approaches and formulate remediation methodologies that are safe for both site personnel and the environment.

References:

[1] Page, J.S., et al., Journal of Hazardous Materials, 384 (2020) 121318

[2] Peterson, R.A., et al., Separation Science and Technology, 42 (2007) 1719-1730

[3] Herting, D.L., et al., US DOE Office of Environmental Management, (2002), OSTI ID: 808264

[4] Yang, L., et al., Lab on a Chip, 11 (2011), 2481-2484

Scientific progress has repeatedly been driven by advances in experimental capability, with many of the most transformative discoveries in physics, chemistry, and materials science arising not solely from new theoretical understanding, but from the development of instrumentation capable of probing nature with greater sensitivity, spatial resolution, temporal resolution, and analytical precision. The ability to observe previously inaccessible phenomena frequently creates entirely new areas of research and enables scientists to ask questions that were once beyond experimental reach. In many cases, breakthroughs in instrumentation have reshaped our understanding of matter at fundamental length and energy scales while simultaneously enabling technological developments that extend far beyond the laboratory environment.

In this talk, we take a brief look at several major advancements in scientific instrumentation spanning the past several decades through the present day and examine how these developments have transformed modern surface science research. The progression of increasingly sophisticated measurement tools has enabled researchers to move from macroscopic characterization toward atomic-scale and electronic-scale investigations, allowing direct access to the structural, chemical, and electronic properties of materials and interfaces.

Particular focus will be placed on techniques that have had substantial impact across both fundamental research and industrial applications. Topics will include angle-resolved photoemission spectroscopy (ARPES), which has provided unprecedented insight into electronic band structures and many-body interactions; scanning probe microscopy (SPM), which has enabled real-space imaging and manipulation at near-atomic and atomic length scales; x-ray photoemission spectroscopy (XPS), which has become an essential tool for understanding surface chemistry and composition; and time-of-flight photoemission electron microscopy (ToF-PEEM), which combines spectroscopic and imaging capabilities to reveal spatially resolved electronic and chemical information.

Both academia and industry have benefited significantly from these developments, which have contributed to technologies that influence everyday life, including semiconductor devices, energy systems, catalysis, advanced materials, and nanotechnology. By examining the historical progression of these techniques and their broader impact, this talk aims to illustrate the central role that instrumentation innovation continues to play in enabling scientific discovery and driving future technological advancement.

Catalysts are central to the transition from fossil-based to renewable energy systems, with both thermal and electrocatalysis playing key roles in enabling carbon-neutral production of chemicals and fuels. However, their investigation presents significant technical challenges. This contribution discusses advanced sample environments for Dip+Pull methodologies and cell-based electrocatalytic systems.

In Dip+Pull catalysis, recent developments emphasize improved usability and experimental efficiency. Sample cell designs have evolved from in-line electrode configurations to on-axis arrangements, thereby reducing electrolyte transport distances. This approach has been successfully applied to a range of systems, including CO reduction catalysis and studies of battery materials and their degradation mechanisms.

The second part focuses on electrochemical cell geometries, particularly configurations in which the catalyst acts as a barrier between the liquid phase and the vacuum environment. Such setups enable the investigation of membrane transport properties and the operando surface states of platinum catalysts and their intermediates under oxygen reduction reaction conditions.

A unifying aspect of both approaches is the investigation of the electrochemical double layer, which plays a critical role in governing catalytic activity and interfacial processes. Its characterization under these experimental conditions is discussed in detail.