Scott K. Shaw

This study reports the physical and chemical features of passively collected environmental films collected near two roadways during the winter season.

This review provides a comprehensive summary overview of cellulose production and utility, ranging from selection considerations for the biological source of the cellulose, to modern applications and advances in cellulose-based products.

Dinuclear Mn and Co complexes with triaryl ligands derived from o -phenylenediamide are described. The Mn complexes possess similar structures and properties whereas the Co complexes exhibit marked differences depending on the flanking donor group.

Ionic liquids behave differently than 'normal' solvents in both the bulk and interfacial domains. Their intermolecular interactions drive intriguing phase behaviours and unexpected molecular architectures. This presentation shares experimental data that examines capacitive responses of several ionic liquids near solid electrode surfaces. We measure these responses with an array of methods including single frequency AC voltammetry to Fourier-transformed large amplitude alternating current voltammetry. We show examples of significant and reproducible capacitive hysteresis, and suggest possible explanations based on the unique behaviors of ionic liquids reported previously. Specifically, EMIM TFO on a polycrystalline gold electrode shows hysteresis of a camel-shaped feature, supposedly near the point of zero charge, of approximately two volts depending on the applied potential scan direction (cathodic vs. anodic). Significant deviations with respect to scan direction persist even when the IL is diluted to >50% in MeCN, suggesting electrode-surface segregation of IL ions. Ultimately, this series of experiments shows the need for considering additional experimental parameter spaces when making measurements in, or with, ionic liquid electrolytes. Image caption: capacitance curves for BMIM BF4 on Au at 9.02 Hz with Δ E amp = 80 mV. Anodic (black line) and cathodic (red line) scan directions. Figure 1

This work investigates the role of ionic liquid (IL) ion (a)symmetry in promoting ordered structures within liquid films by studying a series of six alkylimidazolium cation isomers of varying symmetry paired with a bis(trifluoromethylsulfonyl)imide anion. The cation symmetry is varied by systematic variations in the alkyl tail lengths on either side of the imidazolium ring. IL films are extruded on a silver substrate using an in situ dynamic wetting apparatus and allowed to thin under shearing force due to gravity. Film thicknesses are monitored via spectroscopic ellipsometry. Infrared reflection absorption spectroscopy (IRRAS) with p-polarized light is used to analyze changes in dipole moments with vector components perpendicular to the substrate and thus report changes to molecular orientations and local chemical environments. Multiple vibrational modes are monitored at varying film thicknesses to deliver chemical insight into the evolving net molecular orientation within the IL films. Specifically, average molecular orientations are tracked by monitoring intensity and energy shifts of vibrational modes, including the S-N-S ν_as (∼1054 cm^-1), SO₂ ν_ss (∼1137 cm^-1), and SO₂ ν_as (∼1330 cm^-1) stretches. This provides a unique ability to determine the extent of ordering in the film. As IRRAS probes the entire film, when changes to the spectral profile cease and only a uniform decrease in absorbance is observed, only the ordered domains of the film remain on the substrate; thus, the film's thickness is equal to the extent of ordering in the film. Ultimately, for the six alkylimidazolium IL isomers examined here, the extent of molecular ordering in the films increases with increasing asymmetry of the cation. IL ordered domains extend to 0.4 ± 0.2 μm for the most symmetric systems and to 0.7 ± 0.2 μm for the most asymmetric systems.

Herein we report an electronic structure investigation of neutral and oxidized Ru complexes containing a redox noninnocent N₂S₂ ligand derived from o-phenylenediamide (L1). UV-vis spectroelectrochemistry (SEC) studies were conducted on the square pyramidal complex [Ru^II(L1)(PPh₃)] (1) and the six-coordinate complexes [Ru^II(μ-BH₃)(L1)(PPh₃)] (2) - which has BH₃ bound in a metal-ligand cooperative (MLC) fashion across Ru and L1 - and [Ru^II(L1)(PPh₃)(MeCN)] (3). The SEC results yielded spectra assigned to singly and doubly oxidized 1 and 3, revealing electronic structure changes as a function of oxidation state and in response to the presence and absence of bound MeCN. By contrast, the SEC results of 2 showed that it rapidly loses MLC-bound BH₃ upon oxidation. The SEC results for 1 and 3 were compared to single-crystal XRD data and UV-vis, EPR, and P K-edge, S K-edge, and Ru L₃-edge X-ray absorption spectroscopy (XAS) data collected on isolated samples of chemically oxidized 3. The data revealed that the first two oxidations are primarily localized on the ligand, which was supported by DFT and TDDFT calculations. DFT calculations for the doubly oxidized species revealed a singlet ground state with a singlet-triplet gap of 8.9 kcal/mol. CASPT2 calculations corroborated the DFT calculations and further revealed that the singlet ground state is multiconfigurational with 21% radical character. Collectively, the results establish redox formalisms and the underlying electronic structure of Ru complexes containing a noninnocent tetradentate ligand in different oxidation states.

Course-based undergraduate research experiences (CUREs) allow all students to engage in undergraduate research experiences and gain important skills such as problem solving and critical thinking. The goal of this work was to design a CURE-inspired project for an upper-level analytical chemistry laboratory course that engaged students in novel research to detect and quantify the amount of nitrate and nitrite in indoor surface films. The students searched for and read literature on indoor surface films, collected samples from a location of their choosing, quantitatively analyzed the samples with HPLC, and created a customer report to describe their findings. Two semesters of implementation revealed that the project successfully engaged students in elements of the research process and met many of the learning goals. Student focus group interviews revealed that students were personally invested in the research process because they were investigating indoor spaces where they spend a lot of time and that they perceived this laboratory experience to resemble that of authentic research.

Nonaqueous redox flow batteries (NARFB) present a viable solution for grid-scale energy storage due to their decoupled power and energy densities, long–duration storage, durability, temperature tolerance, low-cost production and use, and limited environmental impact. Nevertheless, implementing NARFB as a major grid-scale energy storage solution requires further property optimization, which necessitates a molecular-level understanding of the fundamental chemical phenomena that take place during battery (dis)charge. Here we focus on the dynamics and interactions of extremely large redox-active species and electrolyte concentrations through molecular dynamics (MD) simulations. We investigated a series of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and TBAPF₆ (tetra-n-butylammonium hexafluorophosphate) concentrations in acetonitrile to determine molecular-scale physicochemical characteristics for comparison to electrochemical experiments. The investigation reveals the importance of solvation and ion-pairing effects of the TBAPF₆ salt. This study provides theoretical insights into designing NARFB solutions with optimal concentrations.

Environmental films form when airborne particles and molecular species adsorb on solid surfaces. Recent studies have characterized these films but overlook how collection methods and host-surface character (orientation, chemical functionality, or height) change the deposition process. In this work, environmental films are collected at a rural location on gold and silicon surfaces (water contact angles of ca. 57° and 5 μm) particles have similar elemental compositions. Minor variations are observed at smaller particle sizes (∼5 μm), which include carbon-rich particles primarily attributed to pollen or biotic activity. Chemical analysis shows the presence of nitrate and sulfate, as well as heterogeneous cation pools on the surfaces.

Ionic liquids have been shown to form extended ordered structures near surfaces and in bulk. Identifying fundamental driving force(s) for this organization has been elusive. In this paper, we test a hypothesis that the ionic liquid asymmetry, inherent in many of the IL formulations to frustrate crystallization, is a significant contributor to the observed ordering. We have carried out measurements to track the ordering of ionic liquids composed of "spherical" cations, namely, tetraoctylphosphonium ([P8888]) and tetra(propoxymethyl)phosphonium [P(3O1)4] paired with tetracyanoborate anion [B(CN)4]. Analysis of the infrared signatures for films of these ionic liquids shows very little evidence of ordered structures. These liquids instead remain in a more isotropic environment even when confined to volumes of few micrometer dimensions.