8 Search Results

The addition of ionic liquids (ILs) to a mixture containing a molecular solvent and other ionic species can induce the heterogeneous redistribution of cations and anions at the gas–liquid interface. This nonuniform redistribution of cations and anions driven by the differences in the solvophilicity of ions can improve the thermophysical and interfacial properties of such mixtures, creating a local chemical environment that is conducive to some reactions. In this work, ILs are added to a mixture of potassium hydroxide (KOH) and ethylene glycol (EG), used as a reactive absorbent and electrolyte in the migration-assisted moisture-gradient (MAMG) process for CO₂ capture.more » Molecular dynamics (MD) simulations are employed to probe into the effects of complex ion–ion and ion–solvent interactions and to examine the chemical composition at the gas–liquid interface. A total of 12 systems are investigated using molecular simulations to identify trends in the performance of IL additives based on the choice of cation, anion, and IL concentration. The cation effects are studied using IL additives based on 1-ethyl-3-methylimidazolium ([EMIM]⁺) and 1-butyl-3-methylimidazolium ([BMIM]⁺), while the impact of anions is examined using additives based on dicyanamide [DCA]⁻, triflate [TfO]⁻, bistriflimide [NTf₂]⁻, and hexafluorophosphate [PF₆]⁻ anions, respectively. The influence of the IL concentration is also evaluated at molar concentrations between 1% and 4%. The simulation results indicate that the use of IL additives can affect the physical CO₂ solubility, surface tension, and the localization of CO₂ around the [OH]⁻ ions at the gas–liquid interface. It is also evident that the choice of cations, anions, and IL concentration determines the extent to which the IL additives impact the local physicochemical properties. Physical dissolution, diffusive transport, and interaction with [OH]⁻ are critical intermediate steps toward reactive CO₂ capture using a liquid absorbent. Hence, the improvement in one or more of these properties, aided by IL additives, is expected to improve the overall CO₂ capture performance. Experiments reaffirmed the impact of IL additives on CO₂ capture performance and the sensitivity to the choice of the cation, anion, and concentration of the IL additive.« less

An overview of neutron skin predictions obtained using an empirical nonlocal dispersive optical model (DOM) is presented. The DOM links both scattering and bound-state experimental data through a subtracted dispersion relation which allows for fully consistent, data-informed predictions for nuclei where such data exist. Large skins were predicted for both ⁴⁸Ca ( R$$^{48}_{skin}$$ = 0.25 ± 0.023 fm in 2017) and ²⁰⁸Pb (R$$^{208}_{skin}$$) = 0.25 ± 0.05 fm in 2020). Whereas the DOM prediction in ²⁰⁸Pb is within 1σ of the subsequent PREX-2 measurement, the DOM prediction in ⁴⁸Ca is over 2σ larger than the thin neutron skin resulting frommore » CREX. From the moment it was revealed, the thin skin in ⁴⁸Ca has puzzled the nuclear-physics community as no adequate theories simultaneously predict both a large skin in ²⁰⁸Pb and a small skin in ⁴⁸Ca. The DOM is unique in its ability to treat both structure and reaction data on the same footing, providing a unique perspective on this R_skin puzzle. It appears vital that more neutron data be measured in both the scattering and bound-state domain for ⁴⁸Ca to clarify the situation.« less

A brief account is given of highlights of our computational efforts – often in collaboration with experimental groups – to understand spectroscopic and chemical properties of ionic liquids (ILs). Molecular dynamics, including their inhomogeneous character, responsible for key spectral features observed in dielectric absorption, infra-red (IR) and fluorescence correlation spectroscopy (FCS) measurements are elucidated. Mechanisms of chemical processes involving imidazolium-based ILs are illustrated for CO₂ capture and related reactions, transesterification of cellulose, and Au nanocluster-catalyzed Suzuki cross-coupling reaction with attention paid to differing roles of IL ions. A comparison with experiments is also made.

Cyanobacteria are photoautotrophic prokaryotes that serve as key model organisms to study basic photosynthetic processes and are potential carbon-negative production chassis for commodity and high-value chemicals. The development of new synthetic biology tools and improvement of current ones is a requisite for furthering these organisms as models and production vehicles. CRISPR interference (CRISPRi) allows for targeted gene repression using a DNase-dead Cas nuclease (“dCas”). Here, we describe a titratable dCas12a (dCpf1) CRISPRi system and apply it to repress key photosynthetic processes in the fast-growing cyanobacterium Synechococcus sp. UTEX 2973 (S2973). The system relies on a lac repressor system that retainsmore » tight regulation in the absence of inducer (0–10% repression) while maintaining the capability for >90% repression of high-abundance gene targets. We determined that dCas12a is less toxic than dCas9. We tested the efficacy of the system toward eYFP and three native targets in S2973: the phycobilisome antenna, glycogen synthesis, and photosystem I (PSI), an essential part of the photosynthetic electron transport chain in oxygenic photoautotrophs. PSI was knocked down indirectly by repressing the protein factor BtpA involved in stabilizing core PSI proteins. We could reduce cellular PSI titer by 87% under photoautotrophic conditions, and we characterized these cells to gain insights into the response of the strain to the low PSI content. The ability to tightly regulate and time the (de)repression of essential genes in trans will allow for the study of photosynthetic processes that are not accessible using knockout mutants.« less

Here we extend the fully analytical, heuristic “Analytical Transport Network Model” for steady-state, diffusive flow in a 3-D network to account for surface reactions. In the limit of negligible reactions, the model reduces to the conserved flow solution. The extension does not increase the time required to run the model, which in Part 1 was shown to be 0.5–1.5 and 5–6 orders of magnitude faster than electrochemical fin (ECF) theory and finite element analysis (FEA) for conserved flow, respectively. The model is compared to reacting-flow ECF and FEA as well as to experiments and is demonstrated as a potentially usefulmore » heuristic for understanding the influence of morphology and topology on reactive-diffusive flow through a 3-D microstructural network.« less

Conventional solar cells absorb photons with energy above the bandgap of the active layer while sub-bandgap photons are unharvested. One way to overcome this loss is to capture the low energy light in the triplet state of a molecule capable of undergoing triplet–triplet annihilation (TTA), which pools the energy of two triplet states into one high energy singlet state that can then be utilized. This mechanism underlies the function of an organic intermediate band solar cell (IBSC). Here, we report a solid-state organic IBSC that shows enhanced photocurrent derived from TTA that converts sub-bandgap light into charge carriers. Femtosecond resolutionmore » transient absorption spectroscopy and delayed fluorescence spectroscopy provide evidence for the triplet sensitization and upconversion mechanisms, while external quantum efficiency measurements in the presence of a broadband background light demonstrate that sub-bandgap performance enhancements are achievable in this device. In conclusion, the solid-state architecture introduced in this work serves as an alternative to previously demonstrated solution-based IBSCs, and is a compelling model for future research efforts in this area.« less

van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p–n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS₂ (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. In this work, we study the kinetics of excited carriers in pentacene–MoS₂ p–n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS₂ excitons occurs by hole transfer to pentacene onmore » the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS₂ decay processes, the hole transfer yield from MoS₂ to pentacene is found to be ~50%, with the remaining holes undergoing trapping due to surface defects. In general, the ultrafast charge transfer and long-lived charge-separated state in pentacene–MoS₂ p–n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.« less