Determination of the lowest energy structure of Ag8_8 from first-principles calculations

The ground-state electronic and structural properties, and the electronic excitations of the lowest energy isomers of the Ag$_8$ cluster are calculated using density functional theory (DFT) and time-dependent DFT (TDDFT) in real time and real space scheme, respectively. The optical spectra provided by TDDFT predict that the D$_{2d}$ dodecahedron isomer is the structural minimum of Ag$_8$ cluster. Indeed, it is borne out by the experimental findings.Comment: 4 pages, 2 figures. Accepted in Physical Review A as a brief repor

Nonmonotonic Evolution of the Blocking Temperature in Dispersions of Superparamagnetic Nanoparticles

We use a Monte Carlo approach to simulate the influence of the dipolar interaction on assemblies of monodisperse superparamagnetic ${\gamma}-Fe_{2}O_{3}$ nanoparticles. We have identified a critical concentration c*, that marks the transition between two different regimes in the evolution of the blocking temperature ($T_{B}$) with interparticle interactions. At low concentrations (c < c*) magnetic particles behave as an ideal non-interacting system with a constant $T_{B}$. At concentrations c > c* the dipolar energy enhances the anisotropic energy barrier and $T_{B}$ increases with increasing c, so that a larger temperature is required to reach the superparamagnetic state. The fitting of our results with classical particle models and experiments supports the existence of two differentiated regimes. Our data could help to understand apparently contradictory results from the literature.Comment: 13 pages, 7 figure

Waste management strategies to mitigate the effects of fluorinated greenhouse gases on climate change

Funding Information: Funding: This work was funded by FCT/MCTES (Portugal), project PTDC/EQU-EQU/29737/2017, and was supported by the Associate Laboratory for Green Chemistry—LAQV, which is financed by national funds from FCT/MCTES (UIDB/50006/2020) and by Marine and Environmental Sciences Centre—MARE, which is financed by national funds from FCT/MCTES (UIDB/04292/2020). Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.Fluorinated greenhouse gases (F-gases) are used for various applications, such as in refrigeration and air conditioning, as substitutes of the ozone-depleting substances. Their utilization has increased drastically over the last few decades, with serious consequences for global warming. The Kigali Amendment to the Montreal Protocol and several national and international legislations, such as the 2014 EU F-gas Regulation, aim to control the utilization and emissions of these gases. In the EU, the phase-down of hydrofluorocarbons (HFCs) is underway, with successive reductions in quotas up to 2050. Under this scenario, efficient strategies for managing the produced and already existing F-gases are of vital importance to guarantee that their effect on the environment is mitigated. Up to now, most of the F-gases recovered from end-of-life equipment or when retrofitting systems are either released into the atmosphere or destroyed. However, in order to put forward a cost-efficient adaptation to the F-gas phase-down, increasing separation and recycling efforts must be made. This critical review aims at providing a revision of the current F-gas management problems and strategies and providing an overview on the innovative strategies that can be applied to contribute to build a sustainable market under circular economy principles.publishersversionpublishe

Understanding the Absorption of Fluorinated Gases in Fluorinated Ionic Liquids for Recovering Purposes Using Soft-SAFT

2020.00835.CEEIND 2021.01432.CEECIND RC2-2019-007It is proven that fluorinated gases (F-gases) have a vast impact on climate change due to their high global warming potential. Hence, it is imperative to search for new molecules to replace them in current applications, as well as technologies to capture, recover, and recycle F-gases to avoid their emissions to the atmosphere. One of the attractive technologies for this purpose is to absorb them in fluorinated ionic liquids (FILs), given their solubilization power. However, the complexity of FILs and the time-consuming experimental methodologies to fully characterize them hinder their prompt usage in this urgent field. In this work, the soft-Statistical Associating Fluid Theory (soft-SAFT) Equation of State is used as a tool to investigate the solubility of six different F-gases (R-32, R-125, R-134a, R-14, R-116, R-218) in five FILs ([C2C1Im][C4F9SO3], [C2C1Im][C4F9CO2], [C2C1py][C4F9SO3], [C2(C6F13)C1Im][N(CF3SO2)2], and [C2(C6F13)C1Im][N(C2F5SO2)2]). The robustness of the soft-SAFT approach allowed the establishment of new FIL models in a simple and fast way, and the calculation of F-gases solubility in them, in excellent agreement with existing experimental data. Once the models were assessed, a systematic study was performed regarding the structural features of FILs favoring their performance to absorb F-gases by using the soft-SAFT approach as a screening tool. It has been obtained that the solubility is favored by the presence of a perfluoroalkyl chain in the imidazolium cation, together with a bulkier anion. In all cases, [C2(C6F13)C1Im][N(C2F5SO2)2] shows a superior solubility of F-gases than the [C2(C6F13)C1Im][N(CF3SO2)2], also indicating that the addition of one carbon to the two anionic symmetric fluorinated chains contributes to the gas-philicity of the FILs. This work proves the relevance of using the soft-SAFT framework to obtain insights into the behavior of such complex systems and key trends, even when experimental data are scarce, as a step forward in assessing systems for separating and recovering F-gases.publishersversioninpres

Unveiling the Influence of Non-Toxic Fluorinated Ionic Liquids Aqueous Solutions in the Encapsulation and Stability of Lysozyme

Proteins are bioactive compounds with high potential to be applied in the biopharmaceutical industry, food science and as biocatalysts. However, protein stability is very difficult to maintain outside of the native environment, which hinders their applications. Fluorinated ionic liquids (FILs) are a promising family of surface-active ionic liquids (SAILs) that have an amphiphilic behavior and the ability to self-aggregate in aqueous solutions by the formation of colloidal systems. In this work, the protein lysozyme was selected to infer on the influence of FILs in its stability and activity. Then, the cytotoxicity of FILs was determined to evaluate their biocompatibility, concluding that the selected compounds have neglected cytotoxicity. Therefore, UV–visible spectroscopy was used to infer the FIL-lysozyme interactions, concluding that the predominant interaction is the encapsulation of the lysozyme by FILs. The encapsulation efficiency was also tested, which highly depends on the concentration and anion of FIL. Finally, the bioactivity and thermal stability of lysozyme were evaluated, and the encapsulated lysozyme keeps its activity and thermal stability, concluding that FILs can be a potential stabilizer to be used in protein-based delivery systems.publishersversionpublishe