| 1. |
- Yaghini, Negin, 1976, et al.
(författare)
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Effect of Water on the Local Structure and Phase Behavior of Imidazolium-Based Protic Ionic Liquids
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 119:4, s. 1611-1622
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Tidskriftsartikel (refereegranskat)abstract
- We report on the effect of water on local structure and phase behavior of two protic ionic liquids, C(2)HImTFSI and C(2)HImTfO. Raman and infrared spectroscopy are employed to investigate the local coordination state. We find that water interacts weakly with TFSI- while more specifically with TfO- through the - SO3 group. Additionally, we observe that upon addition of water the - NH stretching frequency does not change in C(2)HImTFSI, while it red-shifts in C(2)HImTfO, indicative of different hydrogen bonding configurations. Supported by the appearance of some additional features in the 800-1000 cm(-1) frequency range where ring out-of-plane bending (?) modes are found, we hypothesize that in C(2)HImTFSI water interacts only with the cation coordinating to the ring C2H and the N3H sites, while it interacts with both cation and anion in C(2)HImTfO forming hydrogen bonds that involve the cationic N-H site as well as the anionic - SO3 group. These different local structures also reflect in the phase behavior investigated by DSC, which reveals a more homogeneous solution when water is added to C(2)HImTfO, as compared to H2O/C(2)HImTFSI mixtures. Finally we report that the addition of water also significantly affects both T-m and T-g.
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| 2. |
- Yaghini, Negin, 1976, et al.
(författare)
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Effect of water on the transport properties of protic and aprotic imidazolium ionic liquids - an analysis of self-diffusivity, conductivity, and proton exchange mechanism
- 2014
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:20, s. 9266-9275
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report on the transport properties of protic and aprotic ionic liquids of the imidazolium cation (C(2)C(1)Im(+) or C(2)HIm(+)) and the TFSI- or TfO- anion as a function of added water. We observe that the self-diffusion coefficient of the ionic species increases upon addition of water, and that the cation diffuses faster than the anion in the entire water concentration range investigated. We also observe that the overall increase of anionic and cationic diffusion coefficients is significant for C(2)HImTfO while it is rather weak for C(2)C(1)ImTFSI, the former being more hydrophilic. Moreover, the difference between cationic and anionic self-diffusivity specifically depends on the structure of the ionic liquid's ions. The degree of ion-ion association has been investigated by comparing the molar conductivity obtained by impedance measurements with the molar conductivity calculated from NMR data using the Nernst-Einstein equation. Our data indicate that the ions are partly dissociated (A(imp)/A(NMR) in the range 0.45-0.75) but also that the degree of association decreases in the order C(2)HImTfO > C(2)HImTFSI approximate to C(2)C(1)ImTfO > C(2)C(1)ImTFSI. From these results, it seems that water finds different sites of interaction in the protic and aprotic ionic liquids, with a strong preference for hydrogen bonding to the -NH group (when available) and a stronger affinity to the TfO anion as compared to the TFSI. For the protic ionic liquids, the analysis of H-1 NMR chemical shifts (upon addition of H2O and D2O, respectively) indicates a water-cation interaction of hydrogen bonding nature. In addition, we could probe proton exchange between the -NH group and deuterated water for the protic cation, which occurs at a significantly faster rate if associated with the TfO anion as compared to the TFSI.
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| 3. |
- Cabeza, O., et al.
(författare)
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Mesostructure and physical properties of aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl sulfate doped with divalent sulfate salts in the liquid and the mesomorphic states
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 20:13, s. 8724-8736
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Tidskriftsartikel (refereegranskat)abstract
- This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO 4 ]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm] [OSO 4 ] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm] [OSO 4 ] + H 2 O + MgSO 4 . Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.
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| 4. |
- Garaga Nagendrachar, Mounesha, 1985, et al.
(författare)
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Local coordination and dynamics of a protic ammonium based ionic liquid immobilized in nano-porous silica micro-particles probed by Raman and NMR spectroscopy
- 2016
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 12:9, s. 2583-2592
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ionic liquids confined in a solid material, for example, nano-porous silica, are particularly propitious for energy related applications. The aim of this study is to probe the molecular interactions established between the protic ionic liquid diethylmethylammonium methanesulfonate (DEMA-OMs) and silica, where the latter consists of nano-porous micro-particles with pores in the size range of 10 nm. The changes in the local coordination and transport properties induced by the nano-confinement of the ionic liquid are investigated by a combination of Raman and solid-state NMR spectroscopy. In particular, one-dimensional (1D) H-1 and Si-29 and two-dimensional (2D) Si-29{H-1} HETOCR solid-state NMR are combined to identify the sites of interaction at the silica-ionic liquid interface. Pulsed field gradient (PFG) NMR experiments are performed to estimate the self-diffusion of both bulk and nano-confined DEMA-OMs. Complementary information on the overall coordination and interaction scheme is achieved by Raman spectroscopy. All these advanced experimental techniques are revealed to be crucial to differentiate between ionic liquid molecules residing in the inter-or intra-particle domains.
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| 5. |
- Gomes, Adriano, et al.
(författare)
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A micro-Raman spectroscopic study of Cr(OH)3 and Cr2O3 nanoparticles obtained by the hydrothermal method
- 2017
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 48:10, s. 1256-1263
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 John Wiley & Sons, Ltd. Cr 2 O 3 nanoparticles, widely used in the industry, can be obtained by calcination of the nanoparticles synthesized via the hydrothermal method. The chemical nature and the morphology of as-prepared and calcined nanoparticles are investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Our results indicate that the as-prepared nanoparticles mainly consist of amorphous and hydrated Cr(OH) 3 , with only minor amounts of Cr 2 O 3 . By contrast, and as already known before, calcined nanoparticles consist of Cr 2 O 3 . We also demonstrate the effect of inappropriately chosen experimental conditions, because the use of laser intensities above 0.7 mW during the Raman experiments causes a local heating and thus induces the transformation of Cr(OH) 3 into Cr 2 O 3 . The correlation between the laser power and a local heating is further corroborated by thermogravimetric analyses, which show that upon increased temperature, Cr(OH) 3 first dehydrates and then partially condensates to the intermediate CrO(OH) form, to finally attain the crystalline form of Cr 2 O 3 at about 409°C.
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| 6. |
- Yaghini, Negin, 1976, et al.
(författare)
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Achieving enhanced ionic mobility in nanoporous silica by controlled surface interactions
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 19:8, s. 5727-5736
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Tidskriftsartikel (refereegranskat)abstract
- We report a strategy to enhance the ionic mobility in an emerging class of gels, based on robust nanoporous silica micro-particles, by chemical functionalization of the silica surface. Two very different ionic liquids are used to fill the nano-pores of silica at varying pore filling factors, namely one aprotic imidazolium based (1-methyl-3-hexylimidazolium bis(trifluoromethanesulfonyl)imide, C6C1ImTFSI), and one protic ammonium based (diethylmethylammonium methanesulfonate, DEMAOMs) ionic liquid. Both these ionic liquids display higher ionic mobility when confined in functionalized silica as compared to untreated silica nano-pores, an improvement that is more pronounced at low pore filling factors (i.e. in the nano-sized pore domains) and observed in the whole temperature window investigated (i.e. from −10 to 140 °C). Solid-state NMR, diffusion NMR and dielectric spectroscopy concomitantly demonstrate this effect. The origin of this enhancement is explained in terms of weaker intermolecular interactions and a consequent flipped-ion effect at the silica interface strongly supported by 2D solid-state NMR experiments. The possibility to significantly enhance the ionic mobility by controlling the nature of surface interactions is extremely important in the field of materials science and highlights these structurally tunable gels as promising solid-like electrolytes for use in energy relevant devices. These include, but are not limited to, Li-ion batteries and proton exchange membrane (PEM) fuel cells.
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| 7. |
- Yaghini, Negin, 1976
(författare)
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Exploring binary mixtures of protic ionic liquids– Interactions, dynamics, and non-ideal behavior
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ionic liquids are organic salts that melt at low temperatures and provide a set of properties beneficial for diverse applications. These properties include good thermal stability, high ionic conductivity, low volatility and non-flammability. In this thesis protic ionic liquids have been at focus, which are of interest for use as electrolytes in next-generation proton exchange membrane fuel cells. The impact of the molecular structure of the ions as well as of the addition of a second compound on selected physicochemical properties has been investigated.Imidazolium and ammonium based protic ionic liquids have been considered as possible proton conducting materials, whereas water, imidazole and ethylene glycol were chosen as neutral additives, all being a priori capable of forming hydrogen bonds. Transport properties like self-diffusion, ionic conductivity and viscosity have been thoroughly investigated, and the observed behavior explained in terms of established intermolecular interactions. These have been probed by 1H NMR and vibrational (Raman and infrared) spectroscopy, used as powerful and complementary experimental tools.Overall both self-diffusion and ionic conductivity increase upon addition of a second compound, but the extent of this increase very much depends on the molecular structure of the cation-anion pair in the ionic liquid, and the ability of the ions to establish hydrogen bonds. For example, in the case of the protic ionic liquid ethylimidazolium bis(trifluoromethanesulfonyl)imide (C2HImTFSI) added water preferably interacts with the cation, while both cations and anions interact with added imidazole. These coordinations also results in very different phase changes and different mechanism of charge transport, with added imidazole promotingthe Grotthuss mechanism of proton transfer as opposed to the case of added water. In a more hydrophilic protic ionic liquid like ethylimidazolium triflate (C2HImTfO), however, water forms bonds with both cations and anions, and a local and fast proton exchange has been probed. Nevertheless, the choice of the added compound is not straightforward since not all required properties may be enhanced at once. For instance, while ethylene glycol affects ionic conductivity by a lesser extent it can provide a wider window of thermal stability.The effect of confining an ionic liquid into nano-porous silica micro-particles has also been studied. The so called silica supported ionogels that we have considered can retain large volume fractions of the liquid and thus serve as support materials for electrolytes for use in fuel cell applications. Our results show that a strong interaction between the ammonium based protic ionic liquid (DEMA-OMs) and the pore walls of the silica nano-particles restricts the ionic mobility. As a solution to this effect the silica pore walls were functionalized with hydrophobic alkyl groups whereby a significant enhancement of the ionic conductivity was observed for the ionic liquid in the nano-sized pore domains. Our findings provide new useful insights for designing new electrolyte materials, the functionality of which willcrucially depend on a careful selection of the ionic liquid, the added second compound and the surface chemistry of the support material. An optimal combination should be able to provide a fast and selective proton motion as required for use in fuel cells.
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| 8. |
- Yaghini, Negin, 1976, et al.
(författare)
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Structural origin of proton mobility in a protic ionic liquid/imidazole mixture: insights from computational and experimental results
- 2016
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 18:33, s. 23195-23206
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Tidskriftsartikel (refereegranskat)abstract
- The structure, dynamics, and phase behavior of a binary mixture based on the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl) imide (C(2)HImTFSI) and imidazole are investigated by H-1 NMR spectroscopy, vibrational spectroscopy, diffusion NMR, calorimetric measurements, and molecular dynamics simulations. Particular attention is given to the nature of the H-bonds established and the consequent occurrence of the Grotthuss mechanism of proton transfer. We find that due to their structural similarity, the imidazolium cation and the imidazole molecule behave as interchangeable and competing sites of interaction for the TFSI anion. All investigated properties, that is the phase behavior, strength of ion-ion and ion-imidazole interactions, number of specific H-bonds, density, and self-diffusivity, are composition dependent and show trend changes at mole fractions of imidazole (w) approximately equal to 0.2 and 0.5. Beyond chi = 0.8 imidazole is not miscible in C2HImTFSI at room temperature. We find that at the equimolar composition (chi approximate to 0.5) a structural transition occurs from an ionic network mainly stabilized by coulombic forces to a mixed phase held together by site specific H-bonds. The same composition also marks a steeper decrease in density and increase in diffusivity, resulting from the preference of imidazole molecules to H-bond to each other in a chain-like manner. As a result of these structural features the Grotthuss mechanism of proton transfer is less favored at the equimolar composition where H-bonds are too stable. By contrast, the Grotthuss mechanism is more pronounced in the low concentration range where imidazole acts as a base pulling the proton of the imidazolium cation. At high imidazole concentrations the contribution from the vehicular mechanism dominates.
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| 9. |
- Yaghini, Negin, 1976, et al.
(författare)
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Transport properties and intermolecular interactions in binary mixtures based on the protic ionic liquid ethylimidazolium triflate and ethylene glycol
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 20:35, s. 22980-22986
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Tidskriftsartikel (refereegranskat)abstract
- The binary mixture based on the protic ionic liquid (PIL) ethylimidazolium triflate (C2HImTfO) and the diol compound ethylene glycol (EG) has been investigated in the whole composition range from pure PIL to pure EG. At 30 °C the addition of EG increases both the ionic conductivity and the self-diffusivity of the ions. These quantities, however, change at different rates suggesting that the ionicity of the system is composition dependent. This behaviour is explained by means of new intermolecular forces established when a second compound like EG is introduced into the ionic network. More specifically, a complex H-bonded network is formed that involves the -NH group of the cation, the -OH group of EG and the -SO3group of the anion. This configuration may increase the fluidity of the mixture but not necessarily the ionic dissociation. Moreover, diffusion NMR results indicate the occurrence of local proton dynamics, which arise from a proton exchange between the -NH of the cation and the -OH of EG, providing the requisite for a long-range Grotthuss mechanism of proton transport.
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| 10. |
- Yaghini, Negin, 1976, et al.
(författare)
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Transport Properties, Local Coordination, and Thermal Stability of the Water/Diethylmethylammonium Methanesulfonate Binary System
- 2016
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Ingår i: Fuel Cells. - : Wiley. - 1615-6846 .- 1615-6854. ; 16:1, s. 46-54
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Tidskriftsartikel (refereegranskat)abstract
- Ammonium based protic ionic liquids are highlighted for their great potential to sustain proton transport in proton exchange membrane (PEM) fuel cells. Yet, there remain questions concerning the effect of water produced by the fuel cell at the cathode side on the performance of the ionic liquid. In this contribution we report the effect of water on the transport properties and the local coordination in the binary system of the protic ionic liquid diethylmethylammonium methanesulfonate ([DEMA][OMs]) and water, employing 1H NMR, Raman, and infrared spectroscopy. We observe that the self-diffusion of cations and anions increases with the water content and that cations and anions diffuse at the same rate at all concentrations investigated. 1H NMR and vibrational spectroscopy, on the other hand, indicate that added water interacts primarily with the anion and slightly affects the ionicity of the ionic liquid. In addition, by investigating the thermal stability of the binary system we find that although [DEMA][OMs] displays a continuous loss of water upon increasing temperature a fraction of water molecules can be retained even above 120 °C, and that the complete loss of water is immediately followed by decomposition, which is observed to occur at about 185 °C.
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