The impact of methanol mass transport on its conversion for the production of hydrogen and oxygenated reactive species in sono-irradiated aqueous solution.

This study aims principally to assess numerically the impact of methanol mass transport (i.e., evaporation/condensation across the acoustic bubble wall) on the thermodynamics and chemical effects (methanol conversion, hydrogen and oxygenated reactive species production) of acoustic cavitation in sono-irradiated aqueous solution. This effect was revealed at various ultrasound frequencies (from 213 to 1000 kHz) and acoustic intensities (1 and 2 W/cm2) over a range of methanol concentrations (from 0 to 100%, v/v). It was found that the impact of methanol concentration on the expansion and compression ratios, bubble temperature, CH3OH conversion and the molar productions inside the bubble is frequency dependent (either with or without consideration of methanol mass transport), where this effect is more pronounced when the ultrasound frequency is decreased. Alternatively, the decrease in acoustic intensity decreases clearly the effect of methanol mass transport on the bubble sono-activity. When methanol mass transfer is eliminated, the decrease of the bubble temperature, CH3OH conversion and the molar yield of the bubble with the rise of methanol concentration was found to be more amortized as the wave frequency is reduced from 1 MHz to 213 kHz, compared to the case when the mass transport of methanol is taken into account. Our findings indicate clearly the importance of incorporating the evaporation and condensation mechanisms of methanol throughout the numerical simulations of a single bubble dynamics and chemical activity.

Effect of isopropyl side chain branching and different anions on electronic structure, vibrational spectra, and hydrogen bonding of isopropyl-imidazolium-based ionic liquids: Experimental and theoretical investigations.

In the present work, four branched methylated, 1,2-dimethyl-3-isopropyl-imidazolium (i-[C3Dmim+]) and protonated,1-methyl-3-isopropyl-imidazolium (i-[C3mim+])-based ionic liquids (ILs) with varying anion (Br-, BF4-, PF6-, and NTf2-) were synthesized and investigated by NMR, infrared (IR) and Raman spectroscopy. Based on infrared and Raman spectroscopy, complete vibrational assignments have been performed. The IR and Raman analysis revealed that the vibrational spectra are virtually unaffected upon methylation, while significant frequency changes were observed by changing anion. Furthermore, to determine the electronic structure, energetic stability, and vibrational properties of these i-[C3Dmim]Y, i-[C3mim]Y (Y = Br, BF4, PF6, and NTf2) ion pairs, quantum chemical calculations including the dispersion correction method are performed both on single ions and on ionic couples. The calculated electron density was analyzed to expose non-covalent intra- and interionic interactions by the quantum theory of atoms in molecules (AIM) and interpreted in terms of both anion dependence and type of interaction. Computational results suggest that for all ionic couples the most energetically stable configuration is obtained with the anions located close to the C2 position of the imidazolium cation. However, in the case of i-[C3mim]NTf2 and i-[C3Dmim]BF4, similar energies were obtained in configurations 2 and 3 where the anion is located above the imidazolium ring. For i-[C3mim]Br a stronger hydrogen bond is predicted than for other studied ILs. Calculations indicate that a red shift of the CH stretching bands should occur due to hydrogen bonding; indeed, such displacement of bands is experimentally observed.

Thermal Decomposition, Low Temperature Phase Transitions and Vapor Pressure of Less Common Ionic Liquids Based on the Bis(trifuoromethanesulfonyl)imide Anion.

Four ionic liquids (ILs) based on the bis(trifluoromethanesulfonyl)imide (NTf2) anion were synthesized and characterized concerning their thermal stability, the occurrence of low temperature phase transitions and their volatility. All these physical quantities are highly important for possible applications. Both monocationic and dicationic ILs were considered. All ILs exhibit thermal stability exceeding 350 °C, an extremely high value, due to the presence of the NTf2 anion. Monocationic ILs can undergo crystallization, and they melt at 1 and 38 °C. On the contrary, dicationic ILs containing large positively charged ions display only a glass transition around -40 °C, without any crystallization or melting process; this fact is particularly important in view of the possibly low temperature applications of the dication ILs. The vapor pressure, pv, of the four ILs was measured by isothermal thermogravimetry in the temperature range between 250 and 325 °C; the lowest values of pv were obtained for the two dicationic liquids, suggesting that they are particularly well suited for high temperature applications. The vaporization enthalpy was calculated through the Clausius-Clapeyron equation and was found in the range between ~140 and ~180 kJ/mol depending on the specific IL.

Cluster Formation through Hydrogen Bond Bridges across Chloride Anions in a Hydroxyl-Functionalized Ionic Liquid.

Several recent studies of hydroxyl-functionalized ionic liquids (ILs) have shown that cation-cation interactions can be dominating these materials at the molecular level when the anion involved is weakly interacting. The hydrogen bonds between the like ions led to the formation of interesting chain-like, ring-like, or distinct dimeric (i. e. two ion pairs) supermolecular clusters. In the present work, vibrational spectroscopy (ATR-IR and Raman) and density functional theory (DFT) calculations of the hydroxyl-functionalized imidazolium ionic liquid C2 OHmimCl indicate that anion-cation hydrogen bonding interactions are dominating, leading to the formation of distinct dimeric ion pair clusters. In this arrangement, the Cl- anions function as a bridge between the cations by establishing bifurcated hydrogen bonds with the OH group of one cation and the C(2)-H of another cation. Cation-cation interactions, on the other hand, do not play a significant role in the observed clusters.

Clusters of the Ionic Liquid 1-Hydroxyethyl-3-methylimidazolium Picrate: From Theoretical Prediction in the Gas Phase to Experimental Evidence in the Solid State.

Interonic interactions determine the macroscopic properties of ionic liquids (ILs). Hence, unravelling the relationships between the microscopic and macroscopic scales is key for rational design. Combining density functional theory (DFT) calculations of isolated ion pairs and vibrational spectroscopy of the condensed phase (fluid or solid) has become a very common approach. In the present work, we make a step towards understanding how the physicochemical effects in small gas phase clusters of a hydroxyl functionalized imidazolium-picrate IL relate with the molecular structure and interactions of the corresponding solid material taking 1-hydroxyethyl-3-methylimidazolium picrate, C2 OHmimPic, as an example. In the isolated ion pair, strong alkyl-OH⋅⋅⋅Pic hydrogen bonding interactions are found rather than the commonly observed hydrogen bonding interactions at the slightly acidic C(2)-H site of the imidazolium ring. However, this part of the cation plays an important role when clusters of ion pairs in the gas phase and inside a crystal lattice are considered. For example, in the dimeric ion-pair cluster, one centre (O*) with two interaction sites (C(2)-H-O* and alkyl OH-Pic) is observed. This configuration is suggested by single crystal X-ray diffraction (XRD), vibrational spectroscopy, and the dispersion-corrected DFT calculations. Hence, the study provides evidence for the appearance of theoretical gas phase clusters in an actual solidified ionic liquid. This ion pair dimer formation may be a general behavior of hydroxyl functionalized imidazolium ILs, but further research is needed to draw a final conclusion. Moreover, the Raman spectra confirm the exclusive gauche conformation of the hyroxyl functionalized alkyl chain.

Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid.

In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf2]), and in water has been made for a wide range of cavitation parameters including frequency (140-1000kHz), acoustic intensity (0.5-1Wcm-2), liquid temperature (20-50°C) and external static pressure (0.7-1.5atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf2] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water.

DFT/TDDFT computational study of the structural, electronic and optical properties of rhodium (III) and iridium (III) complexes based on tris-picolinate bidentate ligands.

The electronic structures and spectroscopic properties of two complexes [M(pic)3] (M = Ir, Rh) containing picolinate as bidentate ligands have been calculated by means density functional theory (DFT) and time-dependent DFT/TD-DFT using three hybrid functionals B3LYP, PBE0 and mPW1PW91. The PBE0 and mPW1PW91 functionals, which have the same HF exchange fraction (25%), give similar results and do not differ drastically from B3LYP results. Calculated geometric parameters of the complexes are in good agreement with the available experimental data. The UV absorptions observed in acetonitrile were assigned on the basis of singlet state transitions. The most intense band observed in the UV-C region corresponds to ligand-to-ligand charge transfer states (LLCT) in both complexes. The theoretical spectrum of the rhodium complex is characterized by a large degree of mixing between metal-to-ligand-charge-transfer (MLCT), LLCT and metal centered (MC) states in the UV-A region. The presence of low-lying excited states with MC character affects the absorption spectrum under spin-orbit coupling (SOC) effects and play important roles in the photochemical properties. Graphical abstract Frontier molecular orbital diagram of mer-M(pic)3 (M=Ir, Rh).