Interactions of CO2 with the homologous series of СnMIMBF4 ionic liquids studied in situ ATR-FTIR spectroscopy: spectral characteristics, thermodynamic parameters and their correlation

ATR-FTIR spectroscopic imaging with variable angles of incidence of crude oil deposits formed by flocculant flow

Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopic imaging is a method for spatially resolved analysis of materials that combines the capabilities of ATR-FTIR spectroscopy with the use of a focal plane array detector. This paper presents the methodological aspects of adapting the ATR accessory with variable single reflection angle to the FTIR spectroscopic imaging method. The use of a variable reflection angle allows the image to be studied at different sample depths. Using examples of BMIMPF6 ionic liquid and crude oil droplets placed on the working surface of an internal reflection element, the characteristics of image acquisition as the angle of reflection is varied are discussed. The possibility of obtaining crude oil deposits directly on the working surface of the internal reflection element under the influence of a flocculant flow (n-heptane, acetone) and their study by ATR-FTIR spectroscopic image was demonstrated. Crude oil deposits were obtained under different formation conditions (flow rates of flocculant) and their spectroscopic images were also obtained at different single reflection angles. This information gives an indication of the composition of the deposit's functional groups not only at spatial resolution but also at depth.

N-octylpyridine hydrogen sulphate ionic liquid for multifunctional fluorescent response in different solvents

Ionic liquids (ILs) have attracted considerable interest in the last two decades owing to their unique fluorescent properties. Herein, N-octylpyridine hydrogen sulphate ([OP]HSO4) was synthesised and characterised using 1H NMR and infrared spectroscopies. In addition, the fluorescence spectra of [OP]HSO4 in water, methanol, ethanol and acetonitrile were studied. In a single solvent, as the concentration of the solvent (methanol, ethanol or acetonitrile) increases, the fluorescence intensity of the IL first increases and then decreases. A similar trend was observed in their mixed solvents with water. Moreover, the fluorescence intensity of [OP]HSO4 decreases with increasing temperature. A fluorescence intensity reduction of only 4.46% for [OP]HSO4 after continuous scanning for 40 cycles under the maximum excitation state was analysed. The lack of photobleaching observed in [OP]HSO4 indicates its good photobleaching resistance.

What quantum chemical simulations tell us about the infrared spectra, structure and interionic interactions of a bulk ionic liquid

The recently developed efficient protocol to explicit quantum mechanical modeling of the structure and IR spectra of liquids and solutions [Katsyuba et al., J. Phys. Chem. B, 2020, 124, 6664-6670] is applied to ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate [Emim][BF₄], and its C2-deuterated analog [Emim-d][BF₄]. It is shown that the solvation strongly modifies the frequencies and IR intensities of both cationic and anionic components of the ionic liquids. The main features of the bulk spectra are reproduced by the simulations for cluster ([Emim][BF₄])₈, representing an ion pair solvated by the first solvation shell. The geometry of the cluster closely resembles the solid-state structure of the actual ionic liquid and is characterized by short contacts of all CH moieties of the imidazolium ring with [BF₄]^- anions. Both structural and spectroscopic analyses allow the contacts to be interpreted as hydrogen bonds of approximately equal strength. The enthalpies of these liquid-state H-bonds, estimated with the use of empirical correlations, amount to 1.2-1.5 kcal mol^-1, while the analogous estimates obtained for the gas-phase charged species [Emim][BF₄]₂^- and [Emim]₂[BF₄]⁺ increase to 3.6-3.9 kcal mol^-1.