Investigating the effect of systematically modifying the molar ratio of hydrogen bond donor and acceptor on solvation characteristics of deep eutectic solvents formed using choline chloride salt and polyalcohols.

Choline chloride-based deep eutectic solvents (DESs) are immensely popular in organic synthesis, catalysis, electrochemistry, and separation science. A popular choice of hydrogen bond donor (HBD) among these DESs consists of both straight-chain and branched polyols that can incorporate additional functional groups, such as ether linkages. Previous studies have shown that the extraction efficiency is significantly altered when the molar ratio of HBD in choline chloride-based DES systems is varied, but no study has been able to relate it to their solvation characteristics. This is largely due to the limited sensitivity of existing solvatochromic dye techniques to detect minor changes in solvation interactions when the DES composition is varied. In this study, inverse gas chromatography was employed for the first time to investigate the variation in solvation properties for DESs comprised of choline salts as hydrogen bond acceptors (HBAs) and polyols as HBDs when their HBA/HBD ratio is systematically altered. Unlike many organic solvents, DES systems investigated in this work possessed a significant hydrogen bond character. It was observed that the hydrogen bond basicity generally plateaued at higher molar ratios of HBD while the hydrogen bond acidity was observed to be the highest at HBA/HBD ratios of 1:10 in all DESs. Amongst all solvents, neat HBDs (triethylene glycol and 1,8-octane diol) possessed the weakest hydrogen bond basicity since they lack the chloride anion that acts as the primary hydrogen bond acceptor. Results from this study demonstrate that the solvation characteristics of DESs are largely different from their starting materials while the HBA/HBD ratio further influences their solvation interactions that can in turn impact important parameters such as extraction yields.

Analysis of persistent contaminants and personal care products by dispersive liquid-liquid microextraction using hydrophobic magnetic deep eutectic solvents.

In this work, hydrophobic magnetic deep eutectic solvents (HMDESs) were used in the development of a simple and rapid dispersive liquid-liquid microextraction (DLLME) approach coupled to high performance liquid chromatography with UV detection (HPLC-UV) for the determination of ten organic contaminants including five polycyclic aromatic hydrocarbons, four UV filters, and a pesticide from water at trace levels. The HMDESs were prepared by mixing a hydrogen bond acceptor, metal halide salt, and hydrogen bond donor in suitable molar ratios. Two HMDESs, 2 tetraoctylammonium bromide ([N8888+][Br-]): cobalt chloride (CoCl2): 4 octanoic acid (OA) and 3 trioctylphosphine oxide (TOPO): neodymium chloride (NdCl3): 3 OA, offered the highest analyte extraction efficiency overall and were chosen as suitable solvents for validation of the microextraction method. Under optimized extraction conditions, the method required 30 µL of HMDES as extraction solvent, acetone (87.5 µL) as disperser solvent, a NaCl concentration of 30% (w/v), and an extraction time of 120 s at 20°C. Enrichment factors of the analytes ranged from 44.6 for 3-(4-methylbenzylindene) camphor to 66.0 for 2-ethylhexyl-4-(dimethyl)aminobenzoate. The method provided low limits of detection (LODs) ranging from 0.5 to 4.5 µg L-1, and acceptable precision, with RSD values lower than 9.6%. Furthermore, the validated method was successfully applied for tap and lake water analysis, resulting in relative recoveries of spiked samples ranging between 94.7 and 119.2%.

Comparing the extraction performance of cyclodextrin-containing supramolecular deep eutectic solvents versus conventional deep eutectic solvents by headspace single drop microextraction.

A headspace single drop microextraction (HS-SDME) method coupled with high performance liquid chromatography was developed to compare the extraction of eighteen aromatic organic pollutants from aqueous solutions using cyclodextrin-based supramolecular deep eutectic solvents (SUPRADESs) and alkylammonium halide-based conventional deep eutectic solvents (DESs). Different derivatives of beta-cyclodextrin (ß-CD) were employed as hydrogen bond acceptors (HBA) in SUPRADESs and the extraction performance investigated. SUPRADES comprised of the 20 wt% native ß-CD HBA provided the highest enrichment factors of analytes compared to SUPRADESs comprised of other derivatives of ß-CD (random methylated ß-cyclodextrin, heptakis(2,3,6-tri-O-methyl)-ß-cyclodextrin, and 2-hydroxypropyl ß-cyclodextrin). In addition, native ß-CD and its derivatives were dissolved in the neat DESs and their effect on the extraction of analytes examined. Dissolution of 20 wt% native ß-CD in the choline chloride ([Ch+][Cl-]):2Urea DES resulted in a significant increase in the extraction efficiencies of target analytes compared to the neat [Ch+][Cl-]:2Urea DES. Under optimum conditions, the extraction method required a solvent microdroplet of 6.5 µL, 1000 rpm stir rate, 30% (w/v) salt concentration, and a temperature of 40 °C. The tetrabutylammonium chloride: 2 lactic acid DES resulted in the highest enrichment factors while the [Ch+][Cl-]:2Urea DES had the lowest for most of the analytes among the evaluated solvents. The method provided limits of detection (LODs) down to 35 µg L-1. Furthermore, the developed method was applied for the analysis of spiked tap and lake water, where relative recoveries ranging from 83.7% ̶ 119.7% and relative standard deviations lower than 19.2% were achieved.

Modulating solvation interactions of deep eutectic solvents formed by ammonium salts and carboxylic acids through varying the molar ratio of hydrogen bond donor and acceptor.

Deep eutectic solvents (DESs) have gained increasing popularity in separation science due to the fact that their physico-chemical properties can be easily fine-tuned by varying the type or ratio of hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD). While it is well-known that the molar ratio of HBA/HBD affects the melting point of a eutectic mixture, much less is understood regarding its effect on the magnitude of individual solvation interactions. This is largely due to the fact that established solvatochromic dye methods lack sensitivity when the HBA/HBD ratio is varied slightly in a eutectic mixture. Herein, this study is the first to measure the variation of DES solvation interactions with small changes in the molar ratio of HBA/HBD using inverse gas chromatography (IGC). Solute-solvent interactions of three different DES systems comprised of ammonium salts and organic acids were examined. The probe molecules were studied for 18 eutectic mixtures of varied HBA and HBD composition. DES hydrogen bond basicity, hydrogen bond acidity, and dispersive-type interactions exhibited the greatest change when the molar ratio of HBA/HBD was varied in the eutectic mixture. Results from this study demonstrate that the HBA/HBD ratio can be used to modulate the solvation characteristics for this class of DESs in separations and that the stoichiometric ratio of the HBA/HBD is important in ensuring their reproducible preparation.

Fast and non-destructive determination of water content in ionic liquids at varying temperatures by Raman spectroscopy and multivariate regression analysis.

Imidazolium acetate ionic liquids (ILs) have been utilized as promising solvents in many applications that involve varying water content and temperature. These experimental variables affect the anion-cation intermolecular interactions, which in turn influence the performance of the ILs in these applications. This paper shows Raman spectroscopy can be used as an operando method to measure water content in IL solvents when simultaneous temperature changes may occur. The Raman spectra of 1-alkyl-3-methylimidazolium acetate ILs (alkyl chain length n = 2, 4, 6, 8) with varying water content (from 0.028 to 0.899 water mole fraction) and temperature (from 78.1 K to 423.1 K) were measured. Increasing the water content or decreasing the temperature of the tested ILs weakens the anion-cation intermolecular interactions. The water content of these ILs can be quantified even in conditions when the temperature is changing using Raman spectroscopy combined with multivariate regression analysis, including principal component regression (PCR), partial-least-squares regression (PLSR), and artificial neural networks (ANNs). The ANN model combined with partial-least-squares (PLS) achieved the highest prediction accuracy of water content in ILs at varying temperatures (RMSECV = 0.017, R2CV = 99.1%, RMSEP = 0.019, R2P = 98.8%, RPD = 8.93). Raman spectroscopy provides a potential fast non-destructive operando method to monitor the water content of ILs even in applications when the temperature may be simultaneously altered; this information can lead to the optimized use of these ILs in many applications.

Deep eutectic solvents in separations: Methods of preparation, polarity, and applications in extractions and capillary electrochromatography.

Deep eutectic solvents (DESs) have emerged as alternatives to conventional organic solvents and ionic liquids (ILs). Their tunable and designer physio-chemical properties, low cost, and ease of preparation make them attractive solvent systems for use in extractions and additives to chromatographic separations. However, due to the diverse range of hydrogen bond acceptors and donors that comprise DESs, choosing the appropriate solvent for separations can be challenging. This review discusses all methods of DES preparation and details their advantages and disadvantages. Since polarity is an important aspect in their use in separations, the classification of DESs based on the betaine dye and nile red scales as well as Kamlet-Taft parameters is also discussed. Finally, a summary of applications of DESs in various extraction processes (phenolics, fuels, metals, proteins, carbohydrates), solid-phase extraction, solid-phase microextraction, as well as capillary electrochromatography is provided.

Utilization of Biomass Fly Ash for Improving Quality of Organic Dye-Contaminated Water.

Development of innovative methodologies to convert biomass ash into useful materials is essential to sustain the growing use of biomass for energy production. Herein, a simple chemical modification approach is employed to functionalize biomass fly ash (BFA) with 3-aminopropyltriethoxy silane (APTES) to develop an inexpensive and efficient adsorbent for water remediation. The amine-functionalized BFA (BFA-APTES) was fully characterized by employing a range of characterization techniques. Adsorption behavior of BFA-APTES was evaluated against two anionic dyes, namely, alizarin red S (ARS) and bromothymol blue (BTB). In the course of experimental data analysis, the computation tools of data fitting for linear and nonlinear form of Langmuir, Freundlich, and the modified Langmuir-Freundlich adsorption isotherms were used with the aid of Matlab R2019b. In order to highlight the misuse of linearization of adsorption models, the sum of the squares of residues (SSE) values obtained from nonlinear models are compared with R 2 values obtained from the linear regression. The accuracy of the data fitting was checked by the use of SSE as an error function instead of the coefficient of determination, R 2. The dye adsorption capacity of BFA-APTES was also compared with the nonfunctionalized BFA. The maximum adsorption capacities of BFA-APTES for ARS and BTB dye molecules were calculated to be around 13.42 and 15.44 mg/g, respectively. This value is approximately 2-3 times higher than the pristine BFA. A reasonable agreement between the calculated and experimental values of q e obtained from the nonlinear form of kinetic models verified the importance of using equations in their original form. The experimentally calculated thermodynamic parameters including molar standard Gibbs free energy (Δad G m 0) and molar standard enthalpy change (Δad H m 0) reflected that the process of adsorption of dye molecules on the BFA-APTES adsorbent was spontaneous and exothermic in nature. Moreover, the used BFA-APTES adsorbent could be regenerated and reused for several cycles with significant dye adsorption capacity. The remediation capability of the BFA-APTES adsorbent against ARS dye was also demonstrated by packing a small column filled with the BFA-APTES adsorbent and passing a solution of ARS through it. Overall, we provide a simple and scalable route to convert BFA into an efficient adsorbent for water remediation applications.

Diffusional Dynamics of Tetraalkylphosphonium Ionic Liquid Films Measured by Fluorescence Correlation Spectroscopy.

Fluorescence correlation spectroscopy (FCS) is applied to investigate the diffusional dynamics of hydrophilic (Atto 590) and amphiphilic (DiD) fluorophores in a series of alkylphosphonium ionic liquid (IL) films ([P4448][Cl], [P6668][Cl], [P66614][Cl], and [P66614][NTf2]) in order to determine diffusional parameters and to elucidate nanoscale structural heterogeneities within the IL. From the measured correlation functions, the diffusion coefficients of the fluorescent molecules are estimated, rendering values that span from 0.39 to 1.2 and 0.146 to 5.2 µm2/s for Atto 590 and DiD, respectively. An increase in the diffusion coefficient values is correlated to the increase in the alkyl chain length, which in turn is correlated with a decrease in their viscosity. Interestingly, deviations from Brownian diffusion behavior of the fluorescent probes in the ILs are observed, showing a time-dependent diffusion coefficient in most of the cases. These deviations can be attributed to the presence of nanoscale structural heterogeneities in the tetraalkylphosphonium ILs. These results experimentally confirm the presence of nanosegregation in tetraalkylphosphonium ILs, which has been previously observed in molecular dynamics studies.