Liquid Aqueous Solutions Research Articles

Locating the binding domains of lysozyme with ionic liquids in aqueous solution via spectroscopic studies.

The binding domains of lysozyme with ionic liquids (ILs, [C4mim]BF4, [C4mim]Cl, [C4mim]Br and [dmim]I) in aqueous solution was investigated by studying molecular interactions using spectroscopic techniques. Ultraviolet spectroscopy (UV) showed that the addition of ILs increased the absorption peak intensity of lysozyme at 210 nm by enhancing peptide bond valence electron transition. It is also found that a weak interaction between ILs and lysozyme chromophore groups was generated by analyzing the changes of absorption peak intensity near 280 nm. Fluorescence and Synchronous Fluorescence spectra results showed that four ILs had quenching effect on the fluorescent substances of lysozyme, and the quenching effect rose with increasing ILs concentration. Meanwhile, the interaction between lysozyme and ILs molecules is mainly based on Van der Waals force and two Tryptophan (Trp) residues (Trp62 or Trp108) at the active site of lysozyme molecules play a critical role in binding ILs to their own molecules.

Complexation Behavior of β-Lactoglobulin with Surface Active Ionic Liquids in Aqueous Solutions: An Experimental and Computational Approach.

The nature of functionalization of alkyl chains of imidazolium-based surface active ionic liquids (SAILs) with amide or ester moiety led to contrasting complexation behavior toward the globular protein, bovine serum albumin. This prompted us to further investigate the SAIL-dependent colloidal behavior of another globular protein, β-lactoglobulin (βLG), to probe the origin of varying structural transformations in globular proteins induced by SAILs. Herein, we investigated the colloidal systems of βLG, rich in β-sheet structure, in the presence of four structurally different SAILs using a multitechnique approach. The complexation behavior, both at the air-solution interface and in bulk, is supplemented by different techniques. Docking studies have complemented the obtained experimental results. The specificity of structure, H-bonding ability of SAILs, and inherent structure of protein are found to govern their complexation behavior in terms of size, shape, and polarity of protein-SAIL complexes along with varying degrees of structural alterations in globular proteins. The present work is expected to be very useful in establishing a deep understanding of the structure-property relationship between the nature of proteins and SAILs for their complexation and colloidal behavior for various biomedical applications.

Molecular dynamics simulation on LiCl-H2O interfacial phenomenon for liquid desiccant dehumidification

In this paper, molecular dynamics simulation was conducted to analyze the air-solution interface phenomenon of LiCl-H2O for liquid desiccant air dehumidification. Density profiles of ions in liquid desiccant aqueous solutions were plotted along the z axis, and distribution preferences of ions on the air-solution interface were studied. Besides, vapor pressure profiles above the solution surface were plotted, and the saturated vapor pressure was predicted and compared with the empirical data. It was found that water density remained stable in the bulk, and there was a sharp decrease on the air-solution interface. For the ions (Li+ and Cl-), a density peak was observed on the interface, which indicated that ions preferred to appear on the interface rather than in the bulk. When the system temperature was relatively lower, the chloride ions had more preference to exist on the interface than lithium ions. However, when the system temperature reached as high as 350 K, chloride ions and lithium ions had almost the same preference. When the system temperature was 300 K, simulation data of vapor pressure matched well with the empirical data. With the increase of the system temperature, the deviations became larger while the variation tendencies were the same.

Tribological Investigations of Silicon Nitride Lubricated by Ionic Liquid Aqueous Solutions

Water-lubricated ceramic components are promising material combinations for tribological applications because they are wear resistant and can exhibit low coefficients of friction under different loads. The aim of the work was to show in model tribological experiments with silicon nitride that the lubricating properties of water can be improved by adding water-soluble ionic liquids (ILs). The geometry used and the experimental parameters were selected to approximately simulate a piston ring–cylinder liner contact. We found that the addition of 1% IL tributyl methyl phosphonium acetate [P4441][OAc] leads to a reduction of the maximum friction work by 58% compared to pure water lubrication and even by 96% compared to oil-lubricated steel. It was shown that suitable running-in conditions and sufficient cooling by the lubricant at an early stage are important prerequisites for achieving low friction and wear values. In addition, the chemical interaction of water and IL with silicon nitride strongly affects the tribological behavior. As increasing demands on sustainability (green tribology) become more important due to environmental aspects, this work provides important insights for the development of novel water-based lubricant systems.

Polymorphism and piezoelectricity of glycine nano-crystals grown inside alumina nano-pores

Glycine nano-crystals were grown inside alumina nano-pores due to a precipitation process from over-saturated aqueous liquid solutions. The α-glycine polymorph crystals were formed at a higher over-saturation concentration than that of the β-glycine polymorph crystals. The results indicate that the type of the glycine polymorph formed inside the alumina pores is kinetically controlled. A model is suggested to explain the competition between formations of the two polymorphs inside nano-pores. The β-glycine polymorph crystals are distinguished from the α-glycine polymorph crystals not only by XRD measurements but mainly by piezoelectric measurements, where only the non-centro-symmetric β-glycine polymorph crystals show a piezoelectric current response to applied mechanical pressures as low as 1 Pa in the environmental pressure of 1 atm (10–3% pressure change).

Effect of hydrophobicity and H-bonding abilities of ions on osmotic coefficients of aqueous diethylammonium based protic ionic liquid solutions at 298.15 K

The osmotic and activity coefficients of aqueous solutions of diethylammonium based protic ionic liquids (PILs) were determined experimentally using vapor pressure osmometry in the concentration range of (~0.02 to ~0.5) mol·kg−1 at 298.15 K. Osmotic coefficient data show positive deviation from Debye-Hückel limiting law for all the studied PILs. Also a minimum in osmotic coefficient data was observed at higher concentrations and is explained in terms of ion-pair formation. Data of experimental osmotic coefficient were used to obtain activities (aw) and activity coefficients (γ1) of water, mean molal activity coefficient (γ±) of PILs and excess Gibbs free energy change (ΔGE) due to mixing. Observed variations in osmotic coefficients data were explained in terms of hydrophobicity as well as H-bonding. The data of osmotic and activity coefficients were further subjected to analysis through Pitzer ion-interaction model to get an information of ion-ion and ion-solvent interaction to understand ion-pairing, ion hydration and hydrophobic effects in aqueous solutions of PILs. For this, Pitzer ion interaction parameters β(0) and β(1) were estimated and compared with literature data available for other relevant systems. Finally, the results are interpreted in terms ion-ion, ion-solvent interaction along with effect of hydrophobicity on ion-pairing and further discussed the effect of alkyl chain length of anions on solvation behavior of protic ionic liquids in aqueous solutions.

Interactions of sodium polystyrene sulfonate with 4-methylpyridinium based ionic liquids in aqueous solution: Viscometry, conductometry, UV–Vis spectroscopy and density functional theory studies

Viscosity (η) and molar conductivity (Λ) of aqueous solutions of sodium polystyrene sulfonate (NaPSS) in the presence of some 4-methylpyridinium based ionic liquids (1-Butyl-4-methylpyridinium bromide [BMPyr]Br, 1-Hexyl-4-methylpyridinium bromide [HMPyr]Br and 1-Octyl-4-methylpyridinium bromide [OMPyr]Br) were investigated at T = (288.15, 298.15 and 308.15) K. The viscosity values were correlated with the Wolf equation to obtain the intrinsic viscosity ([η]) of NaPSS. The intrinsic viscosity of NaPSS decreases by increasing the concentration of ionic liquids due to screens effects of ionic liquids and decreased with increasing alkyl chain length of ILs. The scaling theory is used for the description of electrical conductance of polyelectrolytes. The values of fractions of uncondensed counterions f have been estimated. The effects of the polyelectrolyte concentration, the relative permittivity of the medium, different alkyl chain length and the temperature on the fractions of uncondensed counterions of NaPSS aqueous solutions have been discussed. UV–Vis spectroscopy and Quantum chemical calculations studies are also used to confirm the existence of interactions between NaPSS and ILs. The UV–Vis spectra of NaPSS show that the conformation of NaPSS changes in the presence of ionic liquids; therefore the value of electric multipole moment decreases. Consequently, the absorption intensity of NaPSS was decreased with the addition of ionic liquids. Density functional theory (DFT) has been used to investigate the interactions between [PSS]− anion and [RMPyr]+ cations. The molecular electrostatic potential, natural bond orbital methodologies and atoms in molecules are used to analyses the nature of interactions of the ion-pairs [RMPyr]+[PSS]−.

Metal ferrites synthesis by AC plasma torch

The article describes the ac air plasma torch with the supply of a liquid aqueous solution of iron (III) nitrate of (mol/l). When the solution is heated, water evaporates, and the iron nitrate is converted to a solid residue (mainly iron oxide). The obtained samples were collected on a heated filter to prevent condensation of water and nitrogen dioxide. The obtained samples were investigated by the X-ray diffractometer and the scanning election microscope with an elemental analyser. The proposed plasma method can be applied to the synthesis of ferrites of various metals.

Aggregation Behavior of Task‐Specific Acidic Ionic Liquid N‐Methyl‐2‐Pyrrolidinium Dihydrogen Phosphate [NMP][H2PO4] in Aqueous and Aqueous Salt Solutions

AbstractThe effect of alkali salt (NaCl, NaBr, and KCl) addition on aggregate formation of N‐methyl‐2‐pyrrolidinium dihydrogen phosphate [NMP][H2PO4] ionic liquid in aqueous solution was determined using surface tension at 298.15K and conductance from 288.15 to 308.15K. The surface parameters such as critical aggregation concentration (CAC), adsorption efficiency, surface pressure, surface tension at CAC, minimum surface cover by a single molecule, and maximum area excess concentration were calculated from surface tension measurements with and without salts. The results show that [NMP][H2PO4] forms aggregates at lower concentrations and is more surface active than classical cationic surfactants.

Binary Mixtures of Ionic Liquids in Aqueous Solution: Towards an Understanding of their Salting-In/Salting-Out Phenomena.

The order of the salting-in or salting-out inducing ability of ions on the aqueous solubility of macromolecules in aqueous solutions is known as the Hofmeister series. Taking into account that ionic liquids (ILs) are constituted by ions, they can exert similar effects on the solubility of other ILs in aqueous media. In order to expand the knowledge on the salting-in/-out ability of ILs, experimental studies on the solubility of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) in water in presence of other IL/salts were conducted at 298.15 K at atmospheric pressure. Both the impact of the anion and cation of the IL were evaluated with the following ILs/salts: 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium hydrogensulfate, cholinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, in a wide composition range. As happens with common salts, both salting-in and salting-out effects exerted by ILs were observed, with a higher impact exerted by the IL anion on the salting-out phenomenon. These data allow to better understand the ILs impact when designing liquid-liquid separation processes.

Separation of Rare Earths from the Transition Metals Using a Novel Ionic-Liquid-Based Aqueous Two-Phase System: Toward Green and Efficient Recycling of Rare Earths from the NdFeB Magnets

An ionic-liquid-based aqueous two-phase system (iL-ATPS) consisting of an ionic liquid, tributylmethylammonium nitrate (N4441NO3), and NaNO3 aqueous solutions was developed for the extraction and separation of rare-earth ions, for example Nd(III), from transition-metal ions. The excellent selectivity of a green nonfluorinated ionic liquid and the low-viscosity feature of an aqueous two-phase system were combined in our suggested iL-ATPS. The results indicated that efficient separation of Nd(III) from transition-metal ions, Fe(III), Ni(II), and Co(II), could be obtained in our suggested iL-ATPS. Furthermore, different parameters of the separation process, including the concentrations of HNO3 and NaNO3 and the added amount of N4441NO3, were optimized. Notably, the extraction kinetics of Nd(III) could be improved significantly in the present iL-ATPS compared with the conventional organic-solvent-based ionic-liquid extraction systems. The similar environment across the liquid–liquid interface was revealed by ...

Tuning the properties of magnesium phosphate-based bone cements: Effect of powder to liquid ratio and aqueous solution concentration

The use of magnesium phosphate-based cements (MPCs) in the biomedical field has recently come under investigation in the scientific community, as these materials display many intriguing properties in the replacement and/or integration of calcium phosphate-based bone cements; however, the diverse preparation conditions reported in the literature make it difficult to evaluate how the modification of a specific parameter in the preparation of the paste affects the final properties of the material. In this paper, we prepared and characterized MPCs by mixing a tri-magnesium phosphate powder with a solution of di-ammonium hydrogen phosphate, so to form struvite as a final setting product. The powder to liquid ratio and the concentration of the aqueous solution were systematically varied, and their effect on the properties of the final product was studied. The handling properties of the pastes were investigated, as well as the crystallinity and the microstructure; the porosity and compressive strength of the final materials were also assessed. The multi-technique approach allowed us to relate the amount of formed struvite with the properties of the material, and to identify the preparation conditions to be used to obtain a cement with desired features.

Carbamate Formation in the System (2-Methylpiperidine + Carbon Dioxide) by Raman Spectroscopy and X-ray Diffraction.

In aqueous solution, 2-methylpiperine (2-MP) has been proposed as a phase-separating amine for carbon-capture applications, whose carbamate is considered to be unstable due to steric hindrance. This paper demonstrates, for the first time, that the carbamate can be synthesized as the salt of the 2-methylpiperidinium cation (2-MPH+) and the 2-methylpiperidine- N-carboxylate anion (2-MPCOO-) by adding carbon dioxide gas to anhydrous liquid 2-MP at CO2/amine ratios α > 0.32 to yield well-defined prismatic crystals. Raman spectra have been measured for anhydrous liquid 2-MP and aqueous solutions of 2-MP and 2-MPH+Cl- at 298 K. The spectra of anhydrous liquid 2-MP, containing dissolved CO2 at lower CO2/amine ratios,. clearly showed the presence of 2-MPH+ and several unidentified bands that were attributed to the carbamate, 2-MPCOO-. Quantum chemical calculations at the B3LYP/6-311++G(d,p) level of theory yielded simulated Raman spectra consistent with the experimental spectra. The spectra show the methyl group of both liquid and aqueous 2-MP and that of aqueous 2-MPH+Cl- to be in the equatorial position. The crystal structure shows the same conformations in the solid state and confirms that Raman spectroscopy can be used to determine the conformation of 2-MP species in the liquid state and aqueous solutions.

Modification to solution-diffusion model for performance prediction of nanofiltration of long-alkyl-chain ionic liquids aqueous solutions based on ion cluster

Mathematical modeling for nanofiltration of ionic liquids (ILs) solutions could assist to understand transfer mechanism and predict experimental values. In this work, modeling by solution-diffusion model for nanofiltration of long-alkyl-chain ILs aqueous solutions was proposed. Molecular simulations were performed to validate the existence of ion cluster in long-alkyl-chain ILs aqueous solution. Based on the results of simulations, parameters used in the solution-diffusion model were modified, such as concentration of ILs and diameter of ion cluster. The modeling process was developed for three long-alkyl-chain ILs aqueous solutions with different concentrations (1-alkyl-3-methylimidazolium chloride: [C6mim]Cl, [C8mim]Cl, [C10mim]Cl). The calculated values obtained from modified solution-diffusion model could well match the experimental values.

Experimental study and thermodynamic modeling of the stability conditions of methane clathrate hydrate in the presence of TEACl and/or BMIM-BF4 in aqueous solution

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) and tetra ethyl-ammonium chloride (TEACl) were investigated to study their effects on thermodynamic stability conditions of methane clathrate hydrate. Different BMIM-BF4 and TEACl aqueous solutions (4.77 wt% (0.57 mol%) TEACl + 4.85 wt% (0.43 mol%) BMIM-BF4, 9.15 wt% (0.20 mol%) TEACl + 9.38 wt% (0.90 mol%) BMIM-BF4 and 11.82 wt% (1.63 mol%) TEACl + 11.82 wt% (1.20 mol%) BMIM-BF4) were used as thermodynamic inhibitors which have not been reported in literature. The experiments were conducted at constant volume from 274.6 K to 283.4 K and 3.18 MPa to 7.93 MPa. Moreover, methane hydrate phase equilibria in the aforementioned ioinic liquids (ILs) aqueous solutions were modeled. For this purpose, the chemical potential of water in hydrate phase is calculated using the van der Waals–Platteeuw (vdWP) theory. The Peng-Robinson (PR) equation of state (EoS) is used for calculation of fugacity in the gas phase. Water activity in the aqueous phase is determined by the NRTL activity coefficient model. Successful comparison of the experimental data with the modeling results confirms the model accuracy. It can also be observed that mixtures of the two aforementioned ionic liquids can inhibit methane hydrate formation more than each of single ILs. Furthermore, the studied ILs inhibit methane hydrate formation more at higher pressures.

Ab initio investigation of possible lower-energy candidate structure for cationic water cluster (H2O) 12+ via particle swarm optimization method

Detecting the underlying performance of hydrated electrons and hydroxyl radicals in the cationic water cluster can greatly help to understand the inter reaction mechanism in the liquid water and aqueous solutions. Based on our previous (H2O)10+ research, we have paid attention to more problems of larger cationic clusters in this work, including the existence of hemibonded type, long-range correction functions, and hydrogen-bonded site analyses. The lower-energy structures of the cationic water cluster (H2O)12+ have been comprehensively explored, and more experienced functions are introduced to check the ground state and vibration spectrum. Unlike the configuration regularity of neutral (H2O)12 clusters and small cationic water clusters, those new-found structures for (H2O)12+ are inclined to adopt three dimension (3D) cage-like structures and the H2O-OH2 structure appears in the higher energy isomer. The calculation reveals that the lowest stable isomer is the 3D cage structure W14 predicted at MP2 level, which has not been reported yet. In the thermal simulation, structure transition from the cage-like to the ring-like occurs at T > ≈256 K, and the two dimension (2D) ring-like structure occupies a dominant position at high temperature range. The infrared spectra explain that the difference of the spectra between the 2D net structures and 3D cage-structures is mainly caused by the weight fluctuation of single acceptor-single donor (AD), double acceptor-single donor (AAD), and single acceptor-double donor (ADD) sites in these isomers. This further gives a similarity relation between (H2O)12+ and H+(H2O)12 clusters in the shape of the network and spectral characteristics. By molecular orbitals and topological analysis, we find that the lone pair orbital on hydroxyl radical dominates the reactivity and stability of cationic system. The present research may be helpful for exploring the evolution law of the larger cationic water clusters in the future.

Production, characterization and adsorption studies of bamboo-based biochar/montmorillonite composite for nitrate removal

Biochar is a promising immobilization tool for various contaminants in liquid wastes, aqueous solutions and soils. To further improve the sorption characteristics, a biochar/montmorillonite composite was produced and synthesized in an experimental pyrolysis reactor, using bamboo as biomass feedstock. The composite was characterized by physico-chemical and structural methods (FTIR, SEM, SEM/EDX, SSA, Low temperature nitrogen adsorption method). Based on these methods, the successful preparation of a bamboo based biochar/montmorillonite composite preparation has been demonstrated. The particles of montmorillonite were distributed across the biochar surface. The adsorption studies for removal nitrates from aqueous solutions were investigated by a batch method at laboratory temperatures. The experimental data were fitted by three adsorption models (Langmuir, Freundlich and DR; R2 > 0.93). The maximum adsorption capacity achieved by biochar at pH 4, was about 5 mg g−1 and by biochar/montmorillonite composite 9 mg g−1. The results suggest that the bamboo-based biochar/montmorillonite composite can be used effectively in the treatment of industrial effluents or waste water containing anionic pollutants such as nitrates.

Salting-out Effect of Ionic Liquid, 1-Butyl-3-methyl Imidazolium Chloride on Aqueous d-Fructose or Sucrose Solutions at T = 298.15 K: Vapor–Liquid Equilibrium Study

Water activity and vapor pressure for aqueous {ionic liquid, 1-butyl-3-methyl imidazolium chloride + sucrose or d-fructose} solutions have been determined using the improved isopiestic method at T = 298.15 K. The reliability of local composition models of NRTL, NRF-NRTL, modified NRTL, Wilson, and UNIQUAC in the fitting the water activity values for the studied systems has been examined. For saccharides in aqueous and aqueous ionic liquid solutions and for ionic liquid in aqueous solutions, the unsymmetrical molal activity coefficients were computed. The interactions present in these systems were interpreted by the comparison of the molal activity coefficients of these saccharides in aqueous and aqueous ionic liquid solutions. Furthermore, salt effect of ionic liquid, 1-butyl-3-methyl imidazolium chloride has been compared with two previously studied ionic liquids 1-butyl-3-methyl imidazolium bromide and 1-hexyl-3-methyl imidazolium chloride. In this study, the effects of chain length and anion type of io...

Synthesis of various gold hierarchical architectures assisted by functionalized ionic liquids in aqueous solutions and their efficient SERS responses

Developing a simple and green route for the controlled synthesis of hierarchical nanomaterials with anisotropic particles as subunits is highly desirable and technically important. Here, a functionalized ionic liquid (FIL) assisted strategy is developed for the preparation of hierarchical Au nanomaterials at room temperature. Various morphologies of Au products, including nanoplate-built flowers, nanobar-built flowers and nanourchins, have been well achieved using the current route in aqueous solutions of imidazolium ILs with different functional groups, such as 1-carboxymethy-3-methylimidazolium chloride ([CMmim]Cl), 1-hydroxylethyl- 3-methylimidazolium chloride ([HEmim]Cl), and 1-(3-aminopropyl)-3- methylimidazolium chloride ([APmim]Cl). The influence of these FILs on the morphology of Au products and their growth process has been studied systematically. It is shown that the functionalized ILs play important roles in the construction of these interesting Au hierarchies. The seed, IL concentration (within a certain range), reaction temperature have negligible influence, but stirring and anions of the ILs have important influences, on the product morphologies. Based on these results, the possible growth mechanism is proposed for the formation of different Au hierarchies. In addition, all the Au samples prepared with the assistance of the functionalized ILs, especially the nanoplate-built flowers, exhibit striking SERS sensitivity and high reproducibility.

Bitumen-silica interactions in the presence of hydrophilic ionic liquids

Ionic liquids have been considered for application in petroleum separation (especially in unconventional oil production) as interfacial functional materials at pure state or aqueous solution state. Herein, the interactions between bitumen and silica in ionic liquids (i.e., [Emim][BF4]) aqueous solution and pure ionic liquids have been investigated by dynamic contact angle, atomic force microscopy (AFM) and sum-frequency generation spectroscopy (SFG). Results show that the addition of ionic liquids in water enhances the equilibrium degree of bitumen recession from silica surface, while negligible change has been observed when the bitumen coated plate was put into the pure ionic liquids. The force measurements by AFM demonstrate that the bitumen-silica adhesion force in different systems are in the order of: DI water >1 mM [Emim][BF4] > pure [Emim][BF4]. Results of SFG detection show that the addition of [Emim][BF4] in the aqueous solution strengthens the orientation of water molecules on the silica surface, while making the water molecules more disordered on the bitumen surface. Consequently, a positively charged Helmholtz-like layer is formed by the [Emim]+ cations on negatively charged silica and bitumen surfaces.