Studies on formation and percolation in ionic liquids/TX-100/water microemulsions

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids

In this paper, three imidazolium-based ionic liquids, viz., 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br), 1-butyl-3-octyl imidazolium bromide ([BOIm]Br), and 1-butyl-3-hexadecyl imidazolium bromide ([BCIm]Br), were synthesized. Three novel microemulsions systems were constructed and then were used to recover Pd (II) from cyanide media. Key extraction parameters such as the concentration of ionic liquids (ILs), equilibration time, phase ratio (R_A/O), and pH were evaluated. The [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system exhibited a higher extraction percentage of Pd (II) than the [BOIm]Br/n-heptane/n-pentanol/sodium chloride and [BCIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion systems. Under the optimal conditions (equilibrium time of 10 min and pH 10), the extraction percentages of these metals were all higher than 98.5% when using the [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system. Pd(CN)₄^2- was separated through a two-step stripping procedure, in which Fe (III) and Co (III) were first separated using KCl solution, then Pd(CN)₄^2- was stripped using KSCN solution (separation factors of Pd from Fe and Co exceeded 10³). After five extraction-recovery experiments, the recovery of Pd (II) through the microemulsion system remained over 90%. The Pd (II) extraction mechanism of the ionic liquid [BUIm]Br was determined to occur via anion exchange, as shown by spectral analysis (UV, FTIR), Job's method, and DFT calculations. The proposed process has potential applications for the comprehensive treatment of cyanide metallurgical wastewater.

About the nanostructure of the ternary system water - [BMIm]PF6 - TX-100

HYPOTHESIS

Many efforts have been made to formulate water-IL microemulsions. One of the most intensely studied systems is H₂O - 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm]PF₆) - 4-octylphenol polyethoxylate (TX-100) and it is not questioned that this system forms microemulsions. The nanostructures observed for traditional microemulsions are postulated with the surfactant being adsorbed at the interface such that the hydrophilic EO sides intrude into the water domains, while the hydrophobic hydrocarbon chains are immersed into [BMIm]PF₆. However, the high polarity of [BMIm]PF₆ and the observation that [BMIm]PF₆ mixes well with oligoethylene oxides but hardly with non-polar solvents like toluene or alkanes are not in line with this picture.

EXPERIMENTS

We re-studied the ternary system H₂O - [BMIm]PF₆ - TX-100 by measuring phase diagrams, determining tie-lines, and carrying out ROESY NMR and PFG NMR measurements.

FINDINGS

We found that the hydrophobic part of the surfactant interacts neither with water nor with [BMIm]PF₆, while both solvents interact with the hydrophilic part of the surfactant. We suggest that the surfactant is not adsorbed at the interface between water and the IL, but forms normal spherical or elongated micelles or even continuous aggregates with the hydrocarbon chains forming the interior of the aggregates.

Ionic liquids for nano- and microstructures preparation. Part 1: Properties and multifunctional role

Ionic liquids (ILs) are a broad group of organic salts of varying structure and properties, used in energy conversion and storage, chemical analysis, separation processes, as well as in the preparation of particles in nano- and microscale. In material engineering, ionic liquids are applied to synthesize mainly metal nanoparticles and 3D semiconductor microparticles. They could generally serve as a structuring agent or as a reaction medium (solvent). This review deals with the resent progress in general understanding of the ILs role in particle growth and stabilization and the application of ionic liquids for nano- and microparticles synthesis. The first part of the paper is focused on the interactions between ionic liquids and growing particles. The stabilization of growing particles by steric hindrance, electrostatic interaction, solvation forces, viscous stabilization, and ability of ILs to serve as a soft template is detailed discussed. For the first time, the miscellaneous role of the ILs in nano- and microparticle preparation composed of metals as well as semiconductors is collected, and the formation mechanisms are graphically presented and discussed based on their structure and selected properties. The second part of the paper gives a comprehensive overview of recent experimental studies dealing with the applications of ionic liquids for preparation of metal and semiconductor-based nano- and microparticles. A wide spectrum of preparation routes using ionic liquids are presented, including precipitation, sol-gel technique, hydrothermal method, nanocasting, and microwave or ultrasound-mediated methods.

Transport properties of microemulsions with ionic liquid apolar domains as a function of ionic liquid content

The conductivity, dynamic viscosity and diffusion coefficient of aqueous ionic liquid microemulsions were measured as a function of ionic liquid content. ​The conclusions from transport properties were supported by UV-Vis as well as FTIR measurements.

Ionic liquids for nano- and microstructures preparation. Part 2: Application in synthesis

Ionic liquids (ILs) are widely applied to prepare metal nanoparticles and 3D semiconductor microparticles. Generally, they serve as a structuring agent or reaction medium (solvent), however it was also demonstrated that ILs can play a role of a co-solvent, metal precursor, reducing as well as surface modifying agent. The crucial role and possible types of interactions between ILs and growing particles have been presented in the Part 1 of this review paper. Part 2 of the paper gives a comprehensive overview of recent experimental studies dealing with application of ionic liquids for preparation of metal and semiconductor based nano- and microparticles. A wide spectrum of preparation routes using ionic liquids is presented, including precipitation, sol-gel technique, hydrothermal method, nanocasting and ray-mediated methods (microwave, ultrasound, UV-radiation and γ-radiation). It was found that ionic liquids formed of a 1-butyl-3-methylimidazolium [BMIM] combined with tetrafluoroborate [BF4], hexafluorophosphate [PF6], and bis(trifluoromethanesulfonyl)imide [Tf2N] are the most often used ILs in the synthesis of nano- and microparticles, due to their low melting temperature, low viscosity and good transportation properties. Nevertheless, examples of other IL classes with intrinsic nanoparticles stabilizing abilities such as phosphonium and ammonium derivatives are also presented. Experimental data revealed that structure of ILs (both anion and cation type) affects the size and shape of formed metal particles, and in some cases may even determine possibility of particles formation. The nature of the metal precursor determines its affinity to polar or nonpolar domains of ionic liquid, and therefore, the size of the nanoparticles depends on the size of these regions. Ability of ionic liquids to form varied extended interactions with particle precursor as well as other compounds presented in the reaction media (water, organic solvents etc.) provides nano- and microstructures with different morphologies (0D nanoparticles, 1D nanowires, rods, 2D layers, sheets, and 3D features of molecules). ILs interact efficiently with microwave irradiation, thus even small amount of IL can be employed to increase the dielectric constant of nonpolar solvents used in the synthesis. Thus, combining the advantages of ionic liquids and ray-mediated methods resulted in the development of new ionic liquid-assisted synthesis routes. One of the recently proposed approaches of semiconductor particles preparation is based on the adsorption of semiconductor precursor molecules at the surface of micelles built of ionic liquid molecules playing a role of a soft template for growing microparticles.

Transport properties of aqueous ionic liquid microemulsions: influence of the anion type and presence of the cosurfactant

Transport properties, viz. specific conductivity, dynamic viscosity and apparent diffusion coefficients, were measured as a function of water content in aqueous ionic liquid microemulsions containing 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6] and bis(trifluoromethanesulphonyl)imide, [BMIM][Tf2N], stabilized by the nonionic surfactant TX-100, or its mixture with a cosurfactant, i.e. butanol. The investigation covered the whole water content range through various (Winsor I-III and dissolved solution) structures of the system. The comparative approach allowed closer inspection into phenomena being on the background of observed transport properties behavior taking into account the influence of the cosurfactant. The addition of butanol offers considerable advantages, such as an increase in conductivity, especially in systems containing ionic liquids with lower conductivity. This is accompanied by a significant decrease in viscosity, even to values that are comparable with those of molecular solvents. Moreover, the reasons for the surprisingly higher conductivity of [BMIM][PF6]-based systems were provided, and the conclusions were supported by cyclic voltammetry as well as spectrophotometric and dynamic light scattering measurements.