Influence of additives on the electrodeposition of zinc from a deep eutectic solvent

The effects of nicotinic acid (NA), boric acid (BA) and benzoquinone (BQ) on the electrodeposition of Zn have been studied in a choline chloride (ChCl) ethylene glycol (EG) based deep eutectic solvent (DES), (1ChCl:2 EG), and for the first time a bright zinc coating has been achieved when NA was used. In metal electroplating processes, small-molecule additives are often included in the plating bath to improve properties of coating such as brightness, roughness, thickness, hardness and resistance to corrosion. The effects of additives on the electrodeposition of Zn from aqueous solution have been extensively investigated. However, very few studies have considered the effects of additives on the electrodeposition of Zn from ionic liquids or deep eutectic solvents. The electrochemical properties of the plating liquid have been studied here using cyclic voltammetry, chronocoulometry, chronoamperometry and microgravimetry (EQCM). Redox peak currents decrease when additives were included in the Zn solution and total charge was also reduced in experiments where additives were present. The Zn deposition in the absence of additive is in good agreement with an instantaneous growth mechanism at short experimental time scales (being indeterminate over longer periods), however, this changes to one of a progressive growth mechanism when additives were included in the coating bath. The current efficiency of zinc deposition in the DES without additives was 95%, which was reduced when additives were included. The resultant surface morphologies, thickness, topography, roughness and crystal structure of the Zn coating were revealed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD), demonstrating that those additives serve as effective brighteners that can produce highly uniform and smooth zinc deposits

Deep eutectic solvents—The vital link between ionic liquids and ionic solutions

When selecting a solvent for a given solute, the strongly held idiom “like dissolves like”, meaning that polar solvents are used for polar solutes, is often used. This idea has resulted from the concept that most molecular solvents are homogeneous. In a deep eutectic solvent (DES), however, both components can be ionic or non-ionic, polar or non-polar. By tuning the components, DESs can solubilize a wide variety of solutes, often mixing hydrophobic and hydrophilic components, and the mixture can be designed to control phase behavior. The liquids often contain significant short-length order, and preferential solvation of one component often occurs. The addition of small polar molecules such as water or alcohols results in non-homogeneous liquids, which have significantly decreased viscosity and increased ionic conductivity. Accordingly, the areas covered in this special issue focus on structure and dynamics, solvation, the mobility of charged species, and the ability to obtain controllable phase behavior by adding polar diluents or using hydrophobic DESs

Controlled release of pharmaceutical agents using eutectic modified gelatin

Deep eutectic solvent (DES) is a class of ionic liquids, consisting of a mixture generally formed by combining hydrogen bond donors (HBDs) such as alcohols, amides and carboxylic acids with various quaternary ammonium salts. The decrease in melting points of the constituents is due to the charge delocalization during formation of hydrogen bonding between the hydrogen bond acceptor with the hydrogen bond donor. This can be considered one of the main reasons for increasing solubility and absorption of DESs. Most active pharmaceutical ingredients (APIs) have polar functional groups containing amide, carboxylic acid, alcohol or quaternary ammonium groups. These tend to increase the melting point of the compounds, but they can be used to form eutectic mixtures. While this concept has previously used, the combination of quaternary ammonium salts with amides, carboxylic acids and alcohols can result in large depressions of freezing points and so-called deep eutectic solvents are formed. DESs mix readily with water and so could increase the uptake of APIs. In this study, pharmaceutical deep eutectic solvents (PDESs) are formulated from 3 APIs: imipramine HCl, ascorbic acid and catechol. These PDESs were used to plasticise gelatine. It is shown that the materials formed can be used to increase the rate of API uptake via both oral and transdermal delivery modes. Thus, the concentration of the PDESs in solution reaches the maximum before the pure drugs. Particularly for catechol, after 1 s, the dissolution of the PDESs was more than twice that of the pure drug. Moreover, the transdermal delivery mode uptake of the PDES based on imipramine HCl from the patch after 15 min was found to be 65% compared with just imipramine HCl which released only 20%

Iron(III) chloride and acetamide eutectic for the electrodeposition of iron and iron based alloys

The electrodeposition of iron and iron-based alloys is important for a variety of coating technologies. This study demonstrates that eutectics of ferric chloride and acetamide are easily formed and a 1:4 M mixture gives a liquid at ambient temperature. This eutectic mixture has a higher conductivity resulting from a lower viscosity than comparable eutectics formed from either aluminium or zinc chloride. Ferric chloride disproportionates to form both anionic and cationic iron containing species and these were identified using a variety of spectroscopic methods. The electrodeposition of iron and iron-nickel alloys was demonstrated and it was shown that the iron-nickel alloys demonstrated improved anti-corrosion properties

Recovery of yttrium and europium from spent fluorescent lamps using pure levulinic acid and the deep eutectic solvent levulinic acid-choline chloride

A solvometallurgical approach for the recovery of rare-earth elements from lamp phosphor waste was developed. The solubility of individual phosphors in different deep-eutectic solvents (DESs) was measured. The DES levulinic acid-choline chloride (xChCl = 0.33) showed high solubility of the YOX phosphor (Y2O3:Eu3+) and low solubility of the HALO phosphor (Sr,Ca)10(PO4)(Cl,F)2:Sb3+,Mn2+, which does not contain any rare-earth element. This DES was selected for further investigation. When the DES was compared to pure levulinic acid, very similar leaching behaviour was observed, showing that the proton activity is more important than the chloride as a metal ligand. The leaching of YOX and HALO using levulinic acid-choline chloride (xChCl = 0.33) or pure levulinic acid was optimised in terms of water content, temperature and leaching time. The optimised parameters were validated in a synthetic mixture of phosphors and in real lamp phosphor waste. The co-dissolution of HALO is higher in the real waste than in the synthetic mixture. The real waste was also leached with an aqueous solution of hydrochloric acid, which was non-selective against dissolution of YOX, and with the functionalised ionic liquid betainium bis(trifluoromethylsulfonyl)imide. The ionic liquid gave a similar selectivity as levulinic acid, but is much more expensive. The recovery of the metals from the pregnant leach solution was tested via precipitation with oxalic acid and solvent extraction. Oxalic acid precipitation was not suitable for the DES system. The metals could be extracted via solvent extraction with the acidic extractant bis(2-ethylhexyl)phosphoric acid (D2EHPA) and stripped by an aqueous hydrochloric acid solution. Pure levulinic acid was found to be more suitable than the corresponding ChCl-based DES for the selective recovery of YOX

Effect of water on the electrodeposition of copper on nickel in deep eutectic solvents

Most studies of metal electrodeposition in ionic liquids dry the electrolyte thoroughly, as water is thought to be detrimental. In some cases, water has a beneficial effect on deposit morphology. The electrodeposition of copper has been studied in 1ChCl: 2EG-water mixtures. It is shown here that the presence of water increases the apparent brightness of the deposit due to changes in the electrodeposit surface feature size, up to a water content of approximately 20 wt-%. This study characterises speciation and mass transport in solution, and shows that diffusion can be controlled independently of speciation. It is shown that there is an optimal water content, which is thought to originate from formation of a bi-continuous micro-emulsion phase in DES-water mixtures. Additionally, the copper species remains in a predominantly ionic medium at low water content but moves to an aqueous environment when water is the main component

Concentrated Ionic Fluids: Is There a Difference Between Chloride-Based Brines and Deep Eutectic Solvents?

Deep Eutectic Solvents (DESs) have been lauded as novel solvents, but is there really a difference between them and concentrated aqueous brines? They provide a method of adjusting the activity of water and chloride ions which can affect mass transport, speciation and reactivity. This study proposes a continuum of properties across concentrated ionic fluids and uses metal processing as an example. Charge transport is shown to be governed by fluidity and there is no discontinuity between molar conductivity and fluidity irrespective of cation, charge density or ionic radius. Diffusion coefficients of iron(III) and copper(II) chloride in numerous concentrated ionic fluids show the same linear correlation between diffusion coefficient and fluidity. These oxidising agents were used to etch copper, silver and nickel and while the etching rate increased with fluidity for copper, etching of silver and nickel only occurred at high chloride and low water activity as passivation occurred when water activity increased. Overall, brines provide a high chloride content at a lower viscosity than DESs, but unlike DESs, brines are unable to prevent passivation due to their high water content. The results show how selective etching of mixed metal waste streams can be achieved by tuning chloride and water activity

The effect of using alternative binders and second life graphite materials on the electrochemical performance of lithium-ion battery electrodes

Lithium-ion battery anodes were produced and tested using gelatin and sodium alginate (NaAlg) biopolymers, modified with a deep eutectic solvent (DES). Anodes created with these alternative binder systems showed comparable capacities and Coulombic efficiencies to cells assembled using commercial PVDF and CMC/SBR binders. Rate tests of these cells found that DES-NaAlg possessed a higher rate capability than PVDF, showing a greater capacity (∼70 mAh.g−1 higher) when cycled at 1C. Anodes using gelatin materials exhibited lower rate stability, showing significant capacity fade at cycling rates </p

Direct re-lithiation strategy for spent lithium iron phosphate battery in Li-based eutectic using organic reducing agents

One of the most commonly used battery cathode types is lithium iron phosphate (LiFePO4) but this is rarely recycled due to its comparatively low value compared with the cost of processing. It is, however, essential to ensure resource reuse, particularly given the projected size of the lithium-ion battery (LIB) market. A simple, green, inexpensive, closed-loop process is proposed for recycling LiFePO4 cathodes, via delamination of the cathode active material from the aluminium current collector by simple immersion in water. Two regeneration routes are compared to demonstrate how recovered Li1−xFePO4 can be regenerated: (1) direct re-lithiation of the spent cathode material under ambient temperature and pressure using a eutectic system made from lithium acetate and ethylene glycol with hydroquinone as a reducing agent, and (2) oxidative leaching of lithium ions in water, with iron(iii) chloride as an oxidising agent, followed by regeneration back to the LiFePO4 olivine structure using same re-lithiation method. The use of this non-aqueous lithium-based eutectic system in combination with a reducing agent decreases the temperature and number of steps required for the regeneration of LiFePO4 and restores the electrochemical performance of the spent material

Selective Extraction of Antioxidants by Formation of a Deep Eutectic Mixture through Mechanical Mixing

Extraction of active compounds from natural materials is commonly used to produce a diverse range of ingredients, nutrients, drugs, flavors, and fragrances. While solvent-based approaches are standard for these extraction procedures, large solvent volumes, greenhouse gas emission (due to atmospheric release of volatile organic compounds), and large energy requirements are significant issues. Here, we describe a novel process wherein a mechanical action is applied to a solid-state mixture comprising a quaternary ammonium salt and a biological material containing active molecules to form a deep eutectic mixture. It is first shown that eutectic mixtures can be formed for a wide range of naturally occurring compounds. Selective extraction of these compounds from natural products is then demonstrated using rosemary leaves with three different quaternary ammonium salts. The eutectic mixture formed is purified by liquid/liquid extraction using an oily phase to concentrate the active constituents in the deep eutectic phase. The resulting natural extracts are shown to exhibit high antioxidant activities, which were measured using the conjugated autoxidizable triene (CAT) and the oxygen radical absorbance capacity (ORAC) assays