Eutectic choline chloride based

Section 4.3 is devoted to electrodeposition in a special class of deep eutectic solvents/ionic liquids which are based on well-priced educts such as e.g. choline chloride. The impressive aspect of these liquids is their easy operation, even under air, as well as their large-scale commercial availability. One disadvantage has to be mentioned the choline chloride-based liquids especially are currently not yet... 

Another reported class of bio-ILs is the group of cholinium-based ILs (choline, an essential nutrient) with amino acids as the anion [16, 17], Reported applications of such ILs have focused on their activities for the pretreatment of lignocellulosic biomass and as catalysts [18, 19]. Recently gel-based electrolytes, choline chloride-based eutectic solvents, were also used as electrolyte for the fabrication of environmentally friendly supercapacitors on paper [20]. 

In the case of Type 1 and 11 eutectics the potential window is limited at high potentials by chlorine gas evolution and at low potentials by the metal ion reduction with metal deposition from the melt. Type I eutectics have been prepared using Zn, Sn, Fe, Al, Ge and Cu chlorides. Their reduction potential is shifted towards more electronegative values as the metal halide is closer by Lewis acid. Because the reduction potential is associated with Lewis acidity, the corresponding proportions of metal and quaternary ammonium salts affect the potential window. Type 11 eutectics have been developed in order to extend the range of metals able to be electrodeposited from ionic liquids and Cr electrodeposition with good characteristics has been reported (Abbott et al., 2004 Abbott et al., 2004 Benaben Sottil, 2006). Hydration water plays a significant role on the stability and fluidity of choline chloride based ionic liquids. In this case water behaviour is different compared to the case of aqueous electrolytes and the potential window is limited rather by the metallic species... 

Patil XJB, Singh AS, Nagarkar JM (2014) Choline chloride based eutectic solvent an efficient and reusable solvent system for the synthesis of primary amides from aldehydes and from nitriles. RSC Adv 4(3) 1102-1106... 

Singh, B. S., Lobo, H. R., Shankarling, G. S. Choline chloride based eutectic solvents magical catalytic system for carbon-carbon bond formation in the rapid synthesis of P-hydroxy functionalized derivatives. Catal Commun 2012,24,70-74. 

Hayyan A, Hashim MA, Hayyan M, Mjalli FS, AlNashef IM (2014) A new processing route for cleaner production of biodiesel fuel using a choline chloride based deep eutectic solvent. J Clean Prod 65 246-251. doi 10.1016/j.jclepro.2013.08.031... 

Wu S-H, Caparanga AR, Leron RB, Li M-H (2012) Vapor pressure of aqueous choline chloride-based deep eutectic solvents (ethaline, glyceline, maline and reUne) at 30-70°C. Thermochim Acta 544 1-5. doi 10.1016/J.tca.2012.05.031... 

Many of these problems may be overcome by using ionic liquids based on sugars [35] or deep eutectic mixtures. Deep eutectic mixtures such as that derived from choline chloride and urea (m. pt. 12°C [36]) or carboxylic acids [37] can be liquids and have very low vapour pressure. They have been successfully used as electrochemical solvents, but their use in catalysis remains little explored. Urea is a fertiliser and choline chloride (Vitamin B4) is a component of chicken feed so the mixture is environmentally acceptable. 

Related to ionic liquids are substances known as deep eutectic solvents or mixtures. A series of these materials based on choline chloride (HOCH2CH2NMe3Cl) and either zinc chloride or urea have been reported (Abbott et al., 2002 2003). The urea/choline chloride material has many of the advantages of more well-known ionic liquids (e.g. low volatility), but can be sourced from renewable feedstocks, is non-toxic and is readily biodegradable. However, it is not an inert solvent and this has been exploited in the functionalisation of the surface of cellulose fibres in cotton wool (Abbott et al, 2006). Undoubtedly, this could be extended to other cellulose-based materials, biopolymers, synthetic polymers and possibly even small molecules. 

The electrodeposition of chromium in a mixture of choline chloride and chromium(III) chloride hexahydrate has been reported recently [39]. A dark green, viscous liquid is obtained by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties of this deep eutectic solvent are characteristic of an ionic liquid. The eutectic composition is found to be 1 2 choline chloride/chromium chloride. From this ionic liquid chromium can be electrode-posited efficiently to yield a crack-free deposit [39]. Addition of LiCl to the choline chloride-CrCl3-6H20 liquid was found to allow the deposition of nanocrystalline black chromium films [40], The use of this ionic liquid might offer an environmentally friendly process for electrodeposition of chromium instead of the current chromic acid-based baths. However, some efforts are still necessary to get shining... 

As explained previously, electrodissolution in ionic liquids is a simple and efficient process, particularly in chloride-based eutectics. Type III eutectics based on hydrogen bond donors are particularly suitable for this purpose. However, it has been noted that the polishing process only occurs in very specific liquids and even structurally related compounds are often not effective. It has been shown that 316 series stainless steels can be electropolished in choline chloride ethylene glycol eutectics [19] and extensive electrochemical studies have been carried out. The dissolution process in aqueous solutions has been described by two main models the duplex salt model, which describes a compact and porous layer at the iron surface [20], and an adsorbate-acceptor mechanism, which looks at the role of adsorbed metallic species and the transport of the acceptor which solubilises... 

Recently a novel class of deep eutectic solvents based on choline chloride have been developed. These can be handled easily under environmental conditions and circumvent many problems that occur in aqueous solutions. They also offer the first economically viable liquids that can be used on an industrial scale. As the interest of electrochemists and classical electroplaters in ionic liquids has risen strongly in the last few years we decided, in 2006, to collect the key aspects of the electrodeposition from ionic liquids in the present book. The book has been written by a panel of expert authors during late 2006 and the first half of 2007 and thus describes the state of the art as of that point in time. 

Cost and biodegradabiUty have also been major concerns, and new families of ILs derived from renewable feedstock or from low-cost starting materials have beat described. These Bio-ILs are entirely composed of biomaterials [183]. An example to be cited is the development of the deep eutectic mixtures liquid systems based on choline chloride [ 184] for which the qualification of ILs is stiU the subject of controversies. Choline can be used as alternative cation in combination with suitable anion to generate ILs. The biodegradable properties of these ILs have been reported [185]. 

Since 1980s, a large number of studies on the electrodeposition of metals have been reported. Historically, the water-sensitive chloroaluminate first-generation ILs are the most intensively studied. However, in future, the focus will rather be on air-and water-stable ionic liquids due to their variety and the less strict conditions under which they can be handled. Several review articles, books, and book chapters on the electrodeposition of metals and alloys from ILs have already been published [27-183], Ionic liquids can be classified as water/air sensitive (first-generation ionic liquids based on AIX3 (X=C1, Br)) and water/air stable (discrete anions based and eutectic solvents/ionic liquids such as ZnCl, urea, ethylene glycol, and choline chloride). A selection of published examples of the electrodeposition of metals and alloys from ionic liquids is listed in Table 5.3 the original work for each metal can be found in Refs. [23, 29-183], In this section, we mainly focus on the electrodeposition of active metals such as Al, Mg, and Ti in ionic liquids. 

Abbott AP, Capper G, Davies DL et al (2006) Solubility of metal oxides in deep eutectic solvents based on choline chloride. J Chem Eng 51 1280-1282... 

Scionix has developed an alternative concept to forming eutectic-based ionic liquids which is to complex the anion of choline chloride with a hydrogen-bonding compound rather than a metal halide [21,22]. The ionic liquids allow electropolishing with high current efficiency (>80%), improved surface finish and improved corrosion resistance [23]. 

Abbott, A. R, Capper, G., McKenzie, K. J., and Ryder, K. S. (2007]. Electrodeposition of zinc-tin alloys from deep eutectic solvents based on choline chloride./ Electroanal. Chem., 599, pp. 288-294. 

Smith et al. [67] studied the Zn electrodeposition from deep eutectic solvents (DES) by an AFM-EQCM system. The DES chosen in this study were the solvents based on a eutectic mixture of choline chloride (ChCl) and ethylene glycol (EG). The peculiarity of the DES is their very high viscosity at room temperature when compared to that of water. The authors proved by combining chronoamperometry, AFM, and EQCM techniques that the initial phases of Zn nucleation from DES resemble the 3D progressive model, as described mathematically by Sharifker and Hills [68]. 

Various ionic liquids based on choline chloride (noted as ChCl) - urea (symbolized IL) and choline chloride - ethylene glycol (symbolized ILEG) (1 2 molar ratio) eutectics have been synthesized involving various Ni salts, respectively NiCl2.6H20 and NiS04.7H20 with... 

Leron RB, Li M-H (2013) Solubility of carbon dioxide in a choline chloride-ethylene glycol based deep eutectic solvent. Thermochim Acta 551 14-19. doi 10.1016/j.tca.2012.09.041... 

Anouti M, Caftlon-Caravanier M, Diidi Y, Gahano H, Lemordant D (2008) Synthesis and characterization of new pyrroUdinium based protic ionic liquids. Good and superionic liquids. J Phys Chem B 112(42) 13335-13343. doi 10.1021/jp805992b Abbott AP, Capper G, Davies DL, McKenzie KJ, Obi SU (2006) Solubility of metal oxides in deep eutectic solvents based on choline chloride. J Chem Eng Data 51(4) 1280-1282. doi 10.1021/je060038c... 

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