Chemical Engineering Journal 273 (2015) 551–567Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Review Potential applications of deep eutectic solvents in nanotechnology Ali Abo-Hamad a,b, Maan Hayyan a,c,⇑, Mohammed AbdulHakim AlSaadi a,d, Mohd Ali Hashim a,b a University of Malaya Centre for Ionic Liquids (UMCiL), University of Malaya, Kuala Lumpur 50603, Malaysia Department of Chemical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia c Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia d Nanotechnology & Catalysis Research Centre (NANOCAT), University of Malaya, Kuala Lumpur 50603, Malaysia b h i g h l i g h t s g r a p h i c a l a b s t r a c t DESs can play a primary role in nanotechnology. Up-to-date articles pertaining to DES contribution in nanotechnology were reviewed. The most current DESs applications are in chemical and electrochemical synthesis. The current vision foreshadowed an entirely new areas of nanotech built on DESs. a r t i c l e i n f o Article history: Received 30 October 2014 Received in revised form 28 February 2015 Accepted 9 March 2015 Available online 25 March 2015 Keywords: Deep eutectic solvent Ionic liquid Nanomaterial Carbon nanotube Electrodeposition Dispersion a b s t r a c t Deep eutectic solvents (DESs) have recently received a great interest in diverse fields including nanotechnology due to their unique properties as new green solvents, efficient dispersants and as large-scale media for chemical and electrochemical synthesis of advanced functional nanomaterials. DESs have also an active role in improving the size and morphology of nanomaterials during synthesis stage. Moreover, DESs confined in nano-size pores or tubes show distinct behavior from those in the same types but in larger scales. Therefore, a numerous studies sprung up to expose the importance of the synergy between DESs and nanomaterials. This review revealed the recent studies that devoted to the impact of involving DESs in nanotechnology and potential applications. Ó 2015 Elsevier B.V. All rights reserved. Contents 1. 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1. History of DESs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2. DESs as analogs of ILs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3. Properties of DESs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1. Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2. Solvation properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main applications of DESs in nanotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ⇑ Corresponding author at: Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia. Tel./fax: +60 3 7967 5311. E-mail address:
[email protected] (M. Hayyan). http://dx.doi.org/10.1016/j.cej.2015.03.091 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. 552 552 552 552 553 554 554 . . . . . . . . There are unlimited opportunities to prepare numerous DESs because of the high flexibility to choose their individual components as well as their composition. . 2. . . . . . . . . . . . . . . . . . . .2. . . . . . . . . . . 2. . . . . . . . . . . which are able to form a eutectic mixture. . . . . . . . .2. . . 2. . . . . DESs were also utilized as a medium for electrochemical deposition and different metals were successfully electrodeposited such as Ag. . .9] The increasing interest of DESs is attributed to their potential to be even more environmentally benign compared to the earlier traditional ILs besides having almost similar solvation properties. . . . . . . as a new type of green solvent. . . a special class of ILs was introduced and believed to be a new generation of ILs which known as DESs. . . . . . . . . . . In literature. . . . . . . [1] as a mixture of two or more components that forms a eutectic. The most popular component among all DESs is choline chloride (ChCl) which is similar to B vitamins. . . . Media to produce efficient and recyclable nano-catalytic assembly . . . . . . . . . DESs are sometimes referred to analogs of ILs [14]. . . . . . . . . . . . . . . . . . . . . . . . . 2. . Thus. . . . . . . 2. . . . 2. . . . . . . . . . .4. . . . . . . . . . . . . . . . . . .2. . . . . . . . and Cu [8. . . . . . . . . . . . . . . . . . . This eutectic phenomenon was first introduced through a mixture of urea and ChCl with a 2:1 molar ratio and melting points 133 °C and 302 °C. . . . . . . . . . . .3. . . . . . . . . . . . . . . . . . . .1. . putting forward many potential applications in different fields of chemistry and electrochemistry. . . . . Properties of DESs DESs are close to ILs regarding the fact of being adoptable in numerous applications [16]. . . DES-based nano production: an overview about applications. . . . . . . . . . . . and results in easily biodegradable products [15]. . Furthermore. DESs as analogs of ILs ILs have been introduced as new alternative solvents to replace conventional ones for the use in synthetic processes [11]. . . Solubility limitations are selected by the HBD of the DES. . Zn. . . . . . respectively. . . . . . . . . . . . 2. . . . This term usually refers to a mixture of a halide salt and a hydrogen bond donor (HBD) to produce liquid [5]. . .1. . . .1. DESs have opened the door for new interesting avenues in chemistry in particular [18]. . . . . . . . . . the cases of using DESs at a commercial scale are still in finite amounts [10]. . . . . . . . . . . . .1. . . . . . . . . . . . . DESs. . . . . . . . . . . 1. . . . . . . and it is a biodegradable and nontoxic salt [1. . . . . . . . . . . . . . . . . . exploiting them attracted other researchers [7]. . . . high thermal stability and low vapor pressure [4]. . Physicochemical properties for DESs are similar to those of ILs. . they can be described either as room temperature ILs when they melt at room temperature or as near room temperature IL if they melt below 100 °C. . . . . . . . . DESs started to be used as solvents for metal cleaning prior to electroplating. 2. . . . . . . .2. . . A great interest of DESs as novel solvents are also placed on the employment of electrochemical procedures to . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Media to split nanomaterials . . Sn. . . . . . .3. . . . Media for sputter deposition to produce nanoparticles . . . . . As a result. . . . . . . . 1. . . . . . . . . . . . . Later. . . . . . . . a comparison between the ILs and DESs use shows rareness for DES cases because of their recent appearance in the few past years. . . . . . . . . . Recently. . . .2]. . . . . . Copper(II) oxide and lithium chloride were successfully dissolved in this DES. These solvents are generally based on mixtures of quaternary ammonium or phosphonium salt and an uncharged hydrogen bond donor such as amide. . . . . such as high viscosity. . The concept of DES was first introduced by Abbott et al. . Solvents and reactants for the physicochemical synthesis of nanomaterials . . Having a combination nature of cation and anion with at least one of them is naturally organic and melts below some arbitrary temperatures is what made them defined as molten salts [12]. . . . . . This review is to focus on nanotechnology side that has employed DESs in the discovery of new routs of synthesis. . . . . . . . . . / Chemical Engineering Journal 273 (2015) 551–567 2. . . . . . . . . . . . Nevertheless. the melting point of this eutectic mixture is lower than both of the individual components. . . . . . . . 1. . . . . . . . . . .1. . . . . . . . . . . . However. . . . . . . .5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [17]. . . . . 2. . Different properties can be attained from DES production and envisaged applications can be achieved especially in high-tech production and processes that demand low costing materials [13]. . . . . . even though they could not be defined as true ILs as they are not completely comprised of ionic species. . . . . . . . . . . . . . . . . . . . . Regarding material synthesis field. . . . . . . . . . . seminal work was reported in ionothermal synthesis for both solvents. . . . . . . . . . . . . . .1. . . . . . . . . . . . . . . advantages and challenges. . . . . . . . . . . . . . . . . . . . . . . . . . . .1. . . . So far and due to economic reasons. . . . 3. . . . Over the last decade. . .3. . . . . . . . .2. . . . . . . . . . . . . . . . . . . 2. . . . . . . . . . . . . . . . . . . Electrolytes for electrochemical systems with nanostructured electrodes . . . . . . . . therefore. . . . . . . . . . . . . . . . . . . . . . . . . Dispersants for nanomaterials to form nanocomposites and nanofluids . .2. . . . . . . . . it is possible to design a task-specific DES that could meet the electrochemical or physicochemical properties required for certain area of application. . . . . . Reaction media for nanomaterial production . . . . . . . . . . Electrolytes for nanomaterial electrodeposition . . . . . . . . . . . . . . . . . Our hope is to encourage researchers to follow up deeply with these aspects in order to spread the use of DESs among the world and make it real in near future. . . . there has been a rapid development in DESs as designer solvents for various applications [3]. imides. . . . . . . . . . . . . . . . . . . . . Media to obtain special sizes and morphologies of nanomaterials . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . acid or alcohol with a much lower melting point than that of any of its individual components have recently gained attention. and carboxylic compounds). have some recognized properties. . . .552 A. .2. . . . . . . . . . . . . Hence. 1. . . . . 2. This does not include any additional solvent or formation of by-products. . . . . . . . . . . . . .4. . .3. . . . History of DESs A new solvent foundation was laid in 2003 reported by Abbott et al. . . Applications of nanosized DESs . The syntheses of these compounds proceed simply by mixing together two components (cheap. Introduction A DES is generally a combination of two or more components which are able to associate with each other. . Conclusion . . . . and dubbed ‘‘deep eutectic solvents’’ (DESs) [1]. . One of the key features that distinguish ILs form other competitive solvents is the low vapor pressure comparably [13]. . . .2. . . . improving the performance and following up with new findings and applications. . Abo-Hamad et al. . . . . . As they are able to dissolve some metal oxides (MOs). . . . . . . . The first appearance of DES was as mixture of salt based on quaternary ammonium cation and a hydrogen donor (amine. . . . Media to disperse nanoparticles and control morphology . .1. . . . . . . . This can be achieved through the proper combining between salts and HBDs. References . . . . . . . . . . . . . . . . . . . . . . . . . . renewable and biodegradable). . . . . . . . . . . . . . . a plenty of room is available for the development of fundamental research in field of DESs. Cr. . . . . . . . . . . .1. . . . . . . . . . . . . based on 555 555 556 556 557 557 557 557 557 557 560 565 565 565 565 melting point range of ILs. . . . The result was a eutectic mixture that melts at 12 °C [6]. . . . . . . . . . . . . . . 962 4445 27. For ILs case.840 0 0 0.053 10. viscosities.5 22 4.1 5.5) Ethylammonium chloride:Acetamide (1:1. they also have lower vapor pressure in comparison to other solvents [20].98. AA: acrylic acid.19 58.8 142 131 2 7 12 7.337 14.8 11. 1st component 1st component Tm/f (°C)a 2nd component 2nd component Tm/f (°C)a DES molar ratio 1st:2nd DES freezing point (°C) Density (g cm3) Viscosity (cP) Surface tension (mN m1) Ref.26.217 0.27 in the first place.68 60.1 0. DESs are characterized by high conductivities. ILs and organic solvents. DU: dimethyl urea.0 3. and surface tensions. U: urea.61 (25 °C) 1. ionic conductivity of ILs and DESs are dominated by their viscosity Table 3 Comparison between the solubility (in ppm) of some MOs in three ChCl based DESs and in two aqueous solutions of sodium chloride and hydrochloric acid at 50 °C after two days [18].98–100] [5.5) EMC:Ethylene glycol (1:3) EMC:Glycerol (1:3) MPB:Ethylene glycol (1:3) MPB:Glycerol (1:3) [EMIM][N(Tf)2] [BMIM][N(Tf)2] [EMIM][BF4] [EMIM][PF6] [BMIM][PF6] Acetone Ethanol 0. Various factors play roles in this respect such as charge carriers available in the material or as-called ‘‘iconicity’’.95.0 (25 °C) 5. less ionic conductivity range was found compared to aqueous electrolytes of high concentrated solutions. Abo-Hamad et al.896 DES 1:ChCl:Malonic acid (1:1 M ratio).7 15 16 18.17. * According to MSDS. TEG: triethylene glycol.8 3616 479 13 12.103] [98] [104] Liquid at Liquid at Liquid at Liquid at 5. However.55 (30 °C) 0.5 148 4593 3 10. The data are taken from references [7.55 49.2 (25 °C) 1. temperature is also as important to determine their conductivity [22–24].3. / Chemical Engineering Journal 273 (2015) 551–567 Table 1 Some physicochemical properties for different types of DESs.00 2.553 A. Table 2 Conductivity of some DESs. TFA: 2. DES 2:ChCl:Urea (1:2 M ratio). Researchers have usually mentioned the poor conduction of DESs when a comparison is made with normal ILs [3. their mobility and the temperature.9 (25 °C) 13.403 166. By contrast DESs have been widely considered as good conductors when compared with conventional organic solvents.105].523 22.4 (25 °C) 3. ChCl: choline chloride. ZC: zinc chloride.062 (25 °C) 8. [BMIM]: 1-butyl-3methylimidazolium.29 49. G: glycerol.429 (25 °C) 0.20 302–305 302–305 TFA AA 73–75 13 ChCl MPB MPB MPB 302–305 230–234 230–234 230–234 ZC G EG TEG 293 20 13 7 37 (25 °C) 259 (25 °C) 450 (20 °C) 503 (20 °C) 77 (40 °C) 115 (22 °C) 77 (22 °C) 85000 (25 °C) 48.98–100] [5. BF4: tetrafluoroborate. TU: thiourea.25 750 (25 °C) 52 1.6 0. MPB: methyl triphenyl phosphonium bromide.58 Tm/f: melting point/freezing point range.99. [N(Tf)2]: bis(trifluoromethylsulfonyl)imide. Giving a general description of DES conductivity as low or high might me sometimes misleading.01 36.27.02 (20 °C)* 1.6 1:2 1:2 1:3 1:4 1:5 [1.047 63.06 (42 °C) 0. Reduced ion mobility accounts for the moderate conductivities caused by the presence of large-sized ions or ion aggregation which affects the available charge carrier amount [21].6 469 0. therefore. This is because the higher viscosities of some DESs compared to ILs [25].9 36 4686 10.100] [100] [96] [101] [101] [102] [98.05 (25 °C) 0. Due to such beneficial properties.65 1.342 35.94 51.7 13. ChCl ChCl ChCl ChCl ChCl 302–305 302–305 302–305 302–305 302–305 U TU 1.6 2 0.3 0.19].N-diethyl ethanol ammonium chloride.18 1. PF6: hexafluorophosphate.2-trifluoroacetamide.95–97] [1] [1] [5. .688 (40 °C) 5.345 106 (25 °C)* EMC: N.008 16.17.34 21 RTb RTb RTb RTb 1.08 4. a According to MSDS.91 ChCl ChCl 1:2 1:2 1:2 1:2 1:2 1:3 1:4 1:2 1:1. they have found plenty of various applications. a b c MO DES 1a DES 2b DES 3c NaCl HCl TiO2 V2O3 V2O5 Cr2O3 CrO3 MnO Mn2O3 MnO2 FeO Fe2O3 Fe3O4 CoO Co3O4 NiO Cu2O CuO ZnO 4 365 5809 4 6415 6816 5380 114 5010 376 2314 3626 5992 151 18.6 30 5 219 4.602 (25 °C) 1.069 0 0 0 2.15 32. DES 3:ChCl:Ethylene glycol (1:2 M ratio).9 1.7 4.2.24. In Table 1 a list of most common properties of DESs are presented.3 0 6. [EMIM]: 1-ethyl-3-methylimidazolium. b Not reported but liquid at room temperature (RT).995 17 2658 28.8 1894 0.0 394 4.3-DU EG G 132–135 170–176 101–104 13 20 12 69 70 66.18 (42 °C) 0. Table 4 Solubility of sodium chloride in different DESs at 60 °C [32].092 (25 °C) 0. 1.260 142.12 1. MPB: methyltriphenylphosphonium bromide.5 0.5 (25 °C) 0.75 (25 °C) 7. Solvent system Conductivity (mS cm1) ChCl:Urea (1:2 M ratio) ChCl:Ethylene glycol (1:2) ChCl:Glycerol (1:2) ChCl:Malonic acid (1:1) ChCl:CrCl36H2O (1:3) ChCl:ZnCl2 (1:2) ZnCl2:Urea (1:3.942 52.865 6109 53.124 25.30 1. explore the mechanisms of electron-transfer reaction [19].00 63. Conductivity Each material has a certain level capability to transmit electric current which determine its electrical conductivity value.1. DES Molar ratio Solubility w/100w ChCl:Zinc(II) chloride ChCl:Zinc(II) chloride ChCl:Zinc(II) chloride ChCl:Tin(II) chloride ChCl:Tin(II) chloride:Zinc(II) chloride 1:1 1:2 1:3 1:3 1:1:1 43.6 9. EG: ethylene glycol.23 1.55 (25 °C) 0. however. Particularly. Therefore. However. In addition. it is worthy to study the solvation properties of solvents before we can determine where they can be highly exploited. 1. Main applications of DESs in nanotechnology The first combination of nanotechnology and ILs was published in 2001 [33]. The proportion of DES and IL articles in nanotechnology fields. ILs and organic solvents were collected and presented in Table 2 [7. All are summarized in the Table 3 below. tendencies of DES use are same for those of ILs.181 mmol L1 NaCl and 3. A list of DESs that have been used so far in nanotechnology field is provided in Table 5 . 93% ILs & Nanotechnology DESs & Nanotechnology Fig. ILs have emerged as ‘‘green’’ alternatives to volatile organic solvents [41]. Among the whole articles that have been published since 2001 combining ILs or DESs with nano-science. This includes almost 40 review articles covering some areas of IL applications in nanotechnology. 7% 1.554 A.26–29]. there are 45 articles studying DESs. According to our statistics. This means there is still a wide range of possibilities to employ DESs ‘‘as alternatives to ILs’’ in nano-science as the last (ILs) have paved the road for that since 2001. the one related to DES was reported as late as 2008 introducing the use of the DES a solvent for the chemical synthesizing of gold nanoparticles.40].3. Solvation properties For all chemical and electrochemical synthesis technology it is quite important to have a solvent or an electrolyte which is capable of dissolving precursors during the reaction time and under synthesis conditions. various solubility values were reported for some types of sodium salts at different temperatures and for a range of mole ratios (salt:HBD). electrochemistry. 2. 2. High sodium salts solubility in certain types of DESs can be employed very well in electrochemistry if they are used as electrolytes to produce sodium metal at mild temperatures. several examples in nanotechnology fields were reported on the use of DESs. Another negative aspect for aggregation is the complication for any modifying process to attain better exploitation in some applications such as sensors and biosensors. we aim to summarize the recent roles of DESs played in every field of nanotechnology. Later on. In different types of DESs.31]. Some examples are given in Table 4 to illustrate the different solubilities of NaCl salt in some types of DESs. 1. there are more than 500 patents studying various types of using ILs/DESs in nano-filed science. Silica nanoparticles come in the second place in terms of their applications with ILs. polymer science and nano-chemistry [34]. In fact. Abo-Hamad et al. / Chemical Engineering Journal 273 (2015) 551–567 Examples for electrical conductivities of some common DESs. Results were compared with the solubilities in aqueous solutions of 0. So far. approximately 50% of the IL 800 673 Number of Arcles 700 564 600 500 392 400 301 300 200 55 92 154 223 45 34 29 24 18 100 1 13 11 6 5 3 3 1 0 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 ILs & Nanotechnology Arcles Year DESs & Nanotechnology Arcles Fig. ILs have shown a special properties when they are in nano-quantities. In this review. Trends of article number studying the application of DESs and ILs in nanotechnology. It was also found that the chemical structure of the DES affects the sodium salts solubility [32]. due to the ability of ILs and DESs as their analogs to interact with some 2. solve. Most nanomaterials are likely to aggregate with each other naturally [39. see Fig. Molar ratio effect was also investigated for one of the studied DES. over about 673 articles on ILs. either if they are confined in nano pores of nanostructured materials [35.14 mmol L1 HCl. see Fig.36] or are interdependently existed in nano-scale volumes like nano-droplets [37] and nano-films [38]. investigated the solubilities of Fe3O4. Figures were found comparable sometimes to ILs and gave the impression about the high chances of using DESs in electrochemical applications [30. This may limit their benign properties required for particular applications like the capability to absorb certain compounds. and split nanomaterials. CuO in different DESs [6]. Abbott et al. single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs respectively) have received a considerable concern in this respect. Various MOs and salts were then tested for their solubility in DESs. . most of the results showed that increasing the temperature and decreasing the molar ratio can increase the solubility. To tackle these difficulties. contribution in nanotechnology was placed for carbon nanomaterial projects. In general. IL applications have been spread over a wide range of fields such as chemical and biochemical reactions.2. They have been considered as convenient media to disperse. all recently reported DES applications in nanotechnology have already been studied before for IL before but with the use of ILs instead. Carbon nanomaterials (CNMs) such as graphene. ZnO. They are also capable of splitting small-scale structures into nano-scale and this aspect is added to their use as a functional dispersing solvent. many cases have been reported regarding the dispersion of solid nanomaterials.25:0. nanofluids or nanocomposites) in order to enhance special properties of the nanomaterials in the mixture or get the mixture itself ready for certain application. in spite of the large number of articles discussing the dispersibility of nanomaterials in ILs. The last is to obtain special properties and/or get as higher benefit as possible.68] [77.79. Abo-Hamad et al. and as known. Uniquely.25 1:1 1:1. Examples were selected from studies where readers can find at least a mentioning about the DES ability to . TU: thiourea.111–117] [77] [57] [118] [86] [52] [76. For first stages of nanomaterial production.1. MA: malonic acid. In synthesis chemistry. Hopefully.6H2O ChCl:AA ChCl:PTSA ChCl:HMP ChCl:ZnCl2 ChCl:GA:G ChCl:MA CA:DU 1:2 2. It is worth mentioning that the main role of these solvents is to homogenize all the reagents in the reaction media.51]. Recently.5 Electrolyte (nanostructure sensor) Media for nanoparticles production by sputter deposition technique Electrolyte (nanoparticle deposition) Media for chemical synthesis of nanoparticles Dispersant Exfoliation Media for chemical synthesis of nanoparticles Media for chemical synthesis of nanoparticles Dispersant Electrolyte (nanoparticle deposition) Media for chemical synthesis of nanoparticles Nanodroplet embedded in microstructure Electrolyte (nanoparticle deposition) Dispersant and media for chemical synthesis of nanoparticles Structure-directing agent and media for chemical synthesis of nanoparticles Dispersant Nano-confinement Media for chemical synthesis of nanoparticles Structure-directing agent and media for chemical synthesis of nanoparticles Nanocatalytic assembly [63] [67. it is highly significant to choose a suitable solvent which can effectively prevent products from being bundled or cluster-assembled. the contribution of DESs in nanomaterial dispersion is still limited.75. These surfactants somehow help prevent nanoparticles agglomeration by forming a protective layer surrounding the surface [45]. The role played by DESs was investigated deeply on how to direct chemistry at the nanoscale. good dispersibility. G: glycerol. viscosity and polarity. wide electrochemical window [43].3DU ChCl:TU ChCl:EG 2:1 1:2 1:2 1:2 ChCl:CrCl3. The same criterion is followed in nanoparticle synthesis.46]. CA: citric acid. large ionic conductivity.3:1 1:1 1:1 1:1 1:0. and DNA/RNA architectures. Our goal here is to cover the recent occupation of DESs in every single area of nanotechnology. it is generally believed that solvents are of essential significance in all synthetic processes [42]. ChCl:U 1:2 ChCl:1. this will add an engineering-looking character to the work away from chemistry sophistication. they are chose depending on the reaction peculiarities and how the solvent may deal with them. Nanomaterial productions were defined in this study in 6 aspects: shape-controlled nanoparticles. 2. size and morphologies [47–49].94.110. ILs as liquid solvents with a special ionic nature have the ability to act as satisfying stabilizers for a wide range of nanoparticles even without using any surfactants [41. However. DES Molar ratio Role Ref. GA: gallic acid. colloidal assemblies. obtained by using ILs solvents for carbon nanotube (CNT) or graphite exfoliation. It leads to a considerable decrease in the surface. but those for their analogs (DESs) are still few in comparison. They have played roles in determining the shape. Up to date. After nanomaterials production. According to literature. Organic and non-organic solvents have been widely used. metal nanoparticles can only show good stability in their suspensions by the coordination of some kinds of surfactants. ILs and DESs have been the solvent of choice for the convenient synthesis of nanoparticles due to thermal stability. The aim of the following sections is to cover and summarize all relevant cases available so far for different DES dispersing purposes.119–123] [74. either early during the nanomaterial synthesis or later for preparation of further application. There has to be known that there are a plenty of fields for the use of original ILs in nanotechnology.80–84.124–126] [93] [127] [85] [58] [128] [91] [129] [49] [64] ChCl: choline chloride. / Chemical Engineering Journal 273 (2015) 551–567 Table 5 DESs used so far in nanotechnology and their main roles. hierarchically porous carbons. with respect to the bulk volume. Media to disperse nanoparticles and control morphology Agglomeration tendency of nanoparticles is one of the basic challenges limiting their applications. but they are existed at least. DESs were reviewed for their recent applications as designer solvents to produce different sorts of nanomaterials. nanoparticles. U: urea. Two different routes of nano-synthesis can be carried out by using ILs/DESs as solvents for chemical syntheses or electrolytes for electrochemical ways. there is no large number of deep studies reporting the dispersibility of nanomaterials in DESs as there is for ILs. support this case [50. the lower surface area. surface tension.e.1.1. the lower chemical and catalytic activity of the particles. Generally. metal–organic frameworks.3:12. ILs may be used to form nano-hybrids (i. In a recent study [44]. electrodeposited films. ILs and DESs have been widely used as efficient dispersants during the synthesis reaction of nanoproducts. DES can act as template. The importance of such dispersion media is hugely considered.555 A.6:11. Dispersants for nanomaterials to form nanocomposites and nanofluids As mentioned earlier. the reported cases of using DESs for the same purposes are still few in comparison. Many examples of graphene-ILs hybrids fabrication.106–110] [69–73. EG: ethylene glycol.107. PTSA: para-toluene sulfonic acid. The reactivity of DESs was found affected by many factors such as hydrogen bonding. AA: acrylic acid. carbon or metal source and as a reactant or auxiliary agent in nanomaterial production. 2. HMP: tris(hydroxymethyl) propane. This work is organized to give a complete and concise summary looking at subjects from a broader perspective.78. DU: dimethyl urea. Table 6 is summarizing some of the related cases of DES as dispersants.0:11. 2.3:1 2. between 1 and 100 nm) [53]. 3. energy and environmental applications DES helped in high dispersed-phase loadings of electrodeposited Ag Improved film properties compared to pure metal Longer storage time was noted for epoxy composition containing DES (more than 60 days) DES could act as an effective GNP dispersing medium. we aim to report some cases where the effect of DESs on shape. disperse nanoparticles during their preparation even it is for another intended application. These small particles were also in nano-size (15–20 nm) as HRTEM images showed. it was a media for the following carbonization process to produce different porous .e.0:1 1. Based on deep [119] [128] [77] understanding of those facts. Abo-Hamad et al. The process was carried out using Fe3O4 nanoparticles and protonated layered dititanate sheets (H2–Ti2O5–H2O) as functionalizing agents in DES medium of ChCl:ethylene glycol (1:2 M ratio). More analyses were conducted to recognize the size and morphology of the exfoliated cuticle cells. Sometimes it is referred to ‘‘template’’ to describe this role of DES. Pictorial imagination for the dual functionalized DNA hybrid material [52]. After hair treatment with DES. apart from the role as reaction media which will be discussed later in details. DES type Type of dispersed nanomaterial Dispersion purpose Remarks & details Ref. To give a clear example. In fact. it was clearly seen that cuticle cells were completely exfoliated from hair. The study involved also DNA stability in the hybrid material and applications were suggested in biosensing and biomedicine fields. this process was called ‘‘exfoliation’’ or ‘‘split’’ of nanomaterials. which positively affected electrical volume resistivity of epoxy composites Poor dispersion stability in DES was reported for P-MWCNTs while it was very high for OMWCNTs (1 year) [85] Type of salt (component 1) Type of HBD (component 2) Molar ratio (Salt:HBD) ChCl Acrylic acid 2. / Chemical Engineering Journal 273 (2015) 551–567 Table 6 Examples of the use of DESs as efficient dispersants. size and morphology is investigated. The DES was used as a media and catalyst for furfuryl alcohol condensation. multi graphene layers need to be rolled and MWCNT is formed [56].556 A.1. DES is polymerizable solvent helped to disperse substances and incorporate carbon nanotubes The composite has great potential in biomedicine.3:1 MWCNT Synthesis of macroporous poly(acrylic acid)–CNT composites ChCl Ethylene glycol 1:2 SiC and Al2O3 nanoparticles ChCl Tris(hydroxymethyl)propane 1:1 Graphite nanoplatelets (GNP) ChCl Urea 1:2 Pristine MWCNTs (P-MWCNTs) and oxidized MWCNTs (O-MWCNTs) Electrodeposition of Ag and formation of Ag/ SiC/Al2O3 nanocomposite film DES as epoxy resin curing agent to fabricate GNP/DES/ epoxy resin nanocomposite Electrodeposition of Ni/ MWCNT composites on copper substrate (coating) Fig. IL and DES natures were found to play a crucial role in determining the size and morphology of the produced nanomaterials. TEM images proved the presence of macrofibrils nano-rods with a diameter of around 200 nm which may be existed due to ‘‘unraveling’’ of cortical cells to their nano-structural components under the DES effect especially in protein denaturing. High pure DES was successfully recycled and reused for solubilization following the same method. In this study. SEM results showed that before DES treatment a typical hair was observed with around 50 lm diameter and some cuticle cells about 5 lm size were covering the hair surface.3. DESs are holding some similar properties with IL and thus play the same role that could be played by ILs in some area of applications. a study was conducted recently regarding the ability of DES for DNA solubilization. [58] reported the functions of DES based on ChCl and para-toluene sulfonic acid (1:1 M ratio) in a process to prepare a porous carbon. Gutiérrez et al. In addition to that. Some micro-structures are in fact a group of bundled particles in nano-size but they are stuck together in somehow to form larger structures. 3. Media to obtain special sizes and morphologies of nanomaterials The role of ILs and DESs as morphology directing agents for the produced materials was frequently investigated in various studies when they are included in the reaction media.55]. Later. TEM images detected small particles in large numbers with a granular morphology which are probably melanin pigments of hair cells. Hence. However. What is more. respectively). is a multi-layer graphene sheets with a much larger overall external dimension [54. If the graphene sheets are rolled to form cylindrical shape. A recent study done by Boulos and co-workers [57] revealed the transformation of human hair into ‘‘functional nano-dimensional material’’ using ChCl:Urea DES (2:1 M ratio. hybrid material was obtained with antibacterial and magnetic properties see Fig. Media to split nanomaterials The hallmark of nanomaterials is to have in the number size distribution at least 50% of particles with one or more external dimensions in nano size (i. CNTs will be formed.6:1 1. it seems that the door of applying DESs to split or exfoliate small-sized materials has just been opened. Eventually and after 6 h.1.2. Mondal et al. Changes might take place either during the production reaction or after reaction for dispersing purposes in colloidal applications. rolling one graphene sheet layer leads to SWCNTs but to have seamless cylinders of more layers. In this section. Graphite for example. many researches have been conducted to find out how we could unbundle the bulky aggregation of materials to reach their smallest possible formula. [52] investigated the suitability of using DES for dual functionalization of DNA (Salmon testes). 2. corrosion-resistant functionalized surfaces. (4) sonochemically (using ultrasound technique). salts and hydroxides in DESs gives them bonus prominence over conventional electrolytes based on aqueous solutions or organic solvents [26]. However. composition and conditions. 95%. high solubility of metal oxides. However. in some cases they were also used as reactants to produce the intended nanoparticles. positive metallic ions of the electrolyte are reduced at cathode electrode and form neutral metal particles deposited on the surface.76 107 mol L1. MWCNTs modified graphite electrode was used as a working electrode in a three-electrode system with platinum and saturated calomel as auxiliary and reference electrodes respectively. (6) by gasphase synthesis using sputtering.2. batteries. namely 2-aminopyridine. They obtained a good linear relationship between quercetin concentration in the electrolyte and the oxidation peak current within concentration range from 9.5. it is clear that ChCl:Urea based DES have been used mostly for chemical syntheses of nanomaterials especially metal oxide nanoparticles.2. Simply in this process. Researchers found that the used DES acted also as ‘‘structure-directing agent’’ for the produced carbons. microwave assisted synthesis and physical vapor deposition (PVD). type of nanomaterial produced. DES has helped not only to recover the catalyst nanoparticles (kept same efficiency for 6 times) but also it played a catalytic role because of its acidity. 2. Eventually. physical sputtering deposition has been shown to offer a clean strategy for forming NPs on solvent surface with low vapor pressure such as ILs and DESs. In 2014. dimethyl formamide as well as some types of DESs. ChCl:Urea based DES have taken the first place in this respect regarding the number of studies it is involved in. [63] used a mixture of PH 4. The optimum catalytic system achieved was based on CuFeO2 nanoparticles in a eutectic solvent of citric acid-dimethyl urea melt (1:1. ILs electrolytes are becoming very popular in electrochemistry applications in general and when nanomaterials are accompanied in particular. This section illustrates the recent applications of DESs as solvents or liquid media in nano-synthetic chemistry and electrochemistry. 2. / Chemical Engineering Journal 273 (2015) 551–567 carbon monoliths including MWCNTs. Reactions were first run using various solvents as a part of the catalytic system such as toluene. In fact.95 107 to 4.3. Oh et al. All available examples for this case are described in Table 8. As mentioned earlier. Electrolytes for nanomaterial electrodeposition Electrodeposition is a process leading to the formation of solid materials by electrochemical reactions in a liquid phase. capacitors. only a single study was reported so far for DES use in electrochemical sensing. . ethanol. developing the magnetic properties of materials and building up functional components for electronic industries such as circuit boards. DESs were not only used as solvents. Reaction media for nanomaterial production When using ILs as solvents. All aspects of DESs in chemical synthesis of nanomaterials are summarized in Table 7 as shown below. All these systems need of course highly specified requirements from every involved component to be serving properly. Zheng et al.A. a counter electrode or anode and a reference electrode [66]). reaction method.2. This was explained by the highly dependency of the DES properties on temperature. [49] used a DES of ChCl and malonic acid as both a reaction medium and structure-directing agent to synthesize highly monodisperse gold microparticles. Abo-Hamad et al. DESs have been successfully used as electrolytes and in similar techniques used for ILs beforehand. (3) photochemically. Applications of metal electrodeposition technique include photoactive semiconductors. Lu and coworkers [64] have developed a recyclable efficient nano-catalytic system to be used for the reaction. This DES was the most common electrolyte especially for platinum and palladium electrodeposition. Different structures were obtained at different temperatures (At 70 °C. Media for sputter deposition to produce nanoparticles There are several effective synthesis methods for nanoparticles such as chemical synthesis. 2. (2) 557 electrochemically. Passivation phenomenon is one of the basic problems inhibiting the deposition progress as a result of poor electrolytic solvation ability toward metal oxides and hydroxides. With a setup of two or three electrodes. aldehydes and alkynes. In this table.1. according to this study. ChCl:ethylene glycol based DES have come in the second place with most interests shown for Ni nanostructures compounds electrodeposition. isotropic small particles with almost 100 nm diameter. nanomaterial production can be achieved in many different ways: (1) chemically. Copper salts along with different metallic oxides nanoparticles were subjected to testify their catalytic efficiency.1. Each one is described through: type of DES. the use of ILs as elements in electrochemical devices has been well identified. suggesting that the DES has essential role as a structure directing reagent and particle stabilizer. Media to produce efficient and recyclable nano-catalytic assembly For the synthesis of Imidazo[1. 2.1. 2. Solvents and reactants for the physicochemical synthesis of nanomaterials ILs were accompanied with the field of reaction chemistry through the use of chloroaluminate(III) ILs. whilst three-dimensionally networked nanostructures were obtained at 90 °C). the system of citric acid–dimethylurea–CuFeO2 nanoparticles was selected based on the best resulted yield. The product had a distinctive surface nanoroughness and highly defined diameters controlled precisely under different reductive conditions.0 acetate buffer solution with a ChCl:Urea DES (1:2 M ration respectively) as an electrolyte for the electrochemical sensing of quercetin. actuators. solar and fuel cells [59–62]. During 1990s. DES segregations were found to be responsible for forming macroporous network during polycondensation. In fact. In this respect they played multiple roles as a solvent and precursor at the same time.2-a]pyridines.4. This catalytic assembly was then used for the further optimization of reaction time and temperature.2. (5) by microwave irradiation. The study involved a series of reactions using three-based components as reactants. 2. Electrolytes for electrochemical systems with nanostructured electrodes Many studies have covered the use of ILs as electrolytes in electrochemical systems such as sensors.2. The most popular electrodeposition setup is composed of a three-electrode electrochemical cell (a specially designed cathode. While.5 M ratio). This method was found much easier and less expensive than the IL/ CNTs composite modified electrodes system used for the same purpose. A direct current method with a two-electrode system can also be used for nanoparticle electrodeposition. ‘‘neutral’’ ILs were developed and a wide range of reactions were performed and spread rapidly [65]. The synthesis was not supported by any surfactants or polymers. DESs have been widely used as electrolytes to produce nanoparticles electrochemically. (7) or by plasma electrolysis [45]. DESs are classified as a type of green solvent with many prominent advantages for chemical synthesis of nanomaterials in many references. 4H2O were added to 15.L1) 1st Step: solutions preparation Sol 1: 40 mg GO + 100 ml DES Sol 2: 2. Reaction medium and composition Reaction type Remarks/conditions Ref.6H2O + 1.2 mol) of ChCl + 24.9134 g) thioacetamide + 12 ml from solvent Sol 2: (12 mmol.6H2O For Ni(NH3)Cl2 and nanosheet-like NiCl: 0.3:1 2.3H2O were added separately into DES Frontal polymerization process At 130 °C [85] Homogeneous precipitation Coordination of Fe(CN)-4 6 ion with Fe3+ ion in the DES Co-precipitation At room temperature (25 ± 3 °C) [124] At 80 °C [118] 1st Step: 600 rpm and 80 °C for 20 min 2nd Step: 600 rpm and 80 °C for 1.2232 g) CuCl2.25 g SnCl2.H2O 85% (slowly) FeCl3.20 g) furfuryl alcohol (FA) (14 mL) DES containing polyvinylpyrrolidone PVP + (2. 5. Abo-Hamad et al.05 M of SnCl2.7 mmol) of KOH to the mixture 1st Step: solvent Preparation (6 mL) deionized water + 30 ml DES 2nd Step: Preparation of solutions: Sol 1: (12 mmol.3:1 1:2 ChCl 1.1 mol. the resulting solution was vortexed for 2 min and treated thermally (first at 37 °C for 8 h and then at 90 °C for 4 days) The resulted condensed FA polymers treated for 4 h at 210 °C followed by another 4 h at 800 °C (1. nanoflower-like NiO Nickel phosphide nano-particles Ni2P (25%) supported on amorphous and mesoporous Ni3(PO4)2-Ni2P2O7 Hierarchical porous MWCNT composites ChCl Urea 1:2 CuCl nanoparticles ChCl Ethylene glycol 1:2 SnO2/reduced graphene oxide nanocomposite SnO2 nanocrystalline Prussian blue nanospheres 1st Step: 2.613 g (46.94 g (0.0:1 1.01.02 g (0.3754 g) ascorbic acid + (50 mL) hydrochloric acid (0.2H2O in DES + 4 ml of H4N2. / Chemical Engineering Journal 273 (2015) 551–567 Nanomaterial produced .05 g respectively) + (1. during which the solution turned black from light green with violently release of gases (as bubbles) for 5 h The suspension (DES + CNT) was stirred for 24 h at room temperature before addition of FA polycondensation and carbonization: FA + (DES + CNT) suspension. 0.DES type 558 Table 7 Chemical and physicochemical nanomaterials production by the means of DESs as reaction media.92 g (0.6H2O and 1.6:1 1.1 M NiCl2 in DES 27.585 g of DES 2nd Step: adding 2.0 g) DES + (0.6H2O and K4Fe(CN)6. 0.2H2O + (1.02 mol) of NH4H2PO2 functionalized MWCNTs (0.03 and 0.2H2O + 100 ml DES 2nd Step: mixing sol 1 + sol 2 furfuryl alcohol (FA) condensation catalyzed by a protic DES Oxidation– reduction reaction Oxidation– reduction reaction between Sn2+ and graphene oxide [58] [112] A.02 mol) of Ni(H2PO)2.0 °C min1 heating ramp) under a N2 atmosphere Reaction time is 1 h.164 g (8 mmol) of FeCl3. Macroporous poly(acrylic acid)–CNT composites DES with ethylene glycol dimethacrylate (EGDMA) as crosslinker and benzoyl peroxide as a thermal initiator 100 ml 0. reaction temperature is 25 °C in the presence of polyvinylpyrrolidone (PVP) in DES [69] 2nd Step: ultrasonically (200 W) for about 4 h [125] Salt HBD Molar ratio (Salt:HBD) ChCl Acrylic acid ChCl Ethylene glycol 2.194 g (6 mmol) of ground FeCl2.3206 g) lead(IV) acetate + 12 ml solvent 3rd Step: mixing Sol 1 + Sol 2 DES + NiCl2.4 mol) of urea + 5.5 h [111] Combining the Pb2+ and S2precursors in hot DES 1st Step: stirring at 80 °C 2nd step: stirring both of solutions in an oil bath at 80 °C until transparent 3rd Step: using a flask with a condenser to mixing at 140 °C till the solution turns black [115] Ionothermal strategy For Ni(NH3)Cl2 and nanosheet-like NiCl: Teflon autoclave 150 °C for 4 h For Ni(NH3)Cl2 and nanosheet-like NiCl: heated under ambient atmospheric pressure [94] Ionothermal strategy At 323 K in N2 for 30 min then 423 K.5 M NiCl2 in DES For nanoflower-like a-Ni(OH)2 and nanoflower-like NiO: 0.3-Dimethyl urea ChCl Urea 1:2 Spherical Fe3O4 magnetic nanoparticles ChCl Urea 1:2 PbS nano/micro superstructures ChCl Urea 1:2 ChCl Urea 1:2 ChCl para-Toluene sulfonic acid 1:1 Nanostructured Ni compounds: nanocrystals Ni(NH3)6Cl2nanosheetlike NiCl2nanoflower-like aNi(OH)2mesoporous.66 g (0. Abo-Hamad et al.1 M CoCl2/DES in a three neck flask. for 40 min under magnetic stirring Followed by adding 100 mL deionized water with vigorous stirring for 1 min Then cooling rapidly with ice [114] [49] [75] [71] A.01% (w/v) + 15 mg gum Arabic + (0.05 g) + HAuCl44H2O (0.1 M Co+2 and 0.addition 50 mL of Co+2.Fe+3/DES in a round-bottom flask.15 M) HAuCl4 + 20 mL of DES + 200lL of (0. and 210 °C. green antisolvent approach Salt HBD Molar ratio (Salt:HBD) ChCl Thiourea ChCl At 100 °C with a heating rate of 5 °C. After another 20 min reaction.25 gum Arabic coated gold nanoparticles ChCl Urea 1:2 Mesoporous NiO ChCl Malonic acid 1:1 Gold Microstructures with Surface Nanoroughness 200lL (0.1 M CoCl2 in DES Ionothermal strategy Reduction of HAuCl4 by ascorbic acid Ionothermal strategy 40 mL of 0. 1:2 a-chitin nanofibers Solvation Stirring at 500 rpm at 100 °C for 2 h [86] Ethylene glycol 1:2 Nanoporous Ag film DES with 10%.1 M AgCl in DES Urea 1:2 Gold Nanoparticles 25 mL DES + L-ascorbic acid (0.Table 7 (continued) DES type Nanomaterial produced Reaction medium and composition Reaction type Remarks/conditions Ref.2H2O was dispersed in 100 ml DES 1st step: 0.035 M Fe+3 in DES from CoCl26H2O and FeCl36H2O Ionothermal strategy ChCl Urea 1:2 Mesoporous Co3O4 sheets or nanoparticles 0. vigorous stirring for 30 min [116] Reduction of HAuCl4 by DES Continuous stirring under ambient conditions [129] Homogeneous precipitation 50 mL 0.min1 under vigorous stirring At 70 °C water bath.36 g of ZnO powder + 150 g of DES 2nd step: bad solvent preparationequal volumes of deionized water and ethylene glycol 3rd step: 5 mL of ZnO-containing DES was injected into 160 mL of the bad solvent Aqueous solution of DES 0.01 or 0. 180.015 g) At room temperature 22 (±2 °C) or at 50 °C.05 M) HAuCl4 in different volumes 0. under magnetic stirring 2nd step: annealing the resulted Ni LDH under Ar atmosphere at 300 °C for 4 h with and without OCN.1 M NiCl2/DES in a three-neck flask under ambient atmosphere pressure at 150 °C for 40 min.1 M NiCl2 in DES Ionothermal strategy ChCl Urea 1:2 Co Fe layered double hydroxide (CoFe LDH) nanosheets 0.1 M NiCl2 in DES 2+ [113] [72] [73] (continued on next page) 559 . under ambient atmospheric pressure Followed by adding 40 mL deionized water with vigorous stirring for 10 min Then cooling rapidly with ice 1st step: 50 mL of 0. w/w Pure chitin powder then adding 10 mL of distilled water 0.1 M FeCl36H2O in DES ChCl Urea 1:2 Ni layered double hydroxide (Ni LDH) as a-Ni(OH)2 nanoflowerNi nanoparticlesNi mesoporous flowerlike structure 0. by immersing a cleaned copper alloy foils into AgClDES solution without stirring At 30 °C. cooling in ice bath Stirring for 3 h at 50 °C [117] Urea 1:2 Cu -doped ZnO nanocrystals ChCl Gallic acid: glycerol 1:0.1 M) ascorbic acid ChCl Urea 1:2 Fe2O3 nanospindles 0. at 210 ± 5 °C. / Chemical Engineering Journal 273 (2015) 551–567 ChCl 2. at 150.25 g SnCl2. under magnetic stirring Followed by adding deionized water Then cooling rapidly with ice 50 mL of 0. Followed by adding 10 mL deionized water under vigorous magnetic stirring. at 150 ± 5 °C. at 200 °C.25:0.1 M FeCl36H2O/DES in a three neck flask. under magnetic agitating [126] ChCl ChCl Urea 1:2 nano-sized SnO crystals Galvanic replacement reaction Reduction of HAuCl4 by Lascorbic acid Ionothermal strategy Facile.1 M NiCl2/DES in a three neck flask. 2) Ethylene glycol ChCl 1:2 Ni–P alloy nanoparticles Ionothermal strategy and facile thermal conversion process Urea ChCl 1:2 MnCO3 mesocrystals nanowire-like MnOx 0. Congo red) from water. and drying under vacuum Ref. cheap and convenient alternative to conventional solvents. [69] produced Ni2P nanoparticles supported on mesoporous and amorphous Ni3(PO4)2–Ni2P2O7 using ChCl:Urea based DES as media for ionothermal reaction. advantages and challenges From previous examples. These nanomaterials can be used as potential energy storage electrodes [71–73]. however. They provide a platform to serve the several physicochemical reaction types perfectly such as ionothermal reaction. size and morphology seemed to be controllable which considered as important to reach the required efficiency in advanced application.4H2O Remarks/conditions Reaction type Reaction medium and composition Nanomaterial produced Molar ratio (Salt:HBD) HBD Salt DES type Table 7 (continued) [74] A. More surprisingly. The benefits of DESs exceeded being safe. DES-based nano production: an overview about applications. Abo-Hamad et al.1st step: 50 ml of 0. Ionothermal strategy A mixture of NiCl26H2O and NaH2PO2H2O in DES. Nanostructured materials obtained ionothermally using DES media were found highly valuable in various application. the same group [68] aimed in other work to estimate the effect of sputtering time on the structure parameters and to evaluate the growth mechanisms of the AuNPs.g. soft-sputtering deposition technique under very clean conditions in a vacuum chamber. This low-energy deposition technique allowed synthesizing AuNPs either directly or in a sequential way with diameters over a wide range from 1 to 100 nm. the number density of AuNPs increased linearly and a very pronounced 1st and 2nd shell ordering was observed. For shorter gold-sputtering times of 30 s the gold atoms started to aggregate on the surface. at 150 °C. Produced nanostructured system showed catalytic activity for hydrodesulfurization of dibenzothiophene. Later on. Anode materials with nanostructures for application in lithium ion batteries can be synthesized from DESs. precipitation. centrifuging and drying 2nd step: annealing the MnCO3 at 300 °C for 4 h then gradual cooling process to room temperature 50 ml of reaction solution in DES in a three neck flask.5 M MnCl2/DES in autoclave at 120. aCo(OH)2 and FeCo LDH) and the derived metal oxides can be ionothermally synthesized from DES based reaction system. which are demonstrated as effective and efficient adsorbents to remove organic waste (e. Their role to determine shape. molar ratios (1:0. Production of nanostructured catalysts for example is still a challenge requiring the efforts to adjust their synthesis conditions. / Chemical Engineering Journal 273 (2015) 551–567 [70] 560 Raghuwanshi et al.4. 2. 150. for 3 h Cooling down to room temperature then centrifuging the precipitate accompanied by washing with deionized water and methanol. ChCl and urea). The self-assembly mechanism was explained by the templating nature of DES combined with the equilibrium between specific physical interaction forces between the AuNPs. polymerization. [67] reported the formation and growth mechanisms of gold nanoparticles (AuNPs) in eco-friendly deep eutectic solvents (DES. for 4 h Cooling down to room temperature then washing the MnCO3 precipitates with methanol and water and ethanol. DESs have shown a versatility to be used in different reaction methods. They managed to establish a deep understanding of the time dependent growth and the stability of AuNPs with respect to the effect of ionic liquids as surrounding environments. and 180 °C. For extended sputtering times. condensation and reduction–oxidation reactions including replacement reactions. see Fig. Data analysis revealed that for a prolonged gold-sputtering time there was no change in the size of the particles. Zhao et al. The porous and nanowire-like MnOx nanostructures can be obtained through a facile thermal conversion process from the diverse MnCO3 precursors. Gold nanoparticles were formed in DES by using a low-energy. 4.5 nm.5 M Mn+2 in DES from MnCl2. hydrodenitrogenation of quinoline and hydrogenation of tetralin. After dispersion into the bulk they self-organized into closed-packed ordered domains (clusters of AuNPs). Ionothermal method in ChCl:Urea media can also fabricate calcite type MnCO3 biominerals with mesocrystal structure [70]. prolongation of gold-sputtering time led to an increase in the concentration of gold atoms on the DES surface.2. Layered double hydroxides (LDHs) such as (a-Ni(OH)2. Only the concentration of AuNPs increased linearly in time. The results showed formation of spherical nanoparticles with a mean diameter of 5–0. Amorphous and . the self-assembly of AuNPs into a first and second shell ordered system was observed directly by in situ SAXS for prolonged goldsputtering times. 0 V are adopted for the RVM 1. two-electrode system ChCl Ethylene glycol 1:2 ChCl Ethylene glycol 1:2 ChCl Urea 1:2 DES containing 0. three-electrode system (a) constant voltage mode (CVM).1 and 0. potential (1. (b) pulse voltage mode (PVM).3 mM H2PtCl6 DESs solution Pt nanoflowers Pt wire Glassy carbon disk (GC.Upos = 1. DES type Electrolyte composition Electrochemical cell information Anode (counter electrode) Cathode (working electrode) ChCl/urea/PdCl2 Nano-sized Pd film Pd sheet Rotating Cu substrate 1:2 19. and (c) reverse pulse voltage mode (RVM).3 mM H2PtCl6/DESs Nanostructured NiO films Ni plate Nanocrystalline Ni film Samarium and cobalt SmCo Nanostructures Electrolytic Ni plate Pt spiral Brass foil (Cu0.5 to 0.3 mM H2PtCl6 DESs solution Triambic icosahedral (TIH) Pt nanocrystals (TIH Pt NCs) Pt wire Glassy carbon (GC) Pt Programmed electrodeposition routine – three electrode system ChCl ChCl Urea Ethylene glycol 1:2 1:2 Platinum 1 mm or 2 mm diameter.5 cm2 ChCl Urea 1:2 HBD Molar ratio (Salt:HBD) ChCl Urea 1:2 ChCl Urea ChCl 19. U = 3 mm) Reference electrode Electrodeposition method Electrodeposition conditions & remarks Ref. two-electrode system ChCl Ethylene glycol 1:2 Mixture of either Al2O3 (50 nm) or silicon carbide (50 nm or 2 mm) with DES Iridium oxide coated Ti mesh Ni substrate Constant potential difference. Upos = 1.2 V. trev = 1 s. the electrochemical potential was firstly stepped from open circuit potential (OCP) to nucleation potential (EN) of –1. at various scan rates: 10 to 50 mV s1 under diffusion control at applied potentials of either 0.30 V. two-electrode system Ag|AgCl/ NaCl 3 M mounted in a Luggin capillary containing the DES solvent Pt quasireference electrode [82] [121] A.30 V. 0.6 V.1 MH2O2 DES containing 1 M NiCl26H2O DES containing 0. three-electrode system At 25 ± 3 °C. two-electrode system Cyclic voltammetry (CV). potential scan range: 1.3 M NiCl26H2O Ag nanocomposites with nanoalumina particles or SiC nanoparticles Nanostructured NiO films Ni plate Direct current (DC).018 M CoCl2 indium tin oxide (ITO) glass with 3 cm 2. and this potential was maintained for 1 s to generate Pt nuclei.36 alloy) Potential step chronoamperometry. and Uneg = 1. threeelectrode system At 80 °C.30 and 0.0 V) [120] Direct current (DC).64Zn0. two-electrode system Cyclic voltammetry (CV). Uneg = 1.1 M KMnO4 and 0.05. copper and nanoporous alumina templates (50 nm porous diameter) Pt Nanocrystals Pt wire Glassy carbon disk (GC.80 V or 1.0 V.045 M SmCl3 + 0.0 V.Table 8 DES-based electrolytes for nanoparticles electrodeposition.29 V At 80 °C. 0. 50 mV s1. (a) Constant voltage mode (CVM). Upos = 1. The applied current density for DC plating j = 0.6 V (negative-going sweep) [122] Programmed electrodeposition method.30 and 0. Applying direct current (DC) or pulse current plating (PP).2 mA cm2 and for PP plating jav = 0. (c) reverse pulse voltage mode (RVM).36 alloy) Vitreous carbon rods.0 Vtfwd = 2 s. for 60 min At 70 °C. three-electrode system At 70 ± °C. respectively [84] Direct current (DC). Upos = 1.2 V was applied between the working and counter electrodes using a 12 V power supply [106] [83] [107] [76] [119] At 35 ± 3 °C.0 V.0 V.00 V At 90 °C. / Chemical Engineering Journal 273 (2015) 551–567 Nanomaterial produced Salt [108] (continued on next page) 561 .0 V) electrodeposition duration 10 s.1 M [CuCl2 2H2O] in DES with 10 wt% 0.3 M NiCl26H2O. electrodeposition starts from 1. and then stayed at EN for 45s to generate Pt nuclei on the GC electrode surface.80 V (vs. electrodeposition occurs at 1. twoelectrode system ChCl Ethylene glycol 1:2 DES containing 0. 30 s and 60 s for Ni film At 70.0 V. at constant potential (1. scan rate of 50 mV s1 and 80 cycles. The development of the Pt nuclei into TIH Pt NCs was achieved by applying a square-wave potential (f = 10 Hz) with the lower (EL) and upper (EU) potentials of –1. working voltage: 1. The growth of the Pt nuclei into concave tetrahexahedral (THH) Pt NCs was achieved by applying a square-wave potential (f = 10 Hz) with the lower (EL) and upper (EU) potential limits of 1. Ø 3 mm) Pt quasireference electrode Urea 1:2 19. potential step from 1.5 cm ITO glass of 3 2. plating time 90 min.1 mA cm2 At 80 °C. (b) pulse voltage mode (PVM). made in-house Ag wire quasireference electrode Ethylene glycol 1:2 Nano-structured Cu (bright metallic coatings) Nanostructured Ni films Pt ChCl 0.05 mm Al2O3 or 10 wt% 1–3 mm SiC 1 M NiCl26H2O in DES Electrolytic Ni plate Brass (Cu0. 80 and 90 °C.64Zn0.20 V (vs Pt) to 1. Pt).50 V. respectively At 20 ± 2 °C. electrodeposition starts from 1. Abo-Hamad et al. 30 M NiCl26H2O– 0. 1.5 and 44.5 mm) diameter FOR Au: gold wire (0.03 mm Direct current (DC). two-electrode system ChCl Urea 1:2 Nanostructured Zn–Ni–P alloy film Ni Cu plate 20 50 mm Ag quasireference electrode Three-electrode system ChCl Ethylene glycol 1:2 Nanostructured Ni–P alloy film Ni Brass (Cu–Zn alloy) Ag quasireference electrode Cyclic voltammetry (CV). The temperature was kept at 70 °C The DES medium was kept under constant magnetic stirring in an electrochemical cell of 10 ml capacity. in an open beaker.562 Table 8 (continued) DES type Electrolyte composition HBD Molar ratio (Salt:HBD) ChCl Urea 1:2 10 mM K2PdCl4 DES solution ChCl Urea 1:2 ChCl Chromium chloride CrCl36H2O ChCl Nanomaterial produced Electrochemical cell information Electrodeposition method Electrodeposition conditions & remarks Ref.1 M NiCl2–0.15 M NaBH4) as a reducing agent FOR Au: DES + (0. Ag and Pd FOR Ag: silver wire (0. 6 mA cm2 and 8 mA cm2 Varied metal contents were dependent on current density and electrolyte composition At 30 ± 2 °C starts at 0. Currents of no more than 0. three-electrode system [109] Ag quasireference electrode Galvanostatic. three-electrode system ChCl Ethylene glycol 1:2 Nanostructured Co–Sn alloy film Sn plate Cu foil (0. at 0. During the process.15 M NaH2PO2H2O DES containing 0.15 A were used The deposition current density was 3.g. NZ30 K) alloy ChCl/ChCl Urea/Ethylene glycol 1:2/1:2 Thin films of noble metallic nanoparticles such as Au.0 V and 1. 30 min–1 h FOR Au: at 50 °C.05 M NaH2PO2H2O (b) NiCl26H2O–0.3 M NiCl2 in DES + 0.4 V was applied during the growth pulse to minimize the size dispersion of the particles two different temperatures were used for each electrodeposition sequence: 32.1 M NH4H2PO2 DES containing: (a) 0.3 A cm2 for a duration of 20 min FOR Pd: at room temperature.1 M NiCl2–0.05 mm thickness) Ag wire Three-electrode system DES containing: (a) 0.2 V) and temperatures (75 °C and 25 °C) Electrodeposition times varied to obtain same electric quantity [77] [127] [110] [123] [80] [79] [78] A.7 V for 5 min (200–300 nm average size and 30–40 nm pore size) At 50 ± 2 °C current densities of 4 mA cm2.1 M NaH2PO2H2O (c) NiCl26H2O–0.0 mA/cm2 and deposition time was 60 min.520 V for electrolyte (a) 0. Ag/AgCl minireference electrode (eDAQ) Cyclic voltammetry (CV).1 M SnCl22H2O Nanoporous thin film of Sn Sn plate Cu foil 0. a mild gas evolution was seen at the cathode in DES medium.5 mm) diameter FOR Ag: Pt/Rh (or W) Wire FOR Au: gold disc 1 mm diameter Chronopotentiometric mode / two-electrode system / anodic dissolution technique ChCl Ethylene glycol 1:2 FOR Ag: DES + 4Mercapto phenyl boronic acid (MPBA.8 V).2Zn– 0.15 M NaBH4) as a reducing agent FOR Pd: DES DES containing 0.6 M NiCl26H2O Ni nanocrystalline Two parallel Ni plates CNT growing on substrates that include titanium nitride coated silicon chips or polished stainless steel Mg–3. FOR Ag: at 50 °C.1 M CoCl26H2O–0. Abo-Hamad et al.5 mm) diameter FOR Pd:Palladium wire (0. threeelectrode system To deposit as many particles as possible.4Zr (wt.1 g/L MWCNT Ni/MWCNT coating Ni 1 cm2 Cu plate 1:2 DES Nano-chromium magnetic domains Platinised Ti anode Two-electrode system Urea 1:2 DES containing 0. 1.05 M NH4H2PO2 or (b) 0. / Chemical Engineering Journal 273 (2015) 551–567 Salt .4 M ZnCl2–0.5 °C At 60 °C.4 M ZnCl2–0.600 V for electrolyte (c) [81] Anode (counter electrode) Cathode (working electrode) Reference electrode Pd nanoparticles Pt Glassy carbon foil 0. current density 1 A cm2 for 30 min At variable applied voltages and ambient temperature (25 ± 3 °C) without the deaeration process e.5 V.0Nd–0. current density 0.5 °C) was used (ca. galvanostatically at a current density of -2 mA/cm2 for 30 min and constant agitation using a magnetic stirrer (900 rpm) At 20 °C. for 2 min and at 0. A lower overpotential of 1. current density 14 mA cm2.05 M SnCl22H2O Galvanostatic method / two-electrode system At variable potentials (0. 5 mM) stabilizer and sodium borohydride (0. the approximate cathodic limit of the electrochemical window of the DES (at 32.%.8 V.550 V for electrolyte (b) 0. / Chemical Engineering Journal 273 (2015) 551–567 563 Fig. good cycle stability and rate performance for the produced electrode in lithium ion battery [75]. Fig. Special morphologies obtained were controllable by changing time. Crystal growth mechanism was studied most often in every ionothermal strategy. crystalline Ni–P nanoparticles were produced in (ChCl:Ethylene glycol) DES with core–shell structure. 5. The key factor was to adjust the dosage between chemical components dissolved in DESs. temperature as well as the applied potential. 4. Cryo-TEM micrographs of gold nanoparticles in DES synthesized by sputter deposition at 20 mA and 0. the environmental aspects of DESs after being employed were not assessed. This was reported for single metal coating (such as Ni [76]) and multi-ingredient coating (such as Ni/MWCNT composite [77]. current density. Co–Sn alloy [78]. This helped to study the various activities obtained and helped to identify the growth mechanism of the produced particles. Schematic illustration of the synthetic procedure for the core–shell structured Ni–P nanoparticles [74]. SEM images of the pure PVDF film (a) and the DES-NiCl2@PVDF film (b). Abo-Hamad et al. Applications of electrochemically produced nanomaterials were almost to fabricate protecting films with high enhanced corrosion resistance. Inset of (b) is the corresponding magnified SEM picture [93]. Catalytic activities of electrochemically produced nanoparticles were also a matter of study for different reactions [82–84].05 mbar (argon pressure). Fig. handling DESs after nanoparticles preparation. no generalization can be confirmed. . Fe2O3 nanospindles were also synthesized ionothermally in ChCl:U and showed a high capacity. 6 illustrates the core– shell procedure to obtain Ni–P nanoparticles [74]. Ni–P alloy [79]. Zn–Ni–P [80] and Mg–Nd– Zn–Zr alloy [81]). Fig. DES electrolytes have offered a flexibility to obtain several film compositions for different coating purposes.A. (a and a0 ) 300 s without stabilizer [68]. This clearly shows the need of environmental studies and studying the environmental impact of DESs. However. 7 summarizes some recent examples for the different mechanisms suggested for ionothermal production of nanostructures. Fig. As each reported study represented a unique reaction mechanism. 6. for instance. 564 A. . / Chemical Engineering Journal 273 (2015) 551–567 Fig. discharging them or using them in recycling processes.58.85. Schematic illustrations for some suggested mechanisms to produce nanostructured materials ionothermally. A few studies reported the successful recycling of DESs after using them as media to disperse and produce nanoparticles and nanocomposites [52.64.86]. Abo-Hamad et al. 7. O’Connor. Del Pópolo. The unique properties of DESs offer them some advantages to in comparison to ILs.K. Opin. De Oliveira Vigier. 202 (2008) 2033–2039. With an increasing size of SWCNTs diameter. Kontturi. physicochemically or electrochemically resembles those for ILs. Applications of nanosized DESs DESs have taken a wide interest since they have been discovered. Data 51 (2006) 1280–1282.L. physically. Rev. Electroanal. Surf. They are usually formed as crystalline or polymeric solid or as solutions of transition metal complexes including the solvent molecule as donor [92]. Ionic Liquids in Synthesis. This was utilized to fabricate a thermochromic poly(vinylidene fluoride) (PVDF) composite film by embedding DES–NiCl2 nanosized droplets in PVDF micropores (Fig. 99 (2014) 1–12.A. Although there have been huge efforts placed on studying ILs applications in nanotechnology. some positive features can be 565 added to DES use over ILs such as their easy preparation and being much eco-friendlier. Recently. and finally. Renew.S. Electrochim. Vainikka. Harris. Phys. However. M. Bahadori. B. Baker. Rev. Ullmann’s Encyclopedia of Industrial Chemistry. Characterisation and application of the Fe(II)/Fe(III) redox reaction in an ionic liquid analogue. L. Soc. Lloyd. Halambek.e. G. Confinement is the most reported case to study the physicochemical behavior of IL in nano-volumes. loading both SWCNTs and DES separately in H-type quartz tube. Abbott. Ryder. Capper. Boothby. Rev. Sust. Technol. Serrano. Abbott. K. F. Phys. V. Ryder.A. R.S. Low melting mixtures in organic synthesis – an alternative to ionic liquids?.D. Tambyrajah.L. These results and others aim to get further understanding of the structure and phase behavior of nano-confined DESs and improve their use in solar cells.and alcohol-functionalized task-specific ionic liquids: attractive properties and applications. [7] Ru. Ionic liquids in biotransformations: from proof-of-concept to emerging deep-eutectic-solvents. R. Dominguez de Maria. Jerome. G. K. Solubility of metal oxides in deep eutectic solvents based on choline chloride. some reports have emerged and revealed novel physicochemical properties of ILs and DESs which designed somehow to be in nano-scale dimensions. M. 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Conclusion This summarized the up-to-date studies of employing DESs in diverse nanotechnology areas. sealing the tube under vacuum (107 torr) and then mixing at 200 °C for 72 h. Abbott. 41 (2012) 4996–5014. Rasheed. Tang. Coat. the basic concern on nanomaterial properties is placed on the solid phase only. [16] S. [6] A. Hence. Investigations can be conducted not only by employing an already-known or famous DES in particular. Abo-Hamad et al. Novel choline-chloride-based deepeutectic-solvents with renewable hydrogen bond donors: levulinic acid and sugar-based polyols. Capper. C.T. Ether. Welton. G. Choline. C. Sustained electroless deposition of metallic silver from a choline chloride-based ionic liquid. Curr.C. Domínguez de María. D.P.C. (3) and as confinement by confining the IL in nano-sized spaces of nanomaterials such as the tubular space in CNT [89] or the narrow pores in nanoporous silica [90]. Davies.L. B 108 (2004) 1744–1752. Maugeri. 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