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High-performance energy-storage devices are receiving great interest in sustainable terms as a required complement to renewable energy sources to level out the imbalances between supply and demand. Besides electrode optimization, a primary objective is also the judicious design of high-performance electrolytes combining novel ionic liquids (ILs) and mixtures of aqueous solvents capable of offering “à la carte” properties. Herein, it is described the stoichiometric addition of a zwitterion such as betaine (BET) to protic ILs (PILs) such as those formed between methane sulfonic acid (MSAH) or p-toluenesulfonic acid (PTSAH) with ethanolamine (EOA). This addition resulted in the formation of zwitterionic-based PILs (ZPILs) containing the original anion and cation as well as the zwitterion. The ZPILs prepared in this work ([EOAH]+[BET][MSA]− and [EOAH]+[BET][PTSA]−) were liquid at room temperature even though the original PILs ([EOAH]+[MSA]− and [EOAH]+[PTSA]−) were not. Moreover, ZPILs exhibited a wide electrochemical stability window, up to 3.7 V vs. Ag wire for [EOAH]+[BET][MSA]− and 4.0 V vs. Ag wire for [EOAH]+[BET][PTSA]− at room temperature, and a high miscibility with both water and aqueous co-solvent (WcS) mixtures. In particular, “WcS-in-ZPIL” mixtures of [EOAH]+[BET][MSA]− in 2 H2O/ACN/DMSO provided specific capacitances of approximately 83 F g−1 at current densities of 1 A g−1, and capacity retentions of approximately 90 % after 6000 cycles when operating at a voltage of 2.0 V and a current density of 4 A g−1.

For many years, the performance of Li-ion batteries (LIBs) and supercapacitors (SCs) has relied mainly on two factors, (1) the optimization of electrodes composition and/or structure and (2) the selection of salts or ionic liquids (ILs) matching well with the compositional and/or structural features of electrodes. Solvents included in electrolyte composition have been typically seen as a mere medium where the electrochemically active salts or ILs are dissolved or mixed. More recently, attention has also been paid to specific issues, such as flammability, toxicity, electrical conductivity and/or electrochemical stability window (ESW). Recent reports describing water-in-salt (WIS), solvent-in-salt (SIS) and bi-solvent-in-salt (BSIS) electrolytes demonstrated that solvent molecules may indeed play a more active role in the achievement of high-performance LIBs and SCs. This work accomplished the design of a tri-solvent-in-salt (TSIS) electrolyte where every solvent contributed (with an IL such as EMIMBF4) to the formation of an electrochemically active hydrogen bond (HB) complex structure. Raman and NMR spectroscopies, as well as molecular dynamic (MD) simulations helped elucidate the ratio among all compounds (e.g., solvents and IL) in the HB complex structure that best works as an electrolyte. For instance, one could start from the eutectic mixture of H2O and dimethylsulfoxide (DMSO) in a 2 to 1 molar ratio and then add acetonitrile (CH3CN) in different molar ratios. Thus, the 2H2O:DMSO mixture offers low melting point and low flammability, and CH3CN provides an improvement of the rate capability to the resulting electrolyte. As compared to other electrolytes, the TSIS electrolyte composed of 1.5EMIMBF4:2H2O:DMSO:3.5CH3CN (5.8 m, TSIS-5.8) was cost efficient and exhibited self-extinction rates as low as 40 s g-1. Moreover, SCs operating with TSIS-5.8, at -70 °C and up to 2.7 V provided energy densities of ca. 49 and 18 Wh kg-1 at, respectively, power densities of 10,000 and 17,000 W kg-1, a capacitance retention of ca. 82% after 15,000 cycles at 4 A g-1 and a self-discharge as low as 22%.

[EN] Knitted iron phthalocyanine-based porous polymer networks (K-FePcs) were prepared in a single step using solvent-knitting strategies with commercial iron phthalocyanine as a building monomer. The incorporation of different aryl comonomers (biphenyl and 1,2,4,5-tetraphenylbenzene) to FePc allowed quantitative yields, high porosities, and excellent ORR activity. The reversible Fe(III)/Fe(II) redox potential of FeN4 centers of the knitted polymer networks in N2-saturated electrolyte solution (i.e., ∼0.8 V vs RHE) were shown as good descriptors of their ORR activity. K-FePc2Ph presented the highest amount of FeN4 active sites and an adequate degree of steric hindrance to maintain the isolation between catalytically active sites. Moreover, it displayed comparable current density limits and superior mass activity and half-wave potential (i.e., 0.88 V vs RHE) than those of 20% Pt/C benchmark catalyst, while keeping higher stability toward methanol oxidation. K-FePc2Ph can be an interesting alternative to Pt-based ORR electrocatalysts., The authors acknowledge MINECO of Spain MAT2017-82288-C2-2-P and RTI2018-097728-B-I00 projects for financial support. A.V.-G. thanks Ministerio de Educación y Formación Profesional for FPU17/03463. L.Z.G. also acknowledges the Chinese Scholarship Council for a PhD research fellowship (CSC no. 201608330266).

Water-in-salt (WIS) electrolytes are gaining increased interest as an alternative to conventional aqueous or organic ones. WIS electrolytes offer an interesting combination of safety, thanks to their aqueous character, and extended electrochemical stability window, thanks to the strong coordination between water molecules and ion salt. Nonetheless, cost, the tendency of salt precipitation, and sluggish ionic transfer leading to poor rate performance of devices are some intrinsic drawbacks of WIS electrolytes that yet need to be addressed for their technological implementation. It is worth noting that the absence of "free'' water molecules could also be achieved via the addition of a certain cosolvent capable of coordinating with water. This is the case of the eutectic mixture formed between DMSO and H2O with a molar ratio of 1:2 and a melting point as low as -140 °C. Interestingly, addition of salts at near-saturation conditions also resulted in an increase of the boiling point of the resulting solution. Herein, we used a eutectic mixture of DMSO and H2O for dissolution of LiTFSI in the 1.1-8.8 molality range. The resulting electrolyte (e.g., the so-called aqueous-eutectic-in-salt) exhibited excellent energy and power densities when operating in a supercapacitor cell over a wide range of extreme ambient temperatures, from as low as -35 °C to as high as +65 °C.

Deep eutectic solvents (DESs) resulting from the right combination between a hydrogen-bond donor (HBD) and a hydrogen-bond acceptor (HBA) are becoming quite popular in number of applications. More recently, natural DESs (NADESs) containing sugars, natural organic acids, and amino acids as HBDs and ChCl as HBA have received great attention because of their further environmental sustainability as compared to regular DESs. Within this context, mixing water in controlled amounts has been widely accepted as a simple and practical way of altering DES chemical and thermodynamic properties, with viscosity and conductivity experiencing the most significant changes. However, the number of papers describing eutectic mixtures with water as the only HBD is scarce and basically none has been done in fundamental terms. Herein, we investigated mixtures composed of water as the only HBD and ChCl as the HBA using differential scanning calorimetry (DSC) as well as

Neural tissue engineering approaches show increasing promise for the treatment of neural diseases including spinal cord injury, for which an efficient therapy is still missing. Encouraged by both positive findings on the interaction of carbon nanomaterials such as graphene with neural components and the necessity of more efficient guidance structures for neural repair, we herein study the potential of reduced graphene oxide (rGO) microfibers as substrates for neural growth in the injured central neural tissue. Compact, bendable, and conductive fibers are obtained. When coated with neural adhesive molecules (poly-L-lysine and N-cadherin), these microfibers behave as supportive substrates of highly interconnected cultures composed of neurons and glial cells for up to 21 days. Synaptic contacts close to rGO are identified. Interestingly, the colonization by meningeal fibroblasts is dramatically hindered by N-cadherin coating. Finally, in vivo studies reveal the feasible implantation of these rGO microfibers as a guidance platform in the injured rat spinal cord, without evident signs of subacute local toxicity. These positive findings boost further investigation at longer implantation times to prove the utility of these substrates as components of advanced therapies for enhancing repair in the damaged central neural tissue including the injured spinal cord., This work was supported by the Instituto de Salud Carlos III-MINECO-FEDER (CP13/00060), the Ministerio de Economía y Competitividad, and the Fondo Europeo de Desarrollo Regional (MAT2016-78857-R and MAT2015-68639-R, MINECO/FEDER, UE). It was also partially funded by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 737116.

The elimination of small amounts of water from alcohols is by no means a trivial issue in many practical applications like, for instance, the dehumidification of biocombustibles. The use of carbonaceous materials as sorbents has been far less explored than that of other materials because their hydrophobic character has typically limited their water uptake. Herein, we designed a synthetic process based on the use of eutectic mixtures that allowed the homogeneous dispersion of graphene oxide (GO) in the liquid containing the carbon precursor, e.g., furfuryl alcohol. Thus, after polymerization and a subsequent carbonization process, we were able to obtain porous carbon–GO composites where the combination of pore diameter and surface hydrophilicity provided a remarkable capacity for water uptake but extremely low methanol and ethanol uptake along the entire range of relative pressures evaluated in this work. Both the neat water uptake and the uptake difference between water and either methanol or ethanol of our carbon–GO composites were similar or eventually better than the uptake previously reported for other materials, also exhibiting preferential water-to-alcohol adsorption, e.g., porous coordination polymers, metal–organic frameworks, polyoxometalates, and covalent two-dimensional nanosheets embedded in a polymer matrix. Moreover, water versus alcohol uptake was particularly remarkable at low partial pressures in our carbon–GO composites. This work was supported by MINECO/FEDER (Project Numbers MAT2015-68639-R, MAT2016-80285-P, and RTI2018-097728-B-I00). L.Z.G. acknowledges the Chinese Scholarship Council for a PhD research fellowship (CSC No. 201608330266). C.C.-C. acknowledges UA for a research contract.

Vortex ring (VR) processes have proved highly effective in tailoring the morphology/shape of particles prepared from nanoclays, silica nanocolloids, magnetic nanoparticles and different polysaccharides. Herein, we have prepared toroidal-, teardrop-, jellyfish-, and cap-shaped vortex ring particles by drip- ping an aqueous suspension of graphene oxide (GO) into a cetyl trimethylammonium bromide (CTAB) aqueous solution that played the role of coagulating agent. Interestingly, the GO suspension exhibited liquid crystalline features. We demonstrated how controlling the drop impact force against the liquid surface was critical to produce VR particles with such intriguing shapes. With the purpose of controlling the drop impact force, we studied the drop density/viscosity, the speed at which the drop impacts the surface of the liquid pool and the surface tension of the CTAB solution. Finally, we also demonstrated the antibacterial activity of the resulting GO-based VR particles against Escherichia coli and Bacillus subtilis, and discussed about the origin of such a behaviour. In particular, we investigated the occurrence of (1) membrane damage by physical contact between GO and bacteria, (2) GO-induced oxidative stress, or (3) CTAB released into the bacteria culture, the antiseptic and disinfectant action of which may ultimately kill bacteria., This work was supported by MINECO/FEDER (Project Numbers MAT2015-68639-R and BIO2015-66203-P). L. Z. Guan also acknowledges Chinese Scholarship Council for a PhD research fellowship.

Deep eutectic solvents (DESs) and dilutions thereof (mainly in H2O but also in many other non-aqueous solvents and co-solvent mixtures) have recently attracted great attention. It is well known that DES dilutions exhibit deviations from ideality. Interestingly, the treatment of DES as a mixture of two components or a pseudo-component is by no means trivial when determining deviations in density and, mainly, in viscosity. Herein, we studied aqueous dilutions of one of the most widely studied DES, this is, that composed of choline chloride and urea in a 1:2 molar ratio (e.g., ChCl2U). Using density and viscosity data reported in previous works, we calculated the excess molar volumes (VE) and excess viscosities (ln ηE) considering ChCl2U as either a mixture of two components or a pseudo-component, that is, taking the DES molecular weight as MChCl2U = fChClMChCl + fUMU = 86.58 g mol−1 (with fChCl = 1/3 and fU = 2/3) or as M*ChCl2U = MChCl + 2 MU = 259.74 g mol−1. We found that neither the sign of VE and VE* nor their evolution with temperature was influenced by the use of either MChCl2U or M*ChCl2U, and only the absolute magnitude of the deviation and the DES content (in wt. %) at which the minimum appears exhibited some differences. However, ln ηE and ln ηE* exhibited opposite signs, negative and positive, respectively. The odd achievement of negative ln ηE in aqueous dilutions of ChCl2U characterized by the formation of HB networks suggest the treatment of ChCl2U as a pseudo-component as more appropriate. Moreover, the role played by the presence of U in the evolution of ln ηE* with temperature was also discussed.

Deep eutectic solvents (DESs) and dilutions thereof are currently gaining increased interest in sustainable processes. DES dilutions are particularly interesting in the so-called “solvent-in-DES” regime where the intriguing features of DESs remain (coming from hydrogen bonding among the components) and some typical drawbacks (e.g., high viscosity, low electrical conductivity, etc.) are mitigated. Actually, DES dilutions may exhibit excellent performances (more so than the original neat DESs) in certain applications. Knowing about the tools that allow predicting (and eventually extending) the dilution range of the “solvent-in-DES” regime is obviously of interest. With this aim, we herein studied two sets of DES dilutions. In the first set, we used the DES composed of choline chloride (ChCl) and urea (U) and its dilutions in H2O, methanol (MeOH) and ethanol (EtOH). In the second set, we studied two DESs composed of ethylene glycol (EG) and either tetraethylammonium bromide (TEABr) or tetrabutylammonium bromide (TBABr), and their dilutions in H2O. Data coming from DSC, 1H NMR spectroscopy, and Brillouin spectroscopy revealed how the dilution range of the “solvent-in-DES” regime in ChClU dilutions in H2O, MeOH and EtOH increased in the order H2O

[EN] In the present contribution, we report how through the use of metal-organic frameworks (MOFs) composed of addressable combinations of up to four different metal elements it is possible to program the composition of multimetal oxides, which are not attainable by other synthetic methodologies. Thus, due to the ability to distribute multiple metal cations at specific locations in the MOF secondary building units it is possible to code and transfer selected metal ratios to multimetal oxides with novel, desired compositions through a simple calcination process. The demonstration of an enhancement in the electrocatalytic activity of new oxides by preadjusting the metal ratios is here reported for the oxygen reduction reaction, for which activity values comparable to commercial Pt/C catalysts are reached, while showing long stability and methanol tolerance., We acknowledge Institut Laue-Langevin and Spanish Initiatives on Neutron Scattering (ILL-SpINS) for beamtime at instrument D1B and G. Cuello for assistance during data acquisition. The Paul Scherrer Institute is also acknowledged for beamtime at instrument HRPT and V. Pomjakhusin for assistance during data acquisition. We thank E. Rodríguez-Cañas and Isidoro Poveda from the Servicio Interdepartamental de Investigación at Universidad Autónoma de Madrid for valuable support with SEM images and EDS analyses and FE-SEM image acquisition, respectively. We acknowledge E. Urones for the TEM images and TEM-EDS analysis acquisition at Centro Nacional de Microscopía Electrónica. Funding: Work at Instituto de Ciencia de Materiales de Madrid−Consejo Superior de Investigaciones Cientifícas (CSIC) has been supported by the Spanish Ministry for Science, Innovation and Universities (MINECO), and FEDER funds: Projects MAT2016-78465-R, MAT2015-68639-R, and CTQ2017-87262-R. F.G. and N.L.-S. acknowledge financial support from MINECO (Ramón y Cajal program and FPI research contract, respectively).

We have investigated the ring-opening polymerization (ROP) of ε-caprolactone using mixtures of methanesulfonic acid and the guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene as the catalyst. Our interest in these mixtures is based on the capability of both acids and bases to behave as bifunctional catalysts; the former by the combined action of acidic hydrogens and basic oxygens, and the latter by the hydrogen-bond acceptor and donor features of, respectively, a basic nitrogen center and an ortho-hydrogen atom. We found that these compounds are capable of forming eutectic mixtures at a certain molar ratio. Upon the use of these mixtures – e.g. with molar ratios near to the eutectic one – as catalysts, neither further solvents nor initiators were required to carry out the ROP of ε-caprolactone. The resulting polycaprolactones (PCLs) were highly crystalline (more than 87%) and exhibited an excellent capability to support the growth of murine L929 fibroblasts. We consider that the preparation of biocompatible PCLs at physiological temperatures and in the absence of reagents other than the monomer and the catalyst offers an interesting alternative to both the self-cross-linked oligomers/macromers of acrylate-based PCL-derivatives and the pH/temperature-sensitive PCL copolymers used to date as injectable biomaterials., This work was supported by MINECO under grants MAT2012-34811 and MAT2011-25329, and by the European Union Seventh Framework Programme (FP7/2007-2013/NMP) under grant agreement #263289 (Green Nano Mesh). M.C.S. is grateful to the Instituto de Salud Carlos III-MINECO for a Miguel Servet type I contract.

Ionic liquids (ILs) are being widely used in many diverse areas of social interest, including catalysis, electrochemistry, etc. However, issues related to hygroscopicity of many ILs and the toxic and/or nonbiodegradable features of some of them limit their practical use. Developing materials capable of IL recovery from aqueous media and dehydration, thus allowing their recycling and subsequent reutilization, in a single and efficient process still poses a major challenge. Herein, electrically conductive aerogels composed of carbon nanofibers (CNFs) with remarkable superhydrophobic features are prepared. CNF-based 3D aerogels are prepared through a cryogenic process, so called ice-segregation-induced self-assembly (ISISA) consisting of the unidirectional immersion of an aqueous chitosan (CHI) solution also containing CNFs in suspension into a liquid nitrogen bath, and subsequent freeze-drying. The CNF-based 3D aerogels prove effective for absorption of ILs from aqueous biphasic systems and recovery with quite low water contents just through a single process of filtration. Moreover, the electrical conductivity of CNF-based 3D aerogels is particularly interesting to treat highly viscous ILs because the Joule effect allows not only shortening of the absorption process but also enhancement of the flux rate when operating in flow-through conditions.

Deep eutectic solvents (DESs) composed of resorcinol, either 2-cyanophenol or 4-cyanophenol, and choline chloride were used for the synthesis of hierarchical nitrogen-doped carbon molecular sieves. Carbons were obtained with high conversions by polycondensation of resorcinol and either 2-cyanophenol or 4-cyanophenol with formaldehyde, and subsequent carbonization at 800 °C in nitrogen atmosphere. The nitrogen content was ca. 2.4 wt%, revealing an excellent nitrogen-doping efficiency for cyanophenol derivatives when used in the form of DES. The use of either 2-cyanophenol or 4-cyanophenol modified the contribution of quaternary-Nvalley groups in the resulting carbons, being larger in carbons coming from 4-cyanophenol than in those coming from 2-cyanophenol. The hierarchical porous structure was composed of micro-, meso- and macropores, and the diameter distribution of mesopores was also related to the use of either 2-cyanophenol or 4-cyanophenol. These structural and compositional differences were critical for the use of the resulting hierarchical nitrogen-doped carbons as efficient metal-free electrocatalysts. In particular, the carbons coming 4-cyanophenol proved particularly effective in the direct reduction of oxygen to OH− (H2O in acidic solution) through a four-electron (4e−) process with high catalytic activity and selectivity, and longer stability and stronger tolerance to crossover effects than platinum-based electrocatalysts.

Eutectic mixtures of the monohydrated form of p-toluenesulfonic acid (pTsOH·HO) and triethyl phosphate (TEP) in a 1: 1 molar ratio were used as the medium to disperse previously functionalized multiwalled carbon nanotubes (MWCNTs), and to catalyse the polycondensation of furfuryl alcohol. Hierarchically structured P-doped carbon-CNT composites were obtained after carbonization. The high surface area, the phosphate functionalization, the hierarchical structure and the good electrical conductivity exhibited by these composites provided remarkable metrics when they were used as electrodes in a supercapacitor cell, with energy densities of around 22.6 W h kg and power densities of up to 10 kW kg for operational voltages of up to 1.5 V. This performance surpasses any performance previously reported for electrodes weighing (at least) 10 mg per cm of current collector and using an aqueous electrolyte. Actually, the supercapacitor cell built up with these electrodes provided enough neat energy to turn an IR LED of 30 mW on and emit light over a certain period., This study was supported by MINECO (MAT2012-34811). J. P. and N. L.-S. acknowledge MINECO for their respective FPI contracts.

Ionic liquids and deep eutectic solvents (a new class of ionic liquids obtained by complexation of quaternary ammonium salts with hydrogen bond donors such as acids, amines, and alcohols among others) have been recently used as solvents and even as precursors in the synthesis of carbonaceous materials. The use of long-alkyl-chain derivatives of ionic liquids that, playing the role of structure directing agents, were capable of designing the mesoporous structure of the resulting carbons is of particular interest. Meanwhile, deep eutectic solvents proved efficient in tailoring the structure comprised between large mesopores and small macropores, but the control over the smaller ones (e.g. small mesopores and micropores) is still a challenge as compared to ILs. Herein, we have used deep eutectic solvents composed of resorcinol, 4-hexylresorcinol and tetraethylammonium bromide for the synthesis of carbon monoliths with a tailor-made narrow microporosity. Behaving as molecular sieves, these carbons exhibited not only good capacities for CO2 adsorption (up to 3 mmol g−1) but also an outstanding – especially at low pressures – CO2–CH4 selectivity., This work was supported by MINECO (MAT2009‐10214 and MAT2011‐25329). DC acknowledges MINECO for a JdelaC research contract. JP acknowledges MINECO for a FPI fellowship. COA and JBP thank the financial support of FICYT (EQUIP08‐36, file num. 04010208000281).

The treatment of bone lesions, including fractures, tumor resection and osteoporosis, is a common clinical practice where bone healing and repair are pursued. It is widely accepted that calcium phosphate-based materials improve integration of biomaterials with surrounding bone tissue and further serve as a template for proper function of bone-forming cells. Within this context, mineralization on preformed substrates appears as an interesting and successful alternative for mineral surface functionalization. However, mineralization of >true> 3D scaffolds -in which the magnitude of the third dimension is within the same scale as the other two- is by no means a trivial issue because of the difficulty to obtain a homogeneous mineral layer deposited on the entire internal surface of the scaffold. Herein, a >flow-through> electrodeposition process is applied for mineralization of 3D scaffolds composed of multiwall carbon nanotubes and chitosan. It is demonstrated that, irrespective of the experimental conditions used for electrodeposition (e.g., time, temperature and voltages), the continuous feed of salts provided by the use of a flow-through configuration is the main issue if one desires to coat the entire internal structure of 3D scaffolds with a homogeneous mineral layer. Finally, mineralized scaffolds not only showed a remarkable biocompatibility when tested with human osteoblast cells, but also enhanced osteoblast terminal differentiation (as early as 7 days in calcifying media). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was supported by grants from MINECO (Project Numbers MAT2009-10214 and MAT2011-25329) and from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement number 263289 (Green Nano Mesh). S.N. acknowledges CSIC for a JAE-Pre fellowship. M. C. S. is greatly in debt with MINECO for a Juan de la Cierva fellowship. Fernando Pinto (from the Instituto de Ciencias Agrarias-CSIC) and Sylvia Gutierrez (from the Centro Nacional de Biotecnologia-CSIC) are acknowledged for their assistance with SEM and confocal microscopy studies, respectively.

The immobilization of more than one single substance within the structure of a biocompatible polymer provides multifunctional biomaterials with attractive and enhanced properties. In the context of bone tissue engineering, it could be of great interest to synthesize a biomaterial that simultaneously contains amorphous calcium phosphate (ACP), to favor calcium and phosphate precipitation and promote osteogenesis, and an antibiotic such as ciprofloxacin (CFX) that can, eventually, avoid infections resulting after surgical scaffold implantation. However, the co-immobilization of multiple substances is by no means a trivial issue because of the enhanced number of interactions that can take place. One of the main issues is controlling not only the diverse solid forms that individual substances can eventually adopt, but also the forces responsible for the self-organization of the individual components. The latter determines whether phase-separated structures or conjugated architectures are obtained and, consequently, may dramatically affect their functionality. Herein, we have observed-by SEM, TEM, and solid-state NMR-that enzymatically-assisted coprecipitation of ACP and CFX resulted in phase-separated structures. Thus, CFX crystals showed identical morphology to that obtained in the absence of ACP, but the size was smaller. Neither the size nor the morphology of ACP exhibited significant differences whether precipitated with or without CFX, but, in the former case, ACP was stabilized over a wider range of pH and temperature. Finally, by using this methodology and the ice segregation induced self-assembly process (ISISA), we have successfully co-immobilized ACP and CFX in chitosan-based scaffolds. Interestingly, the presence of ACP exerted significant control on the CFX release from these materials.

Deep eutectic solvents (DESs) have been used in the synthesis of nitrogen-doped carbons exhibiting a hierarchical porous structure. The CO2 sorption capacity of these solid sorbents was extraordinary because of their relatively high nitrogen content and their bimodal porous structure where micropores provide high surface areas (ca. 700 m2 g−1) and macropores provide accessibility to such a surface. DESs were composed of resorcinol, 3-hydroxypyridine and choline chloride in 2 : 2 : 1 and 1 : 1 : 1 molar ratios. Polycondensation of resorcinol and 3-hydroxypyridine (with formaldehyde) promoted DES segregation in a spinodal-like decomposition process by the formation of a polymer rich phase and a depleted polymer phase. Thus, DESs played a multiple role in the synthetic process; the liquid medium that ensured reagents homogenization, the structure-directing agent that is responsible for the achievement of the hierarchical structure, and the source of carbon and nitrogen of the solid sorbent obtained after carbonization. Interestingly, the homogeneous incorporation of nitrogen at the solution stage of the synthetic process (rather than by post-treatment of the preformed carbon) allowed the achievement of significant nitrogen contents even in carbons obtained at relatively high temperatures (e.g. 8–12 at% for 600 °C and ca. 5 at% for 800 °C). It is worth noting that, despite thermal treatments at high temperatures tend to decrease the nitrogen content, the high surface area of the solid sorbents obtained at 800 °C contributed to a significant enhancement of CO2 capture while providing superior selectivity, recyclability and stability.