Graphene Ionic Liquid Research Articles

Dispersion and Stabilization of Exfoliated Graphene in Ionic Liquids.

The liquid-phase exfoliation of graphite is one of the most promising methods to increase production and commercial availability of graphene. Because ionic liquids can be easily obtained with chosen molecular structures and tuneable physicochemical properties, they can be use as media to optimize the exfoliation of graphite. The understanding of the interactions involved between graphite and various chemical functions in the solvent ions will be helpful to find liquids capable of dissociating and stabilizing important quantities of large graphene layers. After a step of sonication, as a mechanical precursor, samples of suspended exfoliated graphene in different ionic liquids have been characterized experimentally in terms of flake size, number of layers, total concentration and purity of the exfoliated material. Nine different ionic liquids based on imidazolium, pyrrolidinium and ammonium cations and on bis(trifluoromethylsulfonyl)imide, triflate, dicyanamide, tricyanomethanide, and methyl sulfate anions have been tested. UV-vis, Raman and X-ray photoelectron in addition to high resolution transmission electron and atomic force microscopy have been selected to characterize suspended exfoliated graphene in ionic liquids. The number of layers in the flakes exfoliated, the size and concentration depend of the structure of the ionic liquid selected. In order to obtain large flake sizes, ionic liquids with bis(trifluoromethylsulfonyl)imide anions and a cation with an alkyl chain of medium length should be selected. Smaller cation and anion favors the exfoliation of graphene. The exfoliation caused the formation of C-H bonds and the oxidation of the graphitic surface.

Trace determination of cadmium content in Malaysian herbs using graphene–ionic liquid-modified screen-printed carbon electrodes

Abstract. A simple and effective method of square-wave anodic stripping voltammetry (SWASV) with screen-printed carbon electrodes (SPCEs) was used to determine the cadmium concentration in Malaysian herb samples. The optimization process involved the selection of an optimized pH, an acetate buffer as a supporting electrolyte, the deposition potential, deposition time and the surface modification process on an SPCE surface. The optimum conditions were a pH of 4.5, a deposition potential of −1.4 V and a deposition time of 120 s. The SPCE surface was modified with the fabrication of the graphene–ionic liquid composite as the sensing layer. Four herb samples were tested, where herbs A, D, M and C contained 0.0035, 0.0237, 0.0267 and 0.0251 ppm of cadmium, respectively. The sensitivity of the proposed sensor was compared with an inductively coupled plasma–optical emission spectroscopy (ICP–OES). The relative standard deviation (RSD) between the sensor and the ICP–OES indicated that the sensor was sensitive, as RSD was below 20 % with range of 7.93 % to 18.28 %.

A direct “touch” approach for gold nanoflowers decoration on graphene/ionic liquid composite modified electrode with good properties for sensing bisphenol A

In the present work, a direct “touch” method was developed for attaching AuNPs with clean surface on the graphene-ionic liquid modified glassy carbon electrode (G-IL GCE). The morphology and composition of the thus-prepared AuNPs on G-IL GCE were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results showed that AuNPs with interesting flower-like shapes are well dispersed on the G-IL film. Significantly, as it is a surfactant-free synthesis, the AuNPs are very clean and can be directly modified on a G-IL GCE without any pre-treatments. Comparing with the bare or even various AuNPs-G-IL mixtures modified GCEs, the proposed sensor exhibit better electrochemical activity with a higher peak current and a lower overpotential towards bisphenol A (BPA) oxidation. After optimization, a good linear relationship between current response and the concentration of BPA in the range of 0.01–1 and 1–60 μM were obtained, and the detection limit was as low as 4.8 nM. To testify the reliability, the thus-prepared AuNPs/G-IL GCE was used for determining the concentration of BPA in disposable paper cups, plastic bottles and noodles cups.

Structure of a Mixture of Graphene Plates and Ionic Liquid 1-Octyl-3-methylimidazolium Hexafluoroborate

We reported a molecular dynamics simulation study of a mixture of 1-octyl-3-methylimidazolium hexafluoroborate([C8MIN]+[PF6]‒), an ionic liquid, and pristine graphene. Our simulations were performed under various conditions, including several temperatures and distances between graphene plates. By studying the liquid structure of the ionic-liquid graphene mixture, we found that the transition for the ionic liquids entering the middle of two graphene plates should occur within 1.00 and 1.50 nm in the temperature range studied(300―600 K). We also studied the pair correlations between the graphene plates and the head and tail of the cation and the anion. Our study at the molecular level can aid in understanding the detailed molecular structure of the mixture.

Dual functions of imidazole-based polymeric ionic liquid (PIL) on the anticorrosive performance of graphene-based waterborne epoxy coatings

Dispersion of graphene nanosheets in a water and polymer matrix has been rarely achieved due to graphene’s hydrophobicity, which thus impedes its potential anticorrosive application. In this study, stable graphene aqueous dispersion was obtained by using imidazole-based polymeric ionic liquid (PIL) as the dispersant with ultrasonic vibration. Stacked graphene sheets were exfoliated to a few layers via cation-π interaction between PIL and graphene nanosheets. Electrochemical impedance measurements were taken to investigate the anticorrosion performance of epoxy coatings with or without polymeric ionic liquid–graphene (PIL–G) hybrids. Results indicated that the PIL–G hybrid significantly enhanced the long-term protective performance of epoxy coatings, which was attributed to the synergistic effects of the corrosion-inhibitive PIL and impermeable graphene nanosheets.

Electrochemical synthesis and the functionalization of few layer graphene in ionic liquid and redox ionic liquid

Electrochemical reductive exfoliation of graphite to few layered graphene (FLG) in presence of 1-ethyl-2,3-dimethyl imidazolium bis(trifluoromethylsulfonyl) imide ionic liquid and redox ionic liquid based ferrocene has been investigated. Thus, by applying a mild negative potential (−2.7 V vs. Fc/Fc+) to carbon electrode in ionic liquid graphene flakes could be generated. The generated materials have been characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, high resolution transmission electron microscopy and atomic force microscopy. XPS and Raman analysis show that the electrochemical reductive exfoliation provides the formation of FLG. The thickness of the resulting FLG was found to be ranged between 4 and 1 nm. HR-TEM images reveal the formation of few graphene layers and in some cases single graphene layer was observed. Moreover, this electrochemical route conduces to the formation of ionic liquid functionalized FLG. Finally, the reductive exfoliation was further investigated in the presence of redox ionic liquid. XPS and electrochemical measurements confirm the presence of ferrocene.

Exfoliation of graphene and fluorographene in molecular and ionic liquids.

We use molecular dynamics simulations to study the exfoliation of graphene and fluorographene in molecular and ionic liquids, by performing computer experiments in which one layer of the 2D nanomaterial is peeled from a stack, in vacuum and in the presence of solvent. The liquid media and the nanomaterials are represented by fully flexible, atomistic force fields. From these simulations we calculate the potential of mean force, or reversible work, required to exfoliate the materials. Calculations in water and organic liquids showed that small amides (NMP, DMF) are among the best solvents for exfoliation, in agreement with the experiment. We tested ionic liquids with different cation and anion structures, allowing us to learn about their solvent qualities for the exfoliation of the nanomaterials. First, a long alkyl side chain on the cation is favourable for exfoliation of both graphene and fluorographene. The presence of aromatic groups on the cation is also favourable for graphene. No beneficial effect was found between fluorine-containing anions and fluorographene. We also analysed the ordering of ions in the interfacial layers with the materials. Near graphene, nonpolar groups are found along with charged groups, whereas near fluorographene almost exclusively non-charged groups are found, with ionic moieties segregated to the second layer. Therefore, fluorographene appears to be the more hydrophobic surface, as expected.

An ionic liquid-graphene oxide hybrid nanomaterial: synthesis and anticorrosive applications.

Herein, an ionic liquid-graphene oxide hybrid nanomaterial was prepared via a facile grafting reaction between an imidazole ionic liquid and graphene oxide. FTIR, Raman, and XPS spectra demonstrated that imidazole ionic liquids were successfully covalently attached to the surface of graphene oxide nanosheets. The resulting hybrid nanomaterial, with a thickess of ca. 3 nm, can be stably dispersed in water. Results obtained from electrochemical impedance spectroscopy revealed that ionic liquid-graphene oxide hybrids effectively improved the anticorrosion performance of epoxy-based waterborne coatings. Moreover, ionic liquids performed two functions: (a) they facilitated the dispersion of graphene in a polymer matrix and then utilized the impermeable barrier capability of graphene and (b) they endowed the graphene sheets with a corrosion inhibition effect. The scanning vibrating electrode technique combined with electrochemical tests proved that the enhanced protective performance of the as-prepared composite coatings was attributed to the synergistic effect of the impermeable property of graphene nanosheets and the inhibitory function of the imidazole-based ionic liquid.

Enhanced sensing performance of carboxyl graphene–ionic liquid attached ionic polymer–metal nanocomposite based polymer strain sensors

Here, we show that biocompatible IPMNC sensors based on a carboxyl graphene–acidic ionic liquid–polyvinylpyrrolidone–polystyrene sulfonic acid ionic blend membrane can generate a high sensing current (6 mA cm−2) with a bending strain of 0.009.

Non-enzymatic electrochemical detection of glucose with a disposable paper-based sensor using a cobalt phthalocyanine–ionic liquid–graphene composite

We introduce for the first time a paper-based analytical device (PAD) for the non-enzymatic detection of glucose by modifying a screen-printed carbon electrode with cobalt phthalocyanine, graphene and an ionic liquid (CoPc/G/IL/SPCE). The modifying composite was characterized by UV–visible spectroscopy, energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The disposable devices show excellent conductivity and fast electron transfer kinetics. The results demonstrated that the modified electrode on PADs had excellent electrocatalytic activity towards the oxidation of glucose with NaOH as supporting electrolyte (0.1M). The oxidation potential of glucose was negatively shifted to 0.64V vs. the screen-printed carbon pseudo-reference electrode. The paper-based sensor comprised a wide linear concentration range for glucose, from 0.01 to 1.3mM and 1.3–5.0mM for low and high concentration of glucose assay, respectively, with a detection limit of 0.67µM (S/N = 3). Additionally, the PADs were applied to quantify glucose in honey, white wine and human serum. The disposable, efficient, sensitive and low-cost non-enzymatic PAD has great potential for the development of point-of-care testing (POCT) devices that can be applied in healthcare monitoring.

Structure and Capacitance of Electrical Double Layers at the Graphene–Ionic Liquid Interface

Molecular dynamics simulations are carried out to investigate the structure and capacitance of the electrical double layers (EDLs) at the interface of vertically oriented graphene and ionic liquids [EMIM]+/[BF4]−. The distribution and migration of the ions in the EDL on the rough and non-rough electrode surfaces with different charge densities are compared and analyzed, and the effect of the electrode surface morphology on the capacitance of the EDL is clarified. The results suggest that alternate distributions of anions and cations in several consecutive layers are formed in the EDL on the electrode surface. When the electrode is charged, the layers of [BF4]− anions experience more significant migration than those of [EMIM]+ cations. These ion layers can be extended deeper into the bulk electrolyte solution by the stronger interaction of the rough electrode, compared to those on the non-rough electrode surface. The potential energy valley of ions on the neutral electrode surface establishes a potential energy difference to compensate the energy cost of the ion accumulation, and is capable of producing a potential drop across the EDL on the uncharged electrode surface. Due to the greater effective contact area between the ions and electrode, the rough electrode possesses a larger capacitance than the non-rough one. In addition, it is harder for the larger-sized [EMIM]+ cations to accumulate in the narrow grooves on the rough electrode, when compared with the smaller [BF4]−. Consequently, the double-hump-shaped C–V curve (which demonstrates the relationship between differential capacitance and potential drop across the EDL) for the rough electrode is asymmetric, where the capacitance increases more significantly when the electrode is positively charged.

Nanofriction of Graphene/Ionic Liquid-Infused Block Copolymer Homoporous Membranes.

We have infused graphene/ionic liquid into block copolymer homoporous membranes (HOMEs), which have highly ordered uniform cylindrical nanopores, to form compact, dense, and continuous graphene/ionic liquid (Gr/IL) lubricating layers at interfaces, enabling a reduction in the friction coefficient. Raman and XPS analyses, confirmed the parallel alignment of the cation of ILs on graphene by the π-π stacking interaction of the imidazolium ring with the graphene layer. This alignment loosens the lattice spacing of Gr in Gr/ILs, leading to a larger lattice spacing of 0.36 nm in Gr of Gr/ILs hybrids than the pristine Gr (0.33 nm). The loose graphene layers, which are caused by the coexistence of graphene and ILs, would make the sliding easier, and favor the lubrication. An increase in the friction coefficient was observed on ILs-infused block copolymer HOMEs, as compared to Gr/ILs-infused ones, due to the absence of Gr and the unstably formed ILs film. Gr/ILs-infused block copolymer HOMEs also exhibit much smaller residual indentation depth and peak indentation depth in comparison with ILs-infused ones. This indicates that the existence of stably supported Gr/ILs hybrid liquid films aids the reduction of the friction coefficient by preventing the thinning of the lubricant layer and exposure of the underlying block copolymer HOMEs.

Insight into the Electrical Double Layer of an Ionic Liquid on Graphene

Graphene is a promising next-generation conducting material with the potential to replace traditional electrode materials in supercapacitors. Since energy storage in supercapacitors relies on the electrolyte-electrode interface, here we elucidate the interfacial subnanometer structure of a single component liquid composed solely of cations and anions – an ionic liquid- on electrified graphene. We study the effect of applied potential on the interaction between graphene and a silicon tip in an ionic liquid and describe it within the framework of the Derjaguin-Landau-Verwey-Overbeck (DLVO) theory. The energy is stored in an electrical double layer composed of an extended Stern layer, which consists of multiple ion layers over ~2 nanometers, beyond which a diffuse layer forms to compensate the applied potential on graphene. The electrical double layer significantly responds to the applied potential, and it shows the transition from overscreening to crowding of counterions at the interface at the highest applied potentials. It is proposed that surface charging occurs through the adsorption of the imidazolium cation to unbiased graphene (likely due to π-π interactions) and that the surface potential is better compensated when counterion crowding happens. This study scrutinizes the electrified graphene-ionic liquid interface, with implications not only in the field of energy storage, but also in lubrication.

Ultrafast Dye Removal Using Ionic Liquid–Graphene Oxide Sponge

A methylimidazolium ionic-liquid-functionalized graphene oxide (mimGO) sponge was prepared by facile amidation reaction followed by freeze-drying. Covalent functionalization of graphene oxide (GO) was confirmed by SEM, XRD, XPS, FT-IR, Raman and TGA. The mimGO sponge was employed to remove direct red 80 (DR80) dye from aqueous solutions. Results showed exceptional affinity for adsorption of azo dye direct red 80 (DR80) due to the charge-induced adsorption aided by protonated amine and cationic methylimidazolium ionic liquid pendant groups. Detailed adsorption characteristics of mimGO sponge including operational parameters, adsorption kinetics and adsorption isotherms were investigated. Adsorption on the mimGO sponge followed pseudo-second-order kinetic model, and the equilibrium capacity was described by the Langmuir adsorption model. An ultrahigh adsorption rate of 588.2 mg/(g·min) and equilibrium adsorption capacity of 501.3 mg/g for DR80 were observed for the mimGO sponge, which is much higher than th...

Functional Graphene-Ionic Liquid Composites for the Fabrication of a Rapid and Facile Bisphenol A Electrochemical Sensor

Functional Graphene-Ionic Liquid Composites for the Fabrication of a Rapid and Facile Bisphenol A Electrochemical Sensor

Exfoliation of Graphene in Ionic Liquids: Pyridinium versus Pyrrolidinium

Exfoliation is an elegant physical technique to directly obtain graphene from graphite. A search for high-performance exfoliation solvents is actively pursued nowadays. We report potentials of mean force and free energies, characterizing steered separation of graphene sheets and their subsequent solvation by room-temperature ionic liquids (RTILs). The exfoliation performance of N-butylpyridinium bis(trifluoromethanesulfonyl)imide [BPY][TFSI] is compared to that of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide [PYR][TFSI]. Both RTILs are shown to exhibit comparable exfoliation performance, which is superior to the performance of 1-ethyl-3-methylimidazolium tetrafluoroborate by ∼20 kJ mol–1 nm–1. The sulfur atom of TFSI– contributes an essential portion of the solvation enthalpy due to its dispersive attraction to carbon atoms of graphene. Both RTILs maintain a single, moderately defined shell around the graphene surface. [BPY][TFSI] and [PYR][TFSI] are suitable starting compounds to engi...

Dehydrated Sucrose Nanoparticles as Spacers for Graphene–Ionic Liquid Supercapacitor Electrodes

The addition of dehydrated sucrose nanoparticles increases the gravimetric capacitance of electrochemical double-layer capacitor electrodes produced via the evaporative consolidation of graphene oxide–water–ionic liquid gels by more than two-fold. Dehydrated sucrose adsorbs onto graphene oxide and serves as a spacer, preventing the graphene oxide from restacking during solvent evaporation. Despite 61 wt % of the solids being electrochemically inactive dehydrated sucrose nanoparticles, the best electrodes achieved an energy density of ∼13.3 Wh/kg, accounting for the total mass of all electrode components.

Electrochemical detection of ractopamine based on a molecularly imprinted poly-o-phenylenediamine/gold nanoparticle–ionic liquid–graphene film modified glass carbon electrode

An electrochemical sensor for sensitive detection of ractopamine (RAC) was fabricated by using molecularly imprinted polymer (MIP) incorporation with graphene (GR), ionic liquid (IL) and gold nanoparticle (AuNPs) nanocomposites.

Direct electrochemistry of cholesterol oxidase and biosensing of cholesterol based on PSS/polymeric ionic liquid–graphene nanocomposite

In this work, a new biosensor based on PSS/polymeric ionic liquids–graphene nanocomposite with excellent conductivity, favourable biocompatibility and good film-forming properties was constructed to detect cholesterol.

Molecular origin of high free energy barriers for alkali metal ion transfer through ionic liquid-graphene electrode interfaces.

In this work we study mechanisms of solvent-mediated ion interactions with charged surfaces in ionic liquids by molecular dynamics simulations, in an attempt to reveal the main trends that determine ion-electrode interactions in ionic liquids. We compare the interfacial behaviour of Li(+) and K(+) at a charged graphene sheet in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate, and its mixtures with lithium and potassium tetrafluoroborate salts. Our results show that there are dense interfacial solvation structures in these electrolytes that lead to the formation of high free energy barriers for these alkali metal cations between the bulk and direct contact with the negatively charged surface. We show that the stronger solvation of Li(+) in the ionic liquid leads to the formation of significantly higher interfacial free energy barriers for Li(+) than for K(+). The high free energy barriers observed in our simulations can explain the generally high interfacial resistance in electrochemical storage devices that use ionic liquid-based electrolytes. Overcoming these barriers is the rate-limiting step in the interfacial transport of alkali metal ions and, hence, appears to be a major drawback for a generalised application of ionic liquids in electrochemistry. Some plausible strategies for future theoretical and experimental work for tuning them are suggested.