Voltammetry of undiluted redox systems backed by in-situ Raman spectroscopy. Evidence for strong accumulation of ions in the diffusion layer at microelectrode surface

Voltammetry of undiluted redox liquids may result in the formation of thin layers of ionic liquids at the microelectrode surface. Such a situation was postulated for several liquids (solvents) including methanol, however, no direct evidence supporting this expectation was obtained. By using in-situ Raman spectroscopy in combination with voltammetric experiments, we have shown, that the concentration of the counterion, ClO₄⁻, is really much enhanced in the electrode vicinity compared to the methanol bulk.     

Nano‐Roughening a Pt Disk Microelectrode via Electrochemical Alloying‐Dealloying in Ionic Liquid Electrolyte

A green chemistry method to nano‐roughen a Pt disk microelectrode has been successfully developed via electrochemical alloying‐dealloying in an ionic liquid bath comprising of ZnCl₂ and 1‐ethyl‐3‐methylimidazolium chloride. The nano‐roughened Pt layer possesses bark‐like nanoporous structures characteristic of nano‐sized aggregates separated by nano‐cracks whose width ranging from around 50 to 200 nm. The nano‐roughened microelectrode possesses high surface area and diffusional properties typical of a microelectrode. Electrochemical oxidation and reduction of nitrite have been studied as an example for demonstrating that the nano‐roughened microelectrode is a promising technique for electroanalysis and electrocatalysis applications.     

Effect of Ionic Liquid Structure on the Electrochemical Response of Dopamine at Room Temperature Ionic Liquid‐modified Carbon Paste Electrodes (IL–CPE)

In this work 12 different ionic liquids (ILs) have been used added as co‐binders in the preparation of modified carbon paste electrodes (IL–CPEs) used for the voltammetric analysis of dopamine in Britton‐Robinson buffer. The ionic liquids studied were selected based on three main criteria: (1) increasing chain length of alkyl substituents (studying 1‐ethylimidazolium and ethyl, propyl, butyl, hexyl and decylmethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids); (2) nature of the counter ion (dicyanamide, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate) in 1‐butyl‐3‐methylimidazolium ionic liquids; and (3) cation ring structures (1‐butyl‐3‐methylimidazolium, 1‐butyl‐1‐methylpiperidinium, 1‐butyl‐1‐methylpyrrolidinium and 1‐butyl‐3‐methylpyridinium) in bis(trifluoromethylsulfonyl)imide or hexafluorophosphate (1‐butyl‐3‐methylimidazolium or 1‐butyl‐3‐methylpyridinium as cations) ionic liquids. The use of IL as co‐binders in IL–CPE results in a general enhancement of both the sensitivity and the reversibility of dopamine oxidation. In square wave voltammetry experiments, the peak current increased up to a 400 % when 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used as co‐binder, as compared to the response found with the unmodified CPE. Experimental data provide evidence that electrostatic and steric effects are the most important ones vis‐à‐vis these electrocatalytic effects on the anodic oxidation of dopamine on IL–CPE. The relative hydrophilicity of dicyanamide anions reduced the electrocatalytic effects of the corresponding ionic liquids, while the use of 1‐ethyl‐3‐methylimidazolium hexafluorophosphate or 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (two relatively small and highly hydrophobic ionic liquids) as co‐binders in IL–CPE resulted in the highest electrocatalytic activity among all of the IL–CPE studied.     

Co‐electroosmotic capillary electrophoresis of basic proteins with 1‐alkyl‐3‐methylimidazolium tetrafluoroborate ionic liquids as non‐covalent coating agents of the fused‐silica capillary and additives of the electrolyte solution

The paper reports the results of a study carried out to evaluate the use of three 1‐alkyl‐3‐methylimidazolium‐based ionic liquids as non‐covalent coating agents for bare fused‐silica capillaries and additives of the electrolyte solutions (BGE) for CE of basic proteins in the co‐EOF separation mode. The three ionic liquids are differentiated from each other by the length of the alkyl group on the imidazolium cation, consisting of either an ethyl, butyl or octyl substituent, whereas tetrafluoroborate is the common anionic component of the ionic liquids. Coating the capillary with the ionic liquid resulted in improved peak shape and protein separation, while the EOF was maintained cathodic. This indicates that each ionic liquid is effective at masking the protein interaction sites on the inner surface of the capillary, also when its adsorption onto the capillary wall has not completely neutralized all the negative charges arising from the ionization of the silanol groups and the ionic liquid is not incorporated into the BGE employed for separation. Using the coated capillaries with BGE containing the ionic liquid employed for the coating, at concentration low enough to maintaining the EOF cathodic, both peak shape and protein separation varied to different extents, based on the particular ionic liquid used and its concentration. Fast and efficient separation of the model basic protein mixture in co‐electroosmotic CE is obtained with the 1‐butyl‐3‐methylimidazolium tetrafluoroborate coated capillary and 100 mM acetate buffer (pH 4.0) containing 4.4 mM 1‐butyl‐3‐methylimidazolium tetrafluoroborate as the BGE.     

Electrochemical polymerization of imidazolum‐ionic liquids bearing a pyrrole moiety

A series of imidazolium‐based ionic liquid monomers bearing a terminal pyrrole moiety were synthesized and electrochemically polymerized. It is found that the polymerizability of the synthesized ionic liquids is strongly dependent on the type of the counteranions. Although bromide monomer is not polymerizable, well‐defined polymeric films can be formed on various substrates in the cases of flour‐containing anions (BF₄^?, PF₆^?). The performed characterizations show that all resulting polypyrrole films are electroactive, and the imidazolium‐based ionic liquid moieties are correctly incorporated in polymer films during the electropolymerization process. This work not only provides a facile new method to immobilize ionic liquids on solid surface. Interestingly, without use of any template unique “knit” morphology and nanostructure, even hierarchical structures could also be produced by the electropolymerization of these new functionalized pyrrole monomers. We found that the properties of the pendant ionic liquid units on the surface of the formed polymer films preserved, and by simple anion exchange their surface energy and tension could be easily tuned without loss of the electrical, optical properties, and morphology of the polypyrrole films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4151–4161, 2008     

Ionic Liquids Can Permanently Modify Porous Silicon Surface Chemistry

To develop ionic liquid/porous silicon (IL/pSi) microarrays we have contact pin‐printed 20 hydrophobic and hydrophilic ionic liquids onto as‐prepared, hydrogen‐passivated porous silicon (ap‐pSi) and then determined the individual IL spot size, shape and associated pSi surface chemistry. The results reveal that the hydrophobic ionic liquids oxidize the ap‐pSi slightly. In contrast, the hydrophilic ionic liquids lead to heavily oxidized pSi (i.e., ox‐pSi). The strong oxidation arises from residual water within the hydrophilic ILs that is delivered from these ILs into the ap‐pSi matrix causing oxidation. This phenomenon is less of an issue in the hydrophobic ILs because their water solubility is substantially lower.     

Nanostructured Platinum‐iridium Alloy Microelectrode for Ammonia Determination

Nanostructured platinum‐iridium alloy microelectrode with high surface area was successfully prepared by applying successive potential cycles to a conventional PtIr microdisc in ionic liquid electrolyte containing ZnCl₂ at elevated temperature. Scanning‐electron microscope studies show that a very thin nanostructured film was created on the electrode upon 20 potential cycles between −2.0 and 0.75 V versus a Ag pseudo‐reference electrode. The film nanostructures are characteristic of regular hill‐like nano‐spacings separated by valley‐like nano‐cracks, and a roughness factor of approximately 40. The nanostructured electrode is highly active towards electrochemical oxidation of ammonia, and generates a linear relation between voltammetric peak currents (or chronoamperometric currents), and logarithm of ammonia concentration in a range of approximately 1 ppm to 10000 ppm. It has been proposed that the Temkin adsorption of ammonia from the bulk solution onto the electrode surfaces was involved in its electrochemical oxidation and could be responsible for the linear current‐logarithmic concentration relation.     

Electrochemical Determination of NDPhA via its Electrocatalysis at Porous Au Electrode in Room Temperature Ionic Liquid

N‐Nnitrosodiphenylamine (NDPhA) is a typical kind of nonvolatile nitrosamine. Its electrochemical oxidation occurs usually at relative positive potentials (>1.1 V) even at catalytic noble metal electrodes in aqueous solutions. The formation of oxide and evolution of oxygen at such high potentials makes the analysis of NDPhA on noble metal electrodes difficult. Accordingly, its electrochemical analysis is usually performed in anhydrous organic electrolytes. In this work, room temperature ionic liquid [BMIM⁺] [BF ] acting as electrolyte was introduced in this electrochemical analysis systems. It acts as supporting electrolyte itself, has good solubility of organic compounds, and allows a wide performance potential window of noble electrode, and in turn, highly electrocatalytic noble electrode of platinum or gold can be used as working electrodes. After the investigation of the electrocatalytic behavior of NDPhA at a gold electrode in this room temperature ionic liquid electrolyte, high sensitive determination of NDPhA was designed. It is demonstrated that the electrochemical response of NDPhA is determined by a surface‐controlled process. Therefore, a sensor with high sensitivity was constructed by applying porous Au electrodes with highly electrocatalytic activity and large active surface area. The present approach on one hand broadens the application field of room temperature ionic liquids, and on the other hand provides a sensitive analytical method for environmental detection.     

Solubilization of fullerene into ionic liquids by the use of fluoroalkyl end‐capped oligomers

Fluoroalkyl end‐capped oligomers were solubilized into a variety of ionic liquids such as N‐methylpyrazolium tetrafluoroborate, 3‐methylpyrazolium tetrafluoroborate and 1‐butyl‐3‐methylimidazolium hexafluorophosphate, and these fluorinated oligomers were able to reduce the surface tension of these ionic liquids. Interestingly, these fluorinated oligomers were able to solubilize fullerene into ionic liquids effectively. Fluoroalkyl end‐capped fullerene co‐oligomers, which were prepared by the oligomerizations of fluoroalkanoyl peroxides with radical polymerizable monomers such as acryloylmorpholine in the presence of fullerene, were more effective in solubilizing fullerene into ionic liquids compared to the corresponding fluoroalkyl end‐capped homo‐oligomers possessing no fullerene units. Fluoroalkyl end‐capped fullerene co‐oligomers/fullerene/ionic liquid complexes thus obtained were applied to the arrangements of fullerenes above the poly(methyl methacrylate) (PMMA) surface, and the higher fluorescent intensity of fullerene was obtained in the modified PMMA surface, although the reverse side of this modified film surface afforded an extremely weak fluorescent intensity. Copyright © 2005 John Wiley & Sons, Ltd.     

Ionothermal Synthesis of Germanosilicate Zeolites Constructed with Double‐Four‐Ring Structure‐Building Units in the Presence of Organic Base

The crystallization chemistry of silica‐based zeolites in ionic liquids remains highly puzzling and interesting in the field of zeolite science. Herein, we report the successful ionothermal synthesis of germanosilicate zeolites. The ionothermal templating effect with respect to the structure, alkalinity and concentration of organic additives was comparatively studied. The results showed that a small amount of organic base could effectively aid the dissolution of silica source and facilitate the crystallization of germanosilicate zeolites with ionic liquid as template. Remarkably, STW and IRR structures constructed with double‐four‐ring (D4R) structure‐building units were ionothermally prepared using 1‐ethyl/butyl‐3‐methyl imidazolium and 1‐benzyl‐3‐methyl imidazolium ionic liquids as template, respectively. Ionothermal synthesis tailored with organic base showed suitable chemistry for the formation of germanium‐containing siliceous D4R units. This finding will be helpful for the rational exploration of novel extra‐large‐pore zeolitic structures.     

Noncovalent linkage of telechelic oligo(dimethylsiloxanes) via end group attachment of host‐cyclodextrins and guest‐adamantanes or guest‐ferrocenes

In this article, we report the noncovalent linkage of terminal substituted oligo(dimethylsiloxanes) bearing cyclodextrins (CD) as host endgroups and adamantan or ferrocene, respectively, as guest endgroups. Structural characterization was performed by ¹H NMR‐, IR‐, and mass spectroscopy. Electron microscopy studies show significant differences in the surface structure of the individual derivatives. In addition, the ferrocene‐terminated di‐and poly(dimethylsiloxanes) are distinguished by a red‐ox activity and reversibility, which also makes the complexes between the ferrocene‐ and CD functionalized siloxanes switchable via electrochemical stimuli. The evidence for a successful complexation of the end groups, and thus the successful supramolecular formation of the siloxane strands, was even performed by shift of the protons in the ¹H NMR spectra. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2472–2482     

Ionic liquid self‐assembled monolayer and ion exchange for surface force control

Adhesion and lateral force were controlled by the formation of a self‐assembled monolayer combined with the surface ion exchange of ionic liquids on a silicon surface. In this study, the functionalized imidazolium ionic liquids were designed and synthesized with the aim of controlling surface force. N‐[3‐(Trimethoxylsilyl)propyl] ethylenediamine molecules were first self‐assembled onto a surface as an anchor layer and then 1‐propionic acid‐3‐methylimidazolium chloride were successfully grafted onto the amino‐modified surface. The surface force was changed by surface ion exchange in various anionic solutions. The self‐assembly and ion exchange processes were detected by means of attenuated total reflectance‐Fourier transform infrared spectrometry and further confirmed by X‐ray photoelectron spectra. Adhesion and friction behaviors were systematically investigated by atomic force/friction force microscope. The results indicated that anions played a great role in determining surface properties. Furthermore, surface adhesion and friction can be possibly quantitatively determined by the counter‐anions on the surface. Copyright © 2011 John Wiley & Sons, Ltd.     

Mass Distribution and Diffusion of [1‐Butyl‐3‐methylimidazolium][Y] Ionic Liquids Adsorbed on the Graphite Surface at 300–800 K

The structure and diffusion behavior of 1‐butyl‐3‐methylimidazolium ([bmim]⁺) ionic liquids with [Cl]^?, [PF₆]^?, and [Tf₂N]^? counterions near a hydrophobic graphite surface are investigated by molecular dynamics simulation over the temperature range of 300–800 K. Near the graphite surface the structure of the ionic liquid differs from that in the bulk and it forms a well‐ordered region extending over 30 Å from the surface. The bottom layer of the ionic liquid is stable over the investigated temperature range due to the inherent slow dynamics of the ionic liquid and the strong Coulombic interactions between cation and anion. In the bottom layer, diffusion is strongly anisotropic and predominantly occurs along the graphite surface. Diffusion perpendicular to the interface (interfacial mass transfer rate k_t) is very slow due to strong ion–substrate interaction. The diffusion behaviors of the three ionic liquids in the two directions all follow an Arrhenius relation, and the activation barrier increases with decreasing anion size. Such an Arrhenius relation is applied to surface‐adsorbed ionic liquids for the first time. The ion size and the surface electrical charge density of the anions are the major factors determining the diffusion behavior of the ionic liquid adjacent to the graphite surface.     

Electrochemical Study of Dialcarb “Distillable” Room‐Temperature Ionic Liquids

Electrode‐dependent potential windows (see picture, GC=glassy carbon) are determined for five dialkylammonium carbamate (dialcarb) room‐temperature ionic liquids in a systematic study of their physical and electrochemical properties. The viscosity and conductivity of the dialcarb ionic liquids, which are “distillable” at low temperature, are comparable to those of some conventional room‐temperature ionic liquids.

     

Variations of diffusion coefficients of redox active molecules in room temperature ionic liquids upon electron transfer

In ionic liquids, the diffusion coefficients of a redox couple vary considerably between the neutral and radical ion forms of the molecule. For a reduction, the inequality of the diffusion coefficients is characterized by the ratio gamma = D(red)/D(ox), where D(red) and D(ox) are the diffusion coefficients of the electrogenerated radical anion and of the corresponding neutral molecule, respectively. In this work, measurements of gamma have been performed by scanning electrochemical microscopy (SECM) in transient feedback mode, in three different room temperature ionic liquids (RTILs) sharing the same anion and with a series of nitro-derivative compounds taken as a test family. The smallest gamma ratios were determined in an imidazolium-based RTIL and with the charge of the radical anion localized on the nitro group. Conversely, gamma tends to unity when the radical anion is fully delocalized or when the nitro group is sterically protected by bulky substituents. The gamma ratios, standard potentials of the redox couple measured in RTILs, and those observed in a classical organic solvent were compared for the investigated family of compounds. The stabilization energies approximately follow the gamma ratios in a given RTIL but change considerably between ionic liquids with the nature of the cation.     

Detection of Biomarkers for Liver Fibrosis Using High‐Throughput Electrochemical Microimmunosensor

A high‐throughput electrochemical microimmunosensor for the detection of biomarkers for liver fibrosis was developed. The antibodies, hyaluronic acid binding protein (HABP), lamin antibody (a‐LN) and type IV‐collagen antibody (a‐IVC), are immobilized on different electrodes of the microelectrode array by copolymerizing into the partly insulated poly(o‐phenylenediamine) by means of cyclic voltammetry. Electrochemical detection of the corresponding antigen was based on the extent of electrode insulation toward a redox probe (ferrocenemethanol) solubilized in the electrolyte as a result of the formation of the antigen‐antibody complex at the electrode surface. The microimmunosensor exhibits enough sensitivity to detect the three biomarkers at a concentration level down to 3 ng/mL. The microimmunosensor has been applied to real samples, the results agree well with those obtained by radioimmunoassay (RIA). With the possibility of being portable and considering its ease of use, robustness, and simplicity, the microimmunosensor has great potential as a tool for the screening and early detection of liver fibrosis.     

Electrochemical Detection of Nitric Oxide on a SWCNT/RTIL Composite Gel Microelectrode

Single walled carbon nanotubes (SWCNT) and room temperature ionic liquid (RTIL) were used to make a gel microelectrode for studies of the oxidation of nitric oxide (NO). The Faraday response of the gel microelectrode was contributed from two components: an outside‐surface microdisk and a thin‐layer cell formed by inner porous electrode materials, and enhanced by the thin‐layer effect. An EC mechanism, electrochemical NO oxidation followed by a chemical oxidation, was proposed. The gel microelectrode with a Nafion coating eliminated interferences from nitrite and some biomolecules, improved stability, and had a linear response range from 100 nM to 100 μM.     

Isolation and purification of alkaloids from lotus leaves by ionic‐liquid‐modified high‐speed countercurrent chromatography

An effective high‐speed countercurrent chromatography method was successfully established by using ionic liquids as the modifier of the two‐phase solvent system. Adding a small amount of ionic liquids significantly shortens the separation time and improves the separation efficiency. The conditions of ionic‐liquid‐modified high‐speed countercurrent chromatography including solvent systems, types and content of added ionic liquids, and ionic liquids posttreatment were investigated. The established method was successfully applied to separate alkaloids from lotus leaves using a two‐phase solvent system composed of petroleum ether/ethyl acetate/methanol/water/[C₄mim][BF₄] (1:5:1:5:0.15, v/v/v/v/v). Four alkaloids pronuciferine (1.7 mg), N‐nornuciferine (4.3 mg), nuciferine (3.1 mg), and roemerine (2.1 mg) were obtained with the purities of 90.53, 92.25, 99.86, and 98.63%, respectively, from 100 mg crude extract of lotus leaves. The results indicated that the ionic‐liquid‐modified high‐speed countercurrent chromatography method was suitable for alkaloid separation from lotus leaves and would be a promising method for the separation of alkaloids from other natural products.     

Understanding the Effect Models of Ionic Liquids in the Synthesis of NH4‐Dw and γ‐AlOOH Nanostructures and Their Conversion into Porous γ‐Al2O3

Well‐dispersed ammonium aluminum carbonate hydroxide (NH₄‐Dw) and γ‐AlOOH nanostructures with controlled morphologies have been synthesized by employing an ionic‐liquid‐assisted hydrothermal process. The basic strategies that were used in this work were: 1) A controllable phase transition from NH₄‐Dw to γ‐AlOOH could be realized by increasing the reaction temperature and 2) the morphological evolution of NH₄‐Dw and γ‐AlOOH nanostructures could be influenced by the concentration of the ionic liquid. Based on these experimental results, the main objective of this work was to clarify the effect models of the ionic liquids on the synthesis of NH₄‐Dw and γ‐AlOOH nanostructures, which could be divided into cationic‐ or anionic‐dominant effect models, as determined by the different surface structures of the targets. Specifically, under the cationic‐dominant regime, the ionic liquids mainly showed dispersion effects for the NH₄‐Dw nanostructures, whereas the anionic‐dominant model could induce the self‐assembly of the γ‐AlOOH particles to form hierarchical structures. Under the guidance of the proposed models, the effect of the ionic liquids would be optimized by an appropriate choice of cations or anions, as well as by considering the different effect models with the substrate surface. We expect that such effect models between ionic liquids and the target products will be helpful for understanding and designing rational ionic liquids that contain specific functional groups, thus open up new opportunities for the synthesis of inorganic nanomaterials with new morphologies and improved properties. In addition, these as‐prepared NH₄‐Dw and γ‐AlOOH nanostructures were converted into porous γ‐Al₂O₃ nanostructures by thermal decomposition, whilst preserving the same morphology. By using HRTEM and nitrogen‐adsorption analysis, the obtained γ‐Al₂O₃ samples were found to have excellent porous properties and, hence, may have applications in catalysis and adsorption.