Self-Limited Grafting of Sub-Monolayers via Diels-Alder Reaction on Glassy Carbon Electrodes: An Electrochemical Insight.

The grafting of molecular monolayers is critical for the functionalization of surfaces. In molecular electrochemistry, the surface modification of electrodes and the way molecules are attached to the electrode surface are highly critical to electron transfers and electrochemical reactions. In this paper, sub-monolayers were covalently grafted onto glassy carbon (GC) electrodes via Diels-Alder cycloaddition with two soluble dienophiles, that is, propargyl bromide and ethynyl ferrocene. Such an approach is clean (no by-product, no catalyst/additive) and occurs under mild conditions by heating at 50 °C in toluene for few hours. The as-modified electrodes were thoroughly characterized by FTIR, XPS, and cyclic voltammetry using both millimetric GC electrodes and ultra-microelectrodes. Cyclic voltammetry gave access to surface coverage and clearly evidenced the covalent grafting of sub-monolayers. The grafting of functional sub-monolayers via Diels-Alder cycloaddition could be easily extended to various functionalities and carbons to prepare electrochemical sensors or electrocatalytic surfaces.

Biredox ionic liquids with solid-like redox density in the liquid state for high-energy supercapacitors.

Kinetics of electrochemical reactions are several orders of magnitude slower in solids than in liquids as a result of the much lower ion diffusivity. Yet, the solid state maximizes the density of redox species, which is at least two orders of magnitude lower in liquids because of solubility limitations. With regard to electrochemical energy storage devices, this leads to high-energy batteries with limited power and high-power supercapacitors with a well-known energy deficiency. For such devices the ideal system should endow the liquid state with a density of redox species close to the solid state. Here we report an approach based on biredox ionic liquids to achieve bulk-like redox density at liquid-like fast kinetics. The cation and anion of these biredox ionic liquids bear moieties that undergo very fast reversible redox reactions. As a first demonstration of their potential for high-capacity/high-rate charge storage, we used them in redox supercapacitors. These ionic liquids are able to decouple charge storage from an ion-accessible electrode surface, by storing significant charge in the pores of the electrodes, to minimize self-discharge and leakage current as a result of retaining the redox species in the pores, and to raise working voltage due to their wide electrochemical window.

Multiwalled Carbon Nanotube/Cellulose Composite: From Aqueous Dispersions to Pickering Emulsions.

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5. Starting with rather crude initial materials, commercial Sigmacell cellulose and MWCNTs, a significant fraction of composite dispersed in water could be obtained. The solid composites and their colloidal suspensions were characterized by electronic microscopy, thermal analyses, FTIR and Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and light scattering. The composite particles consist of tenuous aggregates of CNTs and cellulose, several hundred nanometers large, and are composed of 55 wt % cellulose and 45 wt % CNTs. Such particles were shown to stabilize cyclohexane-in-water emulsions. The adsorption and the elasticity of the layer they form at interface were characterized by the pendant drop method. The stability of the oil-in-water emulsions was attributed to the formation of an elastic network of composite particles at interface. Cyclohexane droplet diameters could be tuned from 20 to 100 µm by adjusting the concentration of composite particles. This behavior was attributed to the limited coalescence phenomenon, just as expected for Pickering emulsions. Interestingly, cyclohexane droplets were stable over time and sustained pH modifications over a wide range, although acidic pH induced accelerated creaming. This study points out the possibility of combining crude cellulose and MWCNTs through a simple process to obtain colloidal systems of interest for the design of functional conductive materials.

Diacetylenes with Ionic-Liquid-Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N-Doped Carbon Materials.

Imidazolium- and benzimidazolium-substituted diacetylenes with bromide or nitrogen-rich dicyanamide and tricyanomethanide anions were synthesized and used as precursors for the preparation of N-doped carbon materials. On pyrolysis under argon at 800 °C both halide precursors afforded graphite-like structures with nitrogen contents of about 8.5%. When the dicyanamide and tricyanomethanide precursors were thermolyzed at the same temperature, graphite-like structures were obtained that exhibit nitrogen contents in the range 17-20 wt%; thereby, the benefit of associating a polymerizing cation with a polymerizing anion in a single precursor was demonstrated. On pyrolysis at 1100 °C the nitrogen contents of the latter pyrolysates remain high (ca. 6 wt%). Adsorption measurements with krypton at 77 K indicated that the materials are nonporous. The highest electrical conductivity was observed for a pyrolysate with one of the lowest nitrogen contents, which also has the highest degree of graphitization. Thus, the quest for N-rich carbons with high electrical conductivities should include both maximization of the nitrogen content and optimization of the degree of graphitization. Crystallographic investigation of the precursors and spectroscopic characterization of the pyrolysates prepared by heating at 220 °C indicate that construction of the final carbon framework does not involve the intermediate formation of a polydiacetylene.

Surfactant behavior of ionic liquids involving a drug: from molecular interactions to self-assembly.

Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), (1)H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

Drug delivery systems based on pharmaceutically active ionic liquids and biocompatible poly(lactic acid).

Poly(l-lactic acid) (PLLA) membranes containing pharmaceutically active ionic liquids (API-ILs) have been prepared by using a simple film casting from solvent evaporation method. Several sets of membranes were prepared from two different ionic liquids namely 1-methyl-3-butyl-imidazolium ibuprofenate (C4MImIbu) and lidocainium ibuprofenate (LidIbu) with different API-IL contents. Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Wide-Angle and Small-Angle X-ray Scattering (WAXS and SAXS) revealed the strong influence of both the IL nature and content on the morphology and the crystallinity of the resulting PLLA. At 20 weight%, LidIbu was shown to act as a plasticizer for PLLA and homogeneous membranes were obtained. In contrast, at the same IL content, phase separation occurred using C4MImIbu, resulting in the formation of porous PLLA. An increase of LidIbu content to 50 weight% results also in phase separation. 1H and 1H-13C CP-MAS NMR measurements evidenced the influence of different morphologies and crystallinities on IL mobility. C4MImIbu was found to be highly mobile whereas the mobility of LidIbu was content dependent. At low percent, low mobility was observed while at higher content, two populations with respectively high and low mobility were observed. These PLLA-IL membranes were further tested as drug delivery systems. In accordance with the morphology and mobility obtained, we demonstrated that release kinetics from PLLA membranes can be tuned by the nature and the content of API-ILs. Sustainable release kinetics were obtained with API-IL acting as a plasticizer while the fastest release was obtained with API-IL acting as a porogenic agent.

Surfactant properties of ionic liquids containing short alkyl chain imidazolium cations and ibuprofenate anions.

Interfacial tension, electrical conductivity, NMR self-diffusion and DLS experiments have been used to investigate the self-aggregation in water of ionic liquids associating an ibuprofenate anion and 1-alkyl-3-methylimidazolium [C(n)MIm](+) (n = 4, 6, 8) cations. Despite the short alkyl chain on imidazolium cations (n ≤ 8), these ionic liquids exhibit particularly low Critical Aggregation Concentrations (CAC), significantly lower than their parent 1-alkyl-3-methylimidazolium chloride salts. This behaviour is attributed to the formation of catanionic pairs between ibuprofenate and imidazolium.

Loading-Controlled Stiffening in Nanoconfined Ionic Liquids.

An important strategy for using ionic liquids is to immobilize them by impregnation of supports or incorporation into porous solids to obtain materials called "ionogels". Of considerable importance for applications (electrolyte membranes, supported catalysts, etc.), such confinement results in dramatic changes in the physicochemical properties of the ionic liquid. Here, we report molecular simulations of a silica nanopore that is gradually filled with a typical imidazolium salt ionic liquid to obtain a realistic model of these ionogels. Despite the significant layering and stiffening of the ionic liquid in the vicinity of the silica surface, the pair correlation functions and magnitude of its dynamics clearly evidence liquid-like behavior. An increase in the self-diffusivity and ionic conductivity, associated with a decrease in the characteristic residence times of ions at the silica surface, is observed upon increasing the loading as the ionic liquid fills the nanopore center and tends to recover its bulk properties.

Ionogels, ionic liquid based hybrid materials.

The current interest in ionic liquids (ILs) is motivated by some unique properties, such as negligible vapour pressure, thermal stability and non-flammability, combined with high ionic conductivity and wide electrochemical stability window. However, for material applications, there is a challenging need for immobilizing ILs in solid devices, while keeping their specific properties. In this critical review, ionogels are presented as a new class of hybrid materials, in which the properties of the IL are hybridized with those of another component, which may be organic (low molecular weight gelator, (bio)polymer), inorganic (e.g. carbon nanotubes, silica etc.) or hybrid organic-inorganic (e.g. polymer and inorganic fillers). Actually, ILs act as structuring media during the formation of inorganic ionogels, their intrinsic organization and physicochemical properties influencing the building of the solid host network. Conversely, some effects of confinement can modify some properties of the guest IL, even though liquid-like dynamics and ion mobility are preserved. Ionogels, which keep the main properties of ILs except outflow, while allowing easy shaping, considerably enlarge the array of applications of ILs. Thus, they form a promising family of solid electrolyte membranes, which gives access to all-solid devices, a topical industrial challenge in domains such as lithium batteries, fuel cells and dye-sensitized solar cells. Replacing conventional media, organic solvents in lithium batteries or water in proton-exchange-membrane fuel cells (PEMFC), by low-vapour-pressure and non flammable ILs presents major advantages such as improved safety and a higher operating temperature range. Implementation of ILs in separation techniques, where they benefit from huge advantages as well, relies again on the development of supported IL membranes such as ionogels. Moreover, functionalization of ionogels can be achieved both by incorporation of organic functions in the solid matrix, and by encapsulation of molecular species (from metal complexes to enzymes) in the immobilized IL phase, which opens new routes for designing advanced materials, especially (bio)catalytic membranes, sensors and drug release systems (194 references).

Ionic liquid as plasticizer for europium(III)-doped luminescent poly(methyl methacrylate) films.

Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C(6)mim][Tf(2)N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C(6)mim][Eu(nta)(4)], [C(6)mim][Eu(tta)(4)], [Eu(tta)(3)(phen)] and [choline](3)[Eu(dpa)(3)], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with beta-diketonate complexes are characterized by a very intense (5)D(0)-->(7)F(2) transition (up to 15 times more intense than the (5)D(0)-->(7)F(1)) transition, whereas a marked feature of the PMMA films doped with [choline](3)[Eu(dpa)(3)] is the long lifetime of the (5)D(0) excited state (1.8 ms).

Ionogels as drug delivery system: one-step sol-gel synthesis using imidazolium ibuprofenate ionic liquid.

Ionogels containing imidazolium ibuprofenate have been shown to be an efficient drug releasing system with kinetics controlled by the nature of the silica wall.

Removal of dimethylsulfoxide from wastewater using mild oxidation with H2O2 over Ti-based catalysts.

The mild catalytic oxidation of dimethylsulfoxide (DMSO) into biodegradable dimethylsulfone is proposed as an efficient pretreatment of wastewaters subjected to biological treatment processes. A SiO(2)-TiO(2) mesoporous xerogel prepared by a non-hydrolytic route, as well as titanium silicalite TS-1 showed very good activity and stability in the catalytic oxidation of DMSO with H(2)O(2) in dilute aqueous solution, at room temperature.

Immobilization of ionic liquids in translucent tin dioxide monoliths by sol-gel processing.

SnO2 translucent monolith ionogels were obtained by a sol-gel processing using bis(2-methylbutan-2-oxy)di(pentan-2,4-dionato)tin as a precursor in the presence of various ionic liquids: [BMI][Br], [BMI][TFSI], [BMI][BF4]. The confinement of ionic liquids within the gels was evidenced by Differential Scanning Calorimetry, FTIR and FT-Raman spectroscopy. The ionic liquids could be efficiently washed off, which resulted in supermicroporous solids. Calcination in air at 550 degrees C of the dried monoliths resulted in nanoporous nanocrystalline cassiterite tin dioxide particles with crystallite sizes of about 8-12 nm and mean pore sizes around 5 nm.

Lanthanide-doped luminescent ionogels.

Ionogels are solid oxide host networks confining at a meso-scale ionic liquids, and retaining their liquid nature. Ionogels were obtained by dissolving lanthanide(III) complexes in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N], followed by confinement of the lanthanide-doped ionic liquid mixtures in the pores of a nano-porous silica network. [C6mim][Ln(tta)4], where tta is 2-thenoyltrifluoroacetonate and Ln=Nd, Sm, Eu, Ho, Er, Yb, and [choline]3[Tb(dpa)3], where dpa=pyridine-2,6-dicarboxylate (dipicolinate), were chosen as the lanthanide complexes. The ionogels are luminescent, ion-conductive inorganic-organic hybrid materials. Depending on the lanthanide(III) ion, emission in the visible or the near-infrared regions of the electromagnetic spectrum was observed. The work presented herein highlights that the confinement did not disturb the first coordination sphere of the lanthanide ions and also showed the excellent luminescence performance of the lanthanide tetrakis beta-diketonate complexes. The crystal structures of the complexes [C6mim][Yb(tta)4] and [choline]3[Tb(dpa)3] are reported.

Non-hydrolytic synthesis of mesoporous silica-titania catalysts for the mild oxidation of sulfur compounds with hydrogen peroxide.

A SiO(2)-TiO(2) mesoporous xerogel prepared in one-step by a non-hydrolytic route shows excellent performance in the mild oxidation of sulfides, sulfoxides and thiophenes with aqueous solutions of H(2)O(2).

A route to heat resistant solid membranes with performances of liquid electrolytes.

The confinement of ionic liquids within a porous silica matrix was performed by a one-step non-hydrolytic sol-gel route, leading to hybrid materials (called "ionogels") featuring both the mechanical and transparency properties of silica gels and the high ionic conductivity and thermal stability of ionic liquids.

Novel non-hydrolytic synthesis of a V2O5-TiO2 xerogel for the selective catalytic reduction of NOx by ammonia.

A vanadia-titania mesoporous xerogel (10.5 wt% V(2)O(5)) was prepared from chloride precursors using a one-step non-hydrolytic sol-gel route and subsequent drying at ambient pressure; after calcination at 773 K for 5 h no crystalline V(2)O(5) was detected and the resulting mixed oxide exhibited remarkable activity in the selective reduction of NO with NH(3).

Mixed 1D-2D inorganic polymeric zinc ferrocenylphosphonate: crystal structure and electrochemical study.

Needs for ferrocene immobilization on robust host structures are considerable since derivative materials may find applications in medical areas, optical devices, or catalysis. Synthesis of phosphonate functionalized ferrocene allowed its subsequent inorganic polymerization with a zinc salt. The crystallographic structure of the compound obtained, Zn(HO(3)PFc)(2).2H(2)O, shows a unique two-dimensional ferrocene arrangement anchored on a one-dimensional Zn-O-P-O-Zn backbone. The ferrocene packing in the title compound is very similar to the packing found in molecular ferrocene. The electroactivity of Zn(HO(3)PFc)(2).2H(2)O is thoroughly studied. It shows a reversible surface oxidation of ferrocene. Mössbauer spectroscopy for the oxidized compound shows an isomer shift of IS(2b) = 0.432 mm x s(-1) and a quadrupolar splitting of QS(2b) = 0.205 mm x s(-1), which is consistent with a stable S = 1/2 ferrocenium state. The magnetic susceptibility study, Mössbauer spectroscopy, and galvanostatic titration show that only the ferrocene moieties present at the surface of the crystallites are reversibly oxidized. This observation is reinforced by a complex impedance study showing mainly resistive behavior and conductivity measurements indicating weak, thermally assisted, conductivity. The general properties of this compound demonstrate that phosphonato functionalization may be a useful approach for all fields concerned by immobilization of ferrocene.