Iridium-based light-emitting electrochemical cells containing ionic liquids in the luminous layer

To fabricate transition metal complex-based LECs (light-emitting electrochemical cells), ([Ir(ppy)₂(5,6-dime-1,10-phenthroline)]PF₆ was synthesized and used as a luminous material and ILs (ionic liquids) were incorporated into a luminous layer, in which two types of ionic liquid were used; 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄). ILs were added to a [Ir(ppy)₂(5,6-dime-1,10-phenthroline)]PF₆ luminous layer to improve ionic conductivity and light intensity. Both ILs significantly increased the current density and luminance. Due to the small molecule of BF₄^?, turn-on time was reduced and ionic conductivity was increased. However, the device stability was sacrificed. High current efficiency of 34.5 cd/A was investigated at 7 V of BMIMPF₆-doped luminous layer. The LECs based on [Ir(ppy)₂(5,6-dime-1,10-phenthroline)]PF₆ gave yellow emission color when ILs were added into light-emitting layer, and no significant change of color has been found in this study.     

Synthesis of nanostructured TiO2 particles in room temperature ionic liquid and its photocatalytic performance

Nanostructured TiO₂ particles were synthesized by sol-gel method with room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) as a reaction medium. The structure and morphology of TiO₂ nanoparticles were characterized with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ nanoparticles present anatase crystal phase even without being calcined at high temperature, and show better photocatalytic performance in the degradation of methyl orange. The photocatalytic efficiency increases evidently along with increasing the concentration of nanostructure TiO₂, and the degradation percent can reach 100% at the optimal catalyst concentration (2.0 g/L).     

Synthesis of PbS nanocubes using an ionic liquid as the solvent

Lead sulfide (PbS) is a major ore mineral of lead and an important semiconductor. The small band gap and large exciton Bohr radius make PbS an interesting system for studying the effect of size confinement. The precise control of their size and size distribution is an important goal of modern materials chemistry. In this work, lead sulfide (PbS) nanocubes have been successfully synthesized in an ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) (ILs). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the cubic morphology of the synthesized nanocrystals with the length about 100 nm. X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed the nanocubes were cubic PbS with a lattice constant of 5.93 Å.     

Viscosity of Imidazolium-Based Ionic Liquids at Elevated Pressures: Cation and Anion Effects

The viscosity of imidazolium-based ionic liquids with four different cations and three different anions was measured to pressures of 126 MPa and at three temperatures (298.15 K, 323.15 K, and 343.15 K). The high-pressure viscosity of 1-ethyl-3-methylimidazolium ([EMIm]), 1-n-hexyl-3-methylimidazolium ([HMIm]), and 1-n-decyl-3-methylimidazolium ([DMIm]) cations with a common anion, bis(trifluoromethylsulfonyl)imide ([Tf₂N]), was measured to determine the alkyl-chain length effect of the cation. An increase in the alkyl-chain length increased the viscosity at elevated pressures. [DMIm] exhibited a larger nonlinear increase with pressure over the shorter alkyl substituents. Anion effects were investigated with [HMIm] as a common cation and anions of [Tf₂N], hexafluorophosphate ([PF₆]), and tetrafluoroborate ([BF₄]). [HMIm][PF₆], with the highest viscosity, demonstrated a very nonlinear pressure dependence even at relatively moderate pressures (to 30 MPa), similar to the results for [BMIm][PF₆]. A combined Litovitz and Tait equation was utilized to describe the viscosity of the ionic liquids with pressure and temperature and demonstrated good correlation with the experimental data.     

One-pot synthesis of supported-nanoparticle materials in ionic liquid solvents

Highly porous supported-nanoparticle materials were synthesized by a rational method involving the encapsulation of poly(vinylpyrrolidone) (PVP)-stabilized Au nanoparticles into titania xerogels employing room temperature ionic liquids (1-butyl-3-methylimidazolium hexaflurophosphate, [BMIM]PF₆) as a medium followed by solvent extraction of the ionic liquid and calcination of the materials. The materials were thoroughly characterized by TEM, nitrogen adsorption-desorption isotherms, and XRD. After calcinations at 350 °C, the Au-titania system resulted in the formation of a highly mesoporous materials with BET surface areas of 200 m²/g and average pore sizes of 3-5 nm. These materials can find potential applications in catalysis and photocatalysis.     

Quantitative analysis of the (n,m) abundance of single-walled carbon nanotubes dispersed in ionic liquids by optical absorption spectra

Room temperature ionic liquids (ILs) of imidazolium ions were found to be ideal media for dispersing single-walled carbon nanotubes (SWNTs) at relatively high content and for studying their intrinsic properties. Comparing to other dispersion methods IL dispersion do not involve in extensive ultrasonication and centrifugation, thus can reflect the real chiral composition and abundance distribution of the original raw SWNT samples. Optical absorption spectra of 1-N-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆])-dispersed SWNTs at different concentrations are performed based on direct and precise weighing the mass of the SWNT samples. An excellent linear relationship of the absorbance with respect to SWNT concentration is observed not only in a large concentration scale but also over a wide wavelength range. By deconvolution of the absorption spectra in the region of the first subbands transition of semiconducting SWNTs (E₁₁^S region, 800–1400 nm) into individual bands with (n,m) assignment in good agreement with fluorescence spectra, the relative abundance of 12 different semiconducting chiralities is analyzed quantitatively. It is found that the relative abundance of semiconducting SWNTs follows an exponential trend with respect to chiral angle. No clear dependence of the relative abundance on tube diameter is observed.     

A novel ionic liquid/micro-volume back extraction procedure combined with flame atomic absorption spectrometry for determination of trace nickel in samples of nutritional interest

A simple, highly sensitive and environment-friendly method for the determination of trace amount of nickel ion in different matrices is proposed. In the preconcentration step, the nickel from 10 mL of an aqueous solution was extracted into 500 μL of ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate [C₄MIM][PF₆], containing PAN as complexing agent. Subsequently, the PAN complex was back-extracted into 250 μL of nitric acid solution, and 100 μL of it was analyzed by flow injection flame atomic absorption spectrometry (FI-FAAS). The main parameter influencing the extraction and determination of nickel, such as pH, concentration of PAN, extraction time and temperature, ionic strength, and concentration of stripping acid solution, were optimized. An enhancement factor of 40.2 was achieved with 25 mL sample. The limit of detection (LOD) and quantification obtained under the optimum conditions were 12.5 and 41.0 μg L^?1, respectively. To validate the proposed methods two certified reference materials 681-I and BCR No. 288 were analyzed and the results were in good agreement with the certified values. The proposed method was successfully applied to determination of nickel in water samples, rice flour and black tea.     

Solubility of Hydrogen Sulfide in [bmim][PF<Subscript>6</Subscript>]

New experimental data are presented for the solubility of hydrogen sulfide in the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at five temperatures in the range (298–403) K at pressures up to 9.6 MPa. The ionic liquid [bmim][PF₆] is a good solvent for hydrogen sulfide. At 9 MPa the mole fraction H₂S in the liquid is about 0.7. The solubility is a strong function of temperature; at 2 MPa the solubility (mole fraction H₂S) decreases from about 0.84 at 298 K to about 0.2 at 403 K. The Krichevsky–Kasarnovsky equation was used to correlate the experimental data, and Henry’s constants were obtained. The solution thermodynamic properties at standard temperature and pressure were calculated.     

High performance graphene-poly (o-anisidine) nanocomposite for supercapacitor applications

Our previous exciting results on graphene (G)-conducting polymer (polyaniline (PANI) and polyethylenedioxythiophene (PEDOT)) supercapacitors have prompted the investigation of G-substituted conducting polymer nanocomposites used as electrode materials in supercapacitors. The solubility of ortho-substituted PANI derivatives in a few common solvents has allowed the fabrication of stretchable films by the casting technique. The G-poly (o-anisidine) (G-POA) nanocomposites were synthesized with different weight ratios of G to o-anisidine by chemical methods, and characterized by various techniques, such as, scanning electron microscopy, transmission electron microscopy, UV–visible spectroscopy, Raman spectroscopy, thermogravimetric analysis and cyclic voltammetry. The electrical conductivity and specific capacitance obtained for the G-POA nanocomposites were found to be dependent on the weight ratios of G to o-anisidine. The specific capacitance and the charging–discharging behavior of the POA and G-POA supercapacitors were investigated in a 2 M H₂SO₄, 0.2 M LiClO₄ and 1 M 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆) ionic liquid. The specific capacitance of 380 F g⁻¹ was calculated for the 1:1 weight ratio of G to o-anisidine based G-POA supercapacitor in 2 M H₂SO₄. The presence of the electron-donating group (–OCH₃) in the o-anisidine allows the electrons through the lone pair of nitrogen atoms to enhance the electronic charge transport inside the G-POA supercapacitor electrodes. However, the G-POA-based supercapacitors showed a 27% decrease in the specific capacitance in H₂SO₄ and 16% decrease in the ionic liquid (BMIM-PF₆) after 1000 cycles of charging and discharging. The higher stability and rate capability of the G-POA based supercapacitor in an ionic liquid (BMIM-PF₆) as compared to an aqueous electrolytic supercapacitor opens the door for the fabrication of stable supercapacitors for practical applications.     

MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH)₂ nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 μM, with a detection limit of 0.04 μM. Electrochemical studies suggested that the MWCNTs/Cu(OH)₂ nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current.     

Single dopant white electrophosphorescent light emitting diodes using heteroleptic tris-cyclometalated Iridium(III) complexes

We report single dopant single emissive layer white organic electroluminescent (EL) device based on the heteroleptic tris-cyclometalated iridium(III) complex, Ir(dfppy)₂(pq), as the guest, where dfppy and pq are 2-(2,4-difluorophenyl) pyridine and 2-phenylquinoline, respectively, and 1,4-phenylenesis(triphenylsilane) (UGH2) as the host. The maximum luminous and power efficiencies of the device were 11.00 cd/A (J = 0.05 mA/cm²) and 5.60 lm/W (J = 0.001 mA/cm²), respectively. The CIE coordinates of the device with Ir(dfppy)₂(pq) are (0.443, 0.473) and the EL spectrum of device shows emission band at 473 and 544 nm, at the applied voltage of 12 V. The similar phosphorescent decay rate of two ligands can lead to emit luminescence in two ligands at the same time.     

<Emphasis Type="Italic">Ab initio</Emphasis> studies on [bmim][PF<Subscript>6</Subscript>]-CO<Subscript>2</Subscript> mixture and CO<Subscript>2</Subscript> clusters

Ab initio molecular dynamics studies have been carried out on the room temperature ionic liquid, 1,n-butyl,3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) and supercritical carbon dioxide mixture at room temperature and experimental density. Partial radial distribution functions (RDF) for different sites have been computed to see the organization of CO₂ molecules around the ionic liquid. Several partial RDFs around the carbon atom of CO₂ molecule are compared to find out that the CO₂ has specific interaction with a carbon atom present in the imidazolium ring. The CO₂ is also found to be very well organized around the terminal carbon atom of the butyl chain. The partial RDFs for the oxygen atoms around oxygen and carbon atoms of the CO₂ suggests that there is very good organization of CO₂ molecules around themselves even in the [bmim][PF₆]-CO₂ mixture. The instantaneous quadrupole moment tensor has been calculated for the anion and the cation. The ensemble average of diagonal components of quadrupole moment tensor of the cation have finite values, whereas the off-diagonal components of the cation and both the diagonal and off-diagonal components of the anion have the value of zero with a large standard deviation. The CPMD studies performed on CO₂ clusters reveals the greater tendency of the clusters with more CO₂ units, to deviate from the linear geometry.     

Fe(CN)6 incorporation on Poly(3,4-ethylenedioxythiophene) films: Preparation and X-ray Photoelectron Spectroscopy characterization of the modified electrodes

Poly(3,4-ethylenedioxythiophene) (PEDOTh) films were potentiodynamically deposited on platinum from tetrabutylammonium hexafluorophosphate/acetonitrile solutions. Polymers prepared with different number of cycles showed reversible redox behaviour and the X-ray Photoelectron Spectroscopy (XPS) characterization revealed the existence of zones with different conductivity and confirmed the presence of PF₆⁻. The incorporation of the metallic complex Fe(CN)₆³⁻ in the PEDOTh films was made in one step, after the electrosynthesis of a film grown with a given number of potential cycles, and by means of polymerization/incorporation sequences. XPS data confirmed the presence of the inorganic species and the highest Fe 2p_3/2 peak intensity was observed for thin films (30 cycles) when the one step incorporation has been used. The XPS results suggest a partial dissociation of the Fe-(C-N) bond of the complex in the modified electrodes.     

Highly conductive non aqueous polymer gel electrolytes containing ammonium hexafluorophosphate (NH4PF6)

Non aqueous polymer gel electrolytes based on polyethylene oxide (PEO) and ammonium hexafluorophosphate (NH₄PF₆) show high conductivity above 10⁻² S/cm at 25°C. The addition of PEO to liquid electrolytes has been found to result in an increase in free ion concentration by dissociating ion aggregates present in these electrolytes at higher concentrations (≥0.4 M) of NH₄PF₆ alongwith an increase in viscosity. The free ion concentration and viscosity play a dominant role on the conductivity behaviour of these polymer gel electrolytes at low and high concentrations of PEO respectively. The presence of ion aggregates and their dissociation with the addition of PEO has also been checked by FTIR and the results are in agreement with the conductivity behaviour.     

Synthesis and characterization of novel γ-induced porous PHEMA–IL composites

A novel porous polymer-ionic liquid composite with poly(2-hydroxyethyl methacrylate) (PHEMA) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) has been synthesized by γ-irradiation without heat or chemical initiators. The products can be reversibly converted into organogels. The composites are potential candidates for electrochemical applications. The use of γ-radiation can be a simple and versatile alternative way to obtain these materials.     

Selective electrodes for [PF6]− and [BF4]− anions based on the associates formed by ionic liquid and cationic dyes

The feasibility of the newly synthesized ionic associates L1 and L2 formed by ionic liquid [C₄mim][PF₆] and cationic dyes (malachite green and methylene blue) has been tested as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes. The electrode exhibits Nernstian response and enhanced potentiometric selectivity towards [PF₆]^? compared to many other anions. The influence of some experimental parameters such as membrane composition, nature of plasticizer and amount of additive on the potential response of the [PF₆]^? sensor are investigated. Under the optimized conditions, the response slopes of the membrane electrodes towards [PF₆]^? are 59.7 ± 0.5 and 58.1 ± 0.5 mV/decade based on ionophore L1 and L2, respectively, in 1.0 × 10^? 5–1.0 × 10^? 1 or 1.0 × 10^? 6–1.0 × 10^? 1 mol/L concentration range. Interestingly, the optimized electrodes based on ionophores L1 and L2 also exhibit Nernstian response characteristics (60.3 ± 0.5 and 56.0 ± 0.5 mV/decade) for tetrafluoroborate anion [BF₄]^? in a wide concentration range. Thus, the proposed sensor has been used for the determination of [PF₆]^? and [BF₄]^? in aqueous ionic liquids samples and the solubility of the [PF₆]^? and [BF₄]^? based ionic liquids in water. The satisfactory results are obtained.     

Viscosity of [bmim][PF6] and [bmim][BF4] at High Pressure

The viscosities of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim] [PF₆]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) were measured by using a rolling-ball viscometer. The experimental temperatures were from 293.15 to 353.15 K, and the pressures were from 0.1 to 20.0 MPa.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

Visible light response and superior dispersed S-doped TiO2 nanoparticles synthesized via ionic liquid

Visible light response and superior dispersed S⁶⁺-doped TiO₂ nanoparticle catalysts (S-TiO₂) were prepared via ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate. The phenol was used for the evaluation of the S-TiO₂ photocatalytic activity. S-TiO₂ was characterized by XPS, UV–vis DRS, FE-SEM, TEM, XRD, TG/DSC, FTIR, and BET. The results showed that S-TiO₂ with appropriate S doping prepared via ionic liquid had smaller particle size, better dispersion, higher activity, and higher surface area (S_BET) than that prepared in water. Cationic S⁶⁺ incorporation into TiO₂ lattice substitutes for Ti⁴⁺ lattice site, generates Ti–O–S bonds in TiO₂, and leads to the formation of donor defect levels in band gap, so that the photocatalytic sensitization of TiO₂ has been extended to visible light region. The optimal content in S doping for the better photocatalytic performance can optimize electrical properties of the intrinsic n-type TiO₂ by adding the adequate amount of donor defect of S_Ti²⁺ for considering the lifetime of the photo-induced charge pairs.     

Performance evaluation of supported ionic liquid membrane for removal of phenol

This work evaluates the performance of ionic liquid in supported liquid membrane (SLM) for the removal of phenol from wastewater. Ionic liquids are organic salts entirely composed of organic cations and either organic or inorganic anions. Due to the fact that the vapor pressure of ionic liquid is not detectable and they are sparingly soluble in most conventional solvents, they can be applied in SLM as the organic phase. In this work, 1-n-alkyl-3-methylimidazolium salts, [C_nMIM]⁺[X]⁻ have been investigated so as to determine an optimal supported ionic liquid membrane. The effect of operational parameters such as pH, stirring speed and the concentration of stripping agent has been studied, and an evaluation of different membrane supports were also carried out. With a minimal amount of the ionic liquid 1-Butyl-3-methylimidazolium hydrogensulfate, 85% phenol removal could be achieved by using polytetrafluoroethylene hydrophobic membrane filter in the SLM.     

Spectroscopic properties and amplified spontaneous emission of fluorescein laser dye in ionic liquids as green media

The use of ionic liquids (ILs) as milieu materials for laser dyes is a promising field and quite competitive with volatile organic solvents and solid state-dye laser systems. This paper investigates some photo-physical parameters of fluorescein dye incorporated into ionic liquids; 1-Butyl-3-methylimidazolium chloride (BMIM Cl), 1-Butyl-3-methylimidazolium tetrachloroaluminate (BMIM AlCl₄) and 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄) as promising host matrix in addition to ethanol as reference. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to the transition dipole moment, the attenuation length and oscillator strength were also investigated. Lasing characteristics such as amplified spontaneous emission (ASE), the gain, and the photostability of fluorescein laser dye dissolved in different host materials were assessed. The composition and properties of the matrix of ILs were found that it has great interest in optimizing the laser performance and photostability of the investigated laser dye. Under transverse pumping of fluorescein dye by blue laser diode (450 nm) of (400 mW), the initial ASE for dye dissolved in BMIM AlCl₄ and ethanol were decreased to 39% and 36% respectively as time progressed 132 min. Relatively high efficiency and high fluorescence quantum yield (11.8% and 0.82% respectively) were obtained with good photostability in case of fluorescein in BMIM BF₄ that was decreased to ∼56% of the initial ASE after continuously pumping with 400 mW for 132 min.