Dissolution and Regeneration in Films of Natural Luffa in 1-butyl-3-methylimidazolium Chloride

Regenerated cellulose film was successfully prepared from natural luffa, a new cellulose raw material. A pretreatment of natural luffa was carried out by an alkali and hydrogen peroxide mixed solution. The dissolution process of the pretreated luffa in 1-butyl-3-methylimidazolium chloride ([BMIM]C1) was observed by polarized optical microscope. The structures and properties of the luffa films were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), and porosity measurements. The results showed that the luffa fibers were transformed to fibrils after the pretreatment. [BMIM]Cl was a good non-derivatizing solvent for the luffa cellulose. The solution conditions were 80°C and 10 h for a 15% solution. After being regenerated, as films, from the luffa/[BMIM]Cl solution, the crystalline structure of the luffa film was transformed completely from cellulose I to cellulose II. The film showed the strong characteristic functional groups of cellulose in FTIR results. The surface of the film was smooth with a compact structure. The porosity of the film was 66.2% and the average pore size was 17.8 nm. It was thermally stabile up to 280°C.     

Curing temperature- and concentration-dependent dielectric properties of cross-linked poly-4-vinylphenol (PVP)

In this paper, dielectric properties of various thick PVP films cured at temperatures between 125° C and 200 °C are investigated. The thicknesses of PVP films are adjusted by varying their concentration in PGMEA solvent from 10 wt% to 2.5 wt%. Through FT-IR, C–V, SEM, and AFM analyses, the optimum curing process temperatures (150 °C for 10 wt% and 7.5 wt% samples, and 175 °C for 5 wt% samples) where PET substrates can be thermally endured are proposed in terms of their low hysteresis voltage in the C–V curve (1–2 V in 10 wt% samples, below 1 V in 7.5 wt% samples, and 0.5 V in 5 wt% samples).     

Surface characterization of imidazolium ionic liquids by high-resolution Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy

The surface composition of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM] [PF₆]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM] [DCA]) are studied by high-resolution Rutherford backscattering spectroscopy. Although [BMIM] [PF₆] is almost stoichiometric up to the topmost molecular layer, considerable deviation from the theoretical stoichiometry is observed for [BMIM] [DCA] in a surface layer of ～1.5 nm thickness. Nitrogen is almost completely depleted in this layer while carbon is enhanced. In addition, there are oxygen impurities of ～3 × 10¹⁴ atoms/cm² in this surface layer. With the help of X-ray photoelectron spectroscopy measurements it is concluded that the surface of [BMIM] [DCA] is covered by ～1.7 × 10¹⁴ molecules/cm² of esters and/or carboxylic acids. These contaminant molecules have a preferred orientation, i.e. the carbonyl groups are on the surface of [BMIM] [DCA] and the alkyl chains are pointing towards vacuum. The origin of the contamination layer could be the surface segregation of bulk impurities.     

Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.     

Acoustic cavitation in 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide based ionic liquid

In this work, a comparison between the temperatures/pressures within acoustic cavitation bubble in an imidazolium-based room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium bis(triflluoromethyl-sulfonyl)imide ([BMIM][NTf₂]), and in water has been made for a wide range of cavitation parameters including frequency (140–1000 kHz), acoustic intensity (0.5–1 W cm⁻²), liquid temperature (20–50 °C) and external static pressure (0.7–1.5 atm). The used cavitation model takes into account the liquid compressibility as well as the surface tension and the viscosity of the medium. It was found that the bubble temperatures and pressures were always much higher in the ionic liquid compared to those predicted in water. The valuable effect of [BMIM][NTf₂] on the bubble temperature was more pronounced at higher acoustic intensity and liquid temperature and lower frequency and external static pressure. However, confrontation between the predicted and the experimental estimated temperatures in ionic liquids showed an opposite trend as the temperatures measured in some pure ionic liquids are of the same order as those observed in water. The injection of liquid droplets into cavitation bubbles, the pyrolysis of ionic liquids at the bubble-solution interface as well as the lower number of collapsing bubbles in the ionic liquid may be the responsible for the lower measured bubble temperatures in ionic liquids, as compared with water.     

The impact of 1-butyl-3-methylimidazolium chloride on electrospinning process of SAN polymer solutions and electrospun fiber morphology

The aim of this research was to investigate how addition of IL [Bmim]Cl¹ into SAN² solution in 1,2-DCE³ will influence electrospinning variables, stability of process and morphology of obtained nanofibers and find out the appropriate way of utilizing [Bmim]Cl in the electrospinning process. The solutions of pure SAN in 1,2-DCE of different concentrations (10–20%) and solutions with different concentrations (0.5–20%) of IL were spun at different variables (10–20 cm and 10–20 kV). All results were investigated by optical and SEM microscopy. Also solution parameters like electrical conductivity, surface tension and viscosity were measured and their effect on the obtained fibers morphology estimated.     

SiC/SiO2 coating for improving the oxidation resistive property of carbon nanofiber

The SiC/SiO₂ deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol-gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO₂ followed by heat treatment up to 1000 and 1400 °C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO₂ compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70-80% and mixture of SiC, SiO₂ and some residual carbon after exposure to air at 1000 °C.     

Preparation of Cu–Ag core–shell particles with their anti-oxidation and antibacterial properties

Cu–Ag core–shell particles were fabricated from Cu particles and silver sulphate with the environmental-friendly TA (tartaric acid, C₄H₆O₆) as reducing and chelating agent in an aqueous system. The influences of [TA]/[Ag] and [Ag]/[Cu] molar ratios on the formation of Ag coatings on the Cu particles were investigated. The SEM images and SEM–EDS analyses showed that [TA]/[Ag] = 0.5 and [Ag]/[Cu] ≥0.2, the Cu particles were coated with uniform Ag nanoparticles. XRD analyses revealed that for these Cu–Ag particles heated at 250 °C, the oxidation of Cu was significantly reduced. Both anti-Staphylococcus aureus (Gram-positive) and anti-Escherichia coli (Gram-negative) characteristics of this Cu–Ag composite particles showed satisfactory antibacterial ability. The characteristics of the composite Cu–Ag particles were discussed in detail.     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface‐enhanced Raman scattering spectroscopy

Two kinds of room‐temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) and 1‐butyl‐3‐methylimidazolium tetrafluoroboride ([BMIM]BF₄), were used as solvent, and the adsorption of the ionic liquids themselves and of N‐methylimidazole (NMIM) were investigated by electrochemical surface‐enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF₄ liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br⁻, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)₄Br]Br·H₂O and [Cu(NMIM)₄](BF₄)₂ were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

The sublimation growth of AlN fibers: transformations in?morphology & fiber direction

The growth of AlN fibers using sublimation method was investigated in the temperature range from 1600 °C to 2000 °C. Large-scale AlN fibers are obtained with diameters from 100 nm to 50 μm and lengths up to several millimeters. The fiber morphology and growth direction are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman scattering. The fibers change from wire-like to prism-like in morphology and increase in diameter as rising temperatures, accompanying a transformation in axial direction from [10 ] to [0001]. The transformation in the growth direction is discussed in terms of AlN structure and supersaturation of AlN gas species. These results provide useful information for controlling the growth of large-scale AlN fibers.     

Effect of catalytic graphitization on the electric heating performance of electroless nickel-coated carbon fibers

Graphite possesses several desirable properties, which facilitate its applications in several materials. However, the applications of graphitic materials depend on the extent of graphitization. Generally, the heat treatment of carbon is carried out at temperatures above 3000 °C. However, in this study, the catalytic graphitization of carbon fiber (CF) with an electroless Ni–P coating was studied at low temperature. The surface morphology and structural, thermal, and electrical properties of CF with and without electroless Ni–P coating were characterized through scanning electron microscopy, X-ray diffraction, Raman spectroscopy, infrared thermal imaging, and four-probe volume resistivity testing. The results showed that the catalytic graphitization of CF considerably improved at relatively low temperatures when a Ni–P coating was present. Moreover, when the average P content was 15.88 wt%, the degree of catalytic graphitization of Ni–P-coated CF markedly increased with heat treatment at 600 °C.     

Enhanced photocatalytic degradation of organic dyes by ultrasonic-assisted electrospray TiO2/graphene oxide on polyacrylonitrile/β-cyclodextrin nanofibrous membranes

Polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) composite nanofibrous membranes immobilized with nano-titanium dioxide (TiO₂) and graphene oxide (GO) were prepared by electrospinning and ultrasonic-assisted electrospinning. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) confirmed that TiO₂ and GO were more evenly dispersed on the surface and inside of the nanofibers after 45 min of ultrasonic treatment. Adding TiO₂ and GO reduced the fiber diameter; the minimum fiber diameter was 84.66 ± 40.58 nm when the mass ratio of TiO₂-to-GO was 8:2 (PAN/β-CD nanofibrous membranes was 191.10 ± 45.66 nm). Using the anionic dye methyl orange (MO) and the cationic dye methylene blue (MB) as pollutant models, the photocatalytic activity of the nanofibrous membrane under natural sunlight was evaluated. It was found that PAN/β-CD/TiO₂/GO composite nanofibrous membrane with an 8:2 mass ratio of TiO₂-to-GO exhibited the best degradation efficiency for the dyes. The degradation efficiency for MB and MO were 93.52 ± 1.83% and 90.92 ± 1.52%, respectively. Meanwhile, the PAN/β-CD/TiO₂/GO composite nanofibrous membrane also displayed good antibacterial properties and the degradation efficiency for MB and MO remained above 80% after 3 cycles. In general, the PAN/β-CD/TiO₂/GO nanofibrous membrane is eco-friendly, reusable, and has great potential for the removal of dyes from industrial wastewaters.     

Effect of carbon powder thermal activation on characteristics of supercapacitor electrodes

The capacitors are increasingly being used as energy storage devices in various power systems. The scientists of the world are trying to maximize the electrical capacity of the supercapacitors. This research aims to use plasma spray technology in order to develop carbon electrodes with carbon powder thermally treated in the temperatures ranging from 100 °C to 900 °C in the environment of argon gas. The BET research on primary carbon powder reveal that the largest surface area is obtained at 100 °C heating temperature – 577 m²/g, and at 900 °C – 507 m²/g. Meanwhile, at 300–700 °C heating temperatures the powder surface area decreases up to 2.2 times. The measurements of supercapacitor specific capacitance indicate that the largest values, 15 F/g and 8.7 F/g, were obtained when the respective specific surface area of primary powders equalled 577 m²/g and 261 m²/g.     

Electron paramagnetic resonance of sonicated powder suspensions in organic solvents

The chemical effects of the acoustic cavitation generated by ultrasound translates into the production of highly reactive radicals. Acoustic cavitation is widely explored in aqueous solutions but it remains poorly studied in organic liquids and in particular in liquid/solid media. However, several heterogeneous catalysis reactions take place in organic solvents.Thus, we sonicated trimethylene glycol and propylene glycol in the presence of silica particles (SiO₂) of different sizes (5–15 nm, 0.2–0.3 µm, 12–26 µm) and amounts (0.5 wt% and 3 wt%) at an ultrasound frequency of 20 kHz to quantify the radicals generated. The spin trap 5,5-dimethyl-1-pyrrolin–N-oxide (DMPO) was used to trap the generated radicals for study by electron paramagnetic resonance (EPR) spectroscopy. We identified the trapped radical as the hydroxyalkyl radical adduct of DMPO, and we quantified it using stable radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) as a quantitation standard. The concentration of DMPO spin adducts in solutions containing silica size 12–26 µm was higher than the solution without particles. The presence of these particles increased the concentration of the acoustically generated radicals by a factor of 1.5 (29 µM for 0.5 wt% of SiO₂ size 12–26 µm vs 19 µM for 0 wt%, after 60 min of sonication). Ultrasound produced fewest radicals in solutions with the smallest particles; the concentration of radical adducts was highest for SiO₂ particle size 12–26 µm at 0.5 wt% loading, reaching 29 µM after 60 min sonication. Ultrasound power of 50.6 W produced more radicals than 24.7 W (23 µM and 18 µM, respectively, at 30 min sonication). Increased temperature during sonication generated more radical adducts in the medium (26 µM at 75 °C and 18 µM at 61 °C after 30 min sonication). Acoustic cavitation, in the presence of silica, increased the production of radical species in the studied organic medium.     

Photoluminescence characteristics of ZnGa2O4 thin films prepared by chemical solution method

Zinc gallate (ZnGa₂O₄) thin film phosphors have been formed on ITO glass substrates by a chemical solution method with starting materials of zinc acetate dihydrate, gallium nitrate hydrate and 2-methoxiethanol as a solution. The thin films were firstly dried at 100 °C and fired at 500 °C for 30 min and then, annealed at 500 °C and 600 °C for 30 min under an annealing atmosphere of 3% H₂/Ar. XRD patterns of the thin film phosphors showed (311) and (220) peak indicating ZnGa₂O₄ crystalline phase in which all the (311) peaks of the film phosphors synthesized on ITO glass and soda-lime glass revealed high intensity with increasing annealing temperature from 500 °C to 600 °C. The ZnGa₂O₄ thin film phosphors represented marked change in AFM surface morphologies according to an annealing temperature under an annealing atmosphere (3% H2/Ar). The film phosphor, annealed at 600 °C, showed the embossed pattern with relatively regular spacing in AFM surface morphology. The ZnGa₂O₄ thin film phosphors formed on ITO glass, which were annealed at different temperatures and showed distinctive spectra with peak wavelengths of 434 nm and 436 nm in the blue emission region.     

Dielectric analysis of the interfacial polarization of alkali treated woven flax fibers reinforced epoxy composites

Dielectric measurements were performed on alkali treated flax fibers reinforced epoxy composites in the frequency range 0.1 Hz–1 MHz and the temperature range 40–170 °C. Two common dielectric relaxations were observed for all composites. The first one appearing at low temperatures was attributed to the water dipoles polarization due to the hydrophilic character of flax fibers. The second one observed at high temperatures was identified to the interfacial polarization. Analysis of this latter using the Havriliak–Negami model showed an improvement of the fibers/matrix adhesion by these alkali treatments. The best adhesion was obtained by the leaching treatment.     

Thermodynamic properties of the mixtures of some ionic liquids with alcohols using a simple equation of state

In the present work, we have used a simple equation of state called the GMA EoS to calculate the density of three ionic liquid mixtures including 1-butyl-3-methylimidazolum hexafluorophosphate, [BMIM] [PF₆] + methanol, 1-butyl-3-methylimidazolum tetrafluoroborate, [BMIM] [BF₄] + methanol, and [BMIM] [BF₄] + ethanol at different temperatures, pressures, and compositions. The isothermal compressibility, excess molar volumes, and excess Gibbs molar energy of these mixtures have been computed using this equation of state. The values of statistical parameters show that the GMA EoS can predict these thermodynamic properties very well within the experimental errors. The results show that isothermal compressibility of ionic liquids is lower than alcohols and the effect of temperature and pressure on the isothermal compressibility of ionic liquids is lower than alcohols. The excess molar volumes and excess molar Gibbs energy for these ionic liquid mixtures with alcohols are all negative at various temperatures and pressures over the whole composition range. The results have been interpreted in terms of intermolecular interactions and structural factors of the ionic liquids and alcohols.     

Synthesis and characterization of nanostructured titania film for photocatalysis

Nanostructured titania film was synthesized using nonionic triblock copolymer P123 as surfactant template removed by ethanol extraction followed by calcination at different temperatures. The results of SAXRD indicate that the mesostructures of the films are not damaged until the calcination temperature as high to 450 °C. The results of TG/DSC, UV–visible and Raman spectra analyses provide the evidences for anatase phase to occur at 400 °C and above. The results of TEM and N₂ adsorption and desorption measures indicate that, with temperature increasing from 350 to 500 °C, anatase nanocrystal sizes and pore diameter increase, while the calculated BET surface area decreases. The photocatalytic activity of the films was characterized by the degradation test of methylene blue, and the results show that it depends on both the specific surface area and the crystallinity of nanostructured titania film.     

Ultrasound-assisted synthesis of poly(MMA–co–BA)/ZnO nanocomposites with enhanced physical properties

The present study reports synthesis and characterization of poly(MMA–co–BA)/ZnO nanocomposites using ultrasound-assisted in-situ emulsion polymerization. Methyl methacrylate (MMA) was copolymerized with butyl acrylate (BA), for enhanced ductility of copolymer matrix, in presence of nanoscale ZnO particles. Ultrasound generated strong micro-turbulence in reaction mixture, which resulted in higher encapsulation and uniform dispersion of ZnO (in native form – without surface modification) in polymer matrix, as compared to mechanical stirring. The nanocomposites were characterized for physical properties and structural morphology using standard techniques such as XRD, FTIR, particle size analysis, UV–Visible spectroscopy, electrical conductivity, TGA, DSC, FE-SEM and TEM. Copolymerization of MMA and BA (in presence of ZnO) followed second order kinetics. Thermal stability (T_10% = 324.9 °C) and glass transition temperature (T_g = 67.8 °C) of poly(MMA-co-BA)/ZnO nanocomposites showed significant enhancement (35.1 °C for 1 wt% ZnO and 15.7 °C for 4 wt% ZnO, respectively), as compared to pristine poly(MMA–co–BA). poly(MMA–co–BA)/ZnO (5 wt%) nanocomposites possessed the highest electrical conductivity of 0.192 μS/cm and peak UV absorptivity of 0.55 at 372 nm. Solution rheological study of nanocomposites revealed enhancement in viscosity with increasing ZnO loading. Maximum viscosity of 0.01 Pa-s was obtained for 5 wt% ZnO loading.