Liujin Lu

Tensile tests of ropes of very long aligned multiwall carbon nanotubes

We have directly measured the Young’s modulus and tensile strength of multiwall carbon nanotubes by pulling very long (∼2 mm) aligned nanotube ropes with a specially designed stress-strain puller. This puller can apply an axial force to the rope and simultaneously measure the corresponding rope elongation and the change in rope resistance. The average Young’s modulus and tensile strength obtained were 0.45±0.23 TPa and 1.72±0.64 GPa, respectively, which are lower than those calculated and measured previously. The factors that affect the mechanical strengths of nanotubes are discussed.

Novel cyclic sulfonium-based ionic liquids: synthesis, characterization, and physicochemical properties.

A new series of ionic liquids composed of three cyclic sulfonium cations and four anions has been synthesized and characterized. Their physicochemical properties, including their spectroscopic characteristics, ion cluster behavior, surface properties, phase transitions, thermal stability, density, viscosity, refractive index, tribological properties, ion conductivity, and electrochemical window have been comprehensively studied. Eight of these salts are liquids at room temperature, at which some salts based on [NO(3)](-) and [NTf(2)](-) ions exhibit organic plastic crystal behaviors, and all the saccharin-based salts display relatively high refractive indices (1.442-1.594). In addition, some ionic liquids with the [NTf(2)](-) ion exhibit peculiar spectroscopic characteristics in FTIR and UV/Vis regions, whilst those salts based on the [DCA](-) ion show lower viscosities (34.2-62.6 mPa s at 20 degrees C) and much higher conductivities (7.6-17.6 mS cm(-1) at 20 degrees C) than most traditional 1,3-dialkylimidazolium salts.

The influence of the acidity of ionic liquids on catalysis.

In the past 20 years, the concept of ionic liquids (ILs) have been extensively applied in the fields of chemistry, materials, and life sciences. Undoubtedly, the ionic liquids composed of quaternary ammonium cations and anions, such as BF4 , PF6 , Cl , and NTf2 , have been the backbone of this area since immidazolium cation ionic liquids were synthesized by Zaworotko et al. and were brought into catalysis and synthesis by Seddon, Rogers, Welton, Wasserscheid, and others. Thousands of reactions have been performed in these ionic liquids and many of them exhibited better behavior than organic solvents. Normally, the fine performance of these ionic liquids was attributed to the specific ionic environment of the ionic liquid. Nevertheless, the acidity of the airand moisture-stable ionic liquids and its effect on catalysis is an interesting topic. As it is well known, a large amount of organic reactions can be catalyzed or promoted by an acid environment. During our investigation of the function of ionic liquids in catalysis, especially airand moisture-stable ones, we found that these ILs normally exhibit weak acidity in the presence of a small amount of water. That means the interpretations about the function of airand moisture-stable ionic liquids in catalytic reactions are possibly wrong because the presence of trace amount of water is not avoidable in reality. Herein, we present our results on the study of acidity of airand moisture-stable ionic liquids and their activity in some known acid-catalyzed reactions. We hope these results could be helpful for researchers in this area to reconsider the influence of the acidity of airand moisture-stable ionic liquids on catalysis and also in other fields. At the initial stage, the acidity of ionic liquids–water with different cations and anions were measured with a pH meter. The concentration of ionic liquid in water was 0.1 m. The operation was performed with methods given in the Annual Book of American Society for Testing and Materials Standards (ASTM) with slight modification. As shown in Figure 1, ionic liquid–water mixtures with BF4 anions were all acidic. Interestingly, the acidity of the ionic liquids could be tuned via substituted alkyl variation. The pH value of EMImBF4 ionic liquid reached 3.44(0.03) but the pH value of BMImBF4 and HMImBF4 were 4.27(0.14) and 6.61(0.03) respectively. BMImBF4 ionic liquids purchased from Merck (lot code: S5204049909) and Sigma–Aldrich (lot code: 0001415814) were also measured for comparison. Under the same condition, their pH values were 4.70(0.05) and 4.30(0.09), respectively, which are exactly the same as the acidity of the ionic liquids that we synthesized. The incorporation of an hydroxyl group would further enhance the acidity of ionic liquids with BF4 anion. The pH value reached 3.12(0.01) and 3.11(0.02) with hydroxyethyl or hydroxypropyl groups. The substitution of the C2 position with a methyl group weakens the acidity of this kind of ionic liquid. For the ionic liquid BMMImBF4, the pH value was 6.51(0.04). This was almost the same as that with the ionic liquid from Merck, that is, 6.46(0.23) (lot code: EQ005416). For ionic liquids with tetrabutyl ammonium and tetrabutyl phosphonium cations, the IL solutions were close to Figure 1. pH values of the aqueous phase of ionic liquids with BF4 as anion (0.1 m). The numbers in the parentheses are the values of the standard deviation.

A new route of CO2 catalytic activation: syntheses of N-substituted carbamates from dialkyl carbonates and polyureas

This paper reports an effective route for the syntheses of N-substituted dicarbamates from dialkyl carbonates and polyurea derivatives, in which polyurea derivatives could be successfully synthesized from aliphatic diamines and CO2 in the absence of any catalyst. Under the optimized reaction conditions, various N-substituted carbamates were successfully synthesized with 93–98% isolated yields over a MgO–ZnO catalyst. The catalyst could be reused for several runs without deactivation. The catalysts were characterized with X-ray photoelectron spectroscopy, X-ray diffraction and temperature-programmed desorption.

Intrinsic Electric Fields in Ionic Liquids Determined by Vibrational Stark Effect Spectroscopy and Molecular Dynamics Simulation

The electric fields of ionic liquids are only slightly higher than those of common molecular solvents, and are strongly structure-dependent; they noticeably decrease with anion size because of increased separation of ions, and slightly decrease as the alkyl chain elongates due to increasing spatial heterogeneity. These were the key results of vibrational Stark effect spectroscopy and molecular dynamics simulations.

CoO@Co and N-doped mesoporous carbon composites derived from ionic liquids as cathode catalysts for rechargeable lithium–oxygen batteries

The catalytic activity of a cathode material plays a vital role in determining the electrochemical performance of Li–O2 batteries. Herein, N-doped mesoporous carbon-supported CoO@Co nanoparticles are prepared in situ using the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrachlorocobalt ([BMIm]2[CoCl4]) as the precursor with silica as the hard template. The material was characterized by TGA, BET, XRD, TEM, XPS, and H2-TPR. After exposure to air, the species on the surface of the Co is CoO, as verified by XPS. The pore size is about 2 nm, and the CoO@Co nanoparticles were irregularly shaped and sized in the range of 20–300 nm, which may have been due to the aggregation of ultrafine nanoparticles. The existence of an interaction between the CoO@Co nanoparticles and the N-doped support is confirmed by XPS and H2-TPR. The catalyst shows superior activity for oxygen evolution reaction (OER) manifested in its lower charge potential (3.75 V at the current density of 100 mA g−1). Enhanced performances in coulombic efficiency, rate capability, and cycling stability (55 cycles) are also realized. Finally, these improvements, with the exception of the catalytic activity of CoO, may benefit from the interaction between the carbon supporter and the CoO@Co nanoparticles.

Ionic liquid based variable focus lenses

This work presents ionic liquid based variable focus lenses using electrowetting, which exhibit excellent performance over a conventional saline based lens such as good tolerance of sharp temperature variation, wide operating temperature range (which is up to 100 °C) and in particular high stability at high temperatures.

Enhanced and reversible contact angle modulation of ionic liquids in oil and under AC electric field.

Liquid actuation and manipulation using electrowetting is a rapidly growing field of research and has generated considerable interest in developing technologies such as microfluidic devices, liquid optics and displays. Electrowetting is conventionally carried out with (saline) aqueous solution under DC electric field. However, drawbacks such as evaporation and the inconvenient addition of inorganic salts to enhance the electric conductivity have inevitably limited its application. Therefore, development of new and robust media for electrowetting is highly desirable. Ionic liquids (ILs), a novel class of versatile solvents and soft materials possessing unique physicochemical properties, including negligible vapor pressure, being liquid over a wide temperature range, intrinsic ionic conductivity and acceptable electrochemistry stability, and so forth, have recently been developed as a promising alternative medium for electrowetting by Millefiorini et al. and other groups. In comparison with saline, IL-based electrowetting systems may be run under some extreme conditions such as in vacuum, or at temperatures either above 373 K or below 273 K. Recently, studies of electrowetting of ILs in air and under DC electric fields showed some unconventionality compared to saline such as low electrowetting efficiency (contact angle decrease or modulation) and cation/anion-dependent asymmetric behavior, although for the latter there is no unanimity among the different authors. Some effort has also been devoted to the initial applications of electrowetting of ILs as microreactor or microfluidics. Despite its promising potential, the reported electrowetting of ILs exhibits lower efficiency than that of saline with poor reversibility and a narrow range of contact angle modulation (<488). Herein, we presented greatly improved electrowetting efficiency of ILs using oil as the ambient and under AC electric field. Electrowetting behavior of ILs in this case, in particular at a high frequency of 1 kHz, shows greatly enhanced, sensitive, and reversible contact angle modulation in comparison to that in air or under DC electric field.

Hydrophobic 1-allyl-3-alkylimidazolium dicyanamide ionic liquids with low densities

Nine 1-allyl-3-alkylimidazolium ([ACnIm]) or 1-vinyl-3-alkylimidazolium ([VCnIm]) dicyanamides (DCA) were prepared and characterized, and their physicochemical properties were studied in detail. Except for [AVIm]DCA and [AC4Im]DCA, the other dicyanamides with hexyl or longer alkyl chains on the cation exhibited the characteristic of hydrophobicity. Among them, [AC8Im]DCA and [AC10Im]DCA were found to possess similar densities to water, i.e. 1.007 g cm−3 and 0.988 g cm−3 at 25 °C, respectively. Interestingly, a reversible phase reversion of a [AC8Im]DCA/H2O mixture was observed as the temperature varied. These environmentally-friendly liquid materials have potential applications as precursors for syntheses of conducting polymeric materials.

Electrowetting based infrared lens using ionic liquids

We demonstrated an infrared variable focus ionic liquids lens using electrowetting, which could overcome the problems caused by use of water, e.g., evaporation and poor thermostability, while keeping good optical transparency in visible light and near-infrared region. Besides, the type of lens (convex or concave) could be tuned by applied voltage or refractive index of ILs used, and the transmittance was measured to exceed 90% over the spectrum of visible light and near-infrared. We believe this infrared variable focus ionic liquids lens has a great application prospect in both visible light and infrared image systems.