MAO‐free and extremely active catalytic system for ethylene tetramerization

The original Sasol catalytic system for ethylene tetramerization is composed of a Cr source, a PNP ligand, and MAO (methylaluminoxane). The use of expensive MAO in excess has been a critical concern in commercial operation. Many efforts have been made to replace MAO with non‐coordinating anions (e.g., [B(C₆F₅)₄]^?); however, most of such attempts were unsuccessful. Herein, an extremely active catalytic system that avoids the use of MAO is presented. The successive addition of two equivalent [H(OEt₂)₂]⁺[B(C₆F₅)₄]^? and one equivalent CrCl₃(THF)₃ to (acac)AlEt₂ and subsequent treatment with a PNP ligand [CH₃(CH₂)₁₆]₂C(H)N(PPh₂)₂ ( 1 ) yielded a complex presumably formulated as [ 1 ‐CrAl (acac)Cl₃(THF)]²⁺[B(C₆F₅)₄]^?₂, which exhibited high activity when combined with iBu₃Al (1120 kg/g‐Cr/h; ~4 times that of the original Sasol system composed of Cr (acac)₃, iPrN(PPh₂)₂, and MAO). Via the introduction of bulky trialkylsilyl substituents such as –SiMe₃, –Si(nBu)₃, or –SiMe₂(CH₂)₇CH₃ at the para‐position of phenyl groups in 1 (i.e., by using [CH₃(CH₂)₁₆]₂C(H)N[P(C₆H₄‐p‐SiR₃)₂]₂ instead of 1 ), the activities were dramatically improved, i.e., tripled (2960–3340 kg/g‐Cr/h; more than 10 times that of the original Sasol system). The generation of significantly less PE (<0.2 wt%) even at a high temperature is another advantage achieved by the introduction of bulky trialkylsilyl substituents. NMR studies and DFT calculations suggest that increase of the steric bulkiness on the alkyl‐N and P‐aryl moieties restrict the free rotation around (alkyl)N–P (aryl) bonds, which may cause the generation of more robust active species in higher proportion, leading to extremely high activity along with the generation of a smaller amount of PE.     

Enhanced output voltage of nano energy harvester with diverse textiles

Abstract

We demonstrate the electrical properties of nano energy harvesters (NEHs) with various textiles for smart textiles that can be applied to the next generation wearable electronics. Output voltages and currents of NEHs with various fabrics, such as a cotton, rayon and wool that have different triboelectricity were measured. Cotton, rayon and wool shows the maximum output voltages of 1.250, 3.313 and 4.063 V, respectively. In addition, output currents of those textiles were 0.75, 4.4, 1.063 μA, respectively. Wool, in particular, which has the highest triboelectricity of 350 V exhibits the highest output voltage.     

Carbon Nanotubes/Heteroatom‐Doped Carbon Core–Sheath Nanostructures as Highly Active,Metal‐Free Oxygen Reduction Electrocatalysts for Alkaline Fuel Cells

A facile, scalable route to new nanocomposites that are based on carbon nanotubes/heteroatom‐doped carbon (CNT/HDC) core–sheath nanostructures is reported. These nanostructures were prepared by the adsorption of heteroatom‐containing ionic liquids on the walls of CNTs, followed by carbonization. The design of the CNT/HDC composite allows for combining the electrical conductivity of the CNTs with the catalytic activity of the heteroatom‐containing HDC sheath layers. The CNT/HDC nanostructures are highly active electrocatalysts for the oxygen reduction reaction and displayed one of the best performances among heteroatom‐doped nanocarbon catalysts in terms of half‐wave potential and kinetic current density. The four‐electron selectivity and the exchange current density of the CNT/HDC nanostructures are comparable with those of a Pt/C catalyst, and the CNT/HDC composites were superior to Pt/C in terms of long‐term durability and poison tolerance. Furthermore, an alkaline fuel cell that employs a CNT/HDC nanostructure as the cathode catalyst shows very high current and power densities, which sheds light on the practical applicability of these new nanocomposites.     

6,6′-Thiobis(methylene)-β-cyclodextrin dimer as a dimeric host and reusable promoter for synthesis of chromenones in water

Herein, two unit of β-cyclodextrin linked by thiomethylene bridge was synthesized and employed as a novel efficient supramolecular host for the synthesis of biologically active chromenones templates via three-component single-pot reaction. A possible reaction mechanism through molecular complexation is suggested based on 2D ROESY NMR spectroscopic analysis. Moreover, the catalyst could be easily recycled, while a 94% yield and 89% rate of catalyst recovery could be achieved after four cycles of catalyst recycling. Environmentally benign reaction conditions, excellent yields, and avoidance of organic solvent and conventional isolation as well as purification are the noteworthy credits of this developed protocol.     

Mechanical and electrical response variation of the polyurethane–tin oxide–carbon nanotube composite microfiber depending on the chemical solution

Toward the goal of smart sensor systems for wearable electronics, polymer microfiber‐based free‐standing sensors benefit from excellent flexibility, decent ductility, and easy wearability in comparison with thin‐film‐based sensing devices. Herein, we report a hydrophobic and conducting single‐strand microfiber‐based liquid‐phase chemical sensor consisting of polyurethane (PU), tin oxide (SnO₂), and carbon nanotube (CNT) composites with applying a (1H,1H,2H,2H‐heptadecafluorodec‐1‐yl) phosphonic acid (HDF‐PA)‐based self‐assembled monolayer. The free‐standing HDF‐PA‐treated PU–SnO₂–CNT composite microfiber showing selective filtering properties with the repellency of water and the penetration of an organic solvent is electrically and mechanically characterized. Finally, the single‐strand HDF‐PA‐treated PU–SnO₂–CNT composite microfiber‐based chemical sensor, which shows excellent mechanical properties and aqueous stability, is demonstrated to detect the presence of a chemical in pure water or counterfeit gasoline in pure gasoline by observing mechanical changes, especially variations in the length and diameter of the fiber, and monitoring the electrical resistance change. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 495–502     

Solution-Processable Low Voltage Organic Transistors of Thieno[3,2-b]thiophene-Based Conducting Polymer

A low-operating voltage and high performance polymeric field effect transistors using octadecylphosphonic acid-treated high-k AlOx and HfO₂ hybrid dielectrics were demonstrated. High-k metal oxide hybrid dielectrics were prepared by oxygen plasma treatment of deposited Al film for AlOx and by spin coating of solution-processable HfO₂ sol-gel solution for HfO₂ in combination with phosphoric acid-based self-assembled monolayer (SAM), resulting in high capacitance (10 nF/cm² for SiO₂, 600 nF/cm² for AlOx and 580 nF/cm² for HfO₂). With phosphoric acid-based SAM on high-k metal oxide and thermal annealing of thieno[3,2-b]thiophene-based conducting polymer, the device performance was significantly enhanced. The highest mobility of the transistors using ODPA-treated AlOx as a gate dielectric is 2.3 × 10^?2 cm² V^?1 s^?1 in the saturation region with the source-drain of ?2 V. In ODPA-treated HfO₂ hybrid dielectric, the saturated mobility is 1.1 × 10^?2 cm² V^?1 s^?1 and the threshold voltage was measured to be ?0.31 V, which is at least one order lower than SiO₂ hybrid dielectric (?3 V).     

Development of simultaneous analysis of tryptophan metabolites in serum and gastric juice – an investigation towards establishing a biomarker test for gastric cancer diagnosis

To evaluate changes in tryptophan metabolism and discover diagnostic biomarkers for gastric cancer, a quantitative method was developed for tryptophan and its seven metabolites (indole‐3‐lactic acid, anthranilic acid, serotonin, nicotinic acid, kynurenic acid, kynurenine and 3‐indoxyl sulfate) in both human serum and gastric juice using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Serum and gastric juice were prepared with a simple protein precipitation using aqueous 0.1% formic acid and acetonitrile. As a result, it was found that the kynurenine pathway of tryptophan metabolism was activated in gastric cancer and that the metabolic ratio of kynurenine/tryptophan, which reflects the enzyme activity of indoleamine‐2,3‐dioxygenase, was associated with the observed metabolic changes. Finally, the investigation of tryptophan metabolites, especially kynurenic acid, in serum and gastric juice might serve as biomarkers for gastric cancer. The findings in this study provide critical information of tryptophan metabolism which can be applied to a serum‐based diagnostic test for gastric cancer.