Oxygen permeation of various archetypes of oxygen membranes based on BSCF

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3‐δ tubes, capillaries, capillary modules, and asymmetric membranes were prepared and tested for oxygen permeation in a dead‐end vacuum operation mode at temperatures up to 850^°C. The capillary module was built up by reactive air brazing using seven capillaries and a supply tube. Two machined discs were used as an end cap and as a connector plate. The oxygen permeation behaves according to Wagner at small driving forces, but significant negative deviations were observed for asymmetric membranes and single capillaries at higher ones. This is caused by pressure drops at the vacuum side for single capillaries. The highest oxygen flux was revealed for the capillary module with 175.5 mL(STP)/min at a low‐vacuum pressure of 0.042 bar at 850^°C, but the asymmetric membrane showing a little bit higher flux at moderate vacuum pressures above 0.07 bar. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3195–3202, 2012     

Gas permeation properties of new type asymmetric membranes

We have developed a new type of asymmetric membranes having a homogeneous hyperthin skin layer, which was used as a polyimide synthesized by 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 2,2-bis(4-amino phenyl) hexafluoro-propane (BAAF). The skin layer thicknesses of the 6FDA-BAAF polyimide asymmetric membranes were 40–60 nm, and the porosity was 10^-6% when a defect size was assumed as 5 nm. The permselectivity of 6FDA-BAAF polyimide asymmetric membranes after silicone coating had α of 40 for CO₂/CH₄ and a flux of 1.0 [Nm³/m²-h-atm] (=3.7 × 10⁻⁴ [cm³(STP)/cm² s cmHg]) for CO₂, α of 4.3 for O₂/N₂ and a flux of 2.0 × 10⁻¹ [Nm³/m²/h/atm] (=7.1 × 10⁻⁵ [cm³(STP)/cm²s cmHg]) for O₂. These values were constant for large-scale manufacturing. © 1996 John Wiley & Sons, Inc.     

Symmetric and asymmetric membranes based on La0.5Sr0.5Fe0.7Ga0.3O3-δ perovskite with high oxygen semipermeation flux performances and identification of the rate-determining step of oxygen transport

This work focuses on identifying the rate-determining step of oxygen transport through La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ membranes with symmetric and asymmetric architectures. The best oxygen semipermeation fluxes are 3.4 10⁻³ mol. m^-2.s^-1 and 6.3 10⁻³ mol. m^-2.s^-1 at 900 °C for the symmetric membrane and asymmetric membrane with a modified surface. The asymmetric membrane with a modified surface leads to an increase of approximately 7 times the oxygen flux compared to that obtained with the La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ dense membrane without surface modification. This work also shows that the oxygen flux is mainly governed by gaseous oxygen diffusion through the porous support of asymmetric La_0.5Sr_0.5Fe_0.7Ga_0.3O_3-δ membranes.     

The synthesis of chiral derivatives of 1,4,7,10,13,16-hexaoxacyclooctadecane

Summary The asymmetrical poly glycoles obtained by the addition of epoxides to the poly ethylene glycoles condensed with the dihalo glycoles to form the chiral derivatives of 1,4,7,10,13,16-hexa oxacyclooctadecane. Macrocyclic ethers obtained performed the utility of our new procedure.     

Influence of quench medium on the structure and gas permeation properties of cellulose acetate membranes

Integrally skinned asymmetric cellulose acetate membranes made by the wet phase inversion for removal of CO₂ from natural gas were investigated. The membrane was cast with the membrane-forming systems of cellulose acetate–acetone and quench media, such as methanol, ethanol and isopropanol, respectively, without heat-treating and multistage exchange process. By means of evaluation on separating characteristics of the membrane for CO₂/CH₄, observation of morphologies by scanning electron photomicrographs and analysis of the phase diagrams on the membrane-forming systems, it has shown that the membrane-forming system of cellulose acetate–acetone–methanol is quite suitable to prepare integrally skinned asymmetric cellulose acetate membranes for gas separation with good selectivity CO₂/CH₄ = 30 and flux coefficient = 2.4 × 10⁻⁵ cm³/cm² − s − cm Hg. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1269–1276, 1998     

Bifunctional Catalysts Stabilized on Nanocrystalline Magnesium Oxide for One‐Pot Synthesis of Chiral Diols

New bifunctional catalysts composed of PdCl₄²⁻, OsO₄²⁻ and OsO₄²⁻, WO₄²⁻ designed and prepared by a counterionic stabilization technique involving the reactions of Na₂PdCl₄‐K₂OsO₄ and K₂OsO₄‐Na₂WO₄ with nanocrystalline MgO are well characterized. These bifunctional catalysts, NAP‐Mg‐PdOs and NAP‐Mg‐OsW perform tandem Heck asymmetric dihydroxylation and asymmetric dihydroxylation‐N‐oxidation reactions, respectively, in the presence of the chiral ligand 1,4‐bis(9‐o‐dihydroquinidinyl)phthalazine [(DHQD)₂PHAL] in a single pot. It is quite impressive to note that H₂O₂ is used as a terminal oxidant to provide N‐methylmorpholine N‐oxide (NMO) in situ by the oxidation of N‐methylmorpholine (NMM) in the asymmetric dihydroxylation‐N‐oxidation catalyzed by NAP‐Mg‐OsW.     

Gas permeability and selectivity through asymmetric polyimide membranes

Permeability and selectivity of CO₂, O₂, N₂, and CH₄ were determined for the asymmetric membrane of aromatic polyimide derived from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′-diaminodiphenylsulfone (m-DDS) at 35°C and at pressure up to 76 cmHg. The average apparent skin layer thickness of all asymmetric membranes measured was 2.6 μm. The selectivities for (O₂/N₂) and (CO₂/CH₄) in the membranes were 11.5 at O₂ permeance of 3.2 × 10⁻⁷ and 153 at CO₂ of 6.3×10⁻⁷ [cm³(STP)/cm² s cmHg], respectively, without the necessity of an additional coating process. The average gas selectivities of the asymmetric memberanes were much larger than those determined for the dense membrances. The effect of the microstructure of polyimide on the gas selectivity is discussed. © 1996 John Wiley & Sons, Inc.     

Enantioselectivity promotion by achiral surface functionalization on SiO2-supported Cu-bis(oxazoline) catalysts for asymmetric Diels–Alder reactions

Novel SiO₂-supported chiral Cu-bis(oxazoline) (BOX) complexes for asymmetric Diels–Alder reactions were prepared by combining metal-complex immobilization with surface functionalization using achiral silane-coupling reagents on SiO₂. We found that the surface functionalization of a SiO₂-supported Cu-BOX catalyst with achiral 3-methacryloxypropyltrimethoxysilane dramatically increased enantioselectivity in the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. The Cu-BOX complexes on bare and functionalized SiO₂ surfaces were characterized by XAFS, ESR, FT-IR, UV/vis, and ²⁹Si solid-state MAS NMR. The large increase in enantioselectivity by achiral surface species without chiral center may be due to a glue effect, creating a new chiral ensemble structure at the surface.     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Enhancing the performance and stability of NiCo2O4 nanoneedle coated on Ni foam electrodes with Ni seed layer for supercapacitor applications

We introduce a facile way to improve the performance of NiCo₂O₄ electrode by including a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo₂O₄/Ni@NF) shows the superior specific capacity of 1142 C g⁻¹ at 1 A g⁻¹ with the excellent cycle stability of ∼96% even after 5000 cycles at a higher current density of 5 A g⁻¹. These values are about 3.7 times higher than that of the electrode (NiCo₂O₄@NF) without a seed layer, which shows the specific capacity of 305 C g⁻¹@1 A g⁻¹ with cycle stability of 84% even at a lower current density of 1 A g⁻¹. The enhanced performance of the NiCo₂O₄/Ni@NF electrode may be attributed to lower interface resistance, fast redox reversible reaction, and improved surface active sites. Further, the asymmetric solid-state supercapacitor device is fabricated by using the NiCo₂O₄/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe₂O₃ nanograin as a negative electrode with PVA-KOH gel electrolyte, and the NiCo₂O₄/Ni20@NF//rGO-Fe₂O₃@NF asymmetric solid state device delivers an areal capacitance of 446 mF cm⁻² with a low capacitance loss of 18% even after 10000 cycles. Further, the fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm⁻² (at 3.58 kW cm⁻²) and power density of 14.88 kW cm⁻² (at 31.41 Wh cm⁻²).     

V2O5 nanosheets assembled on 3D carbon fiber felt as a free-standing electrode for flexible asymmetric supercapacitor with remarkable energy density

As an emerging energy storage device, supercapacitor is widely investigated owing to its excellent capability, quick charge-discharge and tremendous cycle life. The operation potential window, energy density and mass loading of supercapacitor must be taken into deep consideration for its practical application. In this work, an outstanding electrode based on CFF@V₂O₅ nanosheets was prepared. Then a free-standing asymmetric supercapacitor with CFF@V₂O₅ composite as positive electrode and CFF@AC as negative electrode was assembled. Owing to the functional groups produced on CFF after the activation, V₂O₅ nanosheets was immobilized. The composite exhibits remarkable specific capabilities of 1465 mF cm^?2 (492 F g^?1). The energy density of the assembled free-standing asymmetric supercapacitor achieves 0.928 mWh cm^?3 when the power density is 17.5 mW cm^?3. After 6000 charging-discharging cycles as under normal, bended and anti-bended conditions for respective 2000 cycles, the device retains 89.7% of the initial capacitance, exhibiting fascinating cycle stabilization. Finally, two devices linked series can lighten a LED of 1.8 V for 2 min after charging for 2.5 min, which is inspiring for the practical application and production of self-supporting asymmetric supercapacitors.     

Rational design of binder-free ZnCo2O4 and Fe2O3 decorated porous 3D Ni as high-performance electrodes for asymmetric supercapacitor

The development of hierarchical, porous film based current collector has created huge interest in the area of energy storage, sensor, and electrocatalysis due to its higher surface area, good electrical conductivity and increased electrode-electrolyte interface. Here, we report a novel method to prepare a hierarchically ramified nanostructured porous thin film as a current collector by dynamic hydrogen bubble template electro-deposition method. At a first time, we report a porous 3D-Ni decorated with ZnCo₂O₄ and Fe₂O₃ by simple, low-cost electrochemical deposition method. The fabricated porous 3D-Ni based electrodes showed an excellent electrochemical property such as high specific capacitance, excellent rate capability, and good cycle stability. The asymmetric solid-state supercapacitor device was fabricated using porous, 3D Ni decorated with ZnCo₂O₄ and Fe₂O₃ as the positive and negative electrodes. The fabricated ZnCo₂O₄//Fe₂O₃ asymmetric device delivered an areal capacitance of 92?mF?cm^?2 at a current density of 0.5?mA?cm^?2 with a maximum areal power density of 3?W?cm^?2 and areal energy density of 28.8?mWh?cm^?2. The higher performances of porous, 3D current collector have a huge potential in the development of high performance supercapacitor.     

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)₂-PEO-(PMMA)₂ has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)₂-CHCOOCH₂CH₂OH with an active hydroxyl group. The chlorine was removed to yield the (PS)₂-CHCOOCH₂CH₂OH ((PS)₂-OH). The hydroxyl group of the (PS)₂-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)₂-PEO-OH. The (PS)₂-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)₂-PEO-OCCHCl₂ ((PS)₂-PEO-DCA). The asymmetric H-shaped block polymer (PS)₂-PEO-(PMMA)₂ was prepared via ATRP of MMA at 130 °C using (PS)₂-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)₂-PEO-(PMMA)₂, were confirmed by ¹H NMR, GPC and FT-IR.     

Surface and interfacial fourier transform infrared spectroscopic studies of latexes. XVI. Quantitative analysis of surfactant in multilayered films

Migration and concentration levels of sodium dioctylsulfosuccinate (SDOSS) surfactant molecules in 50%/50% styrene/butyl acrylate latex were detected at the film-substrate (F-S) and film-air (F-A) interfaces in mono- and double-layered films. For the purpose of quantitative analysis, absorption coefficients of the 1,056 and 1,046 cm⁻¹ bands attributed to the SO₃⁻Na⁺…HOOC and SO⁻₃Na⁺…H₂O associations, respectively, were determined. Using group theory formalism, local geometries of the SO⁻₃Na⁺ hydrophilic groups of SDOSS can be predicted. The analysis is extended to the 1,261 and 1,209 cm⁻¹ bands resulting from the S—O asymmetric stretching vibrations, due to the same SO⁻₃Na⁺ … HOOC and SO⁻₃Na⁺ … H₂O associations, and to the 1,290 and 1,236 cm⁻¹ bands, due to asymmetric stretching modes of hydrophobic tails of the SDOSS. By the use of polarization attenuated total reflectance Fourier transform infrared (ATRFT-IR) experiments, these studies show that hydrophilic SO⁻₃Na⁺ ends on SDOSS are preferentially parallel to the film surface. At the same time, hydrophobic tails are perpendicular to the surface. The assessment of the amounts of SDOSS at the F-S and F-A interfaces was obtained by quantitative ATR FTIR analysis, which was extended to the silicone-modified double-layer latex films. In this case, the concentration of SDOSS molecules decreases as the depth of penetration increases. The highest concentrations of SDOSS molecules are detected at the shallowest depths near the surface of the top layer and the interfacial regions between the latex layers. © 1996 John Wiley & Sons, Inc.     

Tunable BaxSr1-xTiO3 nanoparticles induced high energy storage density in layer-structured asymmetric polymer-based nanocomposites

In order to solve the problem of low charging and discharging energy density of dielectric capacitors, the structure design of layered polymer matrix composites is carried out in this paper. Ba_0.7Sr_0.3TiO₃, Ba_0.8Sr_0.2TiO₃ and Ba_0.9Sr_0.1TiO₃ nanoparticles were successfully prepared by the oxalate coprecipitation method. The surface of Ba_xSr_1-xTiO₃ was successfully coated with dopamine, which promoted the dispersion of the polymer matrix of the ceramic powder. Monolayer Ba_xSr_1-xTiO₃/PVDF composites containing Ba_xSr_1-xTiO₃ with different Ba/Sr ratios were successfully prepared by the casting method. Three-layer asymmetric composites with different fillers were successfully prepared by layer-by-layer casting. The phase and microstructure of the as-prepared materials were analyzed by XRD and SEM. The dielectric, electrical conductivity, ferroelectric and energy storage properties of the composites were tested. The effects and laws of the design of the three-layer asymmetric structure on the dielectric properties and energy storage properties of the layered composites are mainly studied. When the structure of the three-layer asymmetric composite is 1-2-3, the breakdown field strength reaches 330 kV/mm, the discharge energy density reaches 8.51 J/cm³, and the charge-discharge efficiency is 67%. This work demonstrates that layered composites with asymmetric properties can facilitate the development of electrical energy storage.     

Facile preparation of Ni-doped MnCO3 materials with controlled morphology for high-performance supercapacitor electrodes

Doping homogeneous elements and conducting morphological adjustment as commonly-used modification methods are both effective to promote the electrochemical properties of electrode materials. In this work, nickel-doped manganese carbonate with 3D flower-like structure was synthesized by a one-step hydrothermal method, and the corresponding growth mechanism was investigated. The electrochemical characteristics of as-fabricated electrode materials were measured, among which 3D self-assembled Ni_0.2Mn_0.8CO₃ nanoflower with large surface area exhibited superior areal capacitance of 583.5?F?g^?1 at 1?A?g^?1 (fourfold more than MnCO₃ microcubes), excellent electrical conductivity as well as satisfactory cycling stability (84.78% capacitance retention after 2000 cycles at 2?A?g^?1). In addition, the asymmetric supercapacitor assembled with Ni_0.2Mn_0.8CO₃ as cathode and commercial activated carbon as anode displayed a high energy density of 24.1?Wh?kg^?1 at the power density of 0.74?kW?kg^?1 and showed a desirable cycle life. In summary, the unique 3D flower-like Ni_0.2Mn_0.8CO₃ nanomaterial could be regarded as a promising electrode material for high-performance supercapacitors.     

A high-performance asymmetric supercapacitor based on carbon and carbon–MnO2 nanofiber electrodes

An asymmetric supercapacitor with high energy and power densities has been fabricated using MnO₂/carbon nanofiber composites as positive electrode and activated carbon nanofibers as negative electrode in Na₂SO₄ aqueous electrolyte. Both electrode materials are freestanding in nature without any conductive additives or binders and exhibit outstanding electrochemical performances. The as-assembled asymmetric supercapacitor with optimal mass ratio can be operated reversibly over a wide voltage range of 0–2.0 V, and presents a maximum energy density of 30.6 Wh kg⁻¹, which is much higher than those of symmetric supercapacitors. Moreover, the supercapacitor exhibits excellent rate capability (high power density of 20.8 kW kg⁻¹ at 8.7 Wh kg⁻¹) and long-term cycling stability with only 6% loss of its initial capacitance after 5000 cycles. These attractive results make these freestanding materials promising for applications in aqueous electrolyte-based asymmetric supercapacitors with high energy and power densities delivery.     

Synthesis of cardo containing asymmetric poly(ether‐naphthalimide‐phthalimide)s

A series of cardo based asymmetric polyimides containing bulky rigid naphthalimide and phthalimide groups were prepared from asymmetric monomer bishaloimide and bisphenols by solution polycondensation. Bishalo(naphthalimide‐phthalimide) monomers containing different terminal leaving groups (Cl, F, NO₂) were synthesized, and the reactivity difference of these monomers was compared for the successful synthesis of polyimides. The inherent viscosities of the polyimides were in the range 0.51 ? 0.60 dL g^?1 in N ‐methyl‐2‐pyrrolidone at 30 °C. These polyimides demonstrated good organosolubility and mechanical properties with tensile strengths of 93 ? 120 MPa, tensile moduli of 3.5 ? 5.3 GPa and elongations at break of 2.8% ? 4.3%. The polyimides showed high glass transition temperatures (T _g) ranging from 330 to 363 °C. The 10% weight loss (T _10%) of asymmetric polyimides reached 436 ? 500 °C in nitrogen and 417 ? 476 °C in air. The water uptake of the polyimides was in the range 0.35% ? 0.72%. © 2017 Society of Chemical Industry     

Asymmetric 1,4‐Addition of Diethylzinc to Cyclic Enones Catalyzed by Cu(I)‐Chiral Sulfonamide‐Thiophosphoramide Ligands and Lithium Salts

The chiral sulfonamide‐thiophosphoramide ligand L1 , prepared from the reaction of (1R,2R)‐(−)‐1,2‐cyclohexanediamine with diphenylthiophosphoryl chloride and p‐toluenesulfonyl chloride, was used as a chiral ligand in Cu(MeCN)₄ClO₄‐promoted catalytic asymmetric addition of diethylzinc to cyclic enones using LiCl as an additive in which up to 90% ee can be realized under mild conditions within 0.5 h. This chiral ligand is stable and recoverable after usual work‐up and can be reused in the same catalytic asymmetric reaction. Moreover, it was found that this series of chiral ligands represents a type of S,O‐bidentate ligands on the basis of ¹H NMR, ³¹P NMR and ¹³C NMR spectroscopic investigations. The linear effect of ligand ee and product ee further revealed that the active species is a monomeric Cu(I) complex bearing a single ligand.     

Convenient General Asymmetric Synthesis of Roche Ester Derivatives through Catalytic Asymmetric Hydrogenation: Steric and Electronic Effects of Ligands

An efficient and concise asymmetric hydrogenation of acrylate esters promoted by the cationic ruthenium monohydride complex [Ru(H)(η⁶‐cot)SYNPHOS]⁺BF₄⁻ is reported. A full investigation of the effects of catalyst precursors, solvents, temperature, hydrogen pressure, substrates as well as steric and electronic properties of ligands was carried out. The corresponding valuable Roche ester derivatives were obtained in good to excellent isolated yields and high enantioselectivities under mild conditions. The robustness and practicability of this highly enantioselective hydrogenation was demonstrated by the synthesis of the 3‐hydroxy‐2‐methylpropanoic acid tert‐butyl ester on a multigram scale, resulting in excellent yield and ee up to 94%.