Porous Carbon Interlayer Derived from Traditional Korean Paper for Li-S Batteries.

A carbonized interlayer effectively helps to improve the electrochemical performance of lithium-sulfur (Li-S) batteries. In this study, a simple and inexpensive carbon intermediate layer was fabricated using a traditional Korean paper called "hanji". This carbon interlayer has a fibrous porous structure, with a specific surface area of 91.82 m2 g-1 and a BJH adsorption average pore diameter of 26.63 nm. The prepared carbon interlayer was utilized as an intermediary layer in Li-S batteries to decrease the charge-transfer resistance and capture dissolved lithium polysulfides. The porous fiber-shaped carbon interlayer suppressed the migration of polysulfides produced during the electrochemical process. The carbon interlayer facilitates the adsorption of soluble lithium polysulfides, allowing for their re-utilization in subsequent cycles. Additionally, the carbon interlayer significantly reduces the polarization of the cell. This simple strategy results in a significant improvement in cycle performance. Consequently, the discharge capacity at 0.5 C after 150 cycles was confirmed to have improved by more than twofold, reaching 230 mAh g-1 for cells without the interlayer and 583 mAh g-1 for cells with the interlayer. This study demonstrates a simple method for improving the capacity of Li-S batteries by integrating a functional carbon interlayer.

Synthesis and Electrochemical Performance of Microporous Hollow Carbon from Milkweed Pappus as Cathode Material of Lithium-Sulfur Batteries.

Microtube-like porous carbon (MPC) and tube-like porous carbon-sulfur (MPC-S) composites were synthesized by carbonizing milkweed pappus with sulfur, and they were used as cathodes for lithium-sulfur batteries. The morphology and uniformity of these materials were characterized using X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy with an energy-dispersive X-ray analyzer, thermogravimetric analysis, and X-ray photoelectron spectrometry. The electrochemical performance of the MPC-S cathodes was measured using the charge/discharge cycling performance, C rate, and AC impedance. The composite cathodes with 93.8 wt.% sulfur exhibited a stable specific capacity of 743 mAh g-1 after 200 cycles at a 0.5 C.

Adhesion of Poly(phenylene sulfide) Resin with Polymeric Film of Triazine Thiol on Aluminum Surface Modified by Anodic Oxidation.

Various surface modifications have been applied to improve the adhesion properties of aluminum for the cap plate and sealing quality of electrolyte on Li ion batteries. In this study, we have tried to find the effective condition for the polymerization of triazine thiols (TT) on modified aluminum surfaces by anodic aluminum oxide. Characterization of polymerized films on aluminum was explored by scanning electron microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy analysis. Scanning electron microscopy results reveal that meaningful roughness was formed on aluminum surfaces by anodic oxidation. Secondary ion mass spectroscopy analysis results represent that the peel strength was found to depend on film thickness and the composition of the adhesion layer. As a result, Al/PPS (polyphenylene sulfide) resin assemblies developed in this study have superior adhesive property. Therefore, these assemblies might be a viable candidate for a sealing technique for Li ion batteries.

Luminescent properties of rare earth fully activated apatites, LiRE9(SiO4)6O2 (RE = Ce, Eu, and Tb): site selective crystal field effect.

Novel LiCe9(SiO4)6O2 and LiTb9(SiO4)6O2 compounds have been successfully synthesized, and the site selectivity and occupancy of activator ions have been estimated including LiEu9(SiO4)6O2 compound. The rare earth (RE) fully occupied compounds, as well as the RE partially occupied congeners are required for the assessment of site selectivity of RE (activator) ions in apatite-type compounds. The splitting energies of the 6H and 4F Wycoff positions of LiRE9(SiO4)6O2 (RE = Ce, Eu, and Tb) compounds are calculated based on crystal field theory: ΔECe(6H) = 3849.3 cm(-1), ΔECe(4F) = 4228.1 cm(-1), ΔEEu(6H) = 3870.0 cm(-1), ΔEEu(4F) = 4092.8 cm(-1), ΔETb(6H) = 3637.6 cm(-1), ΔETb(4F) = 4396.1 cm(-1), indicating that the splitting energy for the 4F site is larger than that for the 6H site in all compounds; thus the absorption energy is higher for the 6H site. In apatite-type LiRE9(SiO4)6O2 (RE = Ce, Eu, and Tb) compounds, the Ce(3+) ions predominantly occupy the 4F site associated with the absorption band around 300 nm at lower Ce(3+) concentration, and then enter the 6H site associated the absorption band around 245 nm. For the Eu(3+)-doped compounds, the 4F site and 6H site are mixed within the charge transfer band (CTB) between 220 and 350 nm. Eu(3+) ions initially preferentially occupy the 6H site (around 290 nm) at lower Eu(3+) concentration and subsequently enter the 4F site (around 320 nm) with increasing Eu(3+) concentration. For the Tb(3+)-doped compounds, the absorption due to the two different sites is mixed within f-d absorption band between 200 and 300 nm. At lower Tb(3+) concentration, the Tb(3+) ions enter favorably 6H site around 240 nm and then enter 4F site around 270 nm. These compounds may provide a platform for modeling a new phosphor and application in the solid-state lighting field.

Development of an improved ligand exchange chiral stationary phase based on leucinol for the resolution of proton pump inhibitors.

As an effort to develop improved ligand exchange chiral stationary phases (CSPs) for the resolution of chiral drugs, the residual silanol groups on the silica surface of a CSP based on sodium N-[(S)-1-hydroxymethyl-3-methylbutyl]-N-undecylaminoacetate, a (S)-leucinol derivative, were protected with n-octyl groups. The residual silanol group-protected CSP was applied to the resolution of proton pump inhibitors (PPIs) such as omeprazole, pantoprazole, lansoprazole and rabeprazole. The resolution of PPIs on the residual silanol group-protected CSP was excellent with the separation factors (α) in the range of 4.32-6.42 and the resolution factors (RS) in the range of 6.70-7.15. The improved chiral recognition ability of the residual silanol group-protected CSP was rationalized to be originated from the protection of the non-enantioselective interaction sites on the silica surface and the improved lipophilicity of the stationary phase.

Orbital interaction and electron density transfer in PdII([9]aneB2A)L2 complexes: theoretical approaches.

The geometric structures of Pd-complexes {Pd([9]aneB2A)L2 and Pd([9]aneBAB)L2 where A = P, S; B = N; L = PH3, P(CH3)3, Cl-}, their selective orbital interaction towards equatorial or axial (soft A…Pd) coordination of macrocyclic [9]aneB2A tridentate to PdL2, and electron density transfer from the electron-rich trans L-ligand to the low-lying unfilled a1g(5s)-orbital of PdL2 were investigated using B3P86/lanl2DZ for Pd and 6-311+G** for other atoms. The pentacoordinate endo-[Pd([9]aneB2A)(L-donor)2]2+ complex with an axial (soft A--Pd) quasi-bond was optimized for stability. The fifth (soft A--Pd) quasi-bond between the σ-donor of soft A and the partially unfilled a1g(5s)-orbital of PdL2 was formed. The pentacoordinate endo-Pd([9]aneB2A)(L-donor)2]2+ complex has been found to be more stable than the corresponding tetracoordinate endo-Pd complexes. Except for the endo-Pd pentacoordinates, the tetracoordinate Pd([9]aneBAB)L2 complex with one equatorial (soft A-Pd) bond is found to be more stable than the Pd([9]aneB2A)L2 isomer without the equatorial (A-Pd) bond. In particular, the geometric configuration of endo-[Pd([9]anePNP)(L-donor)2]2+ could not be optimized.

Effect of the residual silanol group protection on the liquid chromatographic resolution of α-amino acids and proton pump inhibitors on a ligand exchange chiral stationary phase.

A new ligand exchange chiral stationary phase (new CSP) containing residual silanol group-protecting n-octyl groups on the silica surface was prepared by treating a ligand exchange CSP (original CSP) based on sodium N-[(R)-2-hydroxy-1-phenylethyl]-N-undecylaminoacetate bonded to silica gel with excess n-octyltriethoxysilane. The new and original CSPs containing an identical amount of chiral selector were applied to the resolution of α-amino acids and proton pump inhibitors (PPIs) including omeprazole, pantoprazole, lansoprazole, and rabeprazole. The separation factors (α) and resolutions (RS) were greater on the new CSP than on the original CSP except for the resolution of asparagine. The trends of the retention factors (k1) for the resolution of α-amino acids on the new and original CSPs with the variation of the organic modifier content in aqueous mobile phase were opposite to those for the resolution of PPIs. Removal of the nonenantioselective interactions between the residual silanol groups and the analytes and the improved lipophilicity of the new CSP were proposed to be responsible for the improved chiral recognition ability of the new CSP and the different retention behaviors of the enantiomers between the new and original CSPs.

Comparison of polarimetry and crown ether-based HPLC chiral stationary phase method to determine (L)-amino acid optical purity.

Although various pharmacopoeias provide titration methods to assay (L)-amino acid content, none of these methods distinguish between (L)- and (D)-amino acids and do not consider the presence of enantiomeric impurities. Consequently, these methods are limited in scope to describe the relationship between content and specific rotation, [α]. In this study, the US Pharmacopoeia method was compared with the crown ether-based high performance liquid chromatographic (HPLC) chiral stationary phase (CSP) method to determine (L)-amino acid content and specific rotation. The (L)-amino acid content specified by the US Pharmacopoeia method was not consistent with the specific rotation in the presence of enantiomeric impurities, whereas the HPLC-CSP method was very effective for determining the (L)-amino acid content and the optical purity. The other advantage is that the HPLC-CSP method requires amino acid samples of quite low concentration (as low as 1 µg/mL), whereas the pharmacopoeia method requires higher concentrations (20-110 mg/mL).

Photocatalytic performance of nanocrystalline Bi5Ti3FeO15 layered perovskite under visible light.

Nanocrystalline Bi5Ti3FeO15 layered perovskite exhibiting Aurivillius phase was synthesized by polymerized complex (PC) method and investigated for its physico-chemical as well as optical properties. The crystallization of Bi5Ti3FeO15 synthesized by PC method was found to occur in the temperature range of 800-1050 degress C, whereas the single crystalline Bi5Ti3FeO15 formed at 1030 degrees C by solid state reaction (SSR) method. The observation of highly pure phase and such lower crystallization temperature in Bi5Ti3FeO15 prepared by PC method, is in total contrast to that observed in Bi5Ti3FeO15 prepared by the conventional solid-state reaction (SSR) method. The band gap of nanocrystalline Bi5Ti3FeO15 determined from UV-Vis diffusion reflectance spectrometer was 2.38 eV (525 nm). The photocatalytic activity of Pt/Bi5Ti3FeO15 prepared by PC method was investigated with the photodecomposition of isopropyl alcohol (IPA) and hydrogen production from water-methanol mixed solution under visible light (lambda > or = 420 nm). The respective activities for PC sample were higher than that of Pt/Bi5Ti3FeO15 prepared by SSR as well as Pt/TiO(2-x)N(x).

Liquid chromatographic resolution of proton pump inhibitors including omeprazole on a ligand exchange chiral stationary phase.

A ligand exchange chiral stationary phase (CSP) developed previously in this laboratory by bonding (R)-phenylglycinol derivative, sodium N-[(R)-2-hydroxy-1-phenylethyl]-N-undecylaminoacetate, to silica gel was successfully applied to the resolution of proton pump inhibitors (PPIs) including omeprazole, pantoprazole, lansoprazole and rabeprazole. For example, the separation factors (α) for the resolution of omeprazole, pantoprazole, lansoprazole and rabeprazole were 4.27, 5.28, 2.77 and 4.06, respectively, and the resolutions (R(S)) were 2.53, 2.55, 1.93, and 2.01, respectively, when 65% acetonitrile aqueous solution containing 0.5mM CuSO(4) and 0.05mM triethylamine was used as a mobile phase. Based on the chromatographic behaviors for the resolution of PPI analogues on CSP 1, a chiral recognition mechanism utilizing the sulfoxide oxygen and the benzimidazole ring nitrogen of PPIs as bidentate coordination donors to form an enantioselective ternary complex with the central Cu(II) ion and the chiral stationary bidentate ligand was proposed.

Analysis and tentative structure elucidation of new anthocyanins in fruit peel of Vitis coignetiae Pulliat (meoru) using LC-MS/MS: Contribution to the overall antioxidant activity.

The skin of Vitis coignetiae Pulliat (meoru) grown wild in the Republic of Korea was analyzed for anthocyanins via HPLC coupled to ESI-MS/MS in positive ion mode. Chromatographic separation was conducted via RP HPLC using a C(18) column, with a 50-min gradient from 0 to 80% methanol in water containing 0.5% formic acid. A total of 18 anthocyanins were identified. Among them, nine compounds were newly determined by comparing the retention time (t(R)) and mass fragmentation patterns with those of the previously reported anthocyanins for other grape varieties: malvidin hexose, peonidin 3-galactoside, malvidin 3-galactoside, cyanidin, petunidin, petunidin 3-(6''-coumaroyl)-5-diglucoside, peonidin, malvidin, and malvidin 3-(6''-coumaroyl)-5-diglucoside. The antioxidant activity of the V. coignetiae Pulliat anthocyanins was determined via 2,2-diphenyl-2-picrylhydrazyl radical scavenging and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation assays in a range of concentration from 25 to 500 mg/L. The capacity increased with concentration. The IC(50) values, defined as the concentration of sample required to scavenge 50% of free radicals, were calculated as follows: 189.63+/-11.31 mg/L and 141.29+/-6.70 mg/L for 2,2-diphenyl-2-picrylhydrazyl and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation, respectively. The antioxidant activity of the V. coignetiae Pulliat anthocyanins is substantially higher than that of ascorbic acid and is similar to the effects of the extracts obtained from other grape varieties.

Synthesis and electrochemical studies of nano-scale carbon-coated LiFePO4 electrodes for Li-ion batteries.

Regardless of high capacity and stability during lithium extraction, LiFePO4 materials have difficulty in the applications for high electrical density because of low electrical conductivities. In order to optimize this problem, we synthesized carbon coated LiFePO4 by adding humic acid using solid state reaction method. We characterized the synthesized compounds via the crystallinity, the valence states of Fe ions, and their shapes. We found the carbon coating using X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). We also found that the iron ion is substituted from 3+ to 2+ through XPS measurement. We showed that the carbon coating increased the electrochemical behavior by measuring the charge-discharge characteristics.

Fabrication of CaFe2O4/MgFe2O4 bulk heterojunction for enhanced visible light photocatalysis.

A bulk heterojunction photocatalyst of interfacing CaFe(2)O(4) and MgFe(2)O(4) nanoparticles is highly active for oxidative degradation of isopropyl alcohol and hydrogen production from water under visible light, because the exciton easily reaches the interface and dissociates to minimize recombination.

Physical and optical properties of nanocrystalline calcium ferrite synthesized by the polymerized complex method.

Nanocrystalline CaFe2O4 oxide semiconductor with spinel structure was synthesized by polymerized complex (PC) method and investigated for its physical and optical properties. The crystallization of CaFe2O4 made by PC method was found to occur in the temperature range of 700-1100 degrees C. The observation of highly pure phase and such lower crystallization tempearture in CaFe2O4 made by PC method, is in total contrast to that observed in CaFe2O4 prepared by the conventional solid-state reaction (SSR) method. The activation energy required for the growth of nanocrystalline CaFe2O4 in PC sample was found to be 8.4 kJ/mol. The band gap of nanocrystalline CaFe2O4 determined by UV-DRS was 1.91 eV (647 nm). The photocatalytic activity of PC materials for iso-propyl alcohol photodegradation under visible light (> or =420 nm) was much higher than that of SSR materials.