Kinetically Enhanced Reaction Pathway to Form Highly Crystalline Layered LiCoO2 at Low Temperatures Below 300 °C.

Layered LiCoO2 is usually synthesized after a prolonged sintering process at high temperatures (≥800 °C) for 10-20 h. This study developed a "hydroflux process" to obtain highly crystalline and layered LiCoO2 at a low temperature of 300 °C within 30 min. Molten mixed hydroxide-containing water molecules significantly accelerated the formation of LiCoO2, which showed a highly reversible capacity of 120 mAh g-1 without postannealing. The reaction mechanism study showed fast growth of LiCoO2 crystals, suggesting that the excess molten hydroxides containing water dissolve the cobalt species of HCoO2-. Consequently, the accelerated LiCoO2 formation suppresses the competing reaction of Co3O4 formation, leading to spinel LiCoO2 formation at low temperatures. Excess water in the starting materials further accelerated the crystal growth of LiCoO2, forming large particles (>1 µm). Moreover, the layered LiCoO2 began to form at 150 °C. This study is the first experimental demonstration that proves the thermodynamic stability of layered LiCoO2 at low temperatures (150-300 °C) under ambient pressure. This novel process offers significant energy savings in the production process of LiCoO2 and other ceramics materials.

Quantitative NMR of quadrupolar nucleus as a novel analytical method: hydrolysis behaviour analysis of aluminum ion.

In this study, quantitative nuclear magnetic resonance (qNMR) spectroscopy of quadrupolar nuclei has been established. The complicated hydrolysis behavior of the Al3+ ion, which causes fish poisoning and inhibits the growth of plants in environmental water, was clarified by 27Al qNMR spectroscopy. Highly accurate simultaneous multicomponent quantitative analysis of various hydrolyzed forms of the Al ion was achieved in a non-destructive manner. The calibration curve of the external standard aqueous Al(NO3)3 solution showed excellent linearity over a very wide concentration range from 1 × 10-4 to 1 mol L-1 (an increase in concentration of 10 000 times), with a simple experimental and analytical procedure. Furthermore, the weaknesses of the conventional Ferron assay and the advantages of 27Al qNMR spectroscopy were considered. The quantitative determination error for the free [Al(H2O)6]3+ ion and the trinuclear complex, which has a high complexation rate, is higher in the Ferron assay than in the 27Al qNMR technique. The concentrations of four Al species were directly determined by 27Al qNMR, namely, free [Al(H2O)6]3+, the trinuclear complex, Al(OH)4-, and tridecameric hydrolyzed Al, which has a Keggin structure. The concentration of the tridecamer rapidly increased until 100 min after NaOH addition, and showed a local maximum after 1 week. In addition, the concentration of colloidal Al hydroxide, which cannot be detected by NMR spectroscopy, was determined by numerical analysis. This species was generated in the initial stage of reaction, and then the tridecamer formed very slowly.

In Situ Synthesis of a Supramolecular Hydrogelator at an Oil/Water Interface for Stabilization and Stimuli-Induced Fusion of Microdroplets.

Supramolecular hydrogels are expected to have applications as novel soft materials in various fields owing to their designable functional properties. Herein, we developed an in situ synthesis of supramolecular hydrogelators, which can trigger gelation of an aqueous solution without the need for temperature change. This was achieved by mixing two precursors, which induced the synthesis of a supramolecular gelator and its instantaneous self-assembly into nanofibers. We then performed the in situ synthesis of this supramolecular gelator at an oil/water interface to produce nanofibers that covered the surfaces of the oil droplets (nanofiber-stabilized oil droplets). External stimuli induced fusion of the droplets owing to disassembly of the gelator molecules. Finally, we demonstrated that this stimuli-induced droplet fusion triggered a synthetic reaction within the droplets. This means that the confined nanofiber-stabilized droplets can be utilized as stimuli-responsive microreactors.

Room temperature direct imprinting of porous glass prepared from phase-separated glass.

This work describes a room-temperature imprinting of nanoporous glass prepared by selective chemical etching of phase-separated glass. A highly porous (58%) and highly transparent (>90%) porous glass layer can be formed on a transparent phase-separated glass substrate. It is shown that the lateral resolution of the imprinting is a few tens of nanometers. As the porosity increases, the imprint depth increases and reaches up to 90% of the height of the mold pattern. The porous glass has a wider transmittance window (300-2700 nm) and a higher thermal durability (~500 °C) than other materials used for imprinting. The technique has various potential applications such as diffraction optical elements, waveguides, biosensors, and microfluidic devices.

Supramolecular gelators based on benzenetricarboxamides for ionic liquids.

Supramolecular gelators comprising 1,3,5-benzenetricarboxylic acids and amino acid methyl esters (glycine, L-alanine, L-valine, L-leucine, L-methionine, and L-phenylalanine) for ionic liquids were developed. Ten types of ionic liquids were gelated using the above-mentioned gelators at relatively low concentrations. Field emission-scanning electron microscopy and confocal laser scanning microscopy analyses revealed that these gelators self-assembled into an entangled fibrous structure in ionic liquids, leading to the gelation of the ionic liquids. Comparison studies, involving compounds analogous to the gelators, and Fourier transform infrared spectroscopy measurements suggested that hydrogen bonding played a key role in the self-assembly of the gelator molecules. The ionogels displayed reversible thermal transition characteristics and viscoelastic properties typical of a gel. The gelation of the ionic liquids studied under a wide range of gelator concentrations did not affect the intrinsic conductivity of the ionic liquids.

Europium doping induced symmetry deviation and its impact on the second harmonic generation of doped ZnO nanowires.

In this work, we investigated the effects of europium doping on the second harmonic generation (SHG) of ZnO nanowires (NWs). A non-monotonic enhancement in the SHG is observed with the increase of the europium concentration. Maximum SHG is observed from the 1 at.% europium doped ZnO NWs with an enhancement factor of 4.5. To understand the underlying mechanism, the effective second order non-linear coefficient (deff) is calculated from the theoretical fitting with consideration of the absorption effect. Microstructural characterization reveals the structural deformation of the ZnO NWs caused by europium doping. We estimated the deviation in the crystal site symmetry around the Eu(3+) ions (defined as the asymmetric factor) from photoluminescence measurement and it is found to be strongly correlated with the calculated deff value. A strong linear dependence between the magnitudes of deff and the asymmetric factor suggests that deviation in the local site symmetry of the ZnO crystal by europium doping could be the most probable origin of the observed large second order non-linearity.

9Be and ³¹P NMR analyses on the influence of imino groups on Be²âº complex stabilities of a series of cyclo-µ-imido triphosphate anions.

The complexation behaviors of Be²âº with cyclo-µ-imido triphosphate anions, cP3O9-n(NH)n(3-)n= 1, 2),have been investigated by both 9Be and ³¹P NMR techniques at -2.3 °C in order to clarify the coordination structures of the complexes. The spectra showed that cP3O9n(NH)n (n = 1, 2) ligands form ML, ML2, and M2L complexes with Be²âº ions, and the formation of complexes coordinating with nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. These complexation trends are very similar to those of Be²âº-cP3O6(NH)⁻³3system, which has been reported by us. The peak deconvolution of 9BeNMR spectra made these beryllium complexes amenable to stability constant determinations. The stability constants of the complexes increase with an increase in the protonation constants of the ligands as the number of imino groups, which constitute the ligand molecules, is ascended. This increase is primarily attributable to the lower electronegativity of nitrogen atoms than oxygen atoms, which are directly bonded to central phosphorus atoms; moreover, tautomerism equilibrium in the entire of the imidopolyphosphate molecule is also responsible to the higher basicity. ³¹P NMR spectra measured concurrently have verified the formation of the complexes estimated by the 9Be NMR measurement. Intrinsic ³¹P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be²âº cations have been determined. Not only the protonation constants but also the stability constants of all Be²âº complexes increase approximately linearly with an increase in the number of imino groups.

Terahertz wire grid polarizer fabricated by imprinting porous silicon.

A terahertz (THz) wire-grid polarizer is fabricated by imprinting porous Si followed by oblique evaporation of Ag. We demonstrate that it works in a wide frequency region covering from 5 to 18 THz with the extinction ratio of 10 dB. The frequency region is much wider than that of THz wire-grid polarizers fabricated by conventional imprint lithography using organic materials. The result suggests that imprinting of porous Si is a promising fabrication technique to realize low-cost wire-grid polarizers working in the THz region.

Versatile supramolecular gelators that can harden water, organic solvents and ionic liquids.

We developed novel supramolecular gelators with simple molecular structures that could harden a broad range of solvents: aqueous solutions of a wide pH range, organic solvents, edible oil, biodiesel, and ionic liquids at gelation concentrations of 0.1-2 wt %. The supramolecular gelators were composed of a long hydrophobic tail, amino acids and gluconic acid, which were prepared by liquid-phase synthesis. Among seven types of the gelators synthesized, the gelators containing L-Val, L-Leu, and L-Ile exhibited high gelation ability to various solvents. These gelators were soluble in aqueous and organic solvents, and also in ionic liquids at high temperature. The gelation of these solvents was thermally reversible. The microscopic observations (TEM, SEM, and CLSM) and small-angle X-ray scattering (SAXS) measurements suggested that the gelator molecules self-assembled to form entangled nanofibers in a large variety of solvents, resulting in the gelation of these solvents. Molecular mechanics and density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers. Interestingly, the gelation of an ionic liquid by our gelator did not affect the ionic conductivity of the ionic liquid, which would provide an advantage to electrochemical applications.

Efficient near-infrared emission from neodymium by broadband sensitization of bismuth in zeolites.

Nd-Bi codoped zeolites were prepared by an ion-exchange process, and the optical properties were investigated by photoluminescence (PL) and PL excitation spectra, and decay time measurements. The results show that the NIR emission of Nd(3+) ions is significantly enhanced by the introduction of bismuth in codoped samples, and the lifetime reaches 246 µs. It is also observed that NIR-active Bi acts as a sensitizer of Nd(3+) ions. The energy transfer efficiency is also estimated. The peculiar optical properties make Nd-Bi codoped zeolites promising for potential application in biological probes.

Efficient near-infrared luminescence and energy transfer in erbium/bismuth codoped zeolites.

We have shown that tunable and highly efficient broadband near-IR (NIR) luminescence can be realized in erbium/bismuth codoped zeolites. The emission covers the ranges of 930-1450nm and 1450-1630nm. The intensity ratio of the two bands can be tuned by adjusting the concentration of erbium and the excitation wavelength. Steady-state and time-resolved photoluminescence (PL), and PL excitation measurements indicate that two kinds of emitters coexist in the pores of zeolites, and that NIR active bismuth simultaneously acts as a sensitizer of erbium. The present results demonstrate an important rational strategy for the design of a tunable NIR-emitting zeolite-based nanosystem.

Evaluation of nucleic acid duplex formation on gold over layers in biosensor fabricated using Czochralski-grown single-crystal silicon substrate.

With a view to developing an economical and elegant biosensor chip, we compared the efficiencies of biosensors that use gold-coated single-crystal silicon and amorphous glass substrates. The reflectivity of light over a wide range of wavelengths was higher from gold layer coated single-crystal silicon substrates than from glass substrates. Furthermore, the efficiency of reflection from gold layers of two different thicknesses was examined. The thicker gold layer (100 nm) on the single-crystal silicon showed a higher reflectivity than the thinner gold film (10 nm). The formation of a nucleic acid duplex and aptamer-ligand interactions were evaluated on these gold layers, and a crystalline silicon substrate coated with the 100-nm-thick gold layer is proposed as an alternative substrate for studies of interactions of biomolecules.

An experimental and first-principle investigation of the Ca-substitution effect on P3-type layered NaxCoO2.

We experimentally and computationally investigated the Ca substitution effect on the electrochemical performance of P3-NaxCoO2. The cycle performance of Ca-substituted NaxCa0.04CoO2 was effectively improved due to its better crystallinity retention after charging. Our DFT calculations suggested that the presence of Ca2+ ions in Na sites kinetically mitigates phase transition.

Significantly enhanced superbroadband near infrared emission in bismuth/aluminum doped high-silica zeolite derived nanoparticles.

Significantly enhanced superbroadband near infrared emission has been realized in bismuth/aluminum doped high-silica zeolite derived nanoparticles. The emission intensity can be easily tailored by the introduction of aluminum. The luminescence lifetime can reach up to 695 micros. The results reveal that the existence of charge imbalance environment caused by [AlOV(4/2)](-) units in host materials is requisite to the formation of infrared-active Bi(+). The finding presents a feasible route to design high-efficient bismuth activated infrared luminescent nanoparticles. These bismuth doped nanoparticles may find applications as superbroadband near infrared nano optical sources.

One-step synthesis and near-infrared luminescent properties of Er3+ and Ni2+ doped single-crystalline Al18B4O33 nanorods.

Er(3+) and Ni(2+) doped single-crystalline Al(18)B(4)O(33) nanorods were synthesized by a facile one-step toxic-free combustion method. The products were characterized by x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and integrated and time-resolved photoluminescence (PL) measurements. The phase purity, morphology, and PL properties of Er(3+) and Ni(2+) doped Al(18)B(4)O(33) nanorods can be readily controlled by tailoring the annealing temperature. The mechanism for the formation of Al(18)B(4)O(33) nanorods with different aspect ratio is discussed. Er(3+) doped Al(18)B(4)O(33) nanorods show strong PL centered at 1531 nm, while Ni(2+) doped products show superwide PL with a full width at half maximum of up to 250 nm. These aluminum borate nanostructures are promising building blocks for optoelectronics nanodevices.

Controlled synthesis and luminescent properties of erbium silicate nanostructures.

Erbium silicate (Er2SiO5 and Er4Si3O12) nanostructures were successfully synthesized by a facile molten-salt approach in the presence of NaCI and surfactant. The synthesized products were structurally and morphologically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), whereas the luminescent properties were characterized by temperature-dependent luminescence measurements. The results revealed that the composition, crystalline phase, and yield of the final products can be readily controlled by choosing suitable surfactant and tailoring the molar ratio of reactants used for the reactions. Moreover, the single-crystalline nature of Er2SiO5 and of Er4Si3O12 nanostructures results in sharp photoluminescence (PL) of Er3+, and both nanostructures are immunized from temperature quenching of PL. We suggest that the nanostructures developed in the present work are promising building blocks for Si-based optoelectronics nanodevices.

Destabilized Passivation Layer on Magnesium-Based Intermetallics as Potential Anode Active Materials for Magnesium Ion Batteries.

Passivation of magnesium metal anode is one of the critical challenges for the development of magnesium batteries. Here we investigated the passivation process of an intermetallic anode: Mg3Bi2 synthesized by solid-state and thin film process. The Mg3Bi2 composite electrode shows excellent reversibility in magnesium bis(trifluoromethansulfonylamide) dissolved in acetonitrile, while Mg3Sb2, which has same crystal structure and similar chemical properties, is electrochemically inactive. We also fabricated the Mg3Bi2 thin film electrodes, which show reversibility with low overpotential not only in the acetonitrile solution but also glyme-based solutions. Surface layer corresponding to the decomposed TFSA anion is slightly suppressed in the case of the Mg3Bi2 thin film electrode, compared with Mg metal. Comparative study of hydrolysis process of the Mg3Bi2 and the Mg3Sb2 suggests that the both intermetallic anodes are not completely passivated. The bond valence sum mapping of the Mg3Bi2 indicates that the fast Mg2+ diffusion pathway between 2d tetrahedral sites is formed. The electrochemical properties of the Mg3Bi2 anode is mainly due to the less passivation surface with the fast Mg2+ diffusion pathways.

(15)N and (31)P NMR Insights into Lactam-Lactim Tautomerism Activity Using cyclo-µ-Imidopolyphosphates.

The effects of the molecular structure and solution pH on compounds prone to lactam-lactim tautomerism have been evaluated by (15)N NMR spectroscopy. The lactam-lactim tautomerism activities of cP3O6(NH)3(3-) and cP4O8(NH)4(4-) showed a significant pH dependence, with the process being inactivated under alkaline conditions because of the decrease in the number of hydrogen atoms by the deprotonation of the anions. The tautomerism was activated under the acidic conditions by the increase in the number of dissociative hydrogen atoms resulting from the protonation of the anions. cP3O6(NH)3(3-) has much more of a planar molecular structure than cP4O8(NH)4(4-), meaning that the hydrogen atoms in cP3O6(NH)3(3-) would be delocalized over the entire structure to a greater extent than those in cP4O8(NH)4(4-). This difference in the distribution of hydrogen atoms would result in the lactam-lactim tautomerism activity of cP3O6(NH)3(3-) being higher than that of cP4O8(NH)4(4-). The results have shown that the following factors are critical to the achievement of an efficient anhydrous proton conductor: (1) the regular molecular arrangement of highly planar molecules; (2) the existence of a large number of dissociative protons in a molecule; and (3) a molecular structure with a small energy barrier for the structural rearrangement required of the tautomerism process.

Nickel-Aluminum Layered Double Hydroxide Coating on the Surface of Conductive Substrates by Liquid Phase Deposition.

The direct synthesis of the adhered Ni-Al LDH thin film onto the surface of electrically conductive substrates by the liquid phase deposition (LPD) reaction is carried out for the development of the positive electrode. The complexation and solution equilibria of the dissolved species in the LPD reaction have been clarified by a theoretical approach, and the LPD reaction conditions for the Ni-Al LDH depositions are shown to be optimized by controlling the fluoride ion concentration and the pH of the LPD reaction solutions. The yields of metal oxides and hydroxides by the LPD method are very sensitive to the supersaturation state of the hydroxide in the reaction solution. The surfaces of conductive substrates are completely covered by the minute mesh-like Ni-Al LDH thin film; furthermore, there is no gap between the surfaces of conductive substrates and the deposited Ni-Al LDH thin film. The active material layer thickness was able to be controlled within the range from 100 nm to 1 µm by the LPD reaction time. The high-crystallinity and the arbitrary-thickness thin films on the conductive substrate surface will be beneficial for the interface control of charge transfer reaction fields and the internal resistance reduction of various secondary batteries.

Highly Conductive Ionic-Liquid Gels Prepared with Orthogonal Double Networks of a Low-Molecular-Weight Gelator and Cross-Linked Polymer.

We prepared a heterogeneous double-network (DN) ionogel containing a low-molecular-weight gelator network and a polymer network that can exhibit high ionic conductivity and high mechanical strength. An imidazolium-based ionic liquid was first gelated by the molecular self-assembly of a low-molecular-weight gelator (benzenetricarboxamide derivative), and methyl methacrylate was polymerized with a cross-linker to form a cross-linked poly(methyl methacrylate) (PMMA) network within the ionogel. Microscopic observation and calorimetric measurement revealed that the fibrous network of the low-molecular-weight gelator was maintained in the DN ionogel. The PMMA network strengthened the ionogel of the low-molecular-weight gelator and allowed us to handle the ionogel using tweezers. The orthogonal DNs produced ionogels with a broad range of storage elastic moduli. DN ionogels with low PMMA concentrations exhibited high ionic conductivity that was comparable to that of a neat ionic liquid. The present study demonstrates that the ionic conductivities of the DN and single-network, low-molecular-weight gelator or polymer ionogels strongly depended on their storage elastic moduli.