Mitsubishi Chemical Group Science and Technology Research Center (Japan)

Bacterial-cellulose nanofibers obtained from Acetobacter xylinum can reinforce polymer resins while maintaining the transparency of the original resin, even at fiber contents as high as 70 wt.-%, because the nanofibers do not appreciably scatter visible light. The flexible plastic composites (see Figure) reinforced with this renewable resource have thermal expansion coefficients of 6 × 10–6 °C–1, Young's moduli of 20 GPa, and tensile strengths reaching 325 MPa.

Electroluminescence based on TADF, that is, thermally activated delayed fluorescence, is demonstrated in Sn4+–porphyrin complexes. On excitation by a short electrical pulse, prompt and delayed electroluminescence components were clearly observed. The delayed component was composed of both TADF and phosphorescence (see figure), and the TADF component significantly increased with increasing temperature.

1-Butanol, an important chemical feedstock and advanced biofuel, is produced by Clostridium species. Various efforts have been made to transfer the clostridial 1-butanol pathway into other microorganisms. However, in contrast to similar compounds, only limited titers of 1-butanol were attained. In this work, we constructed a modified clostridial 1-butanol pathway in Escherichia coli to provide an irreversible reaction catalyzed by trans-enoyl-coenzyme A (CoA) reductase (Ter) and created NADH and acetyl-CoA driving forces to direct the flux. We achieved high-titer (30 g/liter) and high-yield (70 to 88% of the theoretical) production of 1-butanol anaerobically, comparable to or exceeding the levels demonstrated by native producers. Without the NADH and acetyl-CoA driving forces, the Ter reaction alone only achieved about 1/10 the level of production. The engineered host platform also enables the selection of essential enzymes with better catalytic efficiency or expression by anaerobic growth rescue. These results demonstrate the importance of driving forces in the efficient production of nonnative products.

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn4+ and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies (PCEs). Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of Sn-based halide perovskite solar cells to solve this problem, using MASnI3, CsSnI3, and CsSnBr3 as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with PCEs of 3.89%, 1.83%, and 3.04% for MASnI3, CsSnI3, and CsSnBr3, respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn4+/Sn2+ ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step toward a deeper understanding of the intrinsic Sn-based halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells.

Divalent europium-doped nitride phosphors, Ca1-xEuxAlSiN3 (x = 0−0.2), were successfully prepared by the self-propagating high-temperature synthesis (SHS) by using Ca1-xEuxAlSi alloy powder as a precursor. The Rietveld refinement analysis was carried out on the CaAlSiN3 host lattice to elucidate the luminescence properties of dopant Eu2+ on the tetrahedrally coordinated site. For the Eu2+ doped samples, strong absorption peaking at about 460 nm was observed on the excitation spectra, which matched perfectly with the current blue light of InGaN/GaN light-emitting diodes (LEDs). The optimized sample, Ca0.98Eu0.02AlSiN3, gave the red emission peaking at 649 nm of which the intensity was competitive with the sample prepared from the metal nitride raw materials (Ca3N2, AlN, Si3N4, and EuN). The CIE chromaticity index (0.647, 0.347) with high color saturation indicated that it was a promising candidate as a red-emitting phosphor for the InGaN/GaN-based down-conversion white LEDs for general illumination or displays.

The solid electrolyte interface (SEI) formation on composite graphite and highly oriented pyrolytic graphite in a vinylene carbonate (VC)-containing electrolyte was analyzed using evolved gas analysis, Fourier transform infrared analysis, two-dimensional nuclear magnetic resonance, X-ray photoelectron spectroscopy, time of flight-secondary-ion mass spectrometry, and scanning electron microscopy. We found that the SEI layers derived from VC-containing electrolytes consist of polymer species such as poly (vinylene carbonate) (poly(VC)), an oligomer of VC, a ring-opening polymer of VC, and polyacetylene. Moreover, lithium vinylene dicarbonate, lithium divinylene dicarbonate, lithium divinylene dialkoxide, and lithium carboxylate, RCOOLi, were formed on graphite as VC reduction products. The presence of VC in the ethylene carbonate (EC)-based electrolyte caused a decrease in the reductive gases of the EC dimethyl carbonate solvent such as and CO. The VC-derived SEI layer was formed at a potential more positive than 1.0 V vs. Effective SEI formation by reduction of VC progresses before that of EC. The thermal decomposition temperature of the SEI layer derived from VC shifted to a higher temperature compared to that derived from the VC-free electrolytes. We concluded that the thermal stability of the VC-derived SEI layer has a close relation to high-temperature storage characteristics at elevated temperatures. © 2004 The Electrochemical Society. All rights reserved.

Bacterial cellulose (BC) nanofibers were acetylated to enhance the properties of optically transparent composites of acrylic resin reinforced with the nanofibers. A series of BC nanofibers acetylated from degree-of-substitution (DS) 0 to 1.76 were obtained. X-ray diffraction profiles indicated that acetylation proceeded from the surface to the core of BC nanofibers, and scanning electron microscopy images showed that the volume of nanofibers increases by the bulky acetyl group. Since acetylation decreased the refractive index of cellulose, regular transmittance of composites comprised of 63% BC nanofiber was improved, and deterioration at 580 nm because of fiber reinforcement was suppressed to only 3.4%. Acetylation of nanofibers changed their surface properties and reduced the moisture content of the composite to about one-third that of untreated composite, although excessive acetylation increased hygroscopicity. Furthermore, acetylation was found to reduce the coefficient of thermal expansion of a BC sheet from 3 × 10-6 to below 1 × 10-6 1/K.

In harmony: Nanoparticles of Mn3O4 and core/shell-structured Rh/Cr2O3 as cocatalysts on the surface of a solid solution of GaN and ZnO as catalyst promote O2 and H2 evolution, respectively, under visible light (λ>420 nm), thereby achieving enhanced water-splitting activity compared to analogues modified with either Mn3O4 or Rh/Cr2O3. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Low electrical resistivity (high dark carrier concentration) of CH3NH3SnI3 often leads to short-circuiting in solar cells, and appropriate thin-film modifications are required to ensure functional devices. The long-term durability of organic–inorganic perovskite solar cells necessitates the protection of perovskite thin films from moisture to prevent material decomposition. Herein, we report that the electrical resistivity and the moisture stability of two-dimensional (2D) Ruddlesden–Popper (CH3(CH2)3NH3)2(CH3NH3)n−1SnnI3n+1 perovskites are considerably improved compared to those of the three-dimensional (3D) CH3NH3SnI3 perovskite and subsequently show the solar cell fabrication using a simple one-step spin-coating method. These 2D perovskites are semiconductors with optical band gaps progressively decreasing from 1.83 eV (n = 1) to 1.20 eV (n = ∞). The n = 3 and n = 4 members with optimal band gaps of 1.50 and 1.42 eV for solar cells, respectively, were thus chosen for in-depth studies. We demonstrate that thin films of 2D perovskites orient the {(CH3NH3)n−1SnnI3n+1}2– slabs parallel to the substrate when dimethyl sulfoxide solvent is used for deposition, and this orientation can be flipped to perpendicular when N,N-dimethylformamide solvent is used. We find that high-purity, single-phase films can be grown only by using precursor solutions of “pre-synthesized” single-phase bulk perovskite materials. We introduce for the first time the use of triethylphosphine as an effective antioxidant, which suppresses the doping level of the 2D films and improves film morphology. The resulting semiconducting 2D Sn-based iodide perovskite films were incorporated in solar cells yielding a power conversion efficiency of 2.5% from the Sn4I13 member. From the temporal stability standpoint, the 2D Sn perovskite solar cells outperform their 3D analogs.

Sn-based halide perovskite materials have attracted tremendous attention and have been employed successfully in solar cells. However, their high conductivities resulting from the unstable divalent Sn state in the structure cause poor device performance and poor reproducibility. Herein, we used excess tin iodide (SnI₂) in Sn-based halide perovskite solar cells (ASnI₃, A = Cs, methylammonium and formamidinium tin iodide as the representative light absorbers), combined with a reducing atmosphere to stabilize the Sn²⁺ state. Excess SnI₂ can disperse uniformly into the perovskite films and functions as a compensator as well as a suppressor of Sn²⁺ vacancies thereby effectively reducing the p-type conductivity. This process significantly improved the solar-cell performances of all the ASnI3 materials on mesoporous TiO₂. Optimized CsSnI3 devices achieved a maximum power conversion efficiency of 4.81%, which is the highest among all inorganic Pb-free perovskite solar cells to date.

The development of Sn-based perovskite solar cells has been challenging because devices often show short-circuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas-solid reaction film fabrication method to prepare lead-free CH3NH3SnI3 thin films. We show that the solid SnI2 substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high-quality CH3NH3SnI3 films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one-step-fabricated Sn-based perovskite devices has been overcome. This study facilitates the path to more successful Sn-perovskite photovoltaic research.

We have developed a new oxide-based phosphor , which is applicable as a green-emitting color converter for white light emitting diodes (LEDs). This phosphor absorbs blue light around and emits green luminescence, with a peak wavelength around . It is a promising candidate for application in LEDs as quenching of the phosphor at was smaller than that of yellow phosphor. A white LED with high color rendering was fabricated by combining this phosphor with a blue GaN LED and a red phosphor. The luminescence of this phosphor is derived from the 5d-4f transition of the Ce ion and the luminescence decay curve fit a single exponential function. This phosphor has a garnet-type host crystal structure. X-ray absorption fine structure analysis showed that Ce ions replaced the Ca position of the host crystal as .

This paper reports the two-photon absorbing and orange-red fluorescence emitting properties of a series of new 2,1,3-benzothiadiazole (BTD)-based D-pi-A-pi-D-type and star-burst-type fluorescent dyes. In the D-pi-A-pi-D-type dyes 1-6, a central BTD core was connected with two terminal N,N-disubstituted amino groups via various pi-conjugated spacers. The star-burst-type dyes 8 and 10 have a three-branched structure composed of a central core (benzene core in 8 and triphenylamine core in 10) and three triphenylamine-containing BTD branches. All the BTD-based dyes displayed intense orange-red color fluorescence in a region of 550-689 nm, which was obtained by single-photon excitation with good fluorescent quantum yield up to 0.98 as well as by two-photon excitation. Large two-photon absorption (TPA) cross-sections (110-800 GM) of these BTD dyes were evaluated by open aperture Z-scan technique with a femtosecond Ti/sapphire laser. The TPA cross-sections of D-pi-A-pi-D-type dyes 2-6 with a benzene, thiophene, ethene, ethyne, and styrene moiety, respectively, as an additional pi-conjugated spacer are about 1.5-2.5 times larger than that of 1c with only a benzene spacer. The TPA cross-sections significantly increased in three-branched star-burst-type BTDs 8 (780 GM) with a benzene core and 10 (800 GM) with a triphenylamine core, which are about 3-5 times larger than those of the corresponding one-dimensional sub-units 9 (170 GM) and 11 (230 GM), respectively. The ratios of sigma/e(pi) between three-branched and one-dimensional dyes were 6.5:3.8 (for 8 and 9) and 6.0:4.0 (for 10 and 11), which are larger than those predicted simply on the basis of the chromophore number density (1:1), according to a cooperative enhancement of the two-photon absorbing nature in the three-branched system.

Metal-oxide-recast Nafion composite membranes were studied for operation in hydrogen/oxygen proton-exchange membrane fuel cells (PEMFC) from 80 to 130 °C and at relative humidities ranging from 75 to 100%. Membranes of nominal 125 μm thickness were prepared by suspending a variety of metal oxide particles (SiO2, TiO2, Al2O3, and ZrO2) in solubilized Nafion. The composite membranes were characterized using electrochemical, X-ray scattering, spectroscopic, mechanical, and thermal analysis techniques. Membrane characteristics were compared to fuel cell performance. These studies indicated a specific chemical interaction between polymer sulfonate groups and the metal oxide surface for systems that provide a good elevated-temperature (i.e., fuel-cell operation above 120 °C) performance. Composite systems that incorporate either a TiO2 or a SiO2 phase produced superior elevated-temperature, low-humidity behavior compared to that of a simple Nafion-based fuel cell. Improved temperature tolerance permits the introduction of at least 500 ppm CO contaminant in the H2 fuel stream without cell failure, in contrast to standard Nafion-based cells, which fail below 50 ppm of carbon monoxide.

The intermolecular interaction energies of ion pairs of imidazolium-based ionic liquids were studied by MP2/6-311G level ab initio calculations. Although the hydrogen bond between the C(2) hydrogen atom of an imidazolium cation and anion has been regarded as an important interaction in controlling the structures and physical properties of ionic liquids as in the cases of conventional hydrogen bonds, the calculations show that the nature of the C(2)-H...X interaction is considerably different from that of conventional hydrogen bonds. The interaction energies of the imidazolium cation with neighboring anions in the four crystals of ionic liquids were calculated. The size of the interaction is determined mainly by the distance between the imidazolium ring and anion. The calculated interaction energy is nearly inversely proportional to the distance, which shows that the charge-charge interaction is the dominant interaction in the attraction. The orientation of the anion relative to the C(2)-H bond does not greatly affect the size of the interaction energy. Calculated interaction energy potentials of 1,3-dimethylimidazolium tetrafluoroborate ([dmim][BF(4)]) complexes show that the C(2)-H bond does not prefer to point toward a fluorine atom of the BF(4). This shows that the C(2)-H...X hydrogen bond is not essential for the attraction.

The regioregular narrow band gap (E(g) ~1.5 eV) conjugated polymer PIPCP was designed and synthesized. PIPCP contains a backbone comprised of CPDT-PT-IDT-PT repeat units (CPDT = cyclopentadithiophene, PT = pyridyl[2,1,3]thiadiazole, IDT = indacenodithiophene) and strictly organized PT orientations, such that the pyridyl N-atoms point toward the CPDT fragment. Comparison of PIPCP with the regiorandom counterpart PIPC-RA illustrates that the higher level of molecular order translates to higher power conversion efficiencies (PCEs) when incorporated into bulk heterojunction (BHJ) organic solar cells. Examination of thin films via absorption spectroscopy and grazing incidence wide-angle X-ray diffraction (GIWAXS) experiments provides evidence of higher order within thin films obtained by spin coating. Most significantly, we find that PIPCP:PC61BM blends yield devices with an open circuit voltage (V(oc)) of 0.86 V, while maintaining a PCE of ~6%. Comparison against a wide range of analogous narrow band gap conjugated polymers reveals that this V(oc) value is particularly high for a BHJ system with band gaps in the 1.4-1.5 eV range thereby indicating a very low E(g) - eV(oc) loss.

FePt magnetic nanoparticles (MNPs) are expected to be a high-performance nanoheater for magnetic hyperthermia because of their high Curie temperature, high saturation magnetization, and high chemical stability. Here, we present a theoretical performance assessment of chemically disordered fcc-phase FePt MNPs. We calculate heat generation and heat transfer in the tissue when an MNP-loaded tumor is placed on an external alternating magnetic field. For comparison, we estimate the performances of magnetite, maghemite, FeCo, and L1/sub 0/-phase FePt MNPs. We find that an fcc FePt MNP has a superior ability in magnetic hyperthermia.

Abstract New host lattice materials whose red phosphors for white LEDs have been investigated in the ternary system Ca 3 N 2 –AlN–Si 3 N 4 , just as Ca 2 Si 5 N 8 and CaSiN 2 :Eu were found in the binary system Ca 3 N 2 –Si 3 N 4 . A new red phosphor of CaAlSiN 3 :Eu which is effectively excited by blue‐GaN and near UV‐GaInN LED chips has been synthesized at 1600 °C for 2 h and subsequently at 1800 °C for 2 h under nitrogen pressure of 1 MPa. The host‐compound has an orthorhombic structure with the space group Cmc2 1 (No. 36), which is isotypic with LiSi 2 N 3 and NaSi 2 N 3 . The red phosphor showed the emission peak around 650 nm which was assinged to 5d → 4f of Eu 2+ ion, and its color coordinates were estimated to be 0.667 and 0.327. The optimum concentration of Eu 2+ ion was 1.6 mol%. The phosphor also had a high chemical stability, high quantum output, and especially a good thermal property compared to the other phosphors, Ca 2 Si 5 N 8 :Eu 2+ and CaSiN 2 :Eu 2+ . CaAlSiN 3 :Eu 2+ maintained 83% of the initial efficiency above 150 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ni(II) complexes bearing an o-bis(aryl)phosphinophenolate ligand were synthesized as catalysts for copolymerization of ethylene and alkyl acrylates. When the P-bound aryl group was 2,6-dimethoxyphenyl group, one of the oxygen atoms in the methoxy groups coordinated to the nickel center on its apical position. This complex was a highly active catalyst without any activators to give highly linear and high molecular weight copolymers. The structures of the copolymers were determined by 1H and 13C NMR to clarify that the alkyl acrylate comonomers were incorporated in the main chain and that the structures of the copolymers were significantly influenced by the structure of the aryl group in the ligand.

In order to elucidate the mechanism of gas evolution in lithium-ion batteries, we fabricated carbon– cells employing -labeled ethylene carbonate and diethyl carbonate as solvent components and then stored them at . The gas species evolved during storage tests were analyzed by gas chromatography/atomic emission detector to determine the isotopic ratio of and CO. The relative proportions of the derived from EC, DEC, and nonsolvent components were determined to be 52, 11, and 37%, respectively. The main source of was found to be EC. Further storage tests with either cathode or anode electrodes showed that the cathode components were a source of , but anode components were not. As for evolved CO, the main source was found to be EC. Moreover, we also examined the gas-evolution behavior on the initial charge. The evolved gas species were mainly composed of , , and CO. A minor amount of was also detected. From our isotopic analysis it was shown that was exclusively formed from EC, while derived from DEC. In the case of CO, EC and nonsolvent components were found to be its sources. CO derived from DEC was not detected.