加納 博文

This article reviews the structure, synthesis, host-guest reaction in aqueous phase, and ion-sieve and molecular-sieve properties of porous manganese oxide crystals. Tunnel and layered manganese oxides constitute a large family of porous materials having pore size from ultramicropores to mesopores. The manganese oxide crystals consist of MnO6 octahedral units shared by corners and/or edges. They can be prepared by using various metal ions or organic surfactants as templates. The templates are extracted/inserted topotactically from/into the tunnels or interlayer spaces of the manganese oxides by two different mechanisms: redox-type and ion- exchange-type. These manganese oxides show excellent ion-sieve and molecular- sieve properties for the adsorptions of cations or organic molecules. The adsorptive selectivities are dependent on their structures.

Ion exchange chromatography of lithium was carried out to study the lithium isotope effect in an aqueous ion-exchange system, using titanium phosphate exchangers granulated with polyvinyl chloride or an inorganic binder. The sample granulated with PVC showed significant isotope fractionations when a 0.05 M (NH4)(2)CO3 solution was used as an eluent. The lighter isotope Li-6 was preferentially fractionated into the exchanger phase. The isotope separation factor was roughly evaluated as 1.007, which is smaller than that (1.017) obtained by batch experiment in a preceding paper. The smaller separation factor could be explained by the fact that the number of sites effective for Li+ exchange is less than the number evaluated from the ion exchange capacity. The exchanger granulated with an inorganic binder did not show lithium isotope fractionation in spite of its large capacity for retention of lithium.

10B is more fractionated to B(OH)L {H2L: a ligand having a bis(2-hydroxyalkyl)amino group (alkyl: ethyl and propyl)} with a tetrahedral coordination mode than to B(OH)3 with a planar triangular coordination mode in aqueous solutions, exhibiting an isotope separation factor of 1.027 at 25 °C, which is greater than the upper limit of anion exchangers.

By using a needle-like raw material γ-MnOOH as a Mn-source, single crystals of lithium manganese oxides were synthesized in a variety of lithium-containing fluxes including LiNO3, Li2CO3, LiOH, LiCl and Li2SO4. Needle-like Li1.33Mn1.67O4 and Li2MnO3 crystals and plate-like polyhedral Li2MnO3 crystals were obtained in an LiNO3 flux heated within different temperature ranges (300-400, 500-750 and 900-1000°C, respectively). Not only polyhedral and film Li2MnO3 but also octahedral LiMn2O4 single crystals were obtained in an LiCl flux by use of different shaped containers to control the exposure to the atmosphere. Orthorhombic LiMnO2 crystals with tube- and rod-like shapes could be obtained at the bottom of the LiCl melt at 1000°C. The lithiation reaction (at low temperature) and dissolution-precipitation controlled growth (at high temperature) of Li2MnO3 were also observed in Li2CO3 and LiOH fluxes. According to the reaction mechanism, the Li-containing fluxes investigated can be classified into four types: (1) LiNO3, oxidizing flux (2) LiCl, non- oxide flux (3) LiOH and Li2CO3, oxidic, but non-oxidizing fluxes and (4) Li2SO4, no reaction.

A new type of lithium cobalt oxide was prepared by a LiCl-flux method at 650 degrees C. The sample consists of polyhedron crystals between 1 and 5 mu m in size. X-ray diffraction analysis showed a layered structure with a remarkably high (003) peak intensity (79,000 Hz) and relatively weak (101), (104) peak intensities. The intensity ratios of the (003) peak relative to (104) and (101) peaks were 24 and 45, respectively. The first-cycle discharge capacity of a Li/lithium cobalt oxide cell in the first cycle was 156 mAh/g between 4.3 and 3.0 V, and discharge coulombic efficiencies were above 98% for every discharge/charge repetition from the first to the seventh cycles. The discharge capacity was close to the theoretical value, and the discharge/charge efficiency was higher than those for LiCoO2, samples obtained by solid-state reaction. (C) 1998 The Electrochemical Society. S1099-0062(98)03-084-3. All rights reserved.

The effectiveness of integrated characterization of porous carbons with different approaches such as the high resolution αs-method for N2 adsorption, X-ray diffraction, and magnetic susceptibility measurement is shown. The theoretical basis for the high resolution αs-analysis for N2 adsorption using GCMC simulation and the background of magnetic susceptibility of carbon are given. The applicability of the integrated characterization to changes of ACF with heating at 1473-3173 K in Ar is shown. The activated mesocarbon microbead (a-MCMB) and activated carbon aerogel (a-CA) were examined by the integrated characterization method. a-MCMB showed an unusual magnetic relaxation below 10 K due to random magnetism. The random magnetism was associated with the mutually isolated network structure of nanographitic units. a-CA also showed random magnetism at low temperature, which was associated with the spin isolated nanographitic structure similar to a-MCMB. © 1998 Elsevier Science B.V. All rights reserved.

Raman spectra of λ-MnO2 and LiMn2O4 are characterized by two intense peaks at 593 and 628 cm-1. Although the Raman intensity of λ-MnO2 is generally much greater than that of LiMn2O4, the logarithm of the ratio of the intensity at 593 cm-1 to that at 628 cm-1, log(I593/I628) has been found to be a good measure of the change of the lithium content, x, in LixMn2O4. The relationship between log(I593/I628) and the electrode potential (E) correlated well with that between E and x obtained by coulometric titration. In situ measurement of Li+ electroinsertion into a Pt/λ-MnO2 electrode in an aqueous solution showed spectra similar to the ex situ spectra. The change in log(I593/I628) of the electrode equilibrated at each potential corresponded to the cyclic voltammogram. Raman spectroscopy could be one of the best in situ methods for analyzing the electrochemical reaction of spinel-type manganese oxide with Li+. © 1998 The Electrochemical Society, Inc.

イオンふるい結晶は従来の多孔性材料より狭い細孔を持ち, 特定のイオンに対する認識応答材料としての応用が期待される。主にマンガン酸化物系イオンふるい結晶を対象に, リチウム同位体分離剤, 電気化学的吸着剤, エレクトロクロミック材料, リチウム二次電池材料, などへの応用可能性を検討した。<BR>イオンの選択性とリチウム同位体分別性能との関係を検討した結果, ナトリウムイオン選択吸着性を示す立方晶アンチモン酸が最も高い同位体分離係数を示すことを見いだした。同位体分別挙動は, リチウムイオン交換の際の脱水和に基づく同位体効果と吸着剤中におけるリチウムイオンの安定化に基づく同位体効果を考慮することでよく説明できた。スピネル型マンガン酸化物からなる電極は, 電圧を制御することによって水溶液中からリチウムを選択的に取り込むことができる。リチウム濃度0.75mMの地熱水からリチウムの電気化学的回収を検討した結果, 吸着量は11mg/gに達することがわかった。導電性ガラス上にスピネル型マンガン酸化物薄膜を生成した電極は, リチウムの電気化学的挿入・抽出反応に伴って赤褐色から黒色に変化するエレクトロクロミック現象を示す。このような色調の変化は, リチウムの挿入・抽出に連動してマンガンの酸化還元反応 (Mn<SUP>4+</SUP>⇔Mn<SUP>3+</SUP>) が進むために起こる。 [2×2] トンネル構造のホランダイト型マンガン酸化物は, リチウム二次電池材料として興味深い物質である。電気容量は初回に230mAh/9に達し, 充放電の繰り返しに対する安定性も高い。スピネル型マンガン酸化物薄膜電極の電位はリチウムイオンに対してのみ選択的に応答し, これまで知られているものより優れたリチウムイオン選択電極であり, 臨床化学などの分野で応用が期待される。<BR>今後は, 触媒など気固界面を利用した材料としての展開が期待できる。

Layered titanium phosphates and heat-treated tin phosphate showed high separation factors (1.015-1.018) for lithium isotopes; the fractionation properties could be explained by considering two factors: the degree of Li+ dehydration in the solid phase and the affinity of the ion-exchange site toward Li+.

A thin layer electrode of birnessite-type manganese oxide was prepared by brushing a mixed solution of KOCOCH3 and Mn(OCOCH3)(2) on a platinum substrate, followed by heating at 1073 K. The chemical composition of the electrode was KxMnOy (x = 0.33 and y similar to 2) with an interlayer spacing of c(0) = 0.697 nm. The positive-potential going sweep on the electrode in an aqueous phase caused the deintercalation of K+ with an increase in c(0). The quasi-reversible intercalation of K+ occurred with a subsequent negative-potential going sweep in a 0.2 mol/dm(3) KCl solution. The electrochemical measurements suggested that K+ is not electrochemically active in the deintercalation/intercalation reaction but H+ is. The reaction proceeds based on a mechanism consisting of an electrochemical reaction (the redox reaction between Mn3+ and Mn4+) and an ion-exchange reaction between K+ and H+. The intercalation experiments in various alkali-metal chloride solutions showed the intercalation capacity to be in the order of Na similar to K > Li > Rb > Cs.

The magnetic properties of the divalent metal complexes [ML2(HL)] (M = Co-II, Ni-II, and Cu-II; HL = 2,3-diamino-1,4-diazabuta-1,3-diene-1,4-diol, i.e., diaminoglyoxime) with a slipped-stack structure were examined. The magnetic susceptibilities and the electron spin resonance spectra indicate that [CoL2(HL)] exhibits a ferromagnetic interaction along the stack chain, the strength of which is estimated to be 13.5 K, while [CuL2(HL)] is paramagnetic and [NiL2(HL)] is diamagnetic. The magnetic behaviors of the [ML2(HL)] complexes can be predicted precisely by comparing the spin splittings of the partially occupied molecular orbitals of the monomer complexes ML2 and the dimer complexes 2ML(2) which are equivalent in structure to the relevant moieties in the real stack chains, based on molecular calculations using the DV-X alpha method. The modes of the differential spin densities for the dimers 2ML(2) strongly suggest that the principal mechanism of superexchange on [CoL2(HL)] may operate through strong interaction of the 3d(zx) orbitals of Co atoms with the 2p(z) orbitals of two apical N atoms which form the pi(z)-type systems of the adjacent complex molecules along the stack chain.

The magnetic susceptibility chi of O-2 adsorbed in micropores of activated carbon fibers (ACFs) having different micropore widths was measured at a wide temperature range of 1.7-100 K. The micropore structure of ACF was determined by the analysis of the N-2 adsorption isotherm at 77 K. The adsorption isotherm of O-2 on ACF at 77 K was determined and it was shown that O-2 is adsorbed in the micropore in a similar way to N-2 from the Dubinin-Radushkevich analysis of O-2 and N-2 adsorption isotherms. The chi-T relation suggested the presence of three kinds of O-2 molecular states in the micropore, that is, the isolated, the cluster, and condensed states; their stable region changes with the fractional filling and the temperature. Although the potential energy difference of the O-2-surface interaction of different pore systems is only 150 K by the potential calculation, the magnetic susceptibility measurement can sufficiently evidence distinctly the presence of different states of O-2 molecules in the micropore.

マンガン酸化物への水素イオンやアルカリ金属イオンの挿入/抽出はイオン交換反応だけではなく, 酸化還元反応で進行する。酸化還元反応はマンガンが比較的容易に3価と4価に変わりうることに起因する。このような性質は, 電気化学反応に応用できる。すなわち, マンガン酸化物を電極にし, ある特定の電位を印加することによって, イオンの挿入/抽出反応を制御することが可能となる。スピネル型マンガン酸化物電極によるリチウムイオンの電気化学的挿入/抽出反応を例に挙げ, 電気化学的ホスト・ゲスト反応の基礎について記述した。<BR>スピネル型マンガン酸化物電極は優れたリチウムイオン選択電極として作用し, 電気化学的にリチウムイオンを挿入/抽出する。この反応機構はマンガンの3価/4価の酸化還元反応に基づいて説明できる。電位を掃引することによりリチウムイオンの挿入/抽出を制御でき, また, その移動過程を電気化学的に解析できる。<BR>一方, バーネサイト型マンガン酸化物電極によるアルカリ金属イオンの電気化学的インターカレーションは, スピネル型マンガン酸化物のリチウムイオン抽出/挿入反応とは異なる機構により進行する。その機構は, 酸化還元反応とイオン交換反応が組み合わさったものである。

マンガン酸化物には様々なトンネル構造と層状構造を持つ化合物が報告されている。これらのトンネル構造及び層状構造を持つマンガン酸化物はイオンや分子とホスト・ゲスト反応することができる。そのホスト・ゲスト反応において, イオンふるいや分子ふるい効果を示すので, 選択吸着剤, 触媒及びリチウム二次電池材料等として注目されている。本解説はボアサイズの異なるトンネル構造や層状構造を持つ一連のマンガン酸化物イオンふるい結晶の合成, 金属イオンの抽出/挿入反応及びイオンふるい特性について, 著者らの最近の研究結果を中心に概説した。これらのマンガン酸化物における金属イオンの抽出/挿入反応は酸化還元反応とイオン交換反応で進み, 反応サイトは酸化還元サイトとイオン交換サイトに分類することができる。金属イオンに対する吸着選択性はマンガン酸化物の結晶構造に依存する。スピネル型マンガン酸化物, ホランダイト型マンガン酸化物及びバーネサイト型マンガン酸化物はそれぞれLi<SUP>+</SUP>, K<SUP>+</SUP>及びRb<SUP>+</SUP>イオンに対して高い選択性を示す。これらのマンガン酸化物のトンネルサイズ或いは層間距離はそれぞれこれらのイオンの大きさに対応する。従って, スピネル型, ホランダイト型, バーネサイト型及びトドロカイト型マンガン酸化物の有効ボア半径はそれぞれ0.7, 1.4, 1.5及び2.7となる。種々のトンネル構造を持つマンガン酸化物は水熱ソフト化学法という従来の方法と異なる新規なイオンふるい合成法を用いて合成できる。

イオンふるい結晶の一種であるスピネル型マンガン酸化物はリチウムイオンに対して特異的選択吸着性を示し, 海水からのリチウム採取用吸着剤として最も有望な材料である。近い将来, 需要量の増大が予想されているリチウムを海水から採取する技術の確立を目的として, スピネル型マンガン酸化物系吸着剤の開発, 粉末吸着剤の造粒とリチウム吸着性, カラム吸着一脱着条件の検討, リチウム採取ベンチ試験を行った。これらの結果に基づいて効率的なリチウム採取プロセスを提案し, さらに実用化に向けて今後の課題を考察した。<BR>(Li) [Li<SUB>0.33</SUB>Mn (IV) <SUB>1.67</SUB>] O<SUB>4</SUB>に近い化学組成の前駆体を酸処理してリチウムを溶出した試料が最も高いリチウム吸着性を示した。海水からのリチウム吸着量は20mg・g<SUP>-1</SUP>以上に達し, 鉱石なみのリチウム含量となった。ポリ塩化ビニルをバインダーとして得られた造粒体が良好なリチウム吸着性能を示した。流動床方式によるカラム吸着及び酸脱着試験を行い, 実験室規模での吸脱着特性を明らかにした。その結果に基づいてベンチ試験装置を試作し, kgレベルのリチウムを海水から回収することに成功した。今後の課題として, 更に安定な吸着剤の開発と効率的な吸着システムの構築を提案した。

Lithium transport through a liquid membrane with bisphenanthroline derivatives resulted in the isotope fractionation with separation factors between 1.008 and 1.020. The lithium isotope fractionation depended on the length of the oligomethylene bridge between two phenanthroline units. The isotope separation factor was the highest for the sample bridged by heptamethylene groups.

海水から製塩後のかん水 (ホウ素濃度120ppm) を用いて無機吸着剤 (46種) 有機吸着剤 (12種) のホウ素吸着性を測定した。含水酸化セリウム, 含水酸化ジルコニウム, グルカミン型樹脂が5mg/g以上の高いホウ素吸着量を示した。これらの試料のホウ素吸着等温線を測定し, 含水酸化セリウムとグルカミン型樹脂では海水のような希薄な水溶液からホウ素を選択的に吸着するサイトを有することが示唆された。グルカミン型樹脂によるカラム吸着実験から, かん水を空間速度4h<SUP>-1</SUP>で流すとホウ素が効率的に除去されることがわかった。塩酸を溶離液として用いると吸着したホウ素を効率的に脱着することができた。

Electrochromism of spinel-type manganese oxide accompanying an Li+-insertion in an aqueous phase was examined by visual light spectrometry. An absorbance spectrum for lithiated manganese oxide gave lower absorbance in the wavelength range &lt 700 nm than did an Li+-extracted one. The greatest difference was observed at ∼ 450 nm and is explained by the difference between the spectra for Mn3+ and Mn4+. A reversible change in absorbance at 450 nm occurred with the Li+-insertion/extraction reaction. Cyclic voltammetry indicated that the absorbance change couples with the electro-chemical response of the manganese oxide to Li+ ions.

The kinetics of lithium electroinsertion into a Pt/λ-MnO2 thin-film electrode in a 10 mmol/dm3 LiCl solution was studied by ac impedance spectroscopy between 10-4 and 102 Hz at 25°C. The interfacial charge-transfer process was found to be independent of the composition x in Li1xMn2O4, and the exchange current density was 1.3 × 10-6 A/cm2 irrespective of x, whereas the chemical diffusion coefficient, D̃Li, and the partial conductivity, σLi, of lithium depended greatly on x because of the effect of the thermodynamic enhancement factor, W. The D̃Li value varied between 1.9 × 10-12 and 3.1 × 10-11 cm2/s, reaching a minimum when x = 0.2 approximately. The σLi, value was in the range from 2.8 × 10-6 to 1.2 × 10-5 S/cm. This low σLi, value indicates the predominant contribution of electronic conductivity to the total conductivity of LixMn2O4, which is in the order of 10-4 S/cm. The results show that solid-state diffusion of Li+ ions is a rate-determining process in the system.

The magnetic susceptibility of O-2 molecules confined in slit-shaped graphitic micropore systems with the slit pore width w of 0.75, 0.96, and 1.45 nm was measured at diffrent coverages rho and over the temperature range of 1.7-100 K. For all micropore systems, the adsorbed O-2 at a very low coverage showed the paramagnetism without any obvious magnetic transition, which is quite close to the paramagnetism of bulk gaseous oxygen. An antiferromagnetic behavior appeared with an increase in rho. This behavior was caused not by the formation of 2D lattices or bulk solid phases but by the random magnetism for the systems of w = 0.75 and 0.96 nm. The random magnetism indicates the cluster formation of the O-2 molecules in the nanospace. The paramagnetism and the random magnetism arise from an enhanced intermolecular interaction of O-2 in the unique potential field of the narrow slit space. The O-2 assembly in the micropores showed a different magnetic behavior dpending on the pore width. Besides the cluster formation, a phase like the theta phase, which appears in the O-2 bilayer on the 2D graphite surface, was observed for 0.4 < rho < 0.8 in the micropores of w 1.45 nm. This suggest that the micropores with w = 1.45 nm provide an enhanced formation of the specific 2D phase. These unusual magnetic behaviors were presumed to be caused by the special critical phenomenon in the nanospace.

炭酸リチウム晶析残液からのリチウムを溶媒抽出法で分離回収することを検討した.<BR>β-ジケトンに属するXI51と中性有機リン酸TBPの新しい組み合せの混合抽出剤を用いた.<BR>リチウムの抽出条件および他のアルカリ金属元素との分離, 抽出剤のくり返し使用による劣化, 晶析残液からの回収試験などについて検討した, その結果を以下のように要約する.<BR>XI51あるいはTBP単独ではリチウムの抽出率は低く, 混合抽出剤を用いると, pH10～12.5の範囲で定量的に抽出できる. 抽出種はLi・XI51・2TBPで, 抽出剤にはXI51:TBP=1:2の濃度比で用いた.<BR>抽出時間は10分で平衡に達し, 定量的抽出にはリチウム水溶液濃度の6倍の抽出剤濃度が必要である.<BR>他のアルカリ元素とはpH9.1で抽出するとき分離効率が高く, 抽出溶媒相を0.08M塩酸で2回洗浄すると有効である. 1M塩酸溶液で40分以上逆抽出するときリチウムは定量的に回収できる.<BR>混合抽出剤は安定で, 抽出-逆抽出を7回くり返しても抽出率の低下は小さい.<BR>晶析残液から, 2段抽出処理で97%のリチウム, 約1%のナトリウムが抽出され, リチウムの分離回収に極めて有効であり, リチウム関連工業における含リチウム溶液からのリチウム回収法として利用できる.

The magnetic behavior of O-2 molecules confined in slit-shaped graphitic micropores at different coverages was examined as a function of the slit pore width from 0.75 to 1.45 nm at 1.7-100 K. The adsorbed O-2 at low coverages showed paramagnetism without any obvious magnetic transition, which was quite close to the magnetism of bulk gaseous oxygen. An antiferromagnetic behavior appeared with an increase in rho. This behavior was caused by cluster formation, rather than by the formation of 2D lattices or bulk solid phases. The O-2 submonolayer in the micropore showed different magnetic behavior depending on the pore width.