加納 博文

Porous copolymer beads of 2,3-epoxypropyl methacrylate (glycidyl methacrylate, GMA) crosslinked with 2-ethyl-2-(hydroxymethyl)-propan-1,3-diol trimethacrylate (trimethylolpropane trimethacrylate, TRIM) were prepared with toluene and octan-2-one as porogens by suspension polymerization. With an increase in the ratio of porogen to monomer, the total pore volume of poly(GHA-co-TRIM) increases significantly, whereas the surface area hardly changes. The total pore volume also depends on the nature of the porogen, exhibiting a maximum at the larger GMA contents in the monomer mixture of 50% v/v with octan-2-one and of 60% v/v with toluene, compared to that at the GMA content of 25% v/v with a 9/1 v/v mixture of cyclohexanol and dodecan-1-ol [Verweij, P. D.; Sherrington, D. C. J Mater Chem 1991, 1 (3), 371]. The surface area decreases significantly with an increase in the ratio of GMA to TRIM, almost regardless of the nature of the porogen. The porous properties of poly(GMA-co-TRIM) was well explained on the basis of phase separation, particularly taking into account not only the solubility parameters of the resulting polymer network and porogen but also the rigidity of TRIM. The porous poly(GMA-co-TRIM) may be a promising polymer matrix of novel materials for separation of boron isotopes. (C) 2002 John Wiley Sons, Inc.

A novel silica-pillared manganese oxide (SiHMnO) was synthesized, and its porous structure was exactly determined by assuming a multistep adsorption mechanism (MSAM) using the low-temperature N2, Ar, and CO adsorption and the αs-comparison plot based on a standard N2 adsorption isotherm on a nonporous manganese oxide. The MSAM method gave a good agreement in values of micropore volume (0.155-0.160 mL g-1) and external surface area (61-63 m2·g-1) from the three adsorbates. The standard nonporous manganese oxide was selected by comparing those based on crystalline hydrous birnessite (H-Bir). The H-Bir-393 obtained by calcining H-Bir at 393 K is the most appropriate standard nonporous material. The values of micropore volume and external surface area from the (αs-plot matched very well with those from the MSAM method. SiHMnO has a very high surface area value (483 m2·g-1) by analysis of an αs-plot in contrast to the smaller one (360 m2·g-1) by the ordinary BET analysis.

The electronic structure and chemical bonding nature of spinel-type Li1.33Mn1.67O4 system was calculated by a discrete-variational (DV)-Xalpha clusters method. In order to elucidate the reason for the selective exchange of Li+ ions, the bonding natures between tetrahedral and octahedral Li sites of the Li1.33Mn1.67O4 were compared. Li in the manganese oxides is highly ionized in both sites, but the net charge of Li was greater for tetrahedral sites than octahedral. These calculations suggest that the tetrahedral sites have higher Li+/H+ exchangeability than the octahedral sites, and are preferable for the selective adsorption for Li+ ions. (C) 2002 Elsevier Science Ltd. All rights reserved.

A study of the electronic structure and chemical bonding of the Li ions and protons inserted in manganese oxides was performed by a first-principles molecular-orbital method using model clusters (Mn28O4O)(32+) for lambda-MnO2 and (X5Mn12O40)(n-) for XMn2O4{n = 31 (X = H) and n = 33 (X = Li)}. The discrete-variational (DV)-Xalpha method was employed and Mulliken's population analyses were carried out. Strong covalent interactions operate between Mn and O ions in the manganese oxides. Li and hydrogen in manganese oxides are highly ionized. These results are likely to be a very important factor in determining the excellent selectivity of spinel-type manganese oxides for Li+ ions and the exchange between Li+ and protons.

Microwave irradiation of a suspension of gamma-MnOOH in a 4 mol dm(-3) LiOH solution brought about a rapid formation of semicrystalline orthorhombic LiMnO2 (o-LiMnO2) within 30 min at 120degrees C. Cubic Li1.6Mn1.6O4 was obtained by heating o-LiMnO2 at 400degreesC; lithium could be topotactically extracted from Li1.6Mn1.6O4O4 with acid to form cubic H1.6Mn1.6O4. (C) 2002 Elsevier Science.

Characterization of nanopores must be carried out with integrated information from different levels and angles. It is shown that gas adsorption can provide a key information in the integrated characterization of nanopores. In particular, further understanding of pore filling is necessary; an evidence on quantum effect in pore filling and a new method of adsorption isotherm from P/Po = 10(-9) are introduced with the relevance to the nanopore characterization.

We examined the synthesis and borate uptake of novel chelating resins, named MGR and HMR, derived from the functionalization. of macroporous poly(glycidyl methacrylate-co-trimethylolpropane trimethacrylate) matrixes with N-methyl-D-glucamine (MG) and 2-amino-2-(hydroxymethyl)-1,3-propanediol (HM), respectively. The structures of free matrixes, resins, and borate-loaded resins were confirmed by infrared spectroscopy. The borate uptake depends significantly on the proton capacity, which is proportional to the GMA fraction in matrixes, but little on the pore structure of macroporous matrixes. The,ion-exchange isotherms of borate on MGR and HMR follow the Langmuir equation. MGR shows a larger uptake capacity toward borate than does HMR, comparable to that of Diaion CRB 02, because the tetradentate coordination mode of the former is more stable than the bidentate one of the latter. MGR exhibits a higher rate of borate uptake than does Diaion CRB 02, and the uptake kinetics are explained from a macropore diffusion model.

Structural and surface property changes of macadamia nut-shell (MNS) char upon activation and high temperature treatment (HTT) were studied by high-resolution nitrogen adsorption, diffuse reflectance infra-red Fourier transform spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. It is found that activation of MNS char can be divided into the low extent activation which may involve the reactions of internal oxygen-containing groups and leads to the formation of comparatively uniform micropores, and the high extent activation which induces reactions between carbon and activating gas and produces a large amount of micropores. The surface functional groups (SFGs) basically increase with the increase of activation extent, but high extent activation preferentially increases the amount of -C-O and -C=O. HTT in air for a short tithe at a high temperature (1173 K) greatly increases the micropore volume and the amounts of SFGs. By appropriately choosing the activation and HTT conditions, it is possible to control both the textural structure and the type and amounts of SFG. (C) 2002 Published by Elsevier Science Ltd.

Manganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of 'dioxide' is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H+ for alkali cations incorporated in 'hydrous manganese dioxides'. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO4 and MnSO4, and thermal decomposition of (CH3)3COK and MnCO3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.

NH3 insertion mechanism into the (2 × 2) tunnel structure of a hollandite-type manganese oxide (H-Hol) and the (2 × ∞) layered structure of a birnessite-type manganese oxide (H-Bir) were studied by direct adsorption calorimetry. It was found that H-Bir has a smaller NH3 adsorption enthalpy (-ΔHd1NH3) compared to H-Hol because of the structural flexibility of its MnO sheets. NH3 insertion into the tunnel structure of H-Hol is divided into two stages: in the initial stage, NH3 molecules interact with the H+ sites at the external surfaces and near the tunnel entrance, giving a peak in -ΔHd1NH3 curve at a low adsorption temperature due to the energy barrier required to expand the lattice structure; in the secondary stage, NH3 can access the inner H+ sites in the tunnel, giving a broad shoulder in -ΔHd1NH3 curve. H2O/H+ contents in H-Hol have an important role in NH3 insertion. Porous manganese oxides have a comparable or much higher -ΔHd1NH3 value compared to zeolites having a similar pore dimension or of a same proton form. © 2001 Elsevier Science B.V. All rights reserved.

In order to figure out the catalytic property of hollandite-type hydrous manganese oxide (H-Hol) to remove NH3, the desorption and decomposition properties of NH3 from NH3-chemically adsorbed H-Hol were examined and these properties and NH3 adsorptivity were compared with those of other manganese oxides and a de-NO, catalyst. It was found that the presence of NO accelerates the oxidation of NH3 to form N-2 at a lower temperature. Comparison of NH3 pulse reaction in a flow containing NO on H-Hol with those on a high surface area-manganese oxide and a commercial de-NO, catalyst shows that H-Hol has the greatest N-2 production, but less selectivity to form N-2. H-Hol has a comparable amount of the strong H+ sites with the high surface area manganese oxide, which have relationship with NH3 decomposition. (C) 2001 Elsevier Science B.V. All rights reserved.

Manganese oxide adsorbent (H1.6Mn1.6O4) was synthesized from precursor Li1.6Mn1.6O4 that was obtained by heating LiMnO2 at 400 degreesC. LiMnO2 was prepared by two methods: hydrothermal and reflux. The crystallite size of Li1.6Mn1.6O4 and its delithiated product; was slightly higher by the hydrothermal method as compared to the reflux method. The adsorbents prepared by the two methods were compared in terms of physical characteristics and lithium adsorption from seawater. The maximum uptake of lithium from seawater by the adsorbent was 40 mg/g, which is the maximum value among the adsorbents studied to date.

The N-2, H2O, and NH3 adsorption properties on hollandite-type (H-Hol) and birnessite-type (H-Bir) hydrous manganese oxides were compared with those on zeolitic crystals. It was found that the effective pore openings of H-Bir and H-Hol are below 0.3 nm. Although the geometric spaces on H-Bir and H-Hol available for physical adsorption from a gaseous phase are much smaller than those on zeolites, they can provide a strong chemisorption field for H2O and NH3 intercalation. (C) 2001 Academic Press.

The structural and surface properties of a hydrous hollandite-type manganese oxide (H-Hol) were examined by adsorption using different gases with molecular diameters below 0.4 nm. N-2, O-2, Ar, CO, and CO2 with diameters above 0.33 nm are excluded from the tunnel structure of H-Hol, whereas H2O and NH3 with diameters below 0.265 nm can be inserted into the structure. Disagreements were observed for the first and second run adsorption isotherms of H2O and NH3, indicating that there is a strong interaction contributing to H2O and NH3 adsorption. Insertion of NH3 into the tunnels of H-Hol is a very slow process; the rate-determining step is that of insertion into the inner H+ sites. H+ sites on H-Hol play an important role in both NH3 and H2O adsorption. Adsorption and FT-IR results demonstrate that stepwise dehydration decreases the H+ sites available for NH3 adsorption, some but not all of which are recoverable by rehydration.

イオン交換型抽出剤は, リチウム溶媒抽出反応において, イオン選択性に依存してリチウム同位体分別作用を示した。ナトリウムイオン選択性を示すカリックス [4] アレーン誘導体, モネンシンが高いリチウム同位体分離係数 (それぞれ1.030, 1.022) を示した。

Layered-type hydrous manganese oxides MnO2 · 0.70H2O and MnO2 · 0.22H2O with almost the same rod shape morphology as that of the precursor monoclinic-type LiMnO2 were synthesized. The structural transformations from monoclinic-type LiMnO2 to a birnessite-type MnO2 · 0.70H2O took place after lithium in LiMnO2 was extracted with 0.1 mol dm-3 (NH4)2S2O8 solution without dissolution of manganese. The extraction of lithium from LiMnO2 with 0.5 mol dm-3 HCl solution followed by the dissolution of manganese formed a trigonal-type MnO2 · 0.22H2O. The maximum ion exchange capacity of MnO2 · 0.22H2O toward alkali metal ions was found to be only 3 mmol/g the material did not show any ion sieve properties. The pH titration study suggested that the MnO2 · 0.22H2O was a weak acidic adsorbent which was found to be a metastable phase. © 2001 Academic Press.

Octahedral and rectangle-like LiMn2O4 single crystals larger than 0.1 × 0.1 × 0.1 mm3 in size were synthesized by evaporating a melt of LiCl and MnCl2 at 750 °C. The nucleation and growth of the crystals proceeds on the wall of a pure alumina crucible. Phase analysis showed that purity of phase was affected by MnCl2 partial pressure.

Fe(III)-, Cr(III)-, Al(III)- and La(III)-buserite type manganese oxides were synthesized from a hydrothermally treated, well-crystallized Na+-birnessite through a two-step ion-exchange route, M/Mg2+ ion exchange subsequent to Mg2+/Na+exchange. The ion-exchange reactions progressed smoothly and the layered manganese oxides with multivalent metal ions in the interlayer could be obtained at room temperature.

Magnetic effects on Li+extraction/insertion reactions in manganese oxides λ-MnO2were investigated with cyclic voltammetry (CV) and potential step chronoamperometry (PSCA) under magnetic field less than 30 T. The peak currents of CV were increased by magnetic fields, especially in the reduction side. Since the chemical diffusion coefficient of Li+and the number of electrons involved in a rate-determining step were independent of magnetic fields, magnetic fields may promote the redox reaction and/or increase Li+concentration at manganese oxide surfaces contact with a solution. The latter means Li+-insertion (adsorption).

The reduced partition function ratio for lithium ions in an aqueous solution is derived from the extrapolation of the values of the reduced partition function ratio (f(n)(r)) of hydrated lithium ion clusters [Li(H2O)(n)](+) up to n = 6. In [Li(H2O)(n)](+) clusters, the f(n)(r) values can be calculated from the normal vibration frequencies according to Bigeleisen and Mayer's theory. To obtain the values of f(n)(r), the normal vibration frequency calculations were carried out for optimized structures of [Li(H2O)(n)](+) (n = 1-6) using the RHF/6-31+G(d), RHF/6-31++G(d,p), RHF/6-311+G(d) and MP2/6-31+G(d) methods by means of the ab initio molecular orbital method. All of those structures having high symmetry were confirmed to have real harmonic frequencies at the RHF/6-31+G(d) and RHF/6-31++G(d,p) levels. For the two RHF methods, the value of f(n)(r) increases to about 1.07 with an increase of the hydration number n, and reaches maximum at n = 4. In the most stable isomers of [Li(H2O)(n)](+) clusters for n = 5 and 6, respectively, the first hydration shell is saturated with the four water molecules, and the size dependence of the f(n)(r) values converges for n greater than or equal to 4, The converged value 1.07 can, therefore, be regarded as the reduced partition function ratio for lithium ions in aqueous solution, and gives the upper limit of the isotopic separation factor in an aqueous solution-exchanger system.

Silica-pillared layered manganese oxide with high surface area and high thermal stability was first synthesized from birnessite(H)-type manganese oxide by intercalation of octylamine followed by tetraethyl orthosilicate (TEOS) molecules and then by solvothermal treatment in TEOS liquid. Layered phases of manganese oxide with basal spacings of 2.01 and 2.43 nm, respectively, were obtained for each intercalation reaction. The Si/Mn molar ratio increased from 0.63 to 0.84 by the solvothermal treatment, but the basal spacing (2.44 nm) of the layer barely increased. The increase of silica content stabilized the pillared structure against thermal treatment. Porous layered manganese oxides were obtained by heating the silica-pillared material at appropriate temperatures. The manganese oxide sample obtained at 400 °C had a BET surface area of 260 m2/g with a gallery height of about 1.6 nm between layers.

A new type of adsorbent, MnO2·0.5H2O, was synthesized from Li1.6Mn1.6O4 followed by acid treatment. The hydrothermal reaction of monoclinic type γ-MnOOH with LiOH solution at 120 °C resulted in a H+/Li+ ion exchange, giving orthorhombic LiMnO2. The orthorhombic LiMnO2 was transformed to cubic Li1.6Mn1.6O4 (Li2Mn2O5) at a temperature higher than 400 °C. The conversion of Li1.6Mn1.6O4 to MnO2·0.5H2O by acid treatment resulted in contraction of the lattice constant a0 from 8.14 to 8.05 Å with little dissolution of manganese. The new adsorbent showed a markedly high ion-exchange capacity (7.5 mmol/g) for lithium ions due to its ion-sieve property. The pH titration study suggested the formation of large numbers of uniform sorption sites having relatively high acidity. The uptake of Li+ ions from lithium-enriched seawater was found to be 5.3 mmol/g (37 mg/g), which is the maximum among the adsorbents studied to date.

Hydrothermal lithium was extracted from Li2MnO3, for preparing manganese oxide with a stacked structure. This structure acted as an excellent cathode materials for lithium rechargeable batteries. Lithium extracted was having high discharge capacity and good rechargeability.

5価金属をドープしたリチウムマンガン酸化物を酸処理してリチウムを抽出し, 5価金属を含むマンガン酸化物系吸着剤を調製した. それらのリチウム吸着性をバッチ法で測定した. ニナブ, バナジウム, ビスマスを添加した試料ではリチウム吸着量が25～30%増加した. 化学的安定性とリチウム吸着性能を考慮すると, ニオブを添加した吸着剤が最も有望な吸着剤であると考えられる. リチウム吸着量のpH依存性の測定結果から, ニナブの添加により吸着サイトが増加するとともにサイトの酸強度が上昇しリチウム吸着量が増加したものと考えられた.

Intercalations of tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), and tetrabutylammonium (TBA) ions into layered birnessite-type manganese oxide, BirMO(H), were studied in aqueous tetraalkylammonium hydroxide solutions with different concentrations. Expansions of the interlayer were not observed clearly in the TEA, TPA, or TEA systems. Stable colloidal suspensions were obtained in the TMA system at TA(1)/H-s (molar ratio of tetraalkylammonium ions over exchangeable protons in BirMO(H) larger than 1. XRD analyses for these colloidal sediments in the wet state showed a short-range swelling by the TMA(+) intercalation, with an increase in the basal spacing (d(bs)) from 0.73 to 1.56 nm. The basal spacing decreased stepwise from 1.56 through 1.27 to 0.96 nm with a decrease of the relative humidity during drying. The chemical analysis results showed that the cation intercalation progressed by an ion exchange mechanism. The intrinsic selectivity coefficient for intercalation had a tendency to decrease with an increase in the ionic radius of guest cations, probably owing to the larger steric hindrance for larger ions. The intercalation of TBA(+) ions could be achieved by a two-step reaction involving treatment with (TMA)OH followed by (TBA)OH. The basal spacing increased from 1.56 to 2.19 nm due to the TBA(+) intercalation. No long-range swelling was clearly observed. However, delamination took place and the layered structure collapsed when TMA(+)-intercalated samples obtained at TA(1)/H-s = 25 were washed with distilled water. Delamination was also observed in the washing of the TBA(+)-intercalated sample. Freeze-drying of the washed slurry gave a flakelike manganese oxide, which supports the finding of delamination in wet conditions. Upon air-drying, the reassembling of the manganese oxide sheet progressed and the amorphous phase reverted to the layered structure with basal spacing of 0.96 nm. The origins of short-range swelling and the delamination observed in the BirMO(H)-TMA(+) system are discussed in terms of attractive and repulsive forces by electrostatic interaction, hydration of interlayer cations, and interlayer hydrogen bonding.

ホウ素同位体分離係数の予測を行うため、非経験的分子軌道法を用いて、ホウ酸 (B (OH)₃) 、ホウ酸イオン (B (OH) ₄^-) 、トリエタノールアミンボレート (TEA-B) について、構造の安定化と振動計算を行い、それぞれについてのホウ素同位体換算分配関数比を求めた。8種類の近似方法、10種類の基底で計算したところ、B (OH) ₃下B (OH) ₄^-下系、B (OH) ₃-TEA-B系とも、ホウ素同位体分離係数は約1.03となった。

Spinel-type lithium antimony manganese oxide was first synthesized by aging the precipitates that were obtained by reaction of a mixed aqueous solution of manganese(II) and antimony(V) chlorides (Sb/Mn = 0.25) with (LiOH + H2O2) solution, followed by hydrothermal treatment at 120 degrees C. A well crystallized spinel-type solid with a chemical composition of Li1.16Sb(V)(0.29)Mn(III)(0.77)Mn(IV)(0.77)O-4 was obtained; it had the characteristic of including mixed valence manganese. The spinel structure was preserved during heating up to 600 degrees C. Most of the lithium ions in the prepared material could be extracted by treating with an acid; the extraction progressed topotactically, preserving the spinel structure, accompanied by a decrease in the lattice constant from 8.31 +/- 0.01 Angstrom to 8.13 +/- 0.01 Angstrom. The mean oxidation of manganese increased from 3.50 to 3.98 after acid treatment, due to the disproportionation of trivalent manganese. The DTA-TG analysis and IR spectra showed the formation of lattice protons exchangeable with lithium ions. The pH titration study showed that the acid treated sample had a remarkable lithium ion-sieve property over the entire pH range studied. The affinity order was K < Na << Li and the exchange capacity reached 5.6 mmol g(-1) for Li+. It showed a selective uptake of 14 mg g(-1) of Li+ from LiCl enriched seawater.

Plate-shaped crystals of Li2MnO3, red-colored with glossy surface, were obtained over a tilted crucible by LiCl flux evaporation at 923 K for 5 days. The growth of the Li2MnO3 crystal plates proceeded at the interface of three phases, i.e. the LiCl flux, the precipitated powder, and the atmosphere on the tilted crucible. The moving solid-liquid-air interface due to the continuous evaporation of LiCl flux plays an important role in the growth of Li2MnO3 crystal plate.

A microporous hollandite-type manganese oxide having protons as counter ions (H-Hol) was prepared by hydrothermal reaction and adsorption of various molecules from gas phase was examined. It is found that only H2O and NH3 can be adsorbed in the intra-pores NH3 is inserted as NH4 + as a result of reacting with lattice protons. Chemisorption of NH3 is available even under co-existence of water, indicating that H-Hol can be an excellent selective trapper toward odor NH3.

Layered and fibrous crystals of spinel-type lithium magnesium manganese oxide have been synthesized from Mg-containing birnessite and todorokite precursors respectively by a topotactic reaction in a LiNO3 flux at 400 °C.

A study of the electronic structure and chemical bonding of the Li and proton exchange in spinel-type manganese oxides is performed by a first-principles molecular-orbital method using model clusters composing of 57 atoms. The discrete-variational (DV)-Xα method was employed and Mulliken's population analyses were thoroughly conducted. We found that Li and proton in manganese oxides is highly ionized. Strong covalent interactions between Mn and O can be noted.

Silica-pillared layered manganese oxides with high surface area and high thermal stability have been synthesized for the first time by the two step intercalation of octylamine followed by tetraethylorthosilicate into birnessite type manganese oxide.

From different precursors, including gamma-, beta-MnO2, hollandite, and H+-form birnessite manganese oxides, well-crystallized Li1.33Mn1.67O4 spinels were synthesized at 400 degrees C by using LiNO3 as a flux. Alkali metal ion adsorptivities of the spinels after delithiation were investigated. SEM observation showed that each spinel obtained preserved the morphology of its precursor. The lack of morphology change, and the time-dependence of the lithium insertion into the precursors, illustrate that the formation of the spinel is a topotactic template reaction. None of the delithiated spinels preserved the original ion-exchange sites in their precursors but all showed nearly the same high affinity for Li+, while the amount of uniform acidic sites increased and the steric hindrance during lithiation decreased in the order of spinels obtained from birnessite, hollandite, and gamma-, beta-MnO2. This is probably because birnessite has more (buffer) space for the accommodation of ions in its layered structure than other precursors with a tunnel structure and some part of the space remains after structural transformation to the spinel.

Hydrothermal lithium extraction from well-crystallized Li2MnO3 crystals was studied by scanning electron microscopy (SEM) observation, chemical, and X-ray diffraction analyses. Monoclinic Li2MnO3 polyhedral crystals were prepared in an LiCl flux at 650 °C. The lithium extraction was carried out in a variety of H2SO4 solutions with mole ratios of H+ in the solution to Li+ in the solid ([H+]l/[Li+]s) of 0.1, 0.15, 0.25, 0.50, 0.75, and 1.0 under a hydrothermal condition at 140 °C. The lithium extraction from Li2MnO3 proceeds consuming equimolar H+ in the solution by the mechanism of a Li+/H+ ion exchange reaction when [H+]l/[Li+]s ≤ 0.15 and by the mechanism of a mixture of the Li+/H+ ion exchange reaction and lithium dissolution when 0.25 ≤ [H+]l/[Li+]s ≤ 0.75. The lithium-extracted phase preserves the crystal structure of Li2MnO3 with a partial contraction of the lattice when 0.25 ≤ [H+]l/[Li+]s ≤ 0.75. SEM observation showed that the lithium extraction brings about a cleavage of the Li2MnO3 particle along the (001) plane to result in a unique form in which platelike particles are stacked, preserving the polyhedral outline. High-magnification SEM observation showed that the platelike particles consist of an aggregate of subplates with nanometer thickness in parallel arrangement. Slit-shaped mesopores were formed among the subplates. γ-MnO2 was formed as a final product when [H+]l/[Li+]s = 1. A structural model is proposed to explain the mechanism of lithium extraction as well as the cleavage of the particle.

The lattice vibrational modes of spinel-structured lithium manganese oxides have been calculated using atomistic modeling methods. The simulations allow the Raman and infrared spectra of lithiated, fully delithiated, and partially delithiated phases to be assigned for the first time. Calculations for the spinels LiMn2O4, λ-MnO2, and Li0.5Mn2O4 are compared with experimental Raman data measured for thin films of the oxides coated on a platinum electrode. The appearance of a number of new bands in the Raman spectrum of LiMn2O4 following partial extraction of lithium is shown to result from local lowering of the symmetry and Raman activation of modes which are optically inactive or only infrared active in LiMn2O4. The results support a model for the Li0.5Mn2O4 lattice in which the lithium ions are ordered. The deformation vibrations of lattice hydroxyl `defects' in λ-MnO2 have also been calculated comparison of the calculated and experimental vibrational data supports a model in which hydroxyl species are localized at octahedral Mn vacancies.

Well-crystallized orthorhombic LiMnO2 was prepared by a flux method with a (LiCl + LIOH) mixture as the flux. The study of Lif extraction from the orthorhombic LiMnO2 was carried out batchwise using a solution containing an oxidizing agent (0.5 mol . dm(-3) (NH4)S2O8). Lithium ions could be extracted from the LiMnO2 without the dissolution of manganese. The time course of Li+ extraction showed that the Li+ extraction proceeded in three steps with different extraction rates. Chemical analysis showed that the reaction progressed mainly by a redox mechanism. A structural transformation of orthorhombic LiMnO2 phase to spinel LiMn2O4 took place at the first and second steps, accompanied by the Li+ extraction. The structural transformation could be explained well by considering the migration not only of all the lithium ions but also of half of the manganese ions in both oxygen frameworks. The topotactic extraction of Li+ from LiMnO2 gave a rodlike manganese oxide with a spinel structure. A model of the Li+ extraction process was proposed as well as a model for the structural transformation from the orthorhombic LiMnO2 to spinel LiMn2O4. The Li+ insertion into the Li+-extracted sample did not proceed in a mixed solution containing 0.1 mol . dm(-3)LiOH and 0.5 mol . dm(-3) LiI. (C) 1999 Academic Press.