Vanadium oxide intercalated with polyelectrolytes: novel layered hybrids with anion exchange properties

Novel anion exchange hybrid materials were developed by the insertion of poly(diallymethylammonium chloride) (PDDACl) and poly(allylamine hydrochloride) (PAHCl) polyelectrolytes into V(2)O(5) interlayer spaces using hydrothermal treatment and were used to host an anionic cyanine dye. A systematic study of the hybrid material synthesis by direct in situ reaction of PDDACl and PAHCl polycations with V(2)O(5) powders showed that the interlayer space of V(2)O(5) expands from 0.44 nm to 1.40 nm and 1.80 nm upon intercalation of PDDACl and PAHCl polyelectrolytes, respectively. X-ray photoelectron spectroscopy and DR UV-Vis-NIR spectroscopy revealed that some V(5+) sites were reduced to V(4+) during the intercalation of the polyelectrolytes, these acted as both charge balancing entities for the negative oxide sheets and carriers for exchange sites located in the V(2)O(5) interlayer space. The interlayer separation is consistent with the existence of coiled conformation of the polycations. The hybrid materials produced [PDDACl](0.24)[PDDA](0.29)V(2)O(5) and [PAHCl](0.28)[PAH](0.47)V(2)O(5), exhibited approximately 45.0% and 37.0% of chloride ions still available for anionic exchange, respectively. These materials were used to encapsulate a cyanine anionic dye. The presence of the dye was evidenced in the [PDDACl](0.24)[PDDA](0.29)V(2)O(5) by significant fluorescence, with emission peak centered at 617 nm.     

New layered double hydroxides containing intercalated manganese oxide species: synthesis and characterization

Manganese oxide species (MnO(x)) have been intercalated within the gallery spaces of Mg-Al layered double hydroxides (LDHs). Synthesis of these materials was achieved by ion-exchange of the LDH-nitrate precursor with permanganate anion followed by reduction with organic reagents, such as glucose, ethanol, and ascorbic acid. Elemental analysis, X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, HR-TEM, and N(2) sorption analyses have been used to characterize these materials. TEM micrographs of LDH-MnO(x) materials revealed platelike morphology, characteristic of hydrotalcite-like compounds. Chemical analysis results showed that permanganate anions exchanged with nitrate anions. FT-IR and Raman spectroscopy confirmed the reduction of the permanganate anions after treatment with the organic reagents. The XRD diffraction patterns of LDH-MnO(x) revealed that the layer structure is maintained after all synthetic steps. The observed basal spacings of intercalates varied depending on the reducing agent; the largest expansion was 9.93A, corresponding to the use of ascorbic acid. The specific surface areas were also affected according to the organic reagent used, indicating that the structural modifications in the interlayer domain observed by X-ray diffraction also influence the microtextural properties.     

Electrochemical synthesis of layered manganese oxides intercalated with tetraalkylammonium ions

Thin films of birnessite-type layered manganese oxides with various interlayer spacings have been prepared on a platinum electrode by a one-step electrochemical procedure. The process involves a potentiostatic oxidation of aqueous Mn(2+) ions at around +1.0 V (Ag/AgCl) in the presence of tetraalkylammonium cations with different alkyl chain lengths. X-ray diffraction indicates that the films deposited with tetrabutylammonium (TBA), tetrapropylammonium (TPA), and tetraethylammonium (TEA) ions are composed of a single phase where unhydrated tetraalkylammonium ions are accommodated as a monolayer between manganese oxide layers. The interlayer spacing of the products increases in an order of TEA < TPA < TBA. The film deposited with tetramethylammonium (TMA) is a mixture of two phases relating to hydrated and unhydrated guest cations, the former being predominant probably as a result of less hydrophobic property of TMA compared to that of other tetraalkylammonium ions. The TBA(+)-intercalated Mn oxide film-coated electrode exhibits a good charge/discharge property in a KCl solution between 0 and +0.8 V. In this case, TBA(+) ions between the Mn oxide layers are rapidly replaced with K(+) in solution by ion exchange, accompanying a shrinkage of the interlayer. The incorporated K(+) ions as well as protons play an important role in the electrochemical conversion between Mn(4+) and Mn(3+) in the oxide layer. In the TBACl solution, the interlayer TBA(+) ions can be excluded electrochemically during the positive-going scan, concomitant with the oxidation of Mn(3+) sites. This causes an anodic current and the accompanying shrinkage of the interlayer. On the reverse scan, however, the compressed interlayer does not allow the incorporation of bulky TBA(+) ions from the electrolyte, with virtually no cathodic current observed. Such an obvious difference in electrochemical behavior between the two electrolytes can be recognized by considering that most of the Mn oxide surface is present inside the layered structure, not on the external surface. This indicates that the layered structure is formed over the entire film.     

Pillared layered manganese oxide

Keggin ion-pillared buserite was prepared by ion-exchanging the hexylammonium ion-expanded buserite with Keggin ions, [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. The starting material was synthetic Na-buserite, which is a layered manganese oxide of composition Na₄Mn₁₄O₂₆ xH₂O. The thermal and redox properties of this oxide and its pillared derivative were compared in O₂, N₂ and H₂ environments using TG, DSC and XRD. The results indicated an improvement in thermal stability of pillared compound relative to Na-buserite in all gaseous environments. By using these compounds in catalysing the oxidation of ethane, it was found that they were very active for complete oxidation.     

New layered manganese oxide halides

The first layered manganese(III) oxide chlorides, Sr2MnO3Cl and Sr4Mn3O8-yCl2, have been synthesised; Sr2MnO3Cl adopts a K2NiF4 type structure with sheets of MnO5 square based pyramids linked through oxygen and separated by SrCl layers; it is the end member of a new family of Ruddlesden-Popper type manganese oxide halides which includes the three-layer member Sr4Mn3O8-yCl2 also reported herein.     

Assembly of multilayer films from polyelectrolytes containing weak and strong acid moieties

Multilayer films were assembled from a copolymer containing both weakly and strongly charged pendant groups, poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA), deposited in alternation with poly(allylamine hydrochloride) (PAH). The strongly charged groups (styrene sulfonate, SS) are expected to form electrostatic linkages (to enhance film stability), while the weakly charged groups (maleic acid, MA) can alter multilayer film properties because they are responsive to external pH changes. In this study, we varied several assembly conditions such as pH, SS/MA ratio in PSSMA, and the ionic strength of the polyelectrolyte solutions. The multilayer films were also treated by immersion into pH 2 and 11 solutions after assembly. Quartz crystal microgravimetry and UV-visible spectrophotometry showed that the thickness of PSSMA/PAH multilayers decreases with increasing assembly pH regardless of whether salt was present in the polyelectrolyte solutions. When no salt was added, the multilayers are thinner, smoother, and grow less regularly. Atomic force microscopy images indicate that the presence of salt in polyelectrolyte solutions results in rougher surface morphologies, and this effect is especially significant in multilayers assembled at pH 2 and pH 11. When both polyelectrolytes are adsorbed at conditions where they are highly charged, salt was necessary to promote regular multilayer growth. Fourier transform infrared spectroscopy studies show that the carboxylic acids in the multilayers are essentially ionized when assembled from different pHs in 0.5 M sodium chloride solutions, whereas some carboxylic acids remain protonated in the multilayers assembled from solutions with no added salt. This resulted in different pH stability regimes when the multilayers were exposed to different pH solutions, post assembly.     

Rheological evidence for the microstructure of intercalated polymer/layered silicate nanocomposites

The rheological behavior of intercalated polystyrene/layered silicate nanocomposites was investigated. Both storage and loss moduli increased with silicate loading at all frequencies and showed non‐terminal behavior at low frequencies which is a typical behavior of non‐homogeneous systems with ordered microstructures. The rheological behavior in intercalated polystyrene/layered silicate nanocomposite depends not only on the intercalation of polymers, but also on the alignment of silicate layers. Furthermore, the real time intercalation dynamics of polystyrene into the layered silicate, monitored by rheological measurements, were also consistent with our simple quantitative analysis.     

金属氢氧化物直接制备对苯二甲酸插层水滑石及其应用

以新制备的Mg(OH)_2和Al(OH)_3滤饼与对苯二甲酸通过水热反应制备了对苯二甲酸插层水滑石(TALDHs).使用X射线衍射(XRD)、热重-差热分析、扫描电镜(SEM)等技术对TA-LDHs与碳酸根型水滑石(CO3-LDHs)进行对比研究,结果显示,对苯二甲酸离子成功插入到LDHs层间,产物结构完整、晶相单一,所制得的TA-LDHs为片状.CO3-LDHs和TA-LDHs分别作为纳米填料,以两种不同的添加方式制备聚对苯二甲酸乙二醇酯(PET)/LDHs纳米复合材料.对复合材料进行XRD和SEM研究,结果表明在酯交换反应前添加2%TA-LDHs所制备的PET/LDHs纳米复合材料的层板被部分剥离,分散性最好.     

Photoluminescence spectral change in layered titanate oxide intercalated with hydrated Eu3+

A number of interesting photoluminescence properties of titanate layered oxide intercalated with hydrated Eu3+ have been demonstrated. Photoluminescence intensity of Eu3+ decreased rapidly with time during irradiation by UV light having energy higher than the band gap energy of the host TiO (Ti(1.81)O4) layer. This is presumably due to the decrease in energy transfer from the host TiO layer to Eu3+ as a result of the change in the hydration state of water molecules surrounding Eu3+, which is caused by the hole produced in the TiO valence band. When irradiation was discontinued, the emission intensity gradually recovered. The recovery time increased when the water in the interlayer is removed by heat treatment. This indicates that the state of interlayer water changes during irradiation and returns to its initial state after discontinuation of irradiation. The excitation spectra changed drastically at any given wavelength upon irradiation with UV light. A comparison of the excitation spectra before and after irradiation reveals that only the excitation peak at around the irradiation wavelength decreased upon irradiation, as in the case of spectral hole burning. The hydration state of water molecules surrounding Eu3+ presumably changes depending on the irradiation wavelength, leading to the above spectral change because the Eu/TiO film has a superlattice structure producing holes with different energies.     

A designed single-step method for synthesis and structural study of organic-inorganic hybrid materials: well-ordered layered manganese oxide nanocomposites

A fast and single-step method was successfully developed toward synthesizing well-ordered organic-inorganic hybrid layered manganese oxide (LMO) nanocomposites and Keggin/organic ions intercalated into layered manganese oxide at room temperature in 1 day. The ordering of layered structures is highly dependent on pH and drying conditions. The Keggin/organic intercalated LMO shows improved thermal stability of the layered structure over that of hybrid LMO.     

Gaseous adsorption properties of a silica-pillared layered manganese oxide

Adsorptions of N(2), H(2)O, and organic vapors including CH(2)Cl(2), CCl(4), c-C(6)H(12), C(6)H(6), n-C(6)H(14), and n-C(9)H(20) on a silica-pillared layered manganese oxide (SiHMnO) and nonane-preadsorbed SiHMnO were examined. It is found that SiHMnO has a microporosity with a wide pore width distribution showing different pore wall affinities. Micropores with smaller width preferentially accommodate the nonane preadsorbate while the surface hydrophilicity of pore wall leads to an easier detachment of the adsorbed nonane molecules. H(2)O adsorption influences both the porosity and the surface properties by accelerating a sufficient hydrolysis of the remained TEOS molecules in SiHMnO. Examinations using Dubinin-Radeshkevich (DR) equation and isosteric heat of adsorption of organic molecules provide evidences that the wall surface of micropores with smaller and larger width have less affinity toward nonpolar and polar organic vapors, respectively.     

Intercalation of cobaltammine complex ions into layered manganese oxide

The intercalation of Co(2+), [Co(NH(3))(6)](3+), and [Co(NH(3))(5)Cl](2+) ions into layered manganese oxide (birnessite) was studied by chemical, XRD, SEM, IR, and DTA-TG analyses. The intercalation reaction progressed by a 2:1 or 3:1 ion-exchange mechanism depending on the valence of the starting ions. The oxidation state of cobalt did not change with the intercalation reaction. The intercalation of [Co(NH(3))(6)](3+) ions resulted in an increase of basal spacing from 0.716 to 0.956 nm, giving a layered structure material consisting mainly of platelike particles. The chemical analysis results showed that the structure of [Co(NH(3))(6)](3+) ions was maintained in the interlayer. On the other hand, an H(2)O/NH(3) ligand exchange reaction progressed for the intercalation of [Co(NH(3))(5)Cl](2+) ions, resulting in an increase in the basal spacing from 0.716 to 0.956 nm.     

Facile synthesis and antimicrobial activity of manganese oxide/bentonite nanocomposites

Research on Chemical Intermediates - Manganese-oxide-intercalated bentonite clay (Mn3O4/BC) nanocomposites were synthesized via a thermal decomposition method using different precursors. The...     

Comments on stabilizing layered manganese oxide electrodes for Li batteries

An electrochemical study of structurally-integrated xLi₂MnO₃•(1 −x)LiMn_0.5Ni_0.5O₂ ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li₂MnO₃-rich end of the Li₂MnO₃–LiMn_0.5Ni_0.5O₂ tie-line, i.e., for 0.7 ≤ x ≤ 0.95. Excellent performance was observed for x = 0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥ 0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed.     

Electrodeposition of manganese and molybdenum mixed oxide thin films and their charge storage properties

Manganese and molybdenum mixed oxides in a thin film form were deposited anodically on a platinum substrate by cycling the electrode potential between 0 and +1.0 V vs Ag/AgCl in aqueous manganese(II) solutions containing molybdate anion (MoO(4)2-). A possible mechanism for the film formation is as follows. First, electrooxidation of Mn2+ ions with H2O yields Mn oxide and protons. Then, the protons being accumulated near the electrode surface react with MoO(4)2- to form polyoxomolybdate through a dehydrated condensation reaction (by protonation and dehydration). The condensed product coprecipitates with the Mn oxide. Cyclic voltammetry of the Mn/Mo oxide film-coated electrode in aqueous 0.5 M Na2SO4 solution exhibited a pseudocapacitive behavior with higher capacitance and better rate capability than that of the pure Mn oxide prepared similarly, most likely as a result of an increase in electrical conductivity of the film. Electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy clearly demonstrated that the observed pseudocapacitive behavior results from reversible extraction/insertion of hydrated protons to balance the charge upon oxidation/reduction of Mn3+/Mn4+ in the film.     

Saturation ratio of poly(ethylene oxide) to silicate in melt intercalated nanocomposites

Melt intercalation has been found to be a very successful approach for preparation of polymer-clay nanocomposites. An aspect of this area that has been little investigated is the amount of polymer required to fill the interlayer galleries of the clay. This paper reports experiments which determine the amount of poly(ethylene oxide) (PEO) required to saturate the spacing between montmorillonite (MMT) or organically-modified bentonite (B34) layers. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to determine the saturation ratios of PEO to silicates, which are then compared to theoretical calculations. The deduced saturation ratio of PEO to MMT is 28:72, and PEO to B34 15:85 by XRD and DSC, whilst ratios of PEO to MMT of 21:79 and PEO to B34 10:90 were obtained via TGA. The density of intercalated PEO in the silicate galleries is estimated to be 0.82 g/cm³, which suggests that PEO in the silicate galleries is far less efficiently packed than in the amorphous region of the bulk polymer.     

Voltammetric performance and application of a sensor for sodium ions constructed with layered birnessite-type manganese oxide

The preparation and electrochemical characterization of a carbon paste electrode modified with layered birnessite-type manganese oxide for use as a sodium sensor is described. The effects of powder synthesis process (sol-gel and redox precipitation) for birnessite on the electrochemical activity of the sensor was investigated by cyclic voltammetry. The carbon paste electrode modified with birnessite-type manganese oxide that was synthesized by the sol-gel method showed a best electrochemical for sodium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the sodium ions extraction into the birnessite structure. The best voltammetric response was obtained for an electrode composition of 15% (w/w) birnessite oxide in the paste, a TRIS buffer solution of pH 8.0 and a scan rate of 50 mV s⁻¹. A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 7.89 × 10⁻⁵ to 3.49 × 10⁻⁴ mol L⁻¹ with a slope of 37.5 μA L mmol⁻¹ and a detection limit (3σ/slope) of 3.43 × 10⁻⁵ mol L⁻¹ using cyclic voltammetry. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples.     

层状复合氢氧化物的药物控释动力学机制

以层状复合氢氧化物(LDH)为载体组装乙酰苯甲酸(ASP)的插层复合物LDH-ASP,以pH2.48~6.89的磷酸盐溶液为介质进行药物释放动力学实验,通过对不同时间药物释放度的测定及释放药物后载体结构变化分析研究了LDH对层间药物的控制释放机制。结果表明粉末状LDH-ASP能在较宽的pH范围表现明显缓控释作用,药物释放度积分方程与Higchi方程、Ritger-Peppas方程、Bhaskar方程及一级动力学方程等经验模型吻合。复合物与溶出介质的反应机制研究表明,药物释放速率及释放度大小取决于交换配比n(ASP)/n[HnPO4(3-n)-]所决定的LDH层间通道畅阻情况。     

Water distribution in multilayers of weak polyelectrolytes

The water localization in thin polyelectrolyte multilayers assembled from poly(acrylic acid) and poly(allylamine hydrochloride) was investigated with neutron reflectivity in an atmosphere of controlled humidity and with bulk water. Water was found to be distributed asymmetrically within the multilayer and to localize preferentially at the polymer surface. The diffusion of water into the multilayer did not completely penetrate to the substrate, but instead there appeared to be an exclusion zone near the Si substrate. These results help to explain previous observations of anomalous water transport kinetics in weak polyelectrolyte systems.     

UV-cross-linkable multilayer microcapsules made of weak polyelectrolytes

Microcapsules composed of weak polyelectrolytes modified with UV-responsive benzophenone (BP) groups were fabricated by the layer-by-layer (LbL) technique. Being exposed to UV lights, capsules shrunk in the time course of minutes at irradiation intensity of 5 mW/cm(2). The shrinkage adjusted the capsule permeability, providing a novel way to encapsulate fluorescence-labeled dextran molecules without heating. Cross-linking within the capsule shells based on hydrogen abstraction via excited benzophenone units by UV showed a reliable and swift approach to tighten and stabilize the capsule shell without losing the pH-responsive properties of the weak polyelectrolyte multilayers.