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.     

A direct electrochemical route to construct a polymer/manganese oxide layered structure

A layered nanocomposite with poly(diallyldimethylammonium), PDDA, intercalated between manganese oxide layers can be formed on a platinum electrode in a thin film form through a direct electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn(2+) precursors in the presence of PDDA by applying a constant potential (+1.0 V vs Ag/AgCl).     

Preparation and formation mechanism of a n-butylammonium/MnO2 layered hybrid via a one-pot synthesis under moderate conditions

The preparation of organic/inorganic layered hybrids has relied on multistep processing. Thus, shortening the synthetic procedure is important for possible future applications, but only a few studies report one-pot syntheses. In this work, we established a simple one-pot solution process to synthesize layered alkyl ammonium/MnO(2) hybrids, by stirring MnCl(2) and alkyl amine/H(2)O(2) aqueous solutions at 40 °C; the reaction concept is a chemical oxidation of Mn(II) ions in the presence of alkyl amine in aqueous solution. Furthermore, the formation mechanism of the layered n-butylammonium/MnO(2) hybrid was examined by following the structural and optical changes during the reaction, revealing that the one-pot reaction includes 3 steps; formation of β-MnOOH, topotactic oxidation of β-Mn(III)OOH to form the protonated layered manganese oxide H(x)Mn(III, IV)O(2)·yH(2)O, and ion-exchange of interlayer H(+) (or H(3)O(+)) with n-butylammonium to form layered n-butylammonium/MnO(2).     

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.     

Activity and lifetime of urease immobilized using layer-by-layer nano self-assembly on silicon microchannels

Urease has been immobilized and layered onto the walls of manufactured silicon microchannels. Enzyme immobilization was performed using layer-by-layer nano self-assembly. Alternating layers of oppositely charged polyelectrolytes, with enzyme layers “encased” between them, were deposited onto the walls of the silicon microchannels. The polycations used were polyethylenimine (PEI), polydiallyldimethylammonium (PDDA), and polyallylamine (PAH). The polyanions used were polystyrenesulfonate (PSS) and polyvinylsulfate (PVS). The activity of the immobilized enzyme was tested by pumping a 1 g/L urea solution through the microchannels at various flow rates. Effluent concentration was measured using an ultraviolet/visible spectrometer by monitoring the absorbance of a pH sensitive dye. The architecture of PEI/PSS/PEI/urease/PEI with single and multiple layers of enzyme demonstrated superior performance over the PDDA and PAH architectures. The precursor layer of PEI/PSS demonstrably improved the performance of the reactor. Conversion rates of 70% were achieved at a residence time of 26 s, on d 1 of operation, and >50% at 51 s, on d 15 with a six-layer PEI/urease architecture.     

Immobilization of methylviologen between well-ordered multilayers of manganese oxide during their electrochemical assembly

Methylviologen dications (MV2+) were immobilized between layers of manganese oxide during their electrochemical assembly by an anodic route in a homogeneous aqueous Mn2+ solution. This approach yielded a well-ordered multilayer film on a platinum substrate as a result of dense packing of planar MV2+ molecules to stabilize the layered framework. A grazing angle in-plane X-ray diffraction study revealed that the manganese oxide sheets and the molecular planes of inserted MV2+ ions are oriented parallel to the electrode surface. Cyclic voltammetry of the product film indicated an electron transfer from the underlying Pt substrate to inserted methylviologen ions through the manganese oxide sheets.     

New layered rare-earth hydroxides with anion-exchange properties

We report the synthesis of a new series of layered hydroxides based on rare-earth elements with a composition of RE(OH)2.5Cl(0.5).0.8 H2O (RE: Eu, Tb, etc.) through the homogeneous precipitation of RECl3.x H2O with hexamethylenetetramine (HMT). Rietveld analysis combined with direct methods revealed an orthorhombic layered structure comprising a positively charged layer of [RE(OH)2.5-(H2O)0.8]0.5+ and interlayer Cl- ions. The Cl- ions were readily exchangeable for various anions (NO3-, SO4(2-), dodecylsulfonate, etc.) at ambient temperature. Photoluminescence studies showed that the compounds display typical RE3+ emission. With rare-earth-based host layers and tunable interlayer guests, the new compounds may be of interest for optoelectronic, magnetic, catalytic, and biomedical materials.     

The structure and catalytic activity of anatase and rutile titania supported manganese oxide catalysts for selective catalytic reduction of NO by NH3

The structure and catalytic properties of anatase and rutile supported manganese oxide catalysts prepared by impregnation method have been studied by using X-ray diffraction (XRD), laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), H(2) temperature-programmed reduction (H(2)-TPR) and BET surface area measurements combined with activity testing of selective catalytic reduction (SCR) of NO by NH(3). It has been shown that the manganese oxide loadings on the two TiO(2) supports exert great influences on the SCR activity. For the rutile supported manganese oxide catalysts, increasing manganese oxide loading leads to the increase of reducibility of dispersed manganese oxide species and the rate constant k, which reaches a maximum around 9.6 × 10(-6) mol g(Mn)(-1) s(-1) at 0.5 mmol Mn per 100 m(2) TiO(2). When the manganese oxide loading is beyond this value, the existence of amorphous MnO(x) multiple layers will certainly reduce the ratio of manganese oxide species exposed on the surface and the reducibility of dispersed manganese oxide species, resulting in the rapid decrease of rate constant k. The LRS and XPS results have revealed that for the anatase supported manganese oxide catalysts manganese oxide species exist in Mn(+4) as a major species with Mn(+3) species and partially undecomposed Mn-nitrate as the minor species. Under the SCR reaction conditions, Mn(+3) species on anatase are oxidized to Mn(+4) species, inserting in the surface of anatase and promoting the anatase-to-rutile transformation in the surface layers of the anatase support. Since these Mn(4+) cations are actually dispersed on the support with a rutile shell-anatase core structure and its concentration is very near to that of MnO(x)/TiO(2) (R) catalyst, the relation between the rate constant k and the MnO(x) loading on the anatase support is similar to that on the rutile support, and that the rate constant k values for anatase and rutile supported manganese oxide catalysts are very close at the same MnO(x) loading.     

Layered tungsten oxide-based organic-inorganic hybrid materials: an infrared and Raman study

Tungsten oxide-organic layered hybrid materials have been studied by infrared and Raman spectroscopy and demonstrate a difference in bonding nature as the length of the interlayer organic "spacer" molecule is increased. Ethylenediamine-tungsten oxide clearly displays a lack of terminal -NH3(+) ammonium groups which appear in hybrids with longer organic molecules, thus indicating that the longer chains are bound by electrostatic interactions as well as or in place of the hydrogen bonding that must be present in the shorter chain ethylenediamine hybrids. The presence of organic molecules between the tungsten oxide layers, compared with the layered tungstic acid H2WO4, shows a decrease in the apical W=O bond strength, as might be expected from the aforementioned electrostatic interaction.     

Two-, three-, and four-component magnetic multilayer onion nanoparticles based on iron oxides and manganese oxides

Magnetic multilayered, onion-like, heterostructured nanoparticles are interesting model systems for studying magnetic exchange coupling phenomena. In this work, we synthesized heterostructured magnetic nanoparticles composed of two, three, or four components using iron oxide seeds for the subsequent deposition of manganese oxide. The MnO layer was allowed either to passivate fully in air to form an outer layer of Mn(3)O(4) or to oxidize partially to form MnO|Mn(3)O(4) double layers. Through control of the degree of passivation of the seeds, particles with up to four different magnetic layers can be obtained (i.e., FeO|Fe(3)O(4)|MnO|Mn(3)O(4)). Magnetic characterization of the samples confirmed the presence of the different magnetic layers.     

Na-Mn-O正极材料的合成及电化学性能

以Mn(CH3COO)2·4H2O为锰源, 以Na2CO3为钠源, 通过溶液-凝胶法合成干凝胶前驱体, 将前驱体在空气气氛中焙烧得到Na-Mn-O正极材料. 并用傅立叶红外光谱(FT-IR), 热重分析(TG), X射线衍射(XRD), 扫描电镜(SEM), 恒流充放电测试等对材料结构和性能进行研究. 结果表明,600 ℃焙烧的样品为结构稳定的层状锰酸钠, 属于六方层状P2结构, 空间群为P63/mmc, 通过PowderX软件计算得到其晶胞参数为a=0.284 nm, c=1.116 nm. Na-Mn-O正极材料在Li+嵌入和脱出过程中, 部分Na+从层状主晶格中脱出, 使得Li+在MnO6层间的嵌/脱阻力减小(由于Na+(0.095 nm)半径比Li+(0.076 nm)大), 电化学性能明显改善. 在充放电电流密度为25 mA·g-1, 电压在2.0-4.3 V范围时, 600 ℃焙烧的样品第二次放电容量高达176 mAh·g-1, 20次循环后, 容量保持率仍有90.9%.     

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.     

2D层状焦磷酸锰髤[NH_4]_2[Mn_3(P_2O_7)_2(H_2O)_2]的结构和磁性研究

由于具有开放骨架的金属磷酸盐在催化、吸附、主客体组装以及光学、磁学等方面的应用[1~3],因此合成具有开放骨架的金属磷酸盐一直吸引着人们的广泛关注。自从1982年美国联合碳化公司(U.C.C.)开发出系列磷酸铝分子筛AlPO4鄄n[4]以来,大量具有开放骨架的金属磷酸盐(金属=Ga,In,F     

Structure and magnetism of the topotactically reduced oxychloride Sr4Mn3O(6.5)Cl2

Reaction of the n = 3 Ruddlesden-Popper oxychloride Sr(4)Mn(3)O(7.5)Cl(2) with calcium hydride yields the topotactically reduced phase Sr(4)Mn(3)O(6.5)Cl(2). The deintercalation of oxide ions from the central MnO(1.5) layer of the starting phase is accompanied by a rearrangement of the anion lattice, resulting in a layer of composition MnO(0.5) in the reduced material, consisting of chains of MnO(4) tetrahedra connected by edge and corner sharing. Magnetization and low-temperature neutron diffraction data are consistent with antiferromagnetic coupling of manganese spins, but no long-range magnetic order is observed down to 5 K, presumably due to the large interlayer separation in the reduced phase. The influence of anion substitution on the structural selectivity of low-temperature reduction reactions is discussed.     

层状二氧化锰和2,2'-联吡啶铁自组装膜的制备和光电性能研究

采用静电吸附层-层自组装方法制备了层状二氧化锰/2,2'-联吡啶铁自组装膜材料,借助扫描电镜(SEM),紫外可见光谱(UV-Vis)和电化学工作站等测试手段对自组装膜的结构与性能进行了表征.结果表明,该自组装膜具有均匀的表面和紧密的层状结构,在可见光照射条件下该自组装膜电极的氧化还原电流明显增加了.层状二氧化锰/2,2'-联吡啶铁自组装膜电极,在可见光照射条件下光电降解有机染料罗丹明B(1×10-5mol/L)反应80min降解率达到了57%.     

Redoxable nanosheet crystallites of MnO2 derived via delamination of a layered manganese oxide

This paper reports on the swelling and exfoliation behavior of a layered protonic manganese oxide, H(0.13)MnO(2).0.7H(2)O, in a solution of tetrabutylammonium (TBA) hydroxide and the formation and characterizations of unilamellar two-dimensional crystallites of MnO(2). At low doses of TBA ions, layered manganese oxide was observed to undergo normal intercalation, yielding a TBA intercalated phase with a gallery height of 1.25 nm. With a large excess of TBA ions, osmotic swelling occurred, giving rise to a very large intersheet separation of 3.5-7 nm. In an intermediate TBA concentration range, the sample exhibited a broad X-ray diffraction profile with superimposed diffraction features due to intercalation and osmotic swelling. The component responsible for the broad profile was isolated by centrifuging the mixture twice at different speeds, and the recovered colloid was identified as a pile of MnO(2) nanosheets, corresponding to the individual host layer of the precursor layered manganese oxide. Observations by transmission electron microscopy and atomic force microscopy revealed high two-dimensional anisotropy with a lateral dimension of submicrometers and a thickness of approximately 0.8 nm. The nanosheet exhibited broad optical absorption with a peak at 374 nm (epsilon = 1.13 x 10(4) mol(-1) dm(3) cm(-1)). The restacking process of the colloidal MnO(2) nanosheets was followed by aging the colloid at a relative humidity of 95%. The broad diffraction pattern due to the exfoliated sheets weakened with time and eventually resolved into two sharp distinct profiles attributable to a TBA intercalation compound with an intersheet spacing of 1.72 nm and an osmotically swollen hydrate with >10 nm at a very early stage. As drying progressed, the former phase became more abundant without a change in interlayer distance, while the degree of swelling of the latter phase gradually decreased to 2.7 nm that remained unchanged on further aging. Subsequent drying at a lower humidity collapsed the 2.7 nm phase. The resulting single 1.72 nm phase was dehydrated by heating at 150 degrees C to produce a phase with a contracted interlayer spacing of 1.3 nm.     

MnOx／TiO2催化剂的表面状态与氧化活性

研究了不同负载量的MnO_2/TiO_2系列催化剂的表面状态及CO氧化活性。结果表明,当MnO_2负载量低于5.7wt％时,MnO_2呈Mn_2O_3相;高于5.7wt％时,MnO_2则为Mn_2O_3+MnO_2混合相。Mn_2O_3由分散态到聚集态的分散阀值为0.028g Mn_2O_3/100mm~2 TiO_2。催化剂氧化活性与其表面状态密切相关。当Mn~(3+)、Mn~(4+)共存时,有利于提高氧化活性。     

Topotactic oxidative and reductive control of the structures and properties of layered manganese oxychalcogenides

Topotactic modification, by both oxidation and reduction, of the composition, structures, and magnetic properties of the layered oxychalcogenides Sr4Mn3O7.5Cu2Ch2 (Ch=S, Se) is described. These Mn3+ compounds are composed of alternating perovskite-type strontium manganese oxide slabs separated by anti-fluorite-type copper chalcogenide layers and are intrinsically oxide deficient in the central layer of the perovskite slabs. The systems are unusual examples of perovskite-related compounds that may topotactically be both oxidized by fluorination and reduced by deintercalation of oxygen from the oxide-deficient part of the structure. The compounds exhibit antiferromagnetic ordering of the manganese magnetic moments in the outer layers of the perovskite slabs, while the other moments, in the central layers, exhibit spin-glass-like behavior. Fluorination has the effect of increasing the antiferromagnetic ordering temperature and the size of the ordered moment, whereas reduction destroys magnetic long-range order by introducing chemical disorder which leads to both further disorder and frustration of the magnetic interactions in the manganese oxide slab.     

精氨酸插层氧化锰纳米结构材料的制备和表征

应用氧化法水热合成了Na型层状氧化锰[BirMO(Na)], 通过离子交换反应在0.1 mol/L HCl溶液中Na型层状氧化锰转化成H型层状氧化锰[BirMO(H)]. BirMO(H)在四甲基氢氧化铵[(CH3)4NOH]溶液中搅拌处理7 d后, 剥离生成了MnO2纳米层胶体分散液. 剥离的MnO2纳米层胶体分散液在pH＝4.0～11.0的精氨酸溶液中搅拌2 d, 得到了层间距为1.49 nm的精氨酸插层氧化锰纳米结构材料. 通过XRD, DSC-TGA, SEM, IR及元素分析对合成试样进行了分析表征. 结果表明精氨酸在氧化锰层间的插入量及插入形式与重组溶液的pH值密切相关, 其最大插入量为1.80 mmol/g.     

Theoretical investigation of the reaction of Mn+ with ethylene oxide

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.