Photochemical electron transfer through [corrected] the interface of hybrid films of titania nano-sheets and mono-dispersed spherical mesoporous silica particles

Photochemical Electron Transfer (ET) between an organic dye, the porphyrin derivative TMPyP, and an electron acceptor, methyl viologen MV2+, have been investigated at the interface of two different inorganic films, i.e., layered titania nano-sheets (TNS) and a monolayer film of spherical and mono-dispersed mesoporous silica (sMPS) particles (ca. 0.5 microm). TMPyP ions were intercalated within the sMPS nano-cavities to form (TMPyP-sMPS) while MV2+ ions were intercalated into the TNS interlayers to form (MV2+-TNS). The (TMPyP-sMPS) and (MV2+-TNS) films were then stacked on a silica substrate in this order to form a (MV2+-TNS)/(TMPyP-sMPS) film and, upon UV light irradiation, ET could be induced. However, when this film was stacked inversely, i.e., for the (TMPyP-sMPS)/(MV2+-TNS) films on a silica substrate, no photoinduced ET were observed. Interestingly, however, even for this photo-inactive inversely stacked film, ET could be generated by inserting a gold vapor-deposited layer between the (MV2+-TNS) and (TMPyP-sMPS) films. The conjugation conditions at the interface of the inversely stacked (TMPyP-sMPS)/(MV2+-TNS) hybrid film were, thus, confirmed to strongly affect the photoinduced electron transfers and their efficiencies.     

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.     

Electrodeposition of layered manganese oxide nanocomposites intercalated with strong and weak polyelectrolytes

Multilayered manganese oxide nanocomposites intercalated with strong (poly(diallyldimethylammonium) chloride, PDDA) and weak (poly(allylamine hydrochloride), PAH) polyelectrolytes can be produced on polycrystalline platinum electrode in a thin film form by a simple, one-step electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn2+ ions at around +1.0 V (vs Ag/AgCl) in the presence of polyelectrolytes. Fully charged PDDA polycations are accommodated tightly in the interlayer space by electrostatic interaction with negative charges on the manganese oxide layers, leading to an interlayer distance of 0.97 nm. The layered film prepared with PAH has a larger polymer content (PAH/Mn molar ratio of 0.98) than that (PDDA/Mn molar ratio of 0.43) made with PDDA because of the smaller charging degree of PAH, exhibiting a larger interlayer distance (1.19 nm). The interlayer PAH contains neutral (-NH2) and positively charged (-NH3(+)) amine groups, and the -NH3(+) groups are associated with Cl- (to generate -NH3(+) Cl- ion pairs) as well as the negatively charged manganese oxide layers. Both polyelectrolytes once incorporated were not ion exchanged with small cations in solution. The layered structure of PDDA/MnO(x) was collapsed during the reduction process in a KCl electrolyte solution, accompanying an expansion of the interlayer as a result of incorporation of K+ ions for charge neutrality. On the contrary, the layered PAH/MnO(x) film showed a good electrochemical response due to the redox reaction of Mn3+/Mn4+ couple with no change in the structure. X-ray photoelectron spectroscopy revealed that, in this case, excess negative charges generated on the manganese oxide layers upon reduction can be balanced by the protons being released from the -NH3(+) Cl- sites in the interlayer PAH; the Cl- anions becoming unnecessary are inevitably excluded from the interlayer, and vice versa upon oxidation.     

Cobalt alters the growth of a manganese oxide film

The mobility of dissolved heavy metals in natural waters is partially regulated by interactions with manganese oxide films. In the current work, the effects of aqueous cobalt(II) on manganese oxide film growth are studied by atomic force microscopy. The film is grown on the (104) surface of rhodochrosite (MnCO3). In the presence of O2(aq) and at circumneutral pH, film growth begins as manganese oxide islands that expand laterally across the surface. Addition of Co2+(aq) leads to the partial or complete dissolution of the manganese oxide film. Simultaneously, there is growth of new islands having multilayer structures that are unrestrained in the z-direction. The chemical composition of these new islands appears to include both Co and Mn ions. Empirical rules governing the growth of the two types of islands can be developed for the absence and the presence of Co2+(aq). In the absence of Co2+(aq), islands grow as flat two-dimensional rhombohedral islands of nearly uniform height (2.4 +/- 0.3 nm). These islands do not cross over steps on the substrate. The growth rules change markedly in the presence of Co2+(aq). The islands grow indefinitely in the z-direction as strata structures of polydisperse thickness and rounded tops. The islands readily grow over steps. Cobalt ions, therefore, relieve the two-dimensional restriction on layer formation and allow three-dimensional growth. Moreover, the shape of the dissolution pits on the surface of MnCO3 changes from rhombohedral in the absence of cobalt to partially rounded in the presence of cobalt. The rounding occurs for the obtuse edges of the pit. Direct microscopic observations of the interactions of cobalt with manganese oxide films provide new mechanistic insights that are important in the quantitative modeling of the mobility of heavy metals in the environment.     

不同晶型和形貌MnO2纳米材料的可控制备

以KMnO4为锰源, 采用水热技术在180 ℃条件下于不同种类酸溶液中可控制备了α-, β-, δ-MnO2, 系统研究了 K＋, H＋及阴离子对制备产物MnO2晶型和形貌的影响. 研究结果表明, K＋与H＋在反应体系中对于制备产物晶相的生成形成竞争性影响, 其量的大小对制备产物晶型具有控制作用, 高浓度K＋离子有助于生成α-MnO2, 而高浓度的H＋有利于生成β-MnO2; 阴离子的种类和浓度对制备产物MnO2的晶型和形貌无显著影响. 在对制备产物进行XRD, SEM和元素分析的基础上, 提出了不同晶型和形貌MnO2的可能形成机理.     

Structure analysis of exfoliated unilamellar crystallites of manganese oxide nanosheets

Structure analysis of unilamellar manganese oxide nanosheets obtained via exfoliation of layered manganese oxides was carried out utilizing synchrotron radiation (SR) X-ray in-plane diffraction and polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) analyses. A combination of SR excitation and the total reflection of incoming X-rays provides signals strong enough for both analyses even from a monolayer of the MnO(2) nanosheets having a concentration of 0.7 microg cm(-2). In addition, the mean oxidation state of constituent manganese ions in the MnO(2) sheets was estimated on the basis of XANES spectra, and bond valence sum calculations with the bond length obtained from the present EXAFS analyses. The obtained structural data revealed that the two-dimensional lattice of the MnO(2) sheets underwent a slight elongation upon delamination. These changes correspond to approximately 1% expansion of sheet area and 1-2% expansion of thickness, which can be understood by reduction of the mean oxidation number of manganese ions in the sheet through the exfoliation process.     

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 novel layered oxysulfide intergrowth compound Sr4Mn2Cu5O4S5 containing a fragment of the alpha-Cu2S antifluorite structure

Sr4Mn2Cu5O4S5 contains manganese oxide sheets separated by unusual antifluorite-type Cu3S3 layers in which copper(I) ions are distributed over three- and four-coordinates sites in a similar fashion to in alpha-Cu2-xS and suggestive of high two-dimensional copper ion mobility.     

尖晶石锂锰氧化物锂离子嵌脱过程的交流阻抗谱研究

用粉末微电极研究了尖晶石锂锰氧化物在不同嵌锂状态下嵌脱锂过程的交流阻 抗图谱，提出了新的等效电路模型。描述锂离子在固体中扩散的Warburg阻抗与累 积或消耗的嵌入电容在Lix MnO4中的x≤0．5时串联，0．5＜x≤1时并联。用提出 的等效电路模型分阶段拟合了实验所得的交流阻抗谱，拟合值与实验值相当吻合， 由拟合结果得到不同电位下锂离子在表面膜中的迁移电阻和电容，界面电荷传递电 阻，双层电容，锂离子在固体中扩散系数和累积或消耗的嵌入电容。     

Electrical properties of mineral surfaces for increasing water sorption

Thin films of nanostructures alter the electrical properties of mineral surfaces and thereby affect reactions with charged species such as metal ions and biological cells. In this study, electric-force microscopy is used to probe the electrical properties of a heterogeneous layout of manganese oxide nanostructures grown as a film on a MnCO3 substrate. The role of water sorption is examined by carrying out experiments for increasing relative humidity (RH). Electric-force images collected with a negative dc tip bias show that the apparent heights of the nanostructures decrease from +3.4 nm at 16% RH to +0.7 nm at 33% RH to -5.6 nm at 74% RH, although the topographic height is 2.3 nm regardless of RH. The apparent heights for a positive dc bias also decrease with increasing RH from -3.5 nm at 16% RH to -8.9 nm at 74%. The explanation for these trends is that the dominant electric-force transitions with increasing RH from an electrostatic force attributable to surface potential to a polarization force arising from hydrated, mobile surface ions including Mn2+ and CO3(2-). The positive-to-negative trend in apparent heights implies that either the density or the intrinsic mobility (or both) of mobile ions over the substrate exceeds that over the nanostructures, implying increased water sorption over the former compared to the latter. Ridges around the perimeter of the nanostructures also develop above 40% RH for images collected using a negative dc tip bias. A tip-induced gradient of net positive charge near the nanostructure edges, which implies the nonequivalence of cations and anions there, explain this observation. The findings of this study show that thin films of nanostructures on mineral surfaces have complex but measurable RH-dependent electrical properties.     

The manganese(IV) oxide electrode as a manganese(II) sensor

Manganese(IV) oxide electrodes formed with a graphite/PTFE substrate are shown to have near-theoretical response to manganese(II) ions in pH-4 acetate medium and a sub-Nernstian response in 0.1M nitric acid medium. Lead and iron(III) ions interfere, and iron(II) ions even more so, but other bivalent transition metal ions have little effect. The main drawback of this type of electrode is its long response time (~ 20 min). Some attempts to use manganese(IV) oxide electrodes as the basis for phosphate electrodes by use of MnHPO(4).3H(2)O and MnNH(4)PO(4).H(2)O are also described.     

Anodic deposition of layered manganese oxide into a colloidal crystal template for electrochemical supercapacitor

Electrodeposition of the layered manganese oxide was conducted in a colloidal crystal template formed by self-assembly of polystyrene particles on an indium tin oxide substrate. The resulting macroporous film exhibited good pseudocapacitive behavior in neutral electrolyte, as a result of contributions of the surface of macropores and the interlayer space of the multilayered structure.     

A magnetic route to measure the average oxidation state of mixed-valent manganese in manganese oxide octahedral molecular sieves (OMS)

A magnetic route has been applied for measurement of the average oxidation state (AOS) of mixed-valent manganese in manganese oxide octahedral molecular sieves (OMS). The method gives AOS measurement results in good agreement with titration methods. A maximum analysis deviation error of +/-7% is obtained from 10 sample measurements. The magnetic method is able to (1) confirm the presence of mixed-valent manganese and (2) evaluate AOS and the spin states of d electrons of both single oxidation state and mixed-valent state Mn in manganese oxides. In addition, the magnetic method may be extended to (1) determine AOS of Mn in manganese oxide OMS with dopant "diamagnetic" ions, such as reducible V5+ (3d0) ions, which is inappropriate for the titration method due to interference of redox reactions between these dopant ions and titration reagents, such as KMnO4, (2) evaluate the dopant "paramagnetic" ions that are present as clusters or in the OMS framework, and (3) determine AOS of other mixed-valent/single oxidation state ion systems, such as Mo3+(3d3)-Mo4+(3d2) systems and Fe3+ in FeCl3.     

Preparation, structure, and electrochemistry of a polypyrrole film doped with manganese(III)-substituted Dawson-type phosphopolyoxotungstate

The fabrication, structure, electrochemical properties, and electrocatalytic properties of a manganese(III)-substituted Dawson-type phosphopolyoxotungstate, alpha 2-K7P2W17O61(Mn3+.OH2).12H2O (P2W17Mn), entrapped in polypyrrole (PPy) film have been studied. The hybrid film was prepared by potentiostatic polymerization from aqueous solution containing 20 mM pyrrole (Py) and 2 mM P2W17Mn on a pyrolytic graphite (PG) surface. Chronoamperometry, Raman spectroscopy, UV-visible absorption spectroscopy, and cyclic voltammetry were used to monitor and characterize the growth, structure, and properties of the film. The chronoamperometric curve shows that P2W17Mn can catalyze the electrochemical polymerization of Py. The Raman spectrum suggests that the doped P2W17Mn has little effect on the structure of PPy film. The P2W17Mn/PPy film exhibits good voltammetric response in both the acidic aqueous and acetonitrile solutions. At pH 1.0, the molar ratio of pyrrole to P2W17Mn7- in the hybrid film is 21.1:1, quite close to the expected ratio of 21.2:1 for a PPy film with a +0.33 oxidation level per pyrrole moiety and doped with an anion with a charge of 7. The influence of solution pH on P2W17Mn7- in the film is much smaller than that in the aqueous solution. During the potential scanning in 0.1 M LiClO4 acetonitrile solution, P2W17Mn7- was slowly released from the hybrid film and electrolyte ions (Li+ and ClO4-) were inserted into the film. This was identified by cyclic voltammetry and UV-visible spectroscopy. Additionally, the hybrid film can effectively catalyze the reduction of hydrogen peroxide and nitrite.     

水溶液中Mn2+对硫化锌纳米粒子形貌的调控作用

利用硫代乙酰胺在水溶液中缓慢释放的S2-与Zn2+反应制备了ZnS纳米颗粒,ZnS纳米颗粒沉积吸附在3-磺酸基丙基三甲氧基硅烷自组装单层膜上。 实验发现,溶液中添加少量Mn2+,可以显著影响ZnS纳米颗粒的形貌,对ZnS纳米晶的生长方向也有重要影响。 EDS和XRD谱证实Mn2+并没有掺杂到纳米颗粒中去。 这为纳米粒子形貌的调控提供了新途径。 并对ZnS的形成过程进行了探讨,并提出了可能的影响纳米材料形貌的机制。     

Fast migration of fluoride ions in growing anodic titanium oxide

The rapid inward migration of fluoride ions in growing anodic titanium oxide under a high electric field has been elucidated by anodizing a Ti–12 at% silicon alloy, where film growth proceeds at nearly 100% efficiency in selected electrolytes. Further, incorporated silicon species in the anodic film are immobile, acting as marker species. The migration rate of fluoride ions is determined precisely by three-stage anodizing, consisting of initial anodic film formation at a constant current density to 50 V in ammonium pentaborate electrolyte, subsequent incorporation of fluoride ions by reanodizing to 55 V in ammonium fluoride electrolyte and, finally, anodizing again in ammonium pentaborate electrolyte at high current efficiency. The resultant films were analyzed by glow discharge optical emission spectroscopy to reveal the depth distribution of fluoride ions and the location of the silicon marker species. The fluoride ions migrate inward at twice the rate of O²⁻ ions. Consequently, anodizing of titanium in fluoride-containing electrolytes develops a fluoride-rich layer that separates the alloy substrate from the anodic oxide, with eventual detachment of the film from the substrate.     

Formation of Na1＋xV3O8 Nanoribbon Thin Film from V2O5 Xerogel on Sodium Silicate Glass Substrate

Na1 xV3O8 nanoribbon thin film was successfully fabricated by annealing the V2O5 xerogel film on sodium silicate glass substrate at 450 ℃.It has been identified that the amount of sodium ions diffused into the V2O5 xerogel film increases with the high temperature of annealing treatment.The sodium glass substrate serves as a limited sodium source to induce the transformation from V2O5 to Na1 xV3O8.     

Synthesis of γ-lactones from easily and accessible reactants catalyzed by Cu–MnOx catalysts

The mechanism of the oxidative [3+2] cycloaddition of alkenes with anhydrides using oxygen as an oxidant to synthesize γ-lactones has been studied using a heterogeneous dual copper-manganese–based catalyst. The cyclization takes place through two coexisting reaction mechanisms, the involvement of different reaction intermediates and a clear synergistic effect between copper and manganese. In fact it appears that CuO clusters dispersed on the surface of a manganese-based oxide increase the redox capability of manganese ions and leads to an increase in the release of oxygen from the surface.     

基于铝离子掺杂二氧化钛薄膜的染料敏化太阳能电池的光电性能

采用水热法制备出Al3+掺杂二氧化钛薄膜,通过玻璃棒涂于导电玻璃上,在450°C的温度下烧结并将其用N3染料敏化制成染料敏化太阳能电池(DSSCs).通过X射线光电子能谱(XPS)、X射线衍射(XRD)、扫描电镜(SEM)及DSSCs测试系统对其进行了测试表征,研究了Al3+掺杂对TiO2晶型及染料敏化太阳能电池的光电性能影响.XPS数据显示Al3+成功掺杂到了TiO2晶格内,由于Al3+的存在,对半导体内电子和空穴的捕获及阻止电子/空穴对的复合发挥重要作用.莫特-肖特基曲线显示掺杂Al3+后二氧化钛平带电位发生正移,并导致电子从染料注入到TiO2的驱动力提高.DSSCs系统测试结果表明,Al3+掺杂的TiO2薄膜光电效率达到6.48%,相对于无掺杂的纯二氧化钛薄膜光电效率(5.58%),其光电效率提高了16.1%,短路光电流密度从16.5mA·cm-2提高到18.2mA·cm-2.     

Synthesis and electrochemistry of a vanadium-pillared manganese oxide

A new manganese dioxide pillared by vanadium oxide species has been synthesized hydrothermally from permanganate. It has the electrochemically active MnO₂ layer structure, which has been extensively studied as a battery cathode. The vanadium oxide ions, together with the water molecules, reside in between the oxide sheets; dehydration occurs without structural change. The (VO_y)_0.1MnO₂·nH₂O has a rhombohedral structure, with hexagonal parameters a=2.843(6) Å, c=22.08(2) Å. It reacts readily with lithium with a capacity around 150 mAh g⁻¹; the pillar ions do not appear to impede reaction.