Preparation of Mesoporous 1,4‐Phenylene‐silica Nanorings through a Dual‐templating Approach

Mesoporous 1,4‐phenylene‐silica nanorings were prepared using cetyltrimethylammonium bromide (CTAB) and (S)‐2‐methyl‐1‐butanol as a chiral dopant in concentrated aqueous NH₃ solutions. Transmission electron microscopy images of the samples indicated that the nanorings were formed by bending nanorods 360°. With increasing the stirring speed or the (S)‐2‐methyl‐1‐butanol/CTAB molar ratio, the morphologies of mesoporous 1,4‐phenylene‐silicas changed from helical nanofibers to nanorings, and then to nano‐saddles. Circular dichroism spectra of these hybrid silicas indicated that they were chiral.     

Mesoporous Spherical Li4Ti5O12 as High‐Performance Anodes for Lithium‐Ion Batteries

Porous microspherical Li₄Ti₅O₁₂ aggregates (LTO‐PSA) can be successfully prepared by using porous spherical TiO₂ as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO‐PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO‐PSA at 30 C is as high as 141 mA h g^?1, whereas that of normal Li₄Ti₅O₁₂ powders prepared by a sol–gel method can only achieve 100 mA h g^?1. This improved rate performance can be ascribed to small Li₄Ti₅O₁₂ nanocrystallites, a three‐dimensional mesoporous structure, and enhanced ionic conductivity.     

Preparation of ordered mesoporous TiO2 thin film and its application in methanol catalytic combustion

Ordered mesoporous titania thin films were synthesized by evaporation induced self‐assembly process in the presence of Pluronic block copolymers P123 (EO₂₀‐PO₇₀‐EO₂₀). The influence of several experimental parameters, including aging humidity, aging temperature, substrate properties and methods for organic templates removal, on the mesostructure of titania thin films was investigated in details. The mesoporous titania thin film supported Pt catalyst was prepared, and its methanol catalytic combustion performance was studied. The results showed that mesoporous titania thin film is an active support for catalyst. Mesoporous titania thin film supported platinum catalysts yields 70% methanol conversion at room temperature and 100% conversion at 100 °C. Copyright © 2013 John Wiley & Sons, Ltd.     

Non‐covalent Immobilization of Iron‐triazole (Fe(Htrz)3) Molecular Mediator in Mesoporous Silica Films for the Electrochemical Detection of Hydrogen Peroxide

Mesoporous silica thin films encapsulating a molecular iron‐triazole complex, Fe(Htrz)₃ (Htrz=1,2,4,‐1H‐triazole), have been generated by electrochemically assisted self‐assembly (EASA) on indium‐tin oxide (ITO) electrode. The obtained modified electrodes are characterized by well‐defined voltammetric signals corresponding to the Fe^II/III centers of the Fe(Htrz)₃ species immobilized into the films, indicating fast electron transfer processes and stable operational stability. This is due to the presence of a high density of redox probes in the material (1.6×10^?4 mol g^?1 Fe(Htrz)₃ in the mesoporous silica film) enabling efficient charge transport by electron hopping. The mesoporous films are uniformly deposited over the whole electrode surface and they are characterized by a thickness of 110 nm and a wormlike mesostructure directed by the template role played by Fe(Htrz)₃ species in the EASA process. These species are durably immobilized in the material (they are not removed by solvent extraction). The composite mesoporous material (denoted Fe(Htrz)₃@SiO₂) is then used for the electrocatalytic detection of hydrogen peroxide, which can be performed by amperometry at an applied potential of ?0.4 V versus Ag/AgCl and by flow injection analysis. The organic‐inorganic hybrid film electrode displays good sensitivity for H₂O₂ sensing over a dynamic range from 5 to 300 μM, with a detection limit estimated at 2 μM.     

Easy and General Synthesis of Large‐Sized Mesoporous Rare‐Earth Oxide Thin Films by ′Micelle Assembly′

Large‐sized (ca. 40 nm) mesoporous Er₂O₃ thin films are synthesized by using a triblock copolymer poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide) (PS‐b‐P2VP‐b‐PEO) as a pore directing agent. Each block makes different contributions and the molar ratio of PVP/Er³⁺ is crucial to guide the resultant mesoporous structure. An easy and general method is proposed and used to prepare a series of mesoporous rare‐earth oxide (Sm₂O₃, Dy₂O₃, Tb₂O₃, Ho₂O₃, Yb₂O₃, and Lu₂O₃) thin films with potential uses in electronics and optical devices.     

Li4Ti5O12 Nanoparticles Prepared with Gel-hydrothermal Process as a High Performance Anode Material for Li-ion Batteries

Li₄Ti₅O₁₂ (LTO) nanoparticles were prepared by gel‐hydrothermal process and subsequent calcination treatment. Calcination treatment led to structural water removal, decomposition of organics and primary formation of LTO. The formation temperature of spinel LTO nanoparticles was lower than that of bulk materials counterpart prepared by solid‐state reaction or by sol‐gel processing. Based on the thermal gravimetric analysis (TG) and differential thermal gravimetric (DTG), samples calcined at different temperatures (350, 500 and 700°C) were characterized by X‐ray diffraction (XRD), field emitting scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammogram and charge‐discharge cycling tests. A phase transition during the calcination process was observed from the XRD patterns. And the sample calcined at 500°C had a distribution of diameters around 20 nm and exhibited large capacity and good high rate capability. The well reversible cyclic voltammetric results of both electrodes indicated enhanced electrochemical kinetics for lithium insertion. It was found that the Li₄Ti₅O₁₂ anode material prepared through gel‐hydrothermal process, when being cycled at 8 C, could preserve 76.6% of the capacity at 0.3 C. Meanwhile, the discharge capacity can reach up to 160.3 mAh·g^?1 even after 100 cycles at 1 C, close to the theoretical capacity of 175 mAh·g^?1. The gel‐hydrothermal method seemed to be a promising method to synthesize LTO nanoparticles with good application in lithium ion batteries and electrochemical cells.     

Fast,Reversible Lithium Storage with a Sulfur/Long‐Chain‐Polysulfide Redox Couple

The cathodic reactions in Li–S batteries can be divided into two steps. Firstly, elemental sulfur is transformed into long‐chain polysulfides (S₈?Li₂S₄), which are highly soluble in the electrolyte. Next, long‐chain polysulfides undergo nucleation reaction and convert into solid‐state Li₂S₂ and Li₂S (Li₂S₄?Li₂S) by slow processes. As a result, the second‐step of the electrochemical reaction hinders the high‐rate application of Li–S batteries. In this report, the kinetics of the sulfur/long‐chain‐polysulfide redox couple (theoretical capacity=419 mA h g^?1) are experimentally demonstrated to be very fast in the Li–S system. A Li–S cell with a blended carbon interlayer retains excellent cycle stability and possesses a high percentage of active material utilization over 250 cycles at high C rates. The meso‐/micropores in the interlayer are responsible for accommodating the shuttling polysulfides and offering sufficient electrolyte accessibility. Therefore, utilizing the sulfur/long‐chain polysulfide redox couple with an efficient interlayer configuration in Li–S batteries may be a promising choice for high‐power applications.     

Platinum Ultramicroelectrodes Modified with Electrogenerated Surfactant‐Templated Mesoporous Organosilica Films: Effect of Film Formation Conditions on Its Performance in Preconcentration Electroanalysis

Pt µdisc electrodes have been modified by mesoporous organosilica thin films by electrochemically assisted self‐assembly (EASA) of mercaptopropyltrimethoxysilane (MPTMS), tetraethoxysilane (TEOS), and the surfactant cetyltrimethylammonium bromide (CTAB). The EASA process involves the generation of hydroxide ions at the electrode/solution interface, upon the application of a cathodic current density, leading to TEOS and MPTMS polycondensation around the CTAB template and concomitant growing of a thiol‐functionalized mesoporous film onto the electrode surface. The experimental conditions (current density, deposition time, silane concentration and molar ratio between surfactant template and silane) were optimised to form a thin and permeable film likely to be used in preconcentration electroanalysis. The morphology of the film electrodes were characterised by scanning electron microscopy. The permeability properties of the modified Pt µdisc electrodes have been evidenced by cyclic voltammetry using Ru(NH₃)₆³⁺ as a redox probe. The best parameters identified for the film preparation are a current density of ? 8 mA cm^?2 applied for 15 s in a solution containing 110 mM of hydrolysed silane precursors and 70.4 mM of CTAB. Pt µdisc electrodes modified in these conditions were used for the open‐circuit preconcentration of Hg(II) species prior to their detection by anodic stripping voltammetry in a mercury‐free solution. In the optimized conditions, a sensitivity of 14.3 mA cm^?2 µM^?1 was obtained for the 0.02–0.08 µM concentration range. The analytical performance of such organosilica films could decay by up to two orders of magnitude for the materials prepared in conditions other than the optimized ones, highlighting the need for a fine control of the deposition parameters to elaborate sensors based on such modified ultramicroelectrodes.     

Chemical Preparation of Ferroelectric Mesoporous Barium Titanate Thin Films: Drastic Enhancement of Curie Temperature Induced by Mesopore‐Derived Strain

Mesoporous barium titanate (BT) thin films are synthesized by a surfactant‐assisted sol–gel method. The obtained mesoporous BT thin films show enhanced ferroelectricity due to the effective strains induced by mesopores. The Curie temperature (T_c) of the mesoporous BT reaches approximately 470 °C.     

以混合表面活性剂为模板可控合成MCM-48和MCM-41分子筛

利用阳离子和三嵌段共聚物混合表面活性剂为模板,在水热条件、碱性介质中可控合成出MCM-48和MCM-41分子筛。在固定P123(聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物):TEOS(正硅酸乙酯)(物质的量的比)为0.01875的体系中,调节CTAB(十六烷基三甲基溴化铵)∶TEOS(正硅酸乙酯)物质的量比值m,当m在0.12~0.13范围合成出MCM-48分子筛;当m在0.04~0.08范围合成出MCM-41分子筛。通过XRD,TEM,N2物理吸附,IR等方法进行了表征。结果表明:聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物(P123)的加入可以更大程度地降低合成介孔材料所需阳离子表面活性剂的用量;可控合成的介孔材料具有高比表面积、高度有序的孔道结构、较集中的孔径分布。     

Insertions‐ und Substitutionsreaktion von Ameisensäuremethylester mit [Cp′2ZrCl(PHTipp)] – Molekülstruktur von meso‐trans‐[Cp′2ZrCl{OCH(PHTipp)2}] (Cp′ = η5‐C5MeH4, Tipp = 2,4,6‐Pri3C6H2)

Insertion and Substitution Reaction of Methyl Formate with [Cp′₂ZrCl(PHTipp)] – Molecular Structure of meso‐trans ‐[Cp′₂ZrCl{OCH(PHTipp)₂}] (Cp′ = η⁵‐C₅MeH₄, Tipp = 2,4,6‐Prⁱ₃C₆H₂) [Cp′₂ZrCl(PHTipp)] ( 1 ) (Cp′ = η⁵‐C₅MeH₄, Tipp = 2,4,6‐Prⁱ₃C₆H₂) reacts with methyl formate with insertion and substitution to give [Cp′₂ZrCl{OCH(PHTipp)₂}] ( 2 ). 2 was characterized spectroscopically (¹H, ³¹P NMR, IR, MS) and by X‐ray structure determination. Only the meso‐trans isomer is present in the solid state.     

Solid Polymer Electrolyte Based on Pluronic P123 Triblock Copolymer‐Siloxane Organic‐Inorganic Hybrid

A novel organic‐inorganic hybrid electrolyte based on poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) triblock copolymer (Pluronic P123) complexed with LiClO₄ via the co‐condensation of an epoxy trialkoxysilane and tetraethylorthosilicate was prepared. Characterization was made by a variety of techniques including powder X‐ray diffraction, AC impedance, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and multinuclear solid state NMR measurements. The hybrid with [O]/[Li] = 16 exhibited a mesophase with a certain degree of ordering, which arose by the self‐assembly of P123 with the silica network. The P123 triblock copolymer acts as a structure‐directing surfactant to organize with silica networks and as a polymer matrix to dissolve alkali lithium salts as well. The DSC results indicated the formation of transient crosslinking between Li⁺ ions and the ether oxygens of the EO and PO segments, resulting in an increase the T_g with increasing salt concentrations. Variable temperature ⁷Li‐{¹H} MAS NMR spectra revealed the presence of two different local environments for lithium cations, probably due to the lithium cations in the polymer‐rich domain and in the silica‐rich domain, respectively. A combination of XRD and conductivity results suggests that the drastically enhanced conductivity for the ordered hybrid electrolyte is closely related to the formation of mesophase, which may provide unique Li⁺ conducting pathways.     

In-situ imaging of Li-ion migration at interfaces in an all solid Li-ion battery

We investigated the migration of Li ions at an interface between a Li_xTi₅O₁₂ (LTO) and a solid electrolyte in an all-solid Li-ion battery. The optical reflection of LTO changes with variations in the Li content because the band structures of LTO vary with the changes in the Li content. This enables us to observe Li-ion migration in the interface between the LTO and the solid electrolyte using an optical microscope. To observe the LTO particles optically, they were coated on an indium tin oxide on a glass substrate. Variations in Li migration caused by charging/discharging were clearly observed through the changes in the reflection of the LTO. LTO changed between an insulator Li₄Ti₅O₁₂ of the spinel structure and a conductor Li₇Ti₅O₁₂ of the rock-salt structure according to the changes in the Li content. The spinel LTO has a bandgap energy of approximately 2 eV. When electron–hole pairs were generated, electric strains were produced. Surface force microscopy detected the strains and imaged the distribution of lithiation/delithiation of LTO. Interfacial conduction between a sputtered LTO and Li₃PO₄ particles was imaged with high spatial resolution.     

Synthesis of Mesoporous Transition‐Metal Phosphates by Polymeric Micelle Assembly

Mesoporous iron phosphate (FePO₄) was synthesized through assembly of polymeric micelles made of asymmetric triblock co‐polymer (polystyrene‐b‐poly‐2‐vinylpyridine‐b‐ethylene oxide; PS‐PVP‐PEO). The phosphoric acid solution stimulates the formation of micelles with core–shell‐corona architecture. The negatively charged PO₄^3? ions dissolved in the solution strongly interact with the positively charged PVP⁺ units through an electrostatic attraction. Also, the presence of PO₄^3? ions realizes a bridge between the micelle surface and the metal ions. The removal of polymeric template forms the robust framework of iron phosphate with 30 nm pore diameter and 15 nm wall thickness. Our method is applicable to other mesoporous metal phosphates by changing metal sources. The obtained materials were fully characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption–desorption, Raman spectroscope, and other techniques.     

Formation of Organolithium Hetero‐Aggregates [Li4Ar2(nBu)2] (Ar=C6H4CH(Me)NMe2‐2) during the Directed ortho‐Lithiation of [1‐(Dimethylamino)ethyl]benzene

(R)‐[1‐(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero‐aggregate ( 2 a ) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li₄(C₆H₄CH(Me)NMe₂‐2)₂(nBu)₂] ( 2 b ) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C₆H₄CH(Me)NMe₂‐2) with nBuLi in a 1:1 molar ratio. The mono‐Et₂O adduct [Li₄(C₆H₄CH(Me)NMe₂‐2)₂(nBu)₂(OEt₂)] ( 2 c ) and the bis‐Et₂O adduct [Li₄(C₆H₄CH(Me)NMe₂‐2)₂(nBu)₂(OEt₂)₂] ( 2 d ) were obtained by re‐crystallization of 2 b from pentane/Et₂O and pure Et₂O, respectively. The single‐crystal X‐ray structure determinations of 2 b – d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li₂Ar₂ dimer and a hypothetical Li₂nBu₂ dimer. The stereochemical aspects of the chiral Li₂Ar₂ fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and ¹H, ¹³C, and ⁶Li NMR spectroscopy.     

Supramolecular Formation of Li+@PCBM Fullerene with Sulfonated Porphyrins and Long‐Lived Charge Separation

Lithium‐ion‐encapsulated [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester fullerene (Li⁺@PCBM) was utilized to construct supramolecules with sulfonated meso‐tetraphenylporphyrins (MTPPS^4?; M=Zn, H₂) in polar benzonitrile. The association constants were determined to be 1.8×10⁵ M ^?1 for ZnTPPS^4?/Li⁺@PCBM and 6.2×10⁴ M ^?1 for H₂TPPS^4?/Li⁺@PCBM. From the electrochemical analyses, the energies of the charge‐separated (CS) states were estimated to be 0.69 eV for ZnTPPS^4?/Li⁺@PCBM and 1.00 eV for H₂TPPS^4?/Li⁺@PCBM. Upon photoexcitation of the porphyrin moieties of MTPPS^4?/Li⁺@PCBM, photoinduced electron transfer occurred to produce the CS states. The lifetimes of the CS states were 560 μs for ZnTPPS^4?/Li⁺@PCBM and 450 μs for H₂TPPS^4?/Li⁺@PCBM. The spin states of the CS states were determined to be triplet by electron paramagnetic resonance spectroscopy measurements at 4 K. The reorganization energies (λ) and electronic coupling term (V) for back electron transfer (BET) were determined from the temperature dependence of k_BET to be λ=0.36 eV and V=8.5×10^?3 cm^?1 for ZnTPPS^4?/Li⁺@PCBM and λ=0.62 eV and V=7.9×10^?3 cm^?1 for H₂TPPS^4?/Li⁺@PCBM based on the Marcus theory of nonadiabatic electron transfer. Such small V values are the result of a small orbital interaction between the MTPPS^4? and Li⁺@PCBM moieties. These small V values and spin‐forbidden charge recombination afford a long‐lived CS state.     

Dual Soft‐Template System Based on Colloidal Chemistry for the Synthesis of Hollow Mesoporous Silica Nanoparticles

A new dual soft‐template system comprising the asymmetric triblock copolymer poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide) (PS‐b‐P2VP‐b‐PEO) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to synthesize hollow mesoporous silica (HMS) nanoparticles with a center void of around 17 nm. The stable PS‐b‐P2VP‐b‐PEO polymeric micelle serves as a template to form the hollow interior, while the CTAB surfactant serves as a template to form mesopores in the shells. The P2VP blocks on the polymeric micelles can interact with positively charged CTA⁺ ions via negatively charged hydrolyzed silica species. Thus, dual soft‐templates clearly have different roles for the preparation of the HMS nanoparticles. Interestingly, the thicknesses of the mesoporous shell are tunable by varying the amounts of TEOS and CTAB. This study provides new insight on the preparation of mesoporous materials based on colloidal chemistry.     

(μ‐Tri‐tert‐butoxysilanethiol­ato)­bis[(tetra­hydro­furan)lithium(I)] and catena‐poly[[bis­(μ‐tri‐tert‐butoxy­silanethiol­ato)dilithium(I)]‐μ‐dimethoxy­ethane]: solvent coordination as the structure‐forming factor

The title compounds, μ‐(tri‐tert‐butoxy­silanethiol­ato‐κ²S:S)‐bis[(tetra­hydro­furan‐κO)lithium(I)], [Li₂(C₁₂H₂₇O₃SSi)₂(C₄H₈O)₂], (I), and catena‐poly[[bis­(μ‐tri‐tert‐butoxysilanethiol­ato)‐1:2κ²S;1κS:2κS,O‐dilithium(I)]‐μ‐dimethoxy­ethane‐κ²O:O′], [Li₂(C₁₂H₂₇O₃SSi)₂(C₄H₁₀O₂)]_n, (II), were obtained by the reaction of tri‐tert‐butoxy­silanethiol with metallic lithium. The crude product, when recrystallized from tetra­hydro­furan (THF) yields (I), and when recrystallized from 1,2‐dimethoxy­ethane (DME) gives (II). Compound (I) forms centrosymmetric dimers in the solid state with an Li₂S₂ central core, whereas (II) forms infinitely long chains, in which the centrosymmetric dimeric units are linked together by the bidentate DME ligand (also residing on an inversion centre), thus forming a coordination polymer. The formation of a one‐dimensional structure in (II) is a consequence of replacement of a monodentate THF solvent mol­ecule with a bidentate DME mol­ecule.     

An organic–inorganic hybrid compound containing imidazolium cations and a one‐dimensional lithium hexacyanidocobaltate‐based anionic framework

An organic–inorganic hybrid compound, catena‐poly[bis(3H‐imidazol‐1‐ium) [[tetracyanido‐κ⁴C‐cobalt(III)]‐μ‐cyanido‐κ²C:N‐[diaqualithium(I)]‐μ‐cyanido‐κ²N:C]], {(C₃H₅N₂)₂[CoLi(CN)₆(H₂O)₂]}_n, was synthesized by the reaction of Li₃[Co(CN)₆] with imidazolium chloride in aqueous solution. The compound crystallizes in the monoclinic space group C2/c (data collected at 273 K). In the crystal structure, neighbouring [Co(CN)₆]³⁻ anionic units are linked by Li⁺ cations through the cyanide groups in a trans mode, forming a one‐dimensional zigzag chain structure extending along the c axis. A three‐dimensional supramolecular network is formed through hydrogen‐bonding interactions and is further stabilized by weak CN...π interactions between the cyanide groups and the imidazolium cations.     

The α‐effect in micelles: Nucleophilic substitution reaction of p‐nitrophenyl acetate with N‐phenylbenzohydroxamate ion

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with p‐chlorophenoxide (4‐ClC₆H₄O^?) and N‐phenylbenzohydroxamate (C₆H₅CON(C₆H₅)O^?) ions in phosphate buffer (pH 7.7) at 27°C. The effect of cationic, (CTAB, TTAB, DTAB), anionic (SDS), and nonionic (Brij‐35) surfactants has been studied. The k_obs value increases upon addition of CTAB and TTAB. The effect of DTAB and other surfactants on the reaction is not very significant. The micellar catalysis and α‐effect shown by hydroxamate ion have been explained. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 26–31, 2006