Perforated, freely suspended layer-by-layer nanoscale membranes

Ultrathin, perforated, and freely suspended membranes with uniform nanopores in the range of tens of nanometers have been fabricated using a fast, simple method of spin-assisted layer-by-layer assembly on hydrophobic substrates. Membranes with thicknesses down to 20 nm were robust enough to be released from the sacrificial substrates, transferred onto various surfaces, and suspended over microscopic openings. The nanopore size can be controlled by tuning the number of polyelectrolyte bilayers, spinning speed, and a proper selection of hydrophobic substrates. We demonstrate that the formation of nanopores is caused by the partial dewetting of polyelectrolyte layers in the course of their deposition on the underlying hydrophobic surfaces. The nanoscale thickness of perforated membranes with relatively uniform size and a high concentration of nanopores provides perspectives for higher rates of transport through freely suspended LbL membranes. The highly perforated LbL membranes introduced here can serve as a novel platform for ultrafine separation considering an intriguing combination of nanopores, nanoscale membrane thickness, and easy functionalization.     

Mapping the chemistry in nanostructured materials by energy-filtering transmission electron microscopy (EFTEM)

Energy-filtered transmission electron microscopy (EFTEM) can be used to acquire elemental distribution maps at high lateral resolution within short acquisition times, which makes it quite efficient for a detailed characterization of nanostructures, as illustrated with examples concerning a nanostructured substituted La-based cermet compound and a nanoscale multilayer. In the first example, we show how phases in a rapidly cooled substituted LaNi5 can be visualized by recording jump ratio images. Secondly, EFTEM was capable of imaging individual nanoscale layers in a magnetic multilayer consisting of 2 nm terbium and 3 nm iron.     

Sugar-anionic clay composite materials: intercalation of pentoses in layered double hydroxide

The intercalation of non-ionized guest pentoses (ribose and 2-deoxyribose) into the Mg-Al and Zn-Al layered double hydroxides (LDHs) was carried out at 298 K by the calcination-rehydration reaction using the Mg-Al and Zn-Al oxide precursors calcined at 773 K. The resulting solid products reconstructed the LDH structure with incorporating pentoses, and the maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 20 times that by the Zn-Al oxide precursor. The ribose/Mg-Al LDH was observed to have the expanded LDH structure with a broad (003) spacing of 0.85 nm. As the thickness of the LDH hydroxide basal layer is 0.48 nm, the interlayer distance of the ribose/Mg-Al LDH is 0.37 nm. This value corresponds to molecular size of ribose in thickness (0.36 nm), supporting that ribose is horizontally oriented in the interlayer space of LDH. The maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 5 times that of 2-deoxyribose. Ribose is substituted only by the hydroxyl group at C-2 position for 2-deoxyribose. Therefore, the number of hydroxyl group of sugar is essentially important for the intercalation of sugar molecule into the LDH, suggesting that the intercalation behavior of sugar for the LDH was greatly influenced by hydrogen bond between hydroxyl group of the intercalated pentose and the LDH hydroxide basal layers.     

Investigating the Properties of Graphite Oxide Suspension,Films, and Papers Produced from Natural Graphite of Southern Yakutia

An aqueous suspension of graphite oxide (GrO) was prepared from natural Yakut graphite by modified Hummers′ method. The lateral size of GrO flakes varied from 0.1 μm to 10 μm, their thickness was 20 nm. The fabricated suspension, GrO films (of various thickness and on various substrates), and GrO papers were studied in terms of their structural, optical, and electrophysical characteristics. The obtained GrO films are dielectrics with quite large resistance varying from 12.5.10⁶–4.6.10⁹ Ω depending on their thickness. The films are characterized by the luminescence in the region of 380–650 nm, the presence of oxygen-containing groups–ОН,–СООН,–С=О,–СОН, СОО–, and the transparency of 91% for a 20 nm thick film at the wavelength of 670 nm. The conducted study testifies high quality of Yakut graphite, which can be quite easily exfoliated. GrO films possess high resistance and transparency.     

Patterning phase separation in polymer films with dip-pen nanolithography

We report a rapid-prototyping method for controlling nanoscale phase separation and pattern formation in conjugated polymer blend films using Dip-Pen Nanolithography (DPN). We use DPN to generate patterned alkylthiol monolayers with feature sizes down to 50 nm on gold surfaces and show how such patterns can nucleate the formation of lateral domains in blends of poly-3-hexylthiophene (P3HT) and polystyrene (PS) cast from solution. We show that this process can be used to probe phase nucleation at heterogeneous surface sites ranging in size from 50 to 750 nm, and that polymer features smaller than 150 nm in diameter can be achieved. We anticipate this method will be useful for studying polymer film responses to nanoscale surface fluctuations as well as for correlating nanoscale phase separation with optoelectronic processes in organic films used in light-emitting diode and photovoltaic devices.     

Fast Li-ion Storage and Dynamics in TiO2 Nanoparticle Clusters Probed by Smart Scanning Electrochemical Cell Microscopy

Anatase TiO₂ is a promising material for Li-ion (Li⁺) batteries with fast charging capability. However, Li⁺ (de)intercalation dynamics in TiO₂ remain elusive and reported diffusivities span many orders of magnitude. Here, we develop a smart protocol for scanning electrochemical cell microscopy (SECCM) with in situ optical microscopy (OM) to enable the high-throughput charge/discharge analysis of single TiO₂ nanoparticle clusters. Directly probing active nanoparticles revealed that TiO₂ with a size of ≈50 nm can store over 30 % of the theoretical capacity at an extremely fast charge/discharge rate of ≈100 C. This finding of fast Li⁺ storage in TiO₂ particles strengthens its potential for fast-charging batteries. More generally, smart SECCM-OM should find wide applications for high-throughput electrochemical screening of nanostructured materials.     

Photochromogenic nanosheet crystallites of tungstate with a 2D bronze structure

Layered rubidium tungstate, Rb(4)W(11)O(35), with a two-dimensional (2D) bronze-type tunnel structure was successfully delaminated into colloidal nanosheets via a soft-chemical process involving acid exchange and subsequent intercalation of tetrabutylammonium ions. Characterizations by transmission electron microscopy and atomic force microscopy confirmed the formation of unilamellar 2D nanosheet crystallites with a unique thickness of ～3 nm and an average lateral size of 400 nm. The obtained nanosheets exhibited reversible color change upon UV-light excitation via an optical band gap of 3.5 eV. The ultimate 2D aspect ratio favorable for an adsorption of charge-compensating cations to trapped electrons working as a color center is presumably responsible for highly efficient photochromic behavior. Its coloration mainly consists of a broad band at a wavelength of 1800 nm and longer, which is much different from that of the common tungstate nanomaterials. Thus, the chromogenic nanosheet obtained in this study features the intense UV absorption and optically switchable visible-to-IR absorption, which may be useful for window applications such as cutoff filters and heat-absorbing films.     

Interface proximity effects on ionic conductivity in nanoscale oxide-ion conducting yttria stabilized zirconia: an atomistic simulation study

We present an atomistic simulation study on the size dependence of dopant distribution and the influence of nanoscale film thickness on carrier transport properties of the model oxide-ion conductor yttria stabilized zirconia (YSZ). Simulated amorphization and recrystallization approach was utilized to generate YSZ films with varying thicknesses (3-9 nm) on insulating MgO substrates. The atomic trajectories generated in the molecular dynamics simulations are used to study the structural evolution of the YSZ thin films and correlate the resulting microstructure with ionic transport properties at the nanoscale. The interfacial conductivity increases by 2 orders of magnitude as the YSZ film size decreases from 9 to 3 nm owing to a decrease in activation energy barrier from 0.54 to 0.35 eV in the 1200-2000 K temperature range. Analysis of dopant distribution indicates surface enrichment, the extent of which depends on the film thickness. The mechanisms of oxygen conductivity for the various film thicknesses at the nanoscale are discussed in detail and comparisons with experimental and other modeling studies are presented where possible. The study offers insights into mesoscopic ion conduction mechanisms in low-dimensional solid oxide electrolytes.     

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.     

尼龙6/石墨纳米导电复合材料的制备与性能

通过原位插层聚合制备了尼龙 6 /石墨纳米导电复合材料 ,其室温导电渗滤阈值为 =0 75vol% ,远远低于常规导电粒子填充的聚合物复合材料 .当石墨体积分数为 2 0vol%时 ,室温电导率可达 10 -4 S/cm .透射电镜研究表明 :由于石墨经高温膨胀后其片层被剥离导致了片状石墨粒子具有巨大的径厚比 ,经原位插层聚合其片层厚度进一步被剥离为几十个纳米 ,同时原位插层聚合使得石墨粒子能够均匀分散在尼龙 6基体中 ,因而导致了该导电复合材料的低渗滤阈值和高导电性能 .     

Synthesis of gold nanosheets at a liquid/liquid interface using an amphiphilic polyoxometallate/surfactant hybrid photocatalyst

Control of the morphology of gold nanoparticles has received considerable attention because the physical and chemical properties of gold depend significantly on its size and shape. A novel route for obtaining 2-D gold nanostructures has been developed in which chloroaurate ions (AuCl (4)(-)) are reduced at the 2-D interface between water and chloroform using an amphiphilic polyoxometallate (SiW (12)O (40)(4-))/surfactant (dimethyldioctadecylammonium; DODA) hybrid photocatalyst under UV irradiation at room temperature in air. This simple method can readily produce large single-crystalline gold nanosheets (lateral size, ca. 20 microm; thickness, ca. 150 nm).     

Nanoscale Control of Homoepitaxial Growth on a Two‐Dimensional Zeolite

Nanoscale crystal growth control is crucial for tailoring two‐dimensional (2D) zeolites (crystallites with thickness less than two unit cells) and thicker zeolite nanosheets for applications in separation membranes and as hierarchical catalysts. However, methods to control zeolite crystal growth with nanometer precision are still in their infancy. Herein, we report solution‐based growth conditions leading to anisotropic epitaxial growth of 2D zeolites with rates as low as few nanometers per day. Contributions from misoriented surface nucleation and rotational intergrowths are eliminated. Growth monitoring at the single‐unit‐cell level reveals novel nanoscale crystal‐growth phenomena associated with the lateral size and surface curvature of 2D zeolites.     

Facile fabrication and optical property of hollow SnO2 spheres and their application in water treatment

Hollow SnO(2) spheres with smooth surface have been fabricated by a low temperature template-free solution phase route via self-assembly of small nanocrystalline particles. These hollow spheres have a very thin shell thickness of about 10 nm and are built from SnO(2) nanocrystals of an average size of 5.3 nm. The evacuation behavior of inside-out Ostwald ripening can be used to explain the formation of hollow spheres according to results of time-dependent reactions. The cathodoluminescence spectrum indicates a blue shift of the band gap emission peak of SnO(2), originating from quantum confinement effect due to the nanoscale size of SnO(2) particles. The as-prepared SnO(2) hollow spheres were also found to exhibit excellent performance in wastewater treatment.     

Nanometer-size cluster formation in alkali-metal-doped fullerene layers

Kinetic Monte Carlo methods have been used to simulate structural transformations in fullerene layers during electrochemical intercalation with alkali-metal ions (A). Special attention is paid to the thermodynamic stability of the A(x)C(60) phases. The calculations point out a phase separation in the doped fullerene layer into alkali-metal-rich and alkali-metal-depleted areas at room temperature. The final state is represented by two phases which coexist as a stable fine mixture of nanoscale particles. The instability of homogeneous layers has potentially critical impact on their electrical properties and can explain the formation of nanostructures (20-50 nm) at the fullerene-electrolyte interface. Rb(3)C(60) clusters are predicted to be larger than K(3)C(60) ones for equal mean alkali-metal concentrations. Experimental data on electrochemical metal deposition on alkali-metal-doped fullerene substrates-in particular, atomic force microscopy measurements-are also consistent with the model proposed.     

Nanoscale pore morphology and distribution of lacustrine shale reservoirs:Examples from the Upper Triassic Yanchang Formation,Ordos Basin

Pore structure plays an important role in the gas storage and flow capacity of shale gas reservoirs. Fieldemission environmental scanning electron microscopy(FE-SEM) in combination with low-pressure carbon dioxide gas adsorption(CO2GA),nitrogen gas adsorption(N2GA),and high-pressure mercury intrusion(HPMI) were used to study the nanostructure pore morphology and pore-size distributions(PSDs) of lacustrine shale from the Upper Triassic Yanchang Formation,Ordos Basin. Results show that the pores in the shale reservoirs are generally nanoscale and can be classified into four types: organic,interparticle,intraparticle,and microfracture. The interparticle pores between clay particles and organic-matter pores develop most often,l with pore sizes that vary from several to more than 100 nm. Mercury porosimetry analysis shows total porosities ranging between 1.93 and 7.68%,with a mean value of 5.27%. The BET surface areas as determined by N2 adsorption in the nine samples range from 10 to 20 m2/g and the CO2 equivalent surface areas(2 nm)vary from 18 to 71 m2/g. Together,the HPMI,N2 GA,and CO2 GA curves indicate that the pore volumes are mainly due to pores 100 nm in size. In contrast,however,most of the specific surface areas are provided by the micropores. The total organic carbon(TOC) and clay minerals are the primary controls of the structures of nanoscale pores(especially micropores and mesopores). Micropores are predominantly determined by the content of the TOC,and mesopores are possibly related to the content of clay minerals,particularly the illite-montmorillonite mixed-layer content.     

Structures and properties of the ternary thallium chalcogenides Tl2MQ3 (M = Zr, Hf; Q = S, Se)

We have synthesized new compounds of the formula Tl(2)MQ(3), with M = Zr and Hf and Q = S and Se, and studied their crystallographic features, electronic structures and electrical conductivity. These isostructural compounds crystallize in the monoclinic space group P2(1)/m (Z = 2), with unit cell parameters for the representative Tl(2)ZrS(3) of a = 7.9159(10) ?, b = 3.7651(5) ?, c = 10.275(2) ?, and β = 97.476(2)°. The Zr atoms of Tl(2)ZrS(3) are (distorted) octahedrally coordinated by the S atoms, with two such octahedra sharing edges along the c axis and forming infinite double chains running parallel to the b axis. Tl atoms separate these chains from one another along the a and c axes. The Tl atoms are also surrounded by S atoms in a distorted octahedral coordination. The structure may be viewed as alternating layers of Zr/Tl atoms and S atoms, and is therefore a distorted, ordered variant of the α-NaFeO(2) structure type. All atoms are in their standard oxidation states: Tl(+), Zr(4+), S(2-). The sulphide Tl(2)ZrS(3) has a calculated band gap of 1.15 eV, and the selenide Tl(2)HfSe(3) a gap of 0.57 eV. The electrical conductivity values of Tl(2)ZrS(3) and Tl(2)HfSe(3) at room temperature are 7.1 × 10(-6)Ω(-1) cm(-1) and 3.9 × 10(-3)Ω(-1) cm(-1), respectively.     

Kinetics and Mechanism of Dechlorination of o-Chlorophenol by Nanoscale Pd／Fe

IntroductionTherehasbeenagrowinginterestintheuseofzero valentironforthetreatmentofchlorinatedor ganiccompounds(COCs)inwaterandgroundwater .Thestudieshavebeenfocusedonsuchcompoundsascarbontetrachloride ,trichloroethene ,pesticidesandtherelatedcompounds[1— 7] .Whenironisincontactwithalessreductivemetalsuchaspalladiumwhosecomplexhasbeenusedtohydrogenatenitroben zene[8] ,themetalcouplecanformgalvaniccells .ThisledtothediscoveryofaPd/Febimetalliccomplexofwhichpalladiumservesasacatalystandironasa…     

粒度对石墨负极材料嵌锂性能的影响

研究了不同粒径（13～80 μm）石墨材料作为锂离子电池负极材料的嵌锂性能.结果表明，石墨粒度大小对嵌锂性能有明显影响，石墨的不可逆容量随着粒径的减小而逐渐增大，当粒径从80 μm减小到13 μm时，其不可逆容量增大了10％.而对可逆容量来说，随着粒径的减小，可逆容量逐渐增大;当粒径减小到20 μm时，可逆容量达到最大;再进一步减小石墨颗粒的粒径，可逆容量则随之减小.这表明石墨颗粒过大或过小都不利于锂离子的可逆脱嵌，只有合适的粒度才能最大限度地可逆脱嵌锂离子.根据不同粒度石墨的比表面的变化趋势，阐述了嵌锂性能随粒度变化的原因.     

Atomistic insights into the conversion reaction in iron fluoride: a dynamically adaptive force field approach

Nanoscale metal fluorides are promising candidates for high capacity lithium ion batteries, in which a conversion reaction upon exposure to Li ions enables access to the multiple valence states of the metal cation. However, little is known about the molecular mechanisms and the reaction pathways in conversion that relate to the need for nanoscale starting materials. To address this reaction and the controversial role of intercalation in a promising conversion material, FeF(2), a dynamically adaptive force field that allows for a change in ion charge during reactions is applied in molecular dynamics simulations. Results provide the atomistic view of this conversion reaction that forms nanocrystals of LiF and Fe(0) and addresses the important controversy regarding intercalation. Simulations of Li(+) exposure on the low energy FeF(2) (001) and (110) surfaces show that the reaction initiates at the surface and iron clusters as well as crystalline LiF are formed, sometimes via an amorphous Li-F. Li intercalation is also observed as a function of surface orientation and rate of exposure to the Li, with different behavior on (001) and (110) surfaces. Intercalation along [001] rapid transport channels is accompanied by a slight reduction of charge density on multiple nearby Fe ions per Li ion until enough Li saturates a region and causes the nearby Fe to lose sufficient charge to become destabilized and form the nanocluster Fe(0). The resultant nanostructures are fully consistent with postconversion TEM observations, and the simulations provide the solution to the controversy regarding intercalation versus conversion and the atomistic rationale for the need for nanoscale metal fluoride starting particles in conversion cathodes.     

层状钒青铜纳米片的制备及其锂离子电池阳极材料性能

室温下, 在水溶液中将铵根离子和水分子插入到商用V₂O₅纳米颗粒的层间, 制得了层状的钒青 铜[(NH₄)₂V₆O₁₆·H₂O]纳米片. 该纳米片的尺寸为2~10 μm, 厚度为50~250 nm. 与商用V₂O₅纳米颗粒相比, (NH₄)₂V₆O₁₆·H₂O纳米片用作锂离子电池(LIBs)的阳极材料时, 其性能得到较大提升, 包括大的可逆放电容量 (0.1 A/g时为1148 mA·h/g)、 出色的循环性能(循环70圈后在0.1 A/g时具有1002 mA·h/g的高容量)和高倍率性能(在0.1 A/g时具有1070 mA·h/g的可逆性能). 研究结果表明, (NH₄)₂V₆O₁₆·H₂O纳米片可以作为锂离子电池优良的阳极材料, 也有望应用于其它(如钠离子电池和锌离子电池等)可再充电电池.