Smaller Interlayer Distance Research Articles

To what extent can mutual shifting of folded carbonaceous walls in slit-like pores affect their adsorption properties?

We have performed systematic Monte Carlo studies on the influence of shifting the walls in slit-like systems constructed from folded graphene sheets on their adsorption properties. Specifically, we have analysed the effect on the mechanism of argon adsorption (T = 87 K) and on adsorption and separation of three binary gas mixtures: CO2/N2, CO2/CH4 and CH4/N2 (T = 298 K). The effects of the changes in interlayer distance were also determined. We show that folding of the walls significantly improves the adsorption and separation properties in comparison to ideal slit-like systems. Moreover, we demonstrate that mutual shift of sheets (for small interlayer distances) causes the appearance of small pores between opposite bulges. This causes an increase in vapour adsorption at low pressures. Due to overlapping of interactions with opposite walls causing an increase in adsorption energy, the mutual shift of sheets is also connected with the rise in efficiency of mixture separation. The effects connected with sheet orientation vanish as the interlayer distance increases.

Sulfur-Doped Carbon with Enlarged Interlayer Distance as a High-Performance Anode Material for Sodium-Ion Batteries.

S-doped carbon is investigated as a high-performance anode material for sodium-ion batteries. Due to the introduction of a high-content of S atoms, the as-obtained S-doped carbon shows an enlarged interlayer distance. As an anode, a high specific capacity of up to 303 mAh g-1 is achieved, even after 700 cycles at 0.5 A g-1.

Interlayer Surface Modification of Layered Perovskite HLaNb<sub>2</sub>O<sub>7</sub>·<i>x</i>H<sub>2</sub>O with Diol Compounds Possessing Ethylene Oxide Chains

Grafting reactions between an n-decoxy derivative of ion-exchangeable layered perovskite HLaNb2O7·xH2O and polyethylene glycols (PEGs) with various molecular masses were investigated. X-ray diffraction analysis showed that a reflection corresponding to the interlayer distance of the n-decoxy derivative of HLaNb2O7·xH2O (2.73 nm) disappeared and that new diffraction lines ascribable to smaller interlayer distances, which increased with increases in the molecular mass of PEGs, appeared. The solid-state 13C CP/MAS NMR spectra of the products indicated that ethylene oxide chains were covalently bound to the interlayer surface of HLaNb2O7∙xH2O. The signal assignable the carbons bound to OH groups suggests that the grafting reactions for the formation of Nb-O-C bonds typically involve one of the terminal OH groups in PEGs.

Bandgap opening in silicene: Effect of substrates

Our density functional calculations show that opening a sizeable band gap of silicene without degrading its carrier mobility can be realized by silicene–substrate hybrid structures with noncovalent interface interactions. Several possible two-dimensional semiconducting substrates are selected to find the factors that control the magnitude of band gap. It is found that the more notable charge redistribution in two sublattices of silicene and thus a larger band gap are characterized by a smaller interlayer distance. Thus, the opened band gap in hybrid structures with SiH/π interaction has reached the technique requirement of room-temperature operation in field effect transistors.

Thermal Behavior of the Layered Oxide Li2/3Co2/3Mn1/3O2 Obtained by Ion Exchange from the P2-Type Na2/3Co2/3Mn1/3O2 Phase

Thermal evolution of the layered oxide Li2/3Co2/3Mn1/3O2, showing a T#2 stacking and prepared by a Na/Li ion exchange in P2-Na2/3Co2/3Mn1/3O2, was investigated by thermal analyses and X-ray diffraction. A thermal expansion of the T#2 orthorhombic unit cell is observed from 25 to 350 °C; from 350 °C the T#2 stacking is destabilized to the benefit of an O6-type stacking obtained from the former through slab gliding. The T#2 to O6 phase transformation is allowed to occur from a stacking with larger interlayer distances and the lithium ions in tetrahedral sites to a stacking with smaller interlayer distances and the lithium ions in octahedral sites. This phase transition from T#2 to O6 is reversible, even though its kinetic can be very slow: the thermal treatment of the T#2-type Li2/3Co2/3Mn1/3O2 phase at 450 °C with a quenching in air has shown to stabilize the O6HT-Li2/3Co2/3Mn1/3O2 phase. At temperatures higher than 450 °C, the layered oxide Li2/3Co2/3Mn1/3O2 is gradually decomposed into Li2MnO3 and Co3O4. First electrochemical tests performed in lithium batteries have revealed that O6HT-Li2/3Co2/3Mn1/3O2 delivers as positive electrode material a high reversible capacity of ∼230 mAh·g–1 over two voltage domains around 3 and 4 V vs Li+/Li.

Water confined between sheets of mackinawite FeS minerals

Wet iron-sulfur minerals have been shown to be ideal environments to allow for simple chemical reactions to occur in nature, for instance, in the framework of prebiotic chemistry. Yet, not much is known about such water/mineral interfaces beyond those involving pyrite, FeS(2), which is, however, chemically rather inert. In contrast, mackinawite is chemically reactive and consists of a layered crystal structure comprising FeS sheets that can be easily cleaved. Here, the properties of water confined between such sheets in lamella-like setups is investigated in the spirit of surface science model systems. The properties of this intercalated water are found to depend significantly on the interlayer distance and change from "arrested water" (in the limit of small interlayer distances) to liquid-like behavior.

Local mechanical properties of a hyperswollen lyotropic lamellar phase

The local and slow dynamics of a colloidal particle dispersed in a hyperswollen lyotropic lamellar phase was studied by passive and active microrheological methods. According to observation by a particle-tracking video microscopy, the motion of a particle follows a normal diffusion process in a lamellar phase with a large interlayer distance. However, trap-diffusion motion was also observed for a small interlayer distance. This characteristic motion was discussed by consideration of the time evolution of mean square displacement, the van Hove self-correlation function and the non-Gaussian parameter. These indicate that the dynamics of a particle becomes spatially heterogeneous in a lamellar phase whose interlayer distance is close to the size of the particle. By the measurement of local viscosity using optical tweezers, Newtonian behavior was observed at a high shear rate. In a lamellar phase with a small interlayer distance, non-Newtonian behavior was also observed at a low shear rate. The dependences of effective viscosity on the interlayer distance obtained by both methods are in agreement. The effective viscosity in the lamellar phase was found to be four to five times larger than that of water even for a large interlayer distance. Possible reasons for the increase in effective viscosity are discussed quantitatively.

Exfoliation of a stack of platelets and intercalation of polymer chains: Effects of molecular weight, entanglement, and interaction with the polymer matrix

AbstractExfoliation of a stack of sheets (a model for clay platelets) in a dynamic matrix of polymer chains is investigated by a computer simulation model. How the interplay between the thermodynamics (interaction‐driven) and conformational (structural constraints) entropy affects the exfoliation of sheets is the subject of this study. A stack of four sheets with a small initial interlayer distance constitutes the layer on a discrete lattice. The layered platelets are immersed in a matrix represented by the mobile polymer chains which occupy a fraction (concentration) of the lattice sites. Both sheets and chains are modeled by the bond‐fluctuation mechanism and execute their stochastic motion via Metropolis algorithm. An attractive and a repulsive interaction between the polymer matrix and platelets are considered. Exfoliation of the sheets is examined by varying the molecular weight of the polymer chains forming a dynamic network matrix with various degrees of entanglements. At low‐molecular weight of the polymer, exfoliation is achieved with repulsive interaction and the exfoliation is suppressed with attractive matrix as sheets stick together via polymer mediated interaction introduced by intercalated polymer chains. Increasing the molecular weight of the polymer matrix suppresses the exfoliation of sheets primarily due to enhanced entanglement—at high‐molecular weight (with the radius of gyration of polymer chains larger than the characteristic linear dimension of the platelets), the stacked (layered) morphology is arrested via entropic trapping and exfoliation ceases to occur. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2696–2710, 2008

Structure and melting behavior of classical bilayer crystals of dipoles

We study the structure and melting of a classical bilayer system of dipoles in a setup where the dipoles are oriented perpendicular to the planes of the layers and the density of dipoles is the same in each layer. Due to the anisotropic character of the dipole-dipole interactions, we find that the ground-state configuration is given by two hexagonal crystals positioned on top of each other, independent of the interlayer spacing and dipolar density. For large interlayer distances these crystals are independent, while in the opposite limit of small interlayer distances the system behaves as a two-dimensional crystal of paired dipoles. Within the harmonic approximation for the phonon excitations, the melting temperature of these crystalline configurations displays a nonmonotonic dependence on the interlayer distance, which is associated with a re-entrant melting behavior in the form of solid-liquid-solid-liquid transitions at fixed temperature.

Optical Properties of Porphyrin Chromophores Assembled in Nano-Lamellar Zirconium Phosphate

The supra-molecular assemblies and optical properties of the symmetrical neutral porphyrin chromophore, meso-tetra(4-pyridyl)porphine, bound to a modified α-zirconium phosphate framework have been studied. The interlayer distance of the cetyltrimethylammonium zirconium phosphate framework is 39.6 Å. After the addition of meso-tetra(4-pyridyl)porphine to the framework, the X-ray powder diffraction (XRPD) patterns show that the interlayer distance of the framework is 30.3 Å, demonstrating the formation of novel assemblies. In the framework, organic chromophores are assumed to align in a canted monolayer. The interaction of organic chromophores with the frame-work causes noticeable red shifts of the Soret absorption band from 416 to 427 nm. In contrast, the luminescence peak is blue shifted from 660 nm in aqueous media to 648 nm when mesotetra(4-pyridyl)porphine is bound to the framework. Furthermore, the emission yield of the organic chromophore in the framework is dramatically enhanced compared to that of organic aqueous solutions. The spectroscopic change of meso-tetra(4-pyridyl)porphine is ascribed to the unique microenvironments of the nano-lamellar framework. The juxtaposition of the porphyrin chromophores in the framework tunes their electronic interactions. In comparison, the organic chromophores also attempted to bind with another modified α-zirconium phosphate, n-butylammonium zirconium phosphate. However, the chromophores could not enter into n-butylammonium zirconium phosphate due to its smaller interlayer distance (18.8 Å).

Optical Properties of Porphyrin Chromophores Assembled in Nano-Lamellar Zirconium Phosphate

The supra-molecular assemblies and optical properties of the symmetrical neutral porphyrin chromophore, meso-tetra(4-pyridyl)porphine, bound to a modified alpha-zirconium phosphate framework have been studied. The interlayer distance of the cetyltrimethylammonium zirconium phosphate framework is 39.6 angstroms. After the addition of meso-tetra(4-pyridyl)porphine to the framework, the X-ray powder diffraction (XRPD) patterns show that the interlayer distance of the framework is 30.3 angstroms, demonstrating the formation of novel assemblies. In the framework, organic chromophores are assumed to align in a canted monolayer. The interaction of organic chromophores with the framework causes noticeable red shifts of the Soret absorption band from 416 to 427 nm. In contrast, the luminescence peak is blue shifted from 660 nm in aqueous media to 648 nm when meso-tetra(4-pyridyl)porphine is bound to the framework. Furthermore, the emission yield of the organic chromophore in the framework is dramatically enhanced compared to that of organic aqueous solutions. The spectroscopic change of meso-tetra(4-pyridyl)porphine is ascribed to the unique microenvironments of the nano-lamellar framework. The juxtaposition of the porphyrin chromophores in the framework tunes their electronic interactions. In comparison, the organic chromophores also attempted to bind with another modified alpha-zirconium phosphate, n-butylammonium zirconium phosphate. However, the chromophores could not enter into n-butylammonium zirconium phosphate due to its smaller interlayer distance (18.8 angstroms).

Ab initio study of structural and electronic properties of SrTiO3 (001) oxygen-vacancy surfaces

First-principles calculations are employed to study the surface relaxation and electronic structure of the fully relaxed SrTiO(3) (001) oxygen-vacancy surfaces with both Sr and Ti terminations. In contrast to the perfect surface, the larger surface rumples and smaller interlayer distances have been found. Some in-gap Ti 3d states at about -1.13 eV below the Fermi level were observed in the Ti-terminated surface caused by oxygen vacancies. For the Sr-terminated oxygen-vacancy surface, some in-gap Ti 3d states move into the bulk midgap region to become partially occupied. These theoretical results are in agreement with the experimental data.

Layered Manganese Oxides. Synthesis, Properties, and Applications

AbstractFor Abstract see ChemInform Abstract in Full Text.

Layer stacking implementation of tensor low energy electron diffraction

The introduction of the tensor low energy electronic diffraction (TLEED) approximation greatly enhances the computational efficiency of the scattering calculations required to determine surface structure from electron diffraction data. This increase in efficiency has resulted in complex surface structures being routinely solved. The formalism originally applied to the TLEED methodology requires an initial multiple scattering calculation on a reference structure using the renormalized forward scattering approximation (RFS) to model the multiple scattering in the near surface region of a crystal. However, RFS diverges when the spacing between the atomic planes normal to the surface becomes less than approximately an angstrom. This article describes a TLEED implementation that is based on the Barbieri/Van Hove symmetrized automated LEED package and that incorporates the self-consistent layer stacking approximation for the reference structure. This method does not break down as rapidly as RFS and permits the TLEED approximation to be extended to materials with smaller interlayer distances.

Direct Observation of a Metastable Solid Phase of Mg/Al/CO3-Layered Double Hydroxide by Means of High Temperature in Situ Powder XRD and DTA/TG

In situ XRD measurement of Mg/Al-layered double hydroxide at high temperature reveals that the hydrotalcite-like layered structure, which is stable at room temperature, thermally transforms to a metastable solid phase at 160−200 °C, depending atomic ratio Mg/Al of the layers. This metastable phase has smaller interlayer distance than that of the hydrotalcite-like layered structure and usually disappears at 380 °C. These thermal events are confirmed in DTA/TG measurements.

Far-infrared absorption of acoustic and optical magnetoplasmons in double-layered quantum wires

The far-infrared response of two-layered quantum wires in a perpendicular magnetic field is calculated self-consistently within the Hartree random-phase approximation. It is demonstrated that the oscillator strength of the acoustic mode is strongly enhanced if the lateral confining potential in the two layers is different. In a perpendicular magnetic field it exhibits a splitting in the vicinity of $2{\ensuremath{\omega}}_{c},$ where ${\ensuremath{\omega}}_{c}$ is the cyclotron frequency, similar to the well known Bernstein modes in single-layered quantum wires. For small interlayer distances the acoustic magnetoplasmon shows oscillations which are related to the magnetic depopulation of the one-dimensional subbands.

Magnetic Properties of Metal Halides-Graphite Intercalation Compounds Under Pressure

Abstract Magnetization measurements under pressure of 0–10 kbar have been carried out on GIC's with CoCl2 (stage 1), NiCl2 (stage 2), MnBr2 (stage 3), CrCl3 (stage 3) and biintercalated CrCl3-CoCl2 (pseudo stage 1). For the three former ones, the ordering temperature Tc increases with increasing pressure in agreement with the smaller interlayer distance and the corresponding J' increase. However, for GIC's containing CrCl3, an unexpected decrease of Tc is observed.