Encapsulation of Functional Organic Compounds in Nanoglass for Optically Anisotropic Coatings

A novel approach is presented for the encapsulation of organic functional molecules between two sheets of 1 nm thin silicate layers, which like glass are transparent and chemically stable. An ordered heterostructure with organic interlayers strictly alternating with osmotically swelling sodium interlayers can be spontaneously delaminated into double stacks with the organic interlayers sandwiched between two silicate layers. The double stacks show high aspect ratios of >1000 (typical lateral extension 5000 nm, thickness 4.5 nm). This newly developed technique can be used to mask hydrophobic functional molecules and render them completely dispersible in water. The combination of the structural anisotropy of the silicate layers and a preferred orientation of molecules confined in the interlayer space allows polymer nanocomposite films to be cast with a well‐defined orientation of the encapsulated molecules, thus rendering the optical properties of the nanocoatings anisotropic.     

水化Na-蒙脱石和Na/Mg-蒙脱石的分子动力学模拟

利用分子动力学方法(MD)研究了Na-蒙脱石和Na/Mg-蒙脱石层间的补偿阳离子和水分子的结构及扩散性质. 模拟结果表明, 在一定水含量范围内Na-蒙脱石和Na/Mg-蒙脱石表现出不同的膨胀形式, 特别是层间水分子数目在48～72之间时, Na/Mg-蒙脱石的层间距比Na-蒙脱石有较为明显的增大. Na/Mg-蒙脱石两层水化物的层间水分子与Mg2+形成了明显的两层水合壳; 而与Na+只形成了一层平面的水合壳. 在Na/Mg-蒙脱石中, Na+和 Mg2+的扩散方式不同, Na+的扩散范围相对更广, 自扩散系数更大. Na/Mg-蒙脱石比相同水含量下的Na-蒙脱石层间水的自扩散系数小. 由于Mg2+和Na+对层间结构的强烈影响, 从而使有少量Mg2+取代Na+的Na/Mg-蒙脱石与Na-蒙脱石表现出不同的膨胀性质和层间物质的扩散性质.     

Formability and properties of self-standing clay film by montmorillonite with different interlayer cations

Influences of exchangeable interlayer cations were investigated on self-standing film formability, film morphology, and properties of the clay films such as flexibility and gas barrier property. Ion-exchanged montmorillonite samples were prepared by a cation exchange from naturally bearing cation, mostly Na⁺, to Li⁺, Mg²⁺, Ca²⁺, Al³⁺, and Fe^{2+, 3+}. Self-standing films were prepared from aqueous colloidal dispersions of these montmorillonite samples with no additives. The montmorillonite samples with monovalent or divalent cation formed flat self-standing films while the Al-montmorillonite sample produced a distorted film. The Fe-montmorillonite sample formed many separated reddish-brown rod-shaped pieces. Clay film microstructures were different with interlayer cations. The films with monovalent interlayer cations were constructed by the stacking of units with delicately waved thin clay sheets in the whole film, but other films show different morphologies between the upper side and lower side; the upper side is laminated with thin sheets; the lower side is laminated with large thick sheets.The self-standing films’ flexibility and gas barrier property differed according to the interlayer cations. These properties were good in cases of samples with monovalent cations. The innumerable short wave and sheet thinness are considered to foster good flexibility and gas barrier properties. The differences in film formability and properties of the films are attributable to different swellability among samples with different interlayer cations. The montmorillonite samples with monovalent cations swell sufficiently by water, but those with polyvalent cations swell poorly. In the latter case, clay crystals aggregate in water, then the aggregate grows into large particles, creating a film with large particles.     

A (31) P NMR Investigation of the CoPi Water-Oxidation Catalyst

Beneath the sheets: (31) P?NMR data suggests that phosphates are liberated freely in the interlayer of a cobalt-hydroxide water-oxidation catalyst. The cobalt-hydroxide sheets are separated by an interlayer region with water, counterions and phosphate, which help to shuttle protons as the layer develops charge.     

Dependence of the Properties of 2D Nanocomposites Generated by Covalent Crosslinking of Nanosheets on the Interlayer Separation: A Combined Experimental and Theoretical Study

Covalently cross-linked heterostructures of 2D materials are a new class of materials which possess electrochemical and photochemical hydrogen evolution properties. It was of considerable interest to investigate the role of interlayer spacing in the nanocomposites involving MoS₂ and graphene sheets and its control over electronic structures and catalytic properties. We have investigated this problem with emphasis on the hydrogen evolution properties of these structures by a combined experimental and theoretical study. We have linked MoS₂ based nanocomposites with other 2D materials with varying interlayer spacing by changing the linker and studied their hydrogen evolution properties. The hydrogen evolution activity for these composites decreases with increasing linker length, which we can link to a decrease in magnitude of charge transfer across the layers with increasing interlayer spacing. Factors such as the nature of the sheets, interlayer distance as well as the nature of the linker provide pathways to tune the properties of covalently cross-linked 2D material rendering this new class of materials highly interesting.     

Effect of temperature on the conformation of dibenzotropone adsorbed on montmorillonites

The nature of the adsorption complex formed between dibenzotropone (DBT) and montmorillonite at elevated temperatures is strongly dependent on the interlayer cations. This was shown by electronic and IR spectra, by X-ray diffraction, and by study of the effects of gradual heating of the samples on these analyses. All samples exhibited significant red shifts of the electronic spectra of DBT into the visible range. These red shifts are attributed to two factors, both contributing to the enhancement of the tropylium planar character of DBT: hydrogen-bonding of acidic interlayer water to the carbonyl group, imparting positive charge to the tropone ring; and π interactions between the aromatic moiety and the oxygen planes. The position of the maximum was temperature-dependent for Cu-, Ni-, Al- and Fe-montmorillonites, for which heating (100°) under vacuum increased the red shift. The organic molecule assumes a planar conformation and is oriented parallel to the clay layers. IR spectra confirming this conformational orientation of DBT are discussed. The basal spacings of the DBT montmorillonite associations depend on the number of water and DBT sheets present in the interlayers. Layers with one or two sheets of DBT and with up to two sheets of water could be distinguished, leading to a maximum spacing of 20.4 Å.     

Intercalation of paracetamol into the hydrotalcite-like host

Hydrotalcite-like compounds are often used as host structures for intercalation of various anionic species. The product intercalated with the nonionic, water-soluble pharmaceuticals paracetamol, N-(4-hydroxyphenyl)acetamide, was prepared by rehydration of the Mg-Al mixed oxide obtained by calcination of hydrotalcite-like precursor at 500 °C. The successful intercalation of paracetamol molecules into the interlayer space was confirmed by powder X-ray diffraction and infrared spectroscopy measurements. Molecular simulations showed that the phenolic hydroxyl groups of paracetamol interact with hydroxide sheets of the host via the hydroxyl groups of the positively charged sites of Al-containing octahedra; the interlayer water molecules are located mostly near the hydroxide sheets. The arrangement of paracetamol molecules in the interlayer is rather disordered and interactions between neighboring molecules cause their tilting towards the hydroxide sheets. Dissolution tests in various media showed slower release of paracetamol intercalated in the hydrotalcite-like host in comparison with tablets containing the powdered pharmaceuticals.     

In situ polymerization of the 4-vinylbenzenesulfonic anion in Ni-Al-layered double hydroxide and its molecular dynamic simulation

This paper describes a systematic study on the thermal polymerization of both pristine 4-vinylbenzenesulfonic anion (VBS) and intercalated VBS in the two-dimensional (2D) gallery of Ni-Al layered double hydroxide (VBS/Ni-Al-LDH), by virtue of combining experimental and theoretical investigations. In situ FT-IR, in situ high-temperature X-ray diffraction (HT-XRD), UV-vis absorption spectroscopy, TG-DTA and elemental analysis were used to study the polymerization process, and it was found that the polymerization of VBS/Ni-Al-LDH occurs at ca. 150-170 degrees C, at least 40 degrees C lower than that of the pristine VBS, indicating that the layered structure of LDH is favorable for thermal polymerization of VBS. Therefore, this layered inorganic material may have potential application as a "molecular reactor" for enhancing the efficiency of polymerization reaction. Furthermore, the sheet-like polymerization product was obtained with the LDHs lamella as template. For better understanding the structure and arrangement of intercalated VBS and the polymerization product between the layers of Ni-Al-LDH, molecular dynamics (MD) simulation method was employed. The simulation results of hydration energies show that there are two relatively stable stages upon the increase of the number of interlayer water molecules. VBS molecules exhibit a tendency from tilted to vertical orientation with respect to the layers as the interlayer water content increases. Compared with the experimental results, the calculated interlayer spacing is more severely affected by interlayer water content. Finally, a typical tetramer product of VBS intercalated LDH was studied and the simulated equilibrium interlayer spacing is consistent with the experimental result of in situ HT-XRD. Based on the combination of experimental and theoretical studies on the interlayer polymerization system, the aim of this work is to deeply investigate the differences in thermal polymerization process between pristine monomers and intercalated ones in the gallery of LDHs, and to give detailed information of the arrangement and swelling behavior of guest molecules confined between the sheets of host layers.     

Delamination of Na-montmorillonite particles in aqueous solutions and isopropanol under shear forces

Delamination of montmorillonite (Na-MMT) is an outstanding property of the dispersed MMT particles. Na-MMT particles delaminated in water and isopropanol under shear forces have been studied in this work. The difference in the intercalation and delamination of Na-MMT by water and isopropanol was studied by molecule dynamic simulation and experiment. Molecule dynamic simulation was carried out on Material Studio (MS) 8.0. The experimental study was performed on a Na-MMT through the measurements of Stokes size, optical size, scanning electron microscope, atomic force microscope, and dynamic molecule simulation. The results demonstrated that under the effect of interlayer hydration, the Na⁺ that resides near the siloxane surface was moved to the middle plane of interlayer space, and the interlayer spacing was opened 1.38A. Compared with the interlayer hydration, the interlayer spacing was increased only a little (0.32A) treated by isopropanol; meanwhile, the interlayer sheets were joined together by isopropanol molecule. Because of that the effect of water and isopropanol in the interlayer of Na-MMT was totally different, the Na-MMT particles were indeed delaminated into plate-like super fine particles in water instead of in isopropanol, and delamination was closely correlated with shear force only if hydration was occurred in the interlayer.     

Molecular recognitive adsorption of aqueous tetramethylammonium on the organic derivative of Hiroshima University Silicate-1 with a silane coupling reagent

Hiroshima University Silicate-1 (HUS-1), composed of silicate sheets with a halved sodalite cage and the interlayer tetramethylammonium (TMA) cation in the cage, was modified with dimethyldichlorosilane to form the organic derivative in which a dimethyl group was grafted onto the interlayer surface and a part of the TMA was removed, and the silylated HUS-1 effectively and selectively adsorbed TMA from water even in the presence of aqueous phenol.     

Voltammetric,dynamic light scattering (DLS) and electrophoretic mobility characterization of FeS nanoparticles (NPs) in different electrolyte solutions

Voltammetric response of FeS nanoparticles (NPs) dispersion based on the oxidation exchange voltammetric peak between Hg electrode and FeS NPs at around ?0.45 V was studied in different electrolytes (chloride, acetate, perchlorate). Several experiments were designed to monitor in parallel to voltammetric measurements, physicochemical and surface characteristics of the formed FeS NPs (ζ-potential and size) under same experimental conditions. It was shown that recorded voltammetric peak produced by FeS NPs from bulk solution is changing with electrolyte concentration and composition, as well as observed size and ζ-potential of the studied FeS NPs. Our measurements indicate relationship between measured ζ-potential of FeS NPs dispersions and recorded voltametric peak charge and potential, pointing to a promising potential of voltammetry in characterization of physicochemical and surface chemistry features of metal sulphide NPs in water environment. The best voltammetric response is obtained in presence of small NPs, <100 nm.     

Photoluminescence and electrochemical investigation of curcumin-reduced graphene oxide sheets

This paper reports on a novel low-temperature method for preparing curcumin-reduced graphene oxide (Cur-rGO) from graphene oxide (GO) and investigates their cyclic voltammetry (CV) and photoluminescence (PL) properties. GO sheets were synthesized using modified Hummers’ method and then were chemically reduced using polyphenol curcumin into graphene sheets. Atomic force microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to confirm the formation of Cur-rGO and revealed their functionalization with polyphenol curcumin. The electrochemical and optical properties of the Cur-rGO sheets were investigated using CV and PL spectroscopy. According to the PL and CV characterization for the Cur-rGO sheets, charges and resonant energy were transferred from curcumin molecules to the GO sheets’ surfaces. This arises from the bonding of the fluorescence curcumin molecules to the Cur-rGO surfaces, through π–π stacking of their aromatic rings. It should be noted that curcumin molecules act as electron donors, suppressing the fluorescence of the GO sheets while improving their electrochemical activities.     

Controllable corrugation of chemically converted graphene sheets in water and potential application for nanofiltration

A combination of AFM, SEM and permeation experiments suggests that the amplitude of corrugation of chemically converted graphene (CCG) sheets in water can be readily controlled by hydrothermal treatment, leading to a new class of permeation-tuneable nanofiltration membranes.     

Tuning the Interlayer Spacings in Dry Graphene Oxide Membranes via Ions

We show the experimental achievement of dry GO membranes with interlayer spacings in the range from 7.09 Å to 8.72 Å, tuned and fixed by salts. We found that the interlayer spacings were dominated by the anions or the groups with negative charges in between the GO membranes. Density functional theory (DFT) calculations reveal that the highly efficient tuning of the interlayer spacing in dry GO membranes is due to ion‐π interactions on the graphene sheets, together with the steric effects of anions in between the GO sheets. The findings are helpful for extending their potential applications including chemical sensors, nanomaterial devices preparation, chemical catalysis and synthesis, and gas separation.     

Microscopic structures of adsorbed cationic porphyrins on clay surfaces: molecular alignment in artificial light-harvesting systems

The intercalation behavior of cationic porphyrin derivatives within the interlayer spaces of nano-layered clay minerals has been investigated. The porphyrins were successfully intercalated by the newly adopted method of repeated freeze-thaw cycles. The absorption spectra of the porphyrins were compared in the solution phase, adsorbed onto the exfoliated clay nano-sheets, intercalated within the interlayer spaces of clay sheets dispersed in water and intercalated in dry films. Substantial red shifts of the λ_max values in the absorption spectra of the porphyrins were observed on the exfoliated clay sheets, and further red shifts were induced within the interlayer space. The dry films of the intercalated samples exhibited the largest red shifts. X-ray diffraction studies revealed that the clearance space between the layers in these intercalated hybrid compounds is only large enough for the porphyrins to be rigidly packed parallel to the clay layer. For the exfoliated clay nano-sheets, theoretical calculations were carried out on the correlation between the dihedral angle of the meso-substituted pyridiniumyl plane vs. the porphyrin ring and the λ_max of the porphyrin Soret band. An extrapolation of the experimental λ_max value to the correlation curve, afforded the dihedral angle to be 61.6°. The microscopic structure of the adsorbed state of the cationic porphyrins on the exfoliated clay nano-sheets was, thus, proposed to involve an orientation parallel to the clay surface, with a distance of 0.15 nm from the surface, which implies the expulsion of the solvent water molecules.     

Capture of double-stranded DNA in stacked-graphene: giving new insight into the graphene/DNA interaction

Colloidal chemically converted graphene sheets (CCGs) are able to contact with each other to form stable self-assembled stacked-CCGs via salt "invasion", which can serve as powerful building blocks for capturing double-stranded DNA.     

Determination of FeS(2) in Venezuelan laterites after a sulphurization process

A technique is presented for determination of FeS(2) in Venezuelan laterites after a sulphurization process. The determination is based on a reaction with water followed by a turbidimetric determination of sulphate ions in solution. The effect of the reaction time and of the particle size is investigated. Data are given showing the precision to be better than 3%, and the accuracy was studied by preparation of a series of synthetic samples of FeS(2), FeS and Venezuelan laterite.     

Synthesis and photoluminescent properties of titanate layered oxides intercalated with lanthanide cations by electrostatic self-assembly methods

Various lanthanide cations were intercalated into the interlayer of the exfoliated H(x)Ti((2-x)/4)) square(x/4)O(4) x H(2)O (HTO) by the electrostatic self-assembly deposition (ESD) and layer-by-layer self-assembly (LBL) methods. X-ray diffraction and thermal analysis data indicated that interlayer lanthanide cations existed as an aqua ion and were coordinated with 7-10 water molecules under ambient conditions. The interlayer distances were found to be in the range 6-7 Angstrom for HTO layered oxide intercalated with a lanthanide cation. Intercalation of lanthanide cations into the interlayer by the LBL method was monitored by UV-vis spectrum and X-ray diffraction. Photoluminescence properties were also discussed in detail. Eu(3+) intercalated layered oxide exhibited intense red emission at room temperature. The presence of interlayer water molecules was found to be inevitable for the emission with high intensity. The emission intensity was significantly higher for the films conditioned at 100% RH than those at 5% RH. The icelike behavior of the confined water molecules in the interlayer around lanthanide cations was believed to be contributing highly to the emission mechanism. The mechanism was illustrated and explained by data obtained under several conditions.     

An interlayer model for the complex dielectric constant of composites

The complex dielectric constant of a composite with an interlayer was studied as a function of the volume fractions and the properties of the filler, the interlayer, and the matrix. The theoretical approach is analogous to the calculation of the shear modulus, the bulk modulus, and the termal expansivity of particulate filled polymers using the interlayer model (IM).An analytical expression describing the influence of an interlayer on the generalized dielectric constant of the composite as a function of the volume fraction and interlayer properties is derived.In the case of a composite with non-conductive constituents, the equations for static and oscillatory electric fields are similar. When conductive constituents are present, the complex dielectric constants have to be replaced by the generalized complex dielectric constants.For a composite of non-conductive materials, without interlayer, the obtained relation reduces to the classical Rayleigh equation. In the case of a composite with conductive constituents, also without interlayer, the complete solution of Wagner's theory is found. Special attention has been paid to the case of a water interlayer in a glass-bead filled non-conductive matrix material.     

Amine‐Assisted Syntheses of Carbonate‐Free and Highly Crystalline Nitrate‐Containing Zn‐Al Layered Double Hydroxides

Zn‐Al layered double hydroxides (LDHs), with nitrate as the charge balancing anion in the interlayer space, were synthesized by precipitation from homogeneous solution containing different amines [e.g., hexamethylenetetraamine (HMTA), diethylenediamine (DEDA), trimethylamine (TMA) and dimethylamine (DMA)]. The applied method does not require nitrogen atmosphere. The solution pH and concentration of different amines were varied in order to identify the controlling parameters and whether nitrate or carbonate are the interlayer anion. Particularly, the addition of amines turns out to be an effective tool for the synthesis of nitrate containing Zn‐Al LDHs independent from the nitrogen atmosphere. The structure, textural, composition, and morphological properties were investigated using the powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA), FT‐IR spectroscopy, and scanning electron microscopy (SEM). The analyses showed that the samples had high crystallinity and purity. The NO₃‐ZnAl LDHs samples show that LDH sheets are predominantly smooth textured and the thickness of LDH sheets are found to be around 23 nm. The results also indicate that this method successfully produces a NO₃^– form Zn‐Al LDH that is almost identical to the one synthesized by conventional methods.