Inorganic Layered Research Articles

Toward the Highly Ordered Lamellar Hybrid Membrane for Molecular Sieving by One-Pot Self-Assembly of Hybrid Hyperbranched Polymer

Ordered lamellar hybrid membranes are of great interest, due to their application as functional materials, including molecular sieving, biosensors, optical devices, and drug, as well as gene delive...

Formation processes, size changes, and properties of nanosheets derived from exfoliation of soft layered inorganic-organic composites.

Exfoliation is a general route to obtain two-dimensional (2D) nanomaterials. A variety of methods have been developed for controlled exfoliation of layered materials based on stacking via van der Waals interaction, such as graphite and transition-metal dichalcogenides. On the other hand, rigid layered materials consisting of inorganic layers and interlayer metal ions stacked via electrostatic interaction, such as transition-metal oxides and clays, have a limited number of exfoliation methods. Here we studied a new exfoliation route through formation of soft layered composites. Intercalation of guest organic molecules changed rigid inorganic layered compounds into soft layered composites with stacking via van der Waals interaction. The soft layered inorganic–organic composites were exfoliated into surface-modified nanosheets in organic media. The layered composites showed swelling with dispersion in organic media. The time-course analyses suggest that the layered composites were simultaneously exfoliated in the vertical direction and fractured in the lateral direction. Thinner and smaller nanosheets were obtained with an increase in the exfoliation time. Although the resultant nanosheets gradually aggregated in the colloidal liquid, the original dispersion state was recovered with sonication for 5 min at room temperature. This exfoliation route using soft layered composites can be used in the synthesis and application of a variety of 2D nanomaterials.

Luminescence properties of organic–inorganic layered perovskite-type compounds under vacuum ultraviolet irradiation

We investigated the luminescence properties of organic–inorganic layered perovskite-type compounds under vacuum ultraviolet irradiation. A crystal of (C6H5C2H4NH3)2PbBr4 was fabricated by the poor-solvent diffusion method. Exciton emissions from the inorganic layer were observed at 410 nm under ultraviolet irradiation (excitation wavelengths: 180 and 300 nm). The rise time behavior observed in the luminescence decay curve showed no difference among the excitation wavelengths of 60–300 nm. In addition, no excitation peak of benzene such as an intense peak at 180 nm (1A1g → 1E1u) in the vacuum ultraviolet region was observed in the excitation spectra measured while monitoring the exciton emissions from the inorganic layer. These results indicate that the effect of energy transfer from the organic layer to the inorganic layer has negligible contribution to the luminescence properties of organic–inorganic layered perovskite-type compounds.

Optical properties of Wannier excitons in closely located quantum wells in organic–inorganic layered perovskite-type compounds

We analyzed the optical properties of Wannier excitons in closely located quantum wells in organic–inorganic layered perovskite-type compounds. In the spectra of CnH2n+1NH3X (n = 2, 3, or 4; X = Cl or Br), we observed absorption bands attributed to Wannier excitons. In the case of (C2H5NH3)2PbBr4, two bands were observed in the absorption and luminescence spectra. The two bands are attributed to split Wannier exciton levels arising from the interactions of closely located neighboring quantum wells. Such a split was not observed in the chloride-containing perovskite. This result indicates that the halogens in the inorganic layers have a significant effect on the interactions between the neighboring inorganic layers.

Fabrication of Self-Organized, Two-Dimensional Diluted Magnetic Semiconductors Based on Organic–Inorganic Layered Perovskite-Type Compounds

Abstract We have fabricated diluted magnetic semiconductors (DMSs) based on organic–inorganic layered perovskite-type compounds, in which multiple quantum well structures were formed. DMSs were synthesized by substituting a small fraction of the Pb2+ ions in the inorganic layers with Mn2+ or Cu2+. XRD, ESR, and magnetization results indicate that the samples form mixed crystals. The Mn-doped samples exhibited paramagnetism down to 10 K, whereas the Cu-doped samples exhibited ferromagnetism at temperatures lower than ca. 15 K. In addition, a clear exciton peak was observed in the absorption spectrum of each sample. These results indicate that self-organized DMS quantum wells were successfully fabricated.

Effects of Organic Moieties on Luminescence Properties of Organic–Inorganic Layered Perovskite-Type Compounds

The effects of organic moieties on the luminescence properties of organic–inorganic layered perovskite-type compounds were investigated. Three single crystals were fabricated, namely, (C4H9NH3)2PbBr4 {C4}, (C6H5CH2NH3)2PbBr4 {Ben}, and (C6H5C2H4NH3)2PbBr4 {Phe}. Among the single crystals, the exciton emission of Phe showed the highest quantum efficiencies. The quantum efficiencies of C4 and Ben only were 0.02 and 0.17 times that of Phe, respectively. The radiative and nonradiative decay rates were calculated from the quantum efficiencies and luminescence lifetimes. The relative values of the quantum efficiencies were in accordance with the values of the radiative decay rates. The results indicate that the luminescence properties of the organic–inorganic hybrid compounds may be governed by the excitonic properties of the inorganic layer and not by the concentration of any structural defects. Focusing on the geometry of the inorganic layers, the Pb–Br–Pb bond angles between the adjoining PbBr62– octahedra of each compound were 150° (Ben), 152° (Phe), and 155° (C4). In addition, only Phe showed structural distortion inside the PbBr62– octahedron with Br–Pb–Br bond angles of 171°. The increase in the radiative decay rate can be attributed to the increase in the reduced mass of the excitons from these structural distortions that lead to a decrease in the Bohr radius of the excitons. The results indicate that the luminescence properties of the organic–inorganic hybrid compounds are governed by the structural geometry of the inorganic layer.

Mixed-crystal effect on the scintillation properties of organic–inorganic layered perovskite-type compounds

We investigated mixed-crystal effects on the luminescence and scintillation properties of organic–inorganic layered perovskite-type compounds. The luminescence and scintillation decay accelerated as the iodine content increased. The radiative and non-radiative decay rates under both ultraviolet and X-ray radiation were calculated; quantum efficiency was used under ultraviolet radiation. The radiative decay rate was almost constant with increasing iodine content under both types of radiation; however, the non-radiative decay rate increased with increasing iodine content. These results indicate that the mixed-crystal effects on the luminescence and scintillation properties are governed by non-radiative processes. Besides, the scintillation decay time was longer than the luminescence decay time although the rise times for both profiles were similar, suggesting that the energy transfer from the organic to the inorganic layer had no effect on the scintillation properties. Moreover, these time profiles became similar with increasing iodine content in the inorganic layer. These results suggest that the difference between the two types of decay can be associated with the scintillation process in the inorganic layer.

Klimt artwork: material investigation by backscattering Fe-57 Mössbauer and Raman spectroscopy

The long lost painting “Trumpeting Putto” was discovered and now is not only in the focus of art historian, but has also scientific interest too. We underwent this rare case of an inorganic layered artwork a non-destructive material investigation by employing Raman and MIMOSII Fe-57 Mossbauer spectroscopy. First results indicate several layers, where two layers of different pigments are on an inorganic background layer stabilised by a metallic wire within a wooden frame structure

The Effect of Wannier and Frenkel Exciton Resonance on the Luminescence Properties of Organic–Inorganic Layered Perovskite-Type Compounds

We investigated the optical properties of organic–inorganic layered perovskite-type compounds that contained naphthylmethyl moieties in the organic layer. The Wannier exciton energy in the inorganic layer can be modulated by varying the halogen content. The Wannier or Frenkel exciton emissions in the organic layer were observed in compounds where the exciton energy was lower or higher than that of the triplet energy of the naphthylmethyl moiety, respectively. For the compounds with near-resonant Wannier and Frenkel exciton energies, luminescence was only observed at 490 and 500 nm from the naphthylmethyl moiety while luminescence at 520–566 nm was not detected. This selective quenching of the luminescence can be attributed to an enhancement in oscillator strength of near-resonant transition energies between Wannier and Frenkel excitons.

Accommodating Unwelcome Guests in Inorganic Layered Hosts: Inclusion of Chloranil in a Layered Double Hydroxide

The host-guest chemistry of most inorganic layered solids is limited to ion-exchange reactions. The guest species are either cations or anions to compensate for the charge deficit, either positive or negative, of the inorganic layers. Here, we outline a strategy to include neutral molecules like ortho- and para-chloranil, that are known to be good acceptors in donor-acceptor or charge-transfer complexes, within the galleries of a layered solid. We have succeeded in including neutral ortho- and para-chloranil molecules within the galleries of an Mg-Al layered double hydroxide (LDH) by using charge-transfer interactions with preintercalated p-aminobenzoate ions as the driving force. The p-aminobenzoate ions are introduced in the Mg-Al LDH via ion exchange. The intercalated LDH can adsorb ortho- and para-chloranil from chloroform solutions by forming charge-transfer complexes with the p-aminobenzoate anions present in the galleries. We use X-ray diffraction, spectroscopy, and molecular dynamics simulations to establish the nature of interactions and arrangement of the charge-transfer complex within the galleries of the layered double hydroxide.

Temperature-dependent time-resolved photoluminescence of (C6H5C2H4NH3)2PbX4 (X = Br and I)

This paper describes temperature-dependent time-resolved photoluminescence of two-dimensional organic–inorganic layered perovskite compounds, (C6H5C2H4NH3)2PbX4 (X=Br and I) prepared by solution-based self-assembly. (C6H5C2H4NH3)2PbX4 shows fluorescence from free-exciton even at room temperature. At low temperatures below 90K, the Stokes-shifted fluorescence from bound excitons appears in (C6H5C2H4NH3)2PbI4. In contrast, (C6H5C2H4NH3)2PbBr4 exhibits Stokes-shifted phosphorescence from the triplet excited state to the ground state. The local structure between the organic and inorganic layers plays a prominent role in the formation of triplet excitons.

Lead chloride-based layered perovskite incorporated with an excited state intramolecular proton transfer dye

We successfully fabricated thin films of organic–inorganic layered perovskite-type compound (AEHBA)2PbCl4, where AEHBA stands for N-(2-aminoethyl)-2-hydroxybenzamide, a blue fluorescent dye that shows excited state intramolecular proton transfer (ESIPT) reaction. The formation of its highly ordered structure was readily achieved by the spin-coating of N,N-dimethylformamide solution dissolving PbCl2 and the AEHBA hydrogen chloride salt. X-ray diffraction analysis of the films revealed that organic AEHBA and inorganic PbCl4 perovskite layers were alternately stacked parallel to the substrate. In the absorption spectrum, exciton formation within the perovskite layers was confirmed by the appearance of a characteristic sharp band, while the photoluminescence spectrum showed a large Stokes-shifted band of AEHBA, indicating that it underwent an ESIPT.

Magnetically applicable layered iron-titanate intercalated with biomolecules

We have prepared bio-inorganic nanohybrids consisting of magnetic inorganic nanolayers (iron-titanate) and protein molecules via exfoliation–restacking process in solution. It was found that the protein molecules were electrostatically and spontaneously incorporated into the interlayer space of the inorganic layered structure by adjusting the pH of the solution appropriately. The binding studies demonstrated the high affinity of the iron–titanate nanolayers for the proteins, and the immobilized protein preserved its activity after the hybridization. The catalytic activity measurement and magnetic separation experiment indicate the formation of magnetically applicable inorganic layer–biomolecule nanohybrids. The magnetic layer–biomolecule nanohybrid developed here would be a novel conspicuous material which shows different properties from those of conventional biomolecule-immobilized magnetic particles.

Liquid Crystalline Behavior and Related Properties of Colloidal Systems of Inorganic Oxide Nanosheets

Inorganic layered crystals exemplified by clay minerals can be exfoliated in solvents to form colloidal dispersions of extremely thin inorganic layers that are called nanosheets. The obtained “nanosheet colloids” form lyotropic liquid crystals because of the highly anisotropic shape of the nanosheets. This system is a rare example of liquid crystals consisting of inorganic crystalline mesogens. Nanosheet colloids of photocatalytically active semiconducting oxides can exhibit unusual photoresponses that are not observed for organic liquid crystals. This review summarizes experimental work on the phase behavior of the nanosheet colloids as well as photochemical reactions observed in the clay and semiconducting nanosheets system.

A Computational Study of Gas Molecule Transport in a Polymer/Nanoporous Layered Silicate Nanocomposite Membrane Material

Polymers containing nanoporous, high-aspect-ratio, inorganic layered materials are being investigated as candidates for overcoming the selectivity versus permeability trade-offs imposed by conventional polymeric membranes used in gas separations. We report the first computational investigation of the transport of gas molecules (in particular helium, hydrogen, nitrogen, and oxygen) in a polydimethylsiloxane/porous layered silicate AMH-3 nanocomposite system as a function of its composition, and also study the effects of polymer−inorganic interactions on the polymer dynamics. The performance of the nanocomposite membrane material is found to be substantially enhanced over the polymeric material for certain separations involving the four molecules studied. The transport properties were found to be strongly influenced by the molecular sieving properties of the AMH-3 layer and the segmental mobility of the polymer in confinement between the inorganic layers. A comparison with the resistances-in-series model fo...

PH Sensitive Organic–Inorganic Layered Nanomaterials by Self-Assembly of Indigocarmine Between the Inorganic Layers

New pH sensitive organic-inorganic intercalation compounds having different interlayer spacing were prepared. Zn-Al layered double hydroxide (LDH) is an anion exchangeable inorganic layered compound whose interlayer spacing is 0.76 nm. In the reactions of indigocarmine (IDC) with the calcined Zn-Al LDH at pH = 7 (LDH-IDC7), interlayer spacing increased to 2.25 nm. The interlayer spacing of LDH-IDC7 decreased to 1.89 nm by the treatment in basic solution. In the reaction of IDC with the calcined Zn-Al LDH at pH = 10 (LDH-IDC10), interlayer spacing of the intercalation compounds was 1.89 nm. The interlayer spacing of these intercalation compounds was changed reversibly by the treatments in acidic or basic solution.

Conformation of Methylene Chains in an Intercalated Surfactant Bilayer

Infrared and Raman spectroscopy have been used to establish the conformation and orientation of the methylene “tail” of cetyl trimethylammonium ions intercalated in an inorganic layered host, $CdPS_{3}$. Intercalation, effected by a two-step ion-exchange process leading to the formation of $Cd_{0.83}$$PS_{3}$ $(CTA)_{0.34}$, occurs with a lattice dilation of 26.5 \AA with the surfactant ions within the galleries adopting a bilayer structure. The frequencies of the conformationally sensitive methylene stretching modes in the infrared and Raman spectra indicate that a majority of the bonds in the methylene chain are in a trans conformation. The methylene chains are tilted with respect to the inorganic layer. The tilt angle as determined from orientation-dependent infrared spectra is \sim $35^0$. Although the population of gauche conformers is low, it has been possible to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene chains, by their characteristic frequencies in the infrared spectrum. These high-energy conformers, except for the ones at the chain end, disappear on cooling, leaving on average all 15 methylene units of the intercalated cetyl trimethylammonium ion in trans conformational registry at 40 K. The terminal gauche defects are significant in preventing interdigitation of the low-density intercalated surfactant bilayer.

Surface Characterization of Materials at Ambient Conditions by Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM)

Abstract The creation of a new family of scanning probe techniques is one of the most exciting events in surface analysis in the last decade. The unique results have been achieved with the main representatives of these techniques—scanning tunneling microscopy (STM) and atomic force microscopy (AFM)-in the visualization of topographic and electronic features in the atomic scale. These new methods attracted many research teams. In a relatively short time, surfaces of different materials (metals, semiconductors, inorganic layered compounds, organic layers, single crystals, polymers, and biological objects) were examined by these techniques. This review is based on ambient conditions STM and AFM experiments conducted at the Materials Research Center of Freiburg University. Two main aspects of the results of imaging transition metal chalcogenides and halides, conductive organic salts, and polymers are emphasized. One is related to interpretation of the images, with the separation of the contributions of the electronic and topographic surface features being the main goal. The realization of this aim, which demands the development of theoretical approaches and comparative analysis with the participation of other surface techniques, will contribute strongly to our understanding of the surface properties of materials. The other aspect concerns the accumulation of knowledge about new methods because many important questions of STM and AFM are still open. The backgrounds of STM and AFM are discussed before the experimental results are presented.