hussein kalo | University Of Bayreuth, Germany (original) (raw)

Papers by hussein kalo

ACS Applied Nano Materials

An entry from the Inorganic Crystal Structure Database, the world's repository for inorganic ... more An entry from the Inorganic Crystal Structure Database, the world's repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The Cambridge Structural Database, 2013

Nanoscale

Functionalization by ion exchange allows synthetic hectorite to delaminate via 1D dissolution in ... more Functionalization by ion exchange allows synthetic hectorite to delaminate via 1D dissolution in N-methylformamide. Mixing with a diacrylate monomer and photopolymerization yields a 1D crystalline nanocomposite coating with improved gas barrier properties.

Langmuir, 2018

Delamination by osmotic swelling of layered materials is generally thought to become increasingly... more Delamination by osmotic swelling of layered materials is generally thought to become increasingly difficult, if not impossible, with increasing layer charge density because of strong Coulomb-interactions. Nevertheless, for the class of 2:1 layered silicates, very few examples of delaminating organo-vermiculites were reported in literature. We propose a mechanism for this repulsive osmotic swelling of highly charged vermiculites based on repulsive counter ion translational entropy that dominates the interaction of adjacent layers above a certain threshold separation. Based on this mechanistic insight, we were able to identify several organic interlayer cations appropriate to delaminate highly charged, vermiculite-type clay minerals. These findings suggest that the osmotic swelling of highly charged organo-clays is a generally applicable phenomenon rather than the odd exemption. ASSOCIATED CONTENT Supporting Information. Layer Charge Determination, Organo-Clays: CHN-Analysis and EDX, Static Light Scattering, Volume Fraction of a Gel and Expected d-spacing, Crystalline Swelling of Clays: d-spacings. This material is available free of charge via the Internet at http://pubs.acs.org.

Angewandte Chemie (International ed. in English), Jan 27, 2017

Separation of gas molecules with similar physical and chemical properties is challenging but neve... more Separation of gas molecules with similar physical and chemical properties is challenging but nevertheless highly relevant for chemical processing. By introducing the elliptically shaped molecule, 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane, into the interlayer space of a layered silicate, a two-dimensional microporous network with narrow pore size distribution is generated (MOPS-5). The regular arrangement of the pillar molecules in MOPS-5 was confirmed by the occurrence of a 10 band related to a long-range pseudo-hexagonal superstructure of pillar molecules in the interlayer space. Whereas with MOPS-5 for CO2 adsorption, gate-opening occurs at constant volume by freezing pillar rotation, for CO the interlayer space is expanded at gate-opening and a classical interdigitated layer type of gate-opening is observed. The selective nature of the gate-opening might be used for separation of CO and N2 by pressure swing adsorption.

Macromolecules, 2017

Flexible transparent barrier films are required in various fields of application ranging from fle... more Flexible transparent barrier films are required in various fields of application ranging from flexible, transparent food packaging to display encapsulation. Environmentally friendly, waterborne polymer−clay nanocomposites would be preferred but fail to meet in particular requirements for ultra high water vapor barriers. Here we show that self-assembly of nanocomposite films into one-dimensional crystalline (smectic) polymer−clay domains is a so-far overlooked key-factor capable of suppressing water vapor diffusivity despite appreciable swelling at elevated temperatures and relative humidity (R.H.). Moreover, barrier performance was shown to improve with quality of the crystalline order. In this respect, spray coating is superior to doctor blading because it yields significantly better ordered structures. For spray-coated waterborne nanocomposite films (21.4 μm) ultra high barrier specifications are met at 23°C and 50% R.H. with oxygen transmission rates (OTR) < 0.0005 cm 3 m −2 day −1 bar −1 and water vapor transmissions rates (WVTR) of 0.0007 g m −2 day −1. Even in the most challenging environments (38°C and 90% R.H.), values as low as 0.24 cm 3 m −2 day −1 bar −1 and 0.003 g m −2 day −1 were found for OTR and WVTR, respectively.

Zeitschrift für anorganische und allgemeine Chemie, 2012

Angewandte Chemie International Edition, 2013

Minerals, 2018

A series of laponites and synthetic OH- and fluorinated hectorites prepared from hydrothermal and... more A series of laponites and synthetic OH- and fluorinated hectorites prepared from hydrothermal and melting experiments at both industrial and laboratory scale were examined with XRD and FTIR (MIR and NIR) to determine their mineralogical composition and possible compositional heterogeneity. The end materials contained both Li- and Na-bearing phases. The industrial hydrothermal OH-smectites prepared at low temperatures consist of random mixed layer hectorite-stevensite-kerolite with about 40–50% hectorite layers, the remaining being stevensite and kerolite at roughly equal proportions. The FTIR spectra of these smectites contain, besides the main Mg3OH stretching/overtone bands at 3695–3690 and 7225–7214 cm−1, respectively, additional OH overtone bands at ~3716 and 7265 cm−1 (hydrated state). These bands might be linked to Mg2LiOH stretching modes. The melt-derived smectites are kerolite-free but still contain stevensite layers, although the preparation methods involved heating in the...

Colloid and Polymer Science, 2020

Clays are not only ubiquitous in nature, but they are also used in huge quantities in a broad ran... more Clays are not only ubiquitous in nature, but they are also used in huge quantities in a broad range of industrial applications, such as thixotropic drilling fluids, ore pelletizers, waste disposal sealants, or fillers in polymer nanocomposites. In order to model environmental processes or to design new materials on a rational base, it is of prime importance to determine and possibly modify the interfacial properties of clay platelets at the solid/electrolyte interface. In this context, the fundamental question rises how far the stoichiometric interlayer charges as determined by the composition of the silicate layer correlates with the diffuse double-layer properties. Here, this question is addressed by means of a series of purposely synthesized sodium 2:1 layered silicates with defined composition and hence interlayer charge densities, respectively. Platelets of layered silicates of large enough diameter to perform AFM colloidal probe measurements were produced by melt synthesis. Fo...

Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung von Schichtsilicat-Plattchen mit... more Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung von Schichtsilicat-Plattchen mit hohem Aspektverhaltnis, ein nach dem erfindungsgemasen Verfahren erhaltliches Schichtsilicat-Plattchen, die Verwendung von erfindungsgemasen Schichtsilicat-Plattchen zur Herstellung eines Verbundmaterials, einer Flammschutzbarriere oder einer Diffusionsbarriere und ein Verbundmaterial umfassend oder erhaltlich unter Verwendung von erfindungsgemasen Schichtsilicat-Plattchen.

Journal of Applied Polymer Science, 2015

Chemical communications (Cambridge, England), Jan 17, 2017

Adsorption studies in microporous organically pillared layered silicates (MOPS) show that precise... more Adsorption studies in microporous organically pillared layered silicates (MOPS) show that precise control of micropore size in the sub-Ångström range is crucial for chiral discrimination. The highly modular character of MOPS generally allows for an optimization of guest recognition without the need to explore different framework topologies.

Langmuir : the ACS journal of surfaces and colloids, Jan 16, 2017

Because of strong Coulomb interactions, the delamination of charged layered materials becomes pro... more Because of strong Coulomb interactions, the delamination of charged layered materials becomes progressively more difficult with increasing charge density. For instance, highly charged sodium fluorohectorite (Na0.6Mg2.4Li0.6Si4O10F2, Na-Hec) cannot be delaminated directly by osmotic swelling in water because its layer charge exceeds the established limit for osmotic swelling of 0.55 per formula unit Si4O10F2. Quite surprisingly, we found that this hectorite at the border of the smectite and vermiculite group can, however, be utterly delaminated into 1-nm-thick platelets with a high aspect ratio (24 000) in a two-step process. The hectorite is first converted by partial ion exchange into a one-dimensionally ordered, interstratified heterostructure with strictly alternating Na(+) and n-butylammonium (C4) interlayers. This heterostructure then spontaneously delaminates into uniform single layers upon immersion in water whereas neither of the homoionic phases (Na-Hec and C4-Hec) swells o...

Journal of the American Chemical Society, Jan 18, 2017

Microporous organically pillared layered silicates (MOPS) are a class of microporous hybrid mater... more Microporous organically pillared layered silicates (MOPS) are a class of microporous hybrid materials that, by varying pillar density, allows for optimization of guest recognition without the need to explore different framework topologies. MOPS are found to be capable of discriminating two very similar gases, carbon dioxide and acetylene, by selective gate-opening solely through quenching pillar dynamics. Contrary to conventional gate-opening in metal organic frameworks, the additional adsorption capacity is realized without macroscopic volume changes, thus avoiding mechanical stress on the framework. Of the two gases studied, only CO2 can accomplish freezing of pillar dynamics. Moreover, the shape of the slit-type micropores in MOPS can easily be fine-tuned by reducing the charge density of the silicate layers. This concomitantly reduces the Coulomb attraction of cationic interlayer space and anionic host layers. Surprisingly, we found that reducing the charge density then alters t...

Angewandte Chemie (International ed. in English), Jan 3, 2016

Ordered heterostructures of layered materials where interlayers with different reactivities stric... more Ordered heterostructures of layered materials where interlayers with different reactivities strictly alternate in stacks offer predetermined slippage planes that provide a precise route for the preparation of bilayer materials. We use this route for the synthesis of a novel type of reinforced layered silicate bilayer that is 15 % stiffer than the corresponding monolayer. Furthermore, we will demonstrate that triggering cleavage of bilayers by osmotic swelling gives access to a generic toolbox for an asymmetrical modification of the two vis-à-vis standing basal planes of monolayers. Only two simple steps applying arbitrary commercial polycations are needed to obtain such Janus-type monolayers. The generic synthesis route will be applicable to many other layered compounds capable of osmotic swelling, rendering this approach interesting for a variety of materials and applications.