Synthesis and reversible hydration behavior of the thiosulfate intercalated layered double hydroxide of Zn and Al

The thiosulfate-intercalated layered double hydroxide of Zn and Al undergoes reversible hydration with a variation in the relative humidity of the ambient. The hydrated and dehydrated phases, which represent the end members of the hydration cycle, both adopt the structure of the 3R1 polytype. In the intermediate range of relative humidity values (40-60), the hydrated and dehydrated phases coexist. The end members of the hydration cycle adopt the structure of the same polytype, and vary only in their basal spacings. This points to the possibility that all the intermediate phases have a kinetic origin. © 2013 Elsevier Inc

Relative humidity-​induced reversible hydration of sulfate-​intercalated layered double hydroxides

Layered double hydroxides (LDH) are extremely important materials for industrial processes. In the environment, LDH physicochem. behavior depends in large part on their hydration state, but characterization of these hydration effect on their properties is incomplete. This work examd. interpoly-​type transitions induced by variations in ambient humidity among LDH. The cooperative behavior of intercalated water mols. resulted in a sudden, single-​step, reversible dehydration of the [Zn-​Cr-​SO4] LDH. The [Zn-​Al-​SO4] LDH provided an interesting contrast with: the coexistence of hydration cycle end-​members at a 40-​20​% relative humidity range during the dehydration cycle; and a random inter-​stratified intermediate in the hydration cycle. These observations showed the [Zn-​Al-​SO4] LDH offered sites with a range of hydration enthalpies, where at crit. hydration levels (20-​40​%)​, non-​uniform swelling of the structure resulted in an inter-​stratified phase. Domain size variation during reversible hydration was also responsible for differences obsd. in hydration vs. the dehydration pathways. This behavior was attributed to distortion in the OH-​ array which departs from hexagonal symmetry due to cation ordering as shown in structure refinement by the Rietveld method. This distortion was much less in [Zn-​Cr-​SO4] LDH, where the nearly hexagonal OH-​ array offered sites of uniform hydration enthalpy for intercalated water mols. On this case, all water mols. experienced the same force of attraction and dehydrated reversibly in a single step. Changes in basal spacing were also accompanied by interpoly-​type transitions involving rigid translations of metal hydroxide layers relative to one another

In Depth Insights into the Key Steps of Delamination of Charged 2D Nano Materials

Delamination is a key step to obtain individual layers from inorganic layered materials needed for fundamental studies and applications. For layered van-der-Waals materials like graphene the adhesion forces are small allowing for mechanical exfoliation, whereas for ionic layered materials like layered silicates the energy to separate adjacent layers is considerably higher. Quite counter intuitively, we show for a synthetic layered silicate (Na0.5-hectorite) that a scalable and quantitative delamination by simple hydration is possible for high and homogeneous charge density, even for aspect ratios as large as 20000. A general requirement is the separation of adjacent layers by solvation to a distance where layer interactions become repulsive (Gouy-Chapman length). Further hydration up to 34 nm leads to the formation of a highly ordered lamellar liquid crystalline phase (Wigner crystal). Up to 8 higher-order reflections indicate excellent positional order of individual layers. The Wigner crystal melts when the interlayer separation reaches the Debye length, where electrostatic interactions between adjacent layers are screened. The layers become weakly chargecorrelated. This is indicated by fulfilling the classical Hansen-Verlet and Lindeman criteria for melting. We provide insight into the requirements for layer separation and controlling the layer distances for a broad range of materials and outline an important pathway for the integration of layers into devices for advanced applications

Nematic suspension of a microporous layered silicate obtained by forceless spontaneous delamination via repulsive osmotic swelling for casting high-barrier all-inorganic films

Exploiting the full potential of layered materials for a broad range of applications requires delamination into functional nanosheets. Delamination via repulsive osmotic swelling is driven by thermodynamics and represents the most gentle route to obtain nematic liquid crystals consisting exclusively of single-layer nanosheets. This mechanism was, however, long limited to very few compounds, including 2:1-type clay minerals, layered titanates, or niobates. Despite the great potential of zeolites and their microporous layered counterparts, nanosheet production is challenging and troublesome, and published procedures implied the use of some shearing forces. Here, we present a scalable, eco-friendly, and utter delamination of the microporous layered silicate ilerite into single-layer nanosheets that extends repulsive delamination to the class of layered zeolites. As the sheet diameter is preserved, nematic suspensions with cofacial nanosheets of ≈9000 aspect ratio are obtained that can be cast into oriented films, e.g., for barrier applications

On Arrangements of Orthogonal Circles

In this paper, we study arrangements of orthogonal circles, that is, arrangements of circles where every pair of circles must either be disjoint or intersect at a right angle. Using geometric arguments, we show that such arrangements have only a linear number of faces. This implies that orthogonal circle intersection graphs have only a linear number of edges. When we restrict ourselves to orthogonal unit circles, the resulting class of intersection graphs is a subclass of penny graphs (that is, contact graphs of unit circles). We show that, similarly to penny graphs, it is NP-hard to recognize orthogonal unit circle intersection graphs.Comment: Appears in the Proceedings of the 27th International Symposium on Graph Drawing and Network Visualization (GD 2019

Estableciendo una interfaz ciencia-gestión-sociedad para la conservación de la biodiversidad y el bienestar humano en la Amazonia: el caso de Madre de Dios, Perú

El objetivo de esta investigación transdisciplinaria fue establecer las bases para una interfaz ciencia-gestión-sociedad para la conservación ambiental y el desarrollo sostenible en Madre de Dios, Perú mediante: (1) la identificación y la caracterización de los actores de la conservación de la biodiversidad y el bienestar humano; (2) el análisis de los puntos de vista de los actores sobre las principales tendencias del desarrollo en la región; y (3) un proceso de involucramiento de los actores desde la academia, el gobierno y la sociedad civil. Los métodos usados incluyeron visitas de campo, entrevistas a expertos, un mapeo detallado de actores, una encuesta a actores y un taller participativo multiactor. El mapeo de partes interesadas identificó a 16 categorías de actores clave dentro de los usuarios directos de los recursos de la tierra, los usuarios indirectos de los recursos de la tierra, el sector público, la sociedad civil y las organizaciones de investigación. Según los actores encuestados, la debilidad de las instituciones gubernamentales y la corrupción son unas de las causas subyacentes a los problemas ambientales y sociales en Madre de Dios, y en particular de la minería aurífera y otras actividades extractivas ilegales e informales. El estudio resaltó también el potencial innovador que existe en la región, que ha sido el hogar de varias iniciativas exitosas para la naturaleza y la gente en las últimas décadas