Effect of Different Surface-charged Lamellar Materials on Swelling Properties of Nanocomposite Hydrogels

This study investigated the effect of different surface-charged lamellar materials on the swelling and diffusion properties of synthesized polyacrylamide-methylcellulose hydrogels (HG). Montmorillonite and hydrotalcite thermally activated at two different temperatures (300 and 550 ºC) were incorporated in the preparation of nanocomposite (NC) hydrogels. A series of NC hydrogels were prepared by varying the lamellar material content (1:1, 2:1 and 4:1). The results showed that the HG with hydrotalcite (550 ºC) was strongly dependent on the ionic intensity, and that the swelling degree increased by 50%, 65% and 78% with reducing the hydrotalcite content at (1:1), (2:1) and (4:1), respectively. The water absorption capacity of HG containing montmorillonite or hydrotalcite (300 ºC) was slightly affected when the pH decreased from 7 to 3. However, the pH variation from 7 to 10 increased the water absorption capacity of most HG, except those containing hydrotalcite (550 ºC) at (2:1) and (4:1). The presence of lamellar nanoparticles in hydrogels made the polymer matrix more rigid, and less likely to absorb water. In contrast, HG with hydrotalcite (550 ºC) at (2:1) and (4:1) showed anomalous behavior with an increase in their water absorption capacity. The results support that the developed NC-HG can be suitable candidates for applications as controlled released materials.

Two Spectroscopies as Main Source for Investigation of Polymer-Clay Materials

In the recent years the synthesis and characterization of nanomaterials has been one of the most efficacious way to produce new materials with improved or completely new properties. The polymer-clay nanocomposites are one of the most interesting nanomaterials with the possibility to create a myriad of new materials with many applications. Lamellar materials are classified as two-dimensional (2D), because there are formed by platelets piled up in one crystallographic direction, as the graphite and clays. The synthesis of controlled dimensional nanostructures as well as the characterization of the intrinsic and potentially peculiar properties of these nanostructures are central themes in nanoscience. The study of different nanostructures has great potential to test and understand fundamental concepts about the role of particle dimensionality on their physicochemical properties. Among the various materials studied in the literature, undoubtedly, polymer-clay materials, especially conducting polymers with smectite clays, such as montmorillonites (MMT) are of particular note. Our group have paid many efforts in the characterization of nanomaterials by using powerful spectroscopic techniques to study both the guest and host in case of inclusion compounds, nanofibers, carbon allotropes or many phases present in polymer-clay nanocomposites. There are two central questions that it was possible to address in this study: (i) the molecular structure of the polymer is drastically changed inside the interlayer cavity of clay and (ii) by using the appropriate synthetic or heating route is possible to change the molecular structure of the confined polymer. In the follow lines, it is briefly told the main aspects of resonance Raman and X-ray absorption spectroscopies in the study of polymer-clay nanocomposites.

Ultrahigh strength and ductility in newly developed materials with coherent nanolamellar architectures

Nano-lamellar materials with ultrahigh strengths and unusual physical properties are of technological importance for structural applications. However, these materials generally suffer from low tensile ductility, which severely limits their practical utility. Here we show that markedly enhanced tensile ductility can be achieved in coherent nano-lamellar alloys, which exhibit an unprecedented combination of over 2 GPa yield strength and 16% uniform tensile ductility. The ultrahigh strength originates mainly from the lamellar boundary strengthening, whereas the large ductility correlates to a progressive work-hardening mechanism regulated by the unique nano-lamellar architecture. The coherent lamellar boundaries facilitate the dislocation transmission, which eliminates the stress concentrations at the boundaries. Meanwhile, deformation-induced hierarchical stacking-fault networks and associated high-density Lomer-Cottrell locks enhance the work hardening response, leading to unusually large tensile ductilities. The coherent nano-lamellar strategy can potentially be applied to many other alloys and open new avenues for designing ultrastrong yet ductile materials for technological applications.

The anisotropic optical properties of different polytypes (ε, β, δ, γ) of GaSe lamellar materials

In this paper, we have calculated the optical properties of the different polytypes of GaSe lamellar materials. The calculations are based on the DFT method and is performed using the CASTEP code. All optical properties have been studied in a domain that extends energetically from 10 meV to 35 eV and have been measured for a polarization // and ⊥ with the c axis. A strong anisotropic was observed, which indicates that the optical properties of the GaSe material are essentially determined by the symmetry of a single layer, exactly by the symmetry resulting from the stacking of the layers. Moreover, the absorption starts in the UV–vis spectral range, the peaks appear in the UV range. The refractive index values are nxx = 2.54, 2.55, 2.88, 10.85, nzz = 3.90, 3.90, 3.26, 11.73 for ε, β, γ, δ, respectively at zero photon energy. Furthermore, we notice that the optical properties of different polytypes (ε, β, δ, γ) of GaSe lamellar materials are obtained both in the ultraviolet field or in the visible domain are significant and give a strong argument for the use of these materials in various applications, namely photovoltaic cells, nanoelectronic, optoelectronic, optical fiber and photo-catalytic applications.

Inorganic and Hybrid (Organic–Inorganic) Lamellar Materials for Heavy metals and Radionuclides Capture in Energy Wastes Management—A Review

The energy industry (nuclear, battery, mining industries, etc.) produces a large quantity of hazardous effluents that may contain radionuclides (137Cs and 90Sr in particular) and heavy metals. One of the hardest tasks of environmental safety and sustainable development is the purification of wastewater holding these pollutants. Adsorption is one of the most powerful methods for extracting toxic compounds from wastewater. This study reviews the usefulness of clay minerals as adsorbent for removing these hazardous elements to clean up energy production processes. Phyllosilicates are able to extract several heavy metals from effluent, as widely examined. A particular focus is given to synthetic phyllosilicates and their abilities to entrap heavy metals with a special attention paid to those synthesized by sol-gel route. Indeed, this method is attractive since it allows the development of organic–inorganic hybrids from organosilanes presenting various functions (amino, thiol, etc.) that can interact with pollutants. Regarding these pollutants, a part of this review focuses on the interaction of lamellar materials (natural and synthetic phyllosilicates as well as layered double hydroxide) with heavy metals and another part deals with the adsorption of specific radionuclides, cesium and strontium.