This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymerization and melt intercalation. The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5 wt.%, such as increased Young’s modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy.

Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials

Application of low-cost adsorbents for dye removal – A review

http://dns2.asia.edu.tw/~ysho/YSHO-English/1000%20WC/PDF/App%20Cla%20Sci15,%2011.pdf

Polymer-layered silicate nanocomposites: an overview

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Applications of hybrid organic–inorganic nanocomposites

Rising atmospheric levels of carbon dioxide and the depletion of fossil fuel reserves raise serious concerns about the ensuing effects on the global climate and future energy supply. Utilizing the abundant solar energy to convert CO2 into fuels such as methane or methanol could address both problems simultaneously as well as provide a convenient means of energy storage. In this Review, current approaches for the heterogeneous photocatalytic reduction of CO2 on TiO2 and other metal oxide, oxynitride, sulfide, and phosphide semiconductors are presented. Research in this field is focused primarily on the development of novel nanostructured photocatalytic materials and on the investigation of the mechanism of the process, from light absorption through charge separation and transport to CO2 reduction pathways. The measures used to quantify the efficiency of the process are also discussed in detail.

Photocatalytic reduction of CO2 on TiO2 and other semiconductors.

In this article, the authors review the studies on the photofunctions of intercalation compounds. (The structures and properties of host materials which have been used for immobilizing photoactive species have been summarized in the following section.) some of these studies are for the purpose of characterizing the properties of host materials and host-guest systems, and others are for the purpose of contributing to future practical applications. The well-defined layered structures as well as the ability to accommodate guest species on the surface of the layers are very useful for organizing photoactive species to evaluate and control the photofunctions. Table 1 summarizes the characteristics of typical host-guest systems studied for immobilizing photoactive species. Attention is mainly focused on the role of layered structure on the organization of photoactive species; the photofunctions of intercalation compounds are discussed only in connection with the microscopic structures. 321 refs.

Photofunctions of intercalation compounds

Organic compounds can interact with clay minerals by i) adsorption at the external surfaces, ii) adsorption at the external and internal surfaces, iii) by exchange of exchangeable ions at the external surfaces, iv) by exchange of exchangeable ions at the external and internal surfaces, and v) by grafting reactions with silanol and aluminol groups leading to covalent bonds. Kaolin minerals intercalate only are a limited number of compounds whereas the reactions of 2:1 clay minerals, in particular smectites and vermiculites, are very manifold. Special attention is given to the interaction with neutral organic molecules such as alcohols, fatty acids, amines, amino acids, aromatic compounds, macrocyclic compounds, and nuclein bases. The interaction with complexes and dyes also provides the basis of advanced applications of clay minerals. Binding of long chain alkylammonium ions is a fundamental reaction for hydrophobising clay mineral particles as needed in many applications. The interaction of clay minerals with polymers including proteins is not only an actual field of research but also of practical importance. Organo-clay minerals are used as effective adsorbents. As these materials also adsorb solvent molecules together with the adsorptive, the adsorption process must be considered as adsorption from binary solution which, therefore, is also described in this chapter.

Clay mineral-organic interactions

Recent developments in the study of the intercalation of organoammonium ions into layered silicates are reviewed. The new developments of the applications of the organoammonium-exchanged layered silicates include the selective adsorption of toxic compounds from water, the immobilization of photo and electroactive species to construct novel photo and electrofunctional materials, and the complexation with organic polymers for the enhancement of the mechanical properties. The conversion of the layered solids to three dimensional nanoporous solids with novel microstructures and adsorptive properties has also been successfully done. The novel controlled properties achieved by the modification with the adsorption of organoammonium ions open new opportunities to tailor the properties of the inorganic-organic nanostructured materials.

Preparation of Inorganic–Organic Nanocomposites through Intercalation of Organoammonium Ions into Layered Silicates

Formation of Novel Oriented Transparent Films of Layered Silica-Surfactant Nanocomposites

Hydrotalcite was synthesized by a homogeneous precipitation method utilizing urea hydrolysis. When the homogeneous aqueous solutions containing magnesium chloride, aluminum chloride, and urea were heated, hydrotalcite particles were obtained. Scanning electron micrographs revealed that the products were well-defined hydrotalcite particles. The particle sizes have been controlled from ca. 2 to 20 μm by the reaction temperature and the concentration of the reactants. The particle morphology of hydrotalcite was retained even after thermal decomposition, showing the possible application of the present well-defined hydrotalcite particles for the preparation of layered double hydroxide intercalation compounds by the reconstruction method.

Makoto Ogawa

Papers

Photofunctions of intercalation compounds

Clay mineral-organic interactions

Preparation of Inorganic–Organic Nanocomposites through Intercalation of Organoammonium Ions into Layered Silicates

Formation of Novel Oriented Transparent Films of Layered Silica-Surfactant Nanocomposites

Homogeneous precipitation of uniform hydrotalcite particles