Key Engineering Materials Vol. 571

Abstract: This chapter aims at providing an overview of the potential of layered double hydroxides (LDHs) or hydrotalcite-like compounds (HTs) for contributing to the catalysis of the synthesis of biodiesel through the transesterification of triglycerides. First, the main methods of preparation of HTs and the most relevantfeatures of these materials are presented, with emphasis on their basic properties. Afterwards, the literature on the use of HTs as catalysts, catalysts precursors, and supports of transesterification catalysts is reviewed. HTs are promising materials for the synthesis of biodiesel from refined and waste vegetable oils, showing reasonable resistance to water and free fatty acids but an improvement of the chemical stability under the desired reaction conditions is still necessary.

Abstract: The massive exploitation of modern technology results in increasing demand of energy of the entire world, which has urged extensive research and development in the areas of energy production from non-conventional resources, their storage and distribution. Electrolyte is one of the components in various electrochemical devices, like solar cells, fuel cells, rechargeable battery etc. Besides the conventional liquid electrolytes, polymer based electrolytes gain particular attention because of their solid nature, flexibility and ease of availability. For the last few decades, use of inorganic nanoparticles as additives is one of the most promising ways to improve the electrochemical performance of polymer electrolytes. The resulting nanocomposite polymer electrolytes can display enhanced conductivity, mechanical stability and improved interfacial stability towards electrode materials. This review highlights the recent research efforts given to the nanocomposites systems containing various layered transition metal hydroxides for making solid polymer electrolytes. Also various approaches adopted to understand the ion conduction mechanism of solid polymer electrolytes has also been discussed.

Abstract: Hydrotalcite-like anionic clays have attracted considerable attention in last few decades for their capacity to remove wide range of pollutants from aqueous systems. In this chapter, we discuss our recent studies on synthesis of anionic clays with various compositions (Mg/Al, Zn/Al and Ni/Al) and concentrations and their application for the removal of acid dyes from water. Adsorption efficiencies of the synthesized clays were investigated for the dyes, Acid Blue 113 and Orange II, in aqueous medium. Very high dye uptake capacities were recorded for both the above dyes by using Mg/Al clay (M²⁺: M³⁺ molar ratios 2 and 3) having NO₃^- interstitial ion. Adsorption equilibria data were explained using Langmuir and Freundlich isotherm models, however, Langmuir model fitted better than the Freundlich model. Lagergren first order and pseudo-second order kinetic models were used to explain the dye adsorption kinetics of the pristine clay materials. X-ray diffraction studies of the pristine clays and dye loaded clays indicate both anion exchange and physical adsorption were involved in the Orange II uptake process however, uptake of Acid Blue 113 was solely due to physical adsorption. Influence of solution pH on dye uptake by the clay adsorbents and on equilibrium pH of the solution after adsorption was investigated.

Abstract: Volatile organic compounds (VOCs) are organic chemicals mostly emitted from different sources like industrial or domestic having high vapor pressure at room-temperature conditions. Some of these are also anthropogenic in nature and also these are the major contributor for the photochemical ozone. The different methods available for the abatement of VOCs are thermal oxidation, catalytic oxidation, photocatalytic oxidation, adsorption etc. Due to the stringent regulation of VOCs emission in different countries there is a need of efficient abatement technology to preserve the environment. In this context catalytic combustion of organic pollutants offers considerable advantages over the industrially operated thermal combustion process. Generally, oxidative destruction is possible at low temperature in presence of a catalyst. In addition catalytic process is more energy efficient and can operate with very dilute pollutants. A number of catalysts have been used for the complete oxidation of VOCs, among these Pillared clays type porous materials are also useful for the purpose. Pillared clays have high surface area, pore volume, thermal stability and can be tailor made for particular catalytic application compared with the parent clays. In the present review we will summarize the latest developments on the clay based materials including the effect of different controlling parameters for the synthesis of pillared clay based porous materials and its specific application for the low temperature VOCs decomposition. In particular the effect of transition metals like iron and manganese oxide pillared clay on the VOC decomposition is discussed.

Abstract: There is a large variety of techniques available to protect metals from various types of corrosion. Till date chromate containing metal coatings is one of the most commonly used methods. Layered clays are basically of two types depending on the type of ion exchange capacity. In the recent years different researchers demonstrated the use of such cation/ anionic clays as potential nanocontainers for the inhibitors. These nanocontainers can be used in the coating to induce self-repairing capacity when the coating surface is damaged. Due to the disturbance in the pH and availability of chloride ions clay based nanocontainers can release the inhibitor to protect the surface. In the recent year use of anionic clay like hydrotalcites or layered double hydroxides are much studied in comparison to cationic clay like montmorillonite. This review critically analysed the potential of these clay in the future development of self-healing coating.

Abstract: Controlled drug delivery system is a protocol to develop nanostructures and materials that can efficiently encapsulate drugs at high concentration, cross the cell membrane, and release the drug at the target site in a controlled manner for a prescribed period of time. This system can reduces the patient expenses, and risks of toxicity, while it can increase the drug efficacy, specificity, tolerability and therapeutic index of corresponding drugs. Therefore, construction of stimuli-responsive controlled-release systems is of crucial importance for the development of both fundamental science and clinical medicine. Both natural and synthetic materials have been tested and proposed as components of controlled drug delivery. Clay minerals, synthetic or natural, are an important, widely abundant, and low-cost class of materials with unique swelling, intercalation, adsorption, and ion-exchange properties. The safety proof data of clay minerals clearly suggest them to be non-toxic for transdermal application and oral administration. To accomplish controlled-release systems based on layered clay minerals, one of the best ways is to intercalate organic molecules into the interlayer gallery of clay minerals. Intercalation of organic molecules within the gallery of layered silicates offers a novel route to prepare organic and inorganic hybrids that contain properties of both the inorganic host and organic guest in a single material. In this article we will highlight the applications of clay in pharmaceutics as controlled drug delivery carrier.

Abstract: Methyl isobutyl ketone (MIBK) is one of the most widely produced and used aliphatic ketones worldwide. The one-step MIBK process with no intermediate separation steps using multifunctional catalysts is an important development towards greener organic synthesis and generates tremendous interest among the researcher across the globe. The single step process is facile and more economically viable and has provided opportunity to develop new and improved catalyst systems capable of operating under mild conditions. A widely variety of catalytic systems have been used in one-step process during last three to four decades. The progress in one-pot synthesis of MIBK using different multifunctional catalysts with special reference to layered based catalysts was critically reviewed in this article.

Abstract: The field of nanotechnology is one of the most popular areas for current research and development in virtually all technical disciplines. This obviously includes polymer science and technology. In recent year, researchers have been working on a new scale of reinforcement by incorporating a fine dispersion of clay silicatelayers in the polymer matrix to obtain polymer nanocomposites. Nanoscale layered clays, due to their high aspect ratio and high strength, can play an important role in forming effective polymer nanocomposites. Polymer nanocomposites have received much attention due to its large surface area and very high aspect ratio. Polymer nanocomposites especially rubber based nanocomposites is one of the many composite materials in which researchers and engineers have shown great interest due to their potential to be used in critical applications. Polymer layered silicate (PLS) nanocomposites often exhibit remarkable improvement in materials properties when compared with the virgin polymer or conventional micro and macro composites. These improvements can include high moduli and tear strength, improved heat resistance and electrical properties, decreased gas permeability, swelling to solvents and flammability.