ABSTRACT
Recently, LDH compounds have been investigated worldwide due to their remarkable ability in the elimination of various toxic materials from the environment. In this period to date, a variety of LDHs were synthesized by fine tuning of synthetic parameters. LDHs with varied chemical combinations were attempted by using divalent and trivalent metal cation ratios, along with suitably intercalated anions that result in the formation of a diverse range of inorganic-organic assemblies with desirable physical and chemical properties. Significant advancements have been evident in the research and development of LDHs and their application in resolving environmental problems. For instance, the use of LDHs in membrane fabrication has been extensively studied (Liu et al. 2014; Dong et al. 2015; Liu et al. 2015). Recently, Liu et al. (2014) employed hydrotalcite material for
the preparation of a nanofiltration membrane that efficiently separates organic matter from aqueous media. The admirable performance of LDHs in photocatalyst-assisted degradation of pollutants was examined by several researchers (Yuan et al. 2009; Parida and Mohapatra 2012; Alanis et al. 2013; Prince et al. 2015). Parida and Mohapatra (2012) have reported enhanced photocatalytic activity of a novel carbonate-intercalated LDH catalyst for the degradation of the azo dyes methyl violet and malachite green under solar light, with a high decolorization efficiency of 99% within 2 h. Li and Duan (2006), in their extensive review, described potential applications of LDHs in various ion-exchange and adsorption studies. The rich interlayered chemistry of LDHs suggests great scope for anion-exchange reactions with great vigor. LDHs offer tremendous capacity as anion exchangers, due to the presence of highly labile anions in their interlayer region. This characteristic property further assists in the elimination of undesirable or toxic anions from aqueous phase through exchange with other nonhazardous anions. Miyata (1983) and Yamaoka et al. (1989) gave a comparative list of ion selectivities for monovalent and divalent anions, respectively, in the following order, given as
NO Br Cl OH3 − − − −< < < (10.1)
SO CrO HAsO HPO CO4 2
This list further helps in the synthesis of typical LDH compounds intercalated with the desired anions, which can easily replace targeted anions from effluents. Radha et al. (2005) have attempted the exchange of nitrate anions with chloride ions of NaCl solution from the gallery region of LDH at an initial pH solution value of 12. An interesting investigation was carried out by Costantino and coworkers (Costantino et al. 2014) in which the ion-exchange properties of LDH toward halide ions were investigated. The selectivity of carbonate-intercalated LDHs toward the halides were found to decrease with an increase of the halide−ionic radius, and the selectivity order was analyzed as F− > Cl− > Br− > I−. Thus, LDHs play a momentous role as ion exchangers. Additionally, appealing textural characteristics, such as a high surface area, good porosity, and the presence of a large number of active sites, impelled researchers to explore the potential of LDHs as adsorbents. LDHbased adsorbents exhibited enormous potential to remove a wide range of organic, inorganic, and microbial contaminants from water and wastewater. Undeniably, LDH compounds have proved to be of great importance in dealing with pollution problems; more specifically, their role in dealing with water pollution is highly commendable. In this chapter, attempts have been made to address the vital aspects of LDHs, including their composition, structure, different methods of synthesis, and characterization; moreover, special focus has been directed toward the interpretation of the interaction behavior of LDHs with various pollutants present in the liquid phase.
