Review of the synthesis methods of layers of double hydroxide and theirapplication in removing water pollutants

In recent decades, a class of anionic clays known as layered double hydroxides (LDHs) orhydrotalcite-like compounds (HTlc) has attracted substantial attention. The structure of LDHs isthe intercalation of anions in the hydrated interlayer regions. Double layer hydroxides belong to agroup of clay minerals, that have physical and chemical properties very close to clay minerals andare known as anionic clays. These compounds are obtained naturally and synthetically. LDHs canbe represented by the general formula[M۲۱-X.M۳X(OH)X+] (Anx/n).mH۲O where M۲+ and M۳+ aredivalent and trivalent cations, respectively; the value of x is equal to the molar ratio ofM۳+/(M۲++M۳+), whereas A is the interlayer anion of valence n. The identities of M۲+, M۳+, x, andAn may vary over a wide range, thus giving rise to a large class of isostructural materials withvaried physicochemical properties. LDHs exist as naturally occurring minerals, they are alsorelatively simple and economical to synthesize. LDHs have relatively weak interlayer bondingand, as a consequence, exhibit excellent ability to capture organic and inorganic anions. The mostinteresting properties of LDHs include large surface area, high anion exchange capacity (۲–۳meq/g) that is comparable to those of anion exchange resins, and good thermal stability. LDHshave been studied for their potential use in a wide range of important areas, i.e. catalysis,photochemistry, electrochemistry, and polymerization, considerable interest in using LDHs toremove environmental contaminants since environmental pollution has emerged as an importantissue in recent decades. Significant progress has been achieved in the research and developmentof LDHs’ application in environmental protection, such as their use as environmental catalysts inremoving organic and inorganic wastes. Indeed, increasing interest has recently been diverted toevaluating the ability of LDHs to remove inorganic contaminants such as oxyanions (e.g. arsenite,chromate, phosphate, selenate, borate, nitrate.) and monoatomic anions (e.g. fluoride, chloride,bromide, and iodide) from aqueous solutions by the process of adsorption and ion exchange [۱].This review article provides an overview of LDH synthesis methods and LDH characterizationtechniques.

کلیدواژه ها:

Layered Double Hydroxides ، Brucite-like Sheets ، Anionic Clays