Recently, layered double oxides (LDHs) have received considerable attention due to their potential technological applications. Layered double hydroxides consist of stacked brucite-type [Mg(OH)2] octahedral layers with water molecules and anions occupying the space between the layers, often called the gallery or interlayer region. The role of the interlayer anions is to compensate the excess positive charge due to the partial substitution of trivalent cations for divalent ions. The general formula of the LDHs can be written as follows: [M~(2+)_((1-x))M~(3+)_x(OH)~2]A~(n-)x/n·mH2O, where M~(2+) and M~(3+) represent the divalent and trivalent cations, respectively, and A~(n-) designates the interlayer anion. The stability of the structure is provided by hydrogen bonds between the hydroxyl groups of the inorganic sheets and the intercalated species: anions and water molecules. Arsenic is a notoriously toxic element. In aqueous systems arsenic is dominated by the As(V) oxyanions, H2AsO~-_4 and HASO_4~(2-), at neutral pH. AI-LDHs were primarily investigated as adsorbents of arsenic. Although the iron oxides have high adsorption capacity, Fe-LDHs have been studied by only a few researchers. Moreover, adsorption mechanisms of arsenate by Fe-LDH have not been investigated sufficiently.
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