1. Introduction
Layered double hydroxides (LDHs) are represented by the
chemical formula [M2þ 1exM3þ x(OH)2](Ane)x/n∙mH2O, where Ane is an anion and x is the M3þ/(M2þ þ M3þ) molar ratio (0.20 x 0.33) [1e3]. A LDH consists of a stack of M3þ-bearing brucite-like octahedral layers, in which some of the M2þ ions have been replaced by M3þ ions