Structural characterization of azoic dye hosted layered double hydroxides

Abstract The removal of methyl orange (MO) from an aqueous solution was performed using layered double hydroxides (LDHs) in a move to develop cleaning processes of effluents contaminated with dye molecules. The intercalation of the guest anionic MO species into host M II /Al III LDHs differing by the nature of the divalent cations (M II = Mg, Ni or Zn) was achieved by anionic exchange of the initially NO 3 – present in the interlayer space and led to MO/LDH intercalation compounds. The exchange process was followed by XRD and UV-visible absorption spectroscopy at different stages. Almost all MO in solution is uptaken by the Mg-containing LDH in the concentration range corresponding to its anionic exchange capacity (AEC). A lower exchange is reached with the Ni- and Zn-containing LDHs, for which the diffusion of MO is limited due to a larger crystallite size. MO–Zn/Al LDH intercalation compounds exhibit the highest crystallinity and display a remarkable stacking of the layers at maximal MO exchange. This behaviour can be assigned to the higher intrinsic charge density of the host layers in agreement with its lower M II /Al III molar ratio (Zn II /Al III ≈ 1.5 whereas Mg II /Al III and Ni II /Al III = 2). The maximum amount of MO retained by the different LDHs is higher for Mg-containing LDH, than for Ni- and Zn-containing LDH, reaching respectively 1.15, 0.84 and 0.77 g/g.