Ni-Al layered double hydroxides modified with citrate, malate, and tartrate: Preparation by coprecipitation and uptake of Cu2+ from aqueous solution

We report on aqueous Cu2+ uptake by Ni-Al layered double hydroxides (Ni-Al LDHs) modified with citrate (C6H5O73-), malate (C4H4O52-), and tartrate (C4H4O62-) anions via coprecipitation. Dropwise addition of a mixed aqueous solution of Ni(NO3)(2) and Al(NO3)(3) to the respective organic acid solutions at a constant pH of 7.0-9.0 afforded LDHs with intercalated C6H5O73- and Ni(C6H5O7)-, C4H4O52-, and C4H4O62- in their interlayers. The anions were also likely adsorbed on the LDH surface. Citrate. Ni-Al LDH could rapidly take up Cu2+ at a constant pH of 5.0, mainly via chelation by the intercalated and adsorbed anions, rather than coprecipitation with dissolved Al3+ to form Cu-Al LDH. By contrast, malate and tartrate were not active as chelating agents, probably because they formed bridges between brucite-like layers by direct coordination of the two -COO- groups with Al3+ in those layers. (C) 2011 Elsevier Ltd. All rights reserved.