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.