Adsorption of Cr(VI) and Se(IV) from their aqueous solutions onto Zr4+-substituted ZnAl/MgAl-layered double hydroxides: effect of Zr4+ substitution in the layer

Abstract

Hydrotalcite-like compounds (layered double hydroxides, LDHs) containing varying amounts of Al3+, Zr4+, and Zn2+ or Mg2+ in the metal hydroxide layer have been synthesized and characterized by various physicochemical methods. The adsorption behavior of uncalcined (as-synthesized) and calcined LDHs have been investigated for Cr2O72− and SeO32−. The mixed oxides, obtained on calcination at 450 °C, exhibit high adsorption capacities for Cr2O72− (1.6–2.7 meq/g) and SeO32− (1.1–1.5 meq/g), where adsorption occurs through rehydration. Substitution of Zr4+ in the LDHs, for either M2+ or Al3+ ions, increases the adsorption capacity up to 20%, thus providing an alternative way to enhance the adsorption capacity of this type of material. The high adsorption capacity of these materials could be successfully used for removal of undesirable anions from water and also for synthesis of intercalated materials with tailored acidobasicity.