Enhanced adsorption of bromate from aqueous solutions on ordered mesoporous Mg-Al layered double hydroxides (LDHs).

An ordered mesoporous Mg-Al layered double hydroxide (meso-LDH350) with a fairly high Brunauer-Emmett-Teller (BET) surface area (126m2g-1) has been facilely synthesized and then evaluated for the adsorptive removal of bromate from aqueous solutions. Adsorbents were characterized by a variety of techniques (e.g., XRD, FTIR, SEM, TG-DSC, N2 physisorption, XPS, etc.). The adsorption studies indicated that the presence of background electrolytes and competitive anions can obviously repress the uptake of bromate on LDHs. The adsorption isotherms agree well with the Langmuir model, giving a maximum adsorption capacity of 59.34mgg-1 (pH 7.5, 10°C) for meso-LDH350, which is much higher than other LDH-type adsorbents reported in literature. The adsorption kinetic data can be well fitted with the pseudo-second-order rate model. Based on the macroscopic and microscopic studies, bromate adsorption on meso-LDH350 was associated with two mechanisms: the reconstruction of the layered structures of meso-LDH350 and the anion-exchange between bromate and the intercalated anions.