Adsorption of SeO₄²⁻ by delaminated Mg-Al layered double hydroxide nanosheets

Layered double hydroxides (LDHs) are excellent anion-exchange materials, and are useful in adsorbing hazardous anions. The LDHs form nanosheets upon delamination, which improves their efficiency. In this study, we investigated the SeO₄²⁻ adsorption properties of the nanosheets obtained by the delamination of NO₃⋅Mg-Al LDH in an aqueous solution and compared them with those of the NO₃⋅Mg-Al LDH. The SeO₄²⁻ adsorption by both substances was a “pseudo-second-order rate reaction”. The reaction-rate constant during the early stage was greater for the nanosheets as their surface area was larger than the NO₃⋅Mg-Al LDH. The amorphous nanosheets reverted to an ordered LDH structure after the anion exchange. Atomic force microscopy (AFM) imaging and the corresponding height profile analysis of the samples confirmed the nanosheets stacking post SeO₄²⁻ adsorption. We propose a mechanism of the SeO₄²⁻ adsorption by the NO₃⋅Mg-Al LDH nanosheets. These findings may improve the understanding of the anion exchange by the LDHs, which may lead to the development of high-efficiency materials that extract metals such as Se from wastewater.