Synthesis of layered double hydroxide nanosheets in an aqueous solvent and their Ni²⁺ uptake characteristics

Two-dimensional (2D) nanomaterials have drawn widespread attention because of their unique physical characteristics compared to three-dimensional materials. Delamination and nanosheet formation of layered composites are necessary for 2D nanomaterials. Layered double hydroxides (LDH) exhibit anion exchange properties that can be maximized using different methods such as organic modifications and crystal growth control; delamination is one such method. Delamination of LDH render them in the form of nanosheets, which could not be expressed as interlayers, allowing them to exhibit physical properties completely different from those of bulk LDH. Herein, we propose a novel synthesis method to delaminate LDH in an aqueous solvent. In this method, heat reflux is used to break interlayer hydrogen bonds in the LDH, and the remaining hydrogen bonds are broken using ultrasonic treatment. Finally, we dispersed the material in the solvent to obtain LDH nanosheets. We compared the delamination of Mg[sbnd]Al LDH intercalated with lactate (lactate•Mg–Al LDH) and Mg[sbnd]Al LDH intercalated with NO₃⁻ (NO₃·Mg–Al LDH) in an aqueous solvent. Furthermore, we used the nanosheets obtained from NO₃·Mg–Al LDH and described their Ni²⁺ uptake characteristics. Our results show that without using organic solvents, we could delaminate lactate•Mg–Al LDH and NO₃·Mg–Al LDH by applying the proposed method. The lactate•Mg–Al LDH had approximately ten Mg[sbnd]Al LDH host layers, whereas the corresponding nanosheets had three Mg[sbnd]Al LDH host layers. NO₃·Mg–Al LDH had 14–15 Mg–Al LDH host layers, whereas the corresponding nanosheets had 2–3 Mg–Al LDH host layers. Furthermore, NO₃·Mg–Al LDH and its nanosheets could adsorb Ni²⁺ in an aqueous solvent. Thus, Ni²⁺ uptake capabilities were enhanced by delaminating NO₃·Mg–Al LDH to fabricate nanosheets.