Efficient Capture of Heavy Metal Ions and Arsenic with a CaY-Carbonate Layered Double-Hydroxide Nanosheet

Abstract

Nanosheets consisting of two-dimensional (2-D) nanomaterials made up of Ca²⁺ (Ca), and Y³⁺ (Y) cations and carbonate [CO₃ ^2-] anions in the interlayer with a uniform thickness and lengths of around 10 μm have been successfully synthesized in a hydrotalcite layer structure, otherwise known as a layered double hydroxide, using a facile hydrothermal method. The resulting CaY-CO₃ ^2- layered double-hydroxide (LDH) materials demonstrate outstanding affinity and selectivity for toxic transition metal ions such as Cr³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺, and Hg²⁺ as well as metalloid As³⁺. The adsorption of all of the highly toxic metal ions from the aqueous solution was found to be exceptionally rapid and highly selective, with more than 95% removal achieved within 30 min. For AsO₃, a strong adsorption potential of 452 mg/g was observed at pH 7.0, which is better than most values previously reported. The distribution coefficient K _d values can exceed ∼10⁶ mL/g for Cr³⁺, Pb²⁺, and As³⁺, which are highly toxic. The fabricated materials have excellent chemical stability: they retain their well-defined lamellar shapes even under mildly acidic conditions.