Nanosheets consisting of two-dimensional (2-D) nanomaterials made up of Ca2+ (Ca), and Y3+ (Y) cations and carbonate [CO32–] 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–CO32– 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 Kd 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.