Functionalized layered double hydroxide with nitrogen and sulfur co-decorated carbondots for highly selective and efficient removal of soft Hg and Ag ions.

A facile composite was fabricated via direct assembly of nitrogen and sulfur co-decorated carbon dots with abundant oxygen-containing functional groups on the surface of the positively charged layered double hydroxide (N,S-CDs-LDH). The novel N,S-CDs-LDH demonstrates highly selective bindings (M-S) and an extremely efficient removal capacity for soft metal ions such as Ag and Hg ions. N,S-CDs-LDH displayed a selectivity order of Ag> Hg >> Cu >>> Pb > Zn > Cd for their adsorption. The enormous capacities for Hg (625.0 mg g) and Ag (714.3 mg g) and very high distribution coefficients (K) of 9.9 × 10 mL g (C = 20 mg L) and 2.0 × 10 mL g (C = 20 mg L) for Hg and Ag, respectively, place the N,S-CDs-LDH at the top of LDH based materials known for such removal. The adsorption kinetic curves for Hg and Ag fitted well with the pseudo-second order model. For Hg and Ag, an exceptionally rapid capture with removal ∼100% within 80 min was observed (C = 30 mg L and V/m ratio of 1000). The adsorption isotherms were well described using Langmuir isotherm. The N,S-CDs-LDH was successfully applied to highly efficient removal of Hg and Ag from aqueous solutions.