Functionalized layered double hydroxide with nitrogen and sulfur co-decorated carbondots for highly selective and efficient removal of soft Hg2+ 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 Hg2+ ions. N,S-CDs-LDH displayed a selectivity order of Ag+> Hg2+ >> Cu2+ >>> Pb2+ > Zn2+ > Cd2+ for their adsorption. The enormous capacities for Hg2+ (625.0 mg g-1) and Ag+ (714.3 mg g-1) and very high distribution coefficients (Kd) of 9.9 × 106 mL g-1 (C0 = 20 mg L-1) and 2.0 × 107 mL g-1 (C0 = 20 mg L-1) for Hg2+ 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 Hg2+ and Ag+ fitted well with the pseudo-second order model. For Hg2+ and Ag+, an exceptionally rapid capture with removal ∼100% within 80 min was observed (Cions = 30 mg L-1 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 Hg2+ and Ag+ from aqueous solutions.