Layered double hydroxides intercalated with sulfur-containing organic solutes for efficient removal of cationic and oxyanionic metal ions

Mg/Al layered double hydroxides (LDH) intercalated with sulfur containing-organic anions (l-cysteine, potassium ethyl xanthate, and sulfate sodium dodecyl) were directly synthesized through a facile co-precipitation method at low supersaturation, yielding Cys-LDH, PEX-LDH, and SDS-LDH, respectively. The synthetic LDH samples were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction, and were then applied to remove various potentially toxic metal ions from aqueous solutions. The results demonstrated that the Cys and PEX anions were successfully intercalated into the interlayer region of LDH as a horizontal orientation, while the SDS anions as vertical orientation with a tilt angle of 23°. The synthetic LDH samples were a non-porous material with their low specific surface area (2.99–18.2 m2/g). The Langmuir maximum adsorption capacity (Qomax) of LDH generally exhibited the following order: SDS-LDH > Cys-LDH > PEX-LDH > LDH. The Qomax of SDS-LDH was 418 mg/g for Cd2+, 402 mg/g for Pb2+, 206 mg/g for Cu2+, 156 mg/g for Ni2+, and 97.4 mg/g for MnO4− adsorption. The feasible adsorption mechanism was also discussed and proposed. LDH intercalated with sulfur containing-organic anions are a promising dual-electronic adsorbent for efficiently removing cationic and oxyanionic metal ions from water environment.