[C3N3S3]3- intercalated Mg/Al layered double hydroxide for high-efficiency and superfast removal of Pb2+, Hg2+, and separation of Ag+ ions: Performance and mechanism

Reducing the levels of heavy metal ions in practical waters to below the limitation for drinking water remains a great challenge. Herein, [C3N3S3]3- anions with the advantages of strong binding affinity, robust stability, low toxicity, and low cost were intercalated into Mg/Al-LDH to prepare a high-performance LDH (MgAl-C3N3S3-LDH) for highly selective capture of heavy metal ions. Owing to the strong binding capability of [C3N3S3]3- anions and excellent accessibility of LDH, the as-prepared MgAl-C3N3S3-LDH displays superior performance for the selective capture of Pb2+, Ag+, and Hg2+ ions, including superfast kinetics (15 min, 1 min, and 3 min for Pb2+, Hg2+, and Ag+), high capacity (Pb2+: 295.5 mg & sdot;g-1, Hg2+: 480.8 mg & sdot;g-1, Ag+: 454.5 mg & sdot;g-1), superior anti-interference ability, and preeminent selectivity. Importantly, MgAl-C3N3S3-LDH could effectively remove trace amounts of Pb2+, Hg2+, and Ag+ under the coexistence of excessive interfering cations and reduce the concentrations of these ions to lower than the acceptable limits of drinking water. Apart from the superior removal performance, the stability and low cost of interlayer [C3N3S3]3- anions could overcome the limitations of the widely applied LDHs intercalated with S-containing polysulfide anions, including high price, inferior chemical stability, sensitivity to atmospheric oxygen, and harsh synthesis conditions. Taken together, the MgAl-C3N3S3-LDH is a promising scavenger for the trap of toxic heavy metal ions from wastewater and the extraction of low-grade silver from copper-rich environments. The elucidation on the removal mechanism may promote the exploration of other new LDHs as high-performance scavengers for the purification of heavy metal ions polluted water.