Enhanced removal of multiple metal ions on S-doped graphene-like carbon-supported layered double oxide: Mechanism and DFT study

In this study, an innovative sulfur-doped graphene-like carbon-supported layered double oxide (G/S-LDO) was developed for removing toxic heavy metal ions (HMIs; Pb(II), Cd(II), and Co(II)) that are frequently found in wastewater. In single-solute systems, the maximum adsorption capacities were 720.01 (Pb(II)), 473.11 (Cd(II)), and 170.91 (Co(II)) mg/g, which were significantly higher than that of pure LDO and other materials reported in the literature. Even in mixed systems, the outstanding adsorption performance of G/S-LDO toward HMIs was observed with high distribution coefficient values (Kd, > 100 L/g). We found that the excellent performance of G/S-LDO depended both on LDO and sulfur-doped graphene-like carbon (G/S) in a complicated manner. In detail, the released OH– from LDO as precipitate agent contributed to HMIs removal. Further, G/S enhanced the 35.42% Pb(II) adsorption, 58.19% for Cd(II) and 48.69% for Co(II) via the complexation and the cation-π interaction from graphene, and coordination and precipitation effect resulting from the doped S. Consistent with experimental results, density functional theory (DFT) calculations unveiled the essence of the enhancement by G/S, and showed that the orbital hybridization between S p and the HMIs p and d states electrons played an important role on HMIs removal. Finally, the recyclability and leaching experimental results suggested the high stability and reusability of G/S-LDO. This work provides new insights into the interactions of HMIs with G/S-based materials, which may facilitate the development of prospective HMIs capturing agents in future studies.