Uniformly coating ZnAl layered double oxide nanosheets with ultra-thin carbon by ligand and phase transformation for enhanced adsorption of anionic pollutants

The increasing severity of water pollution has strongly urged to develop green and efficient adsorbents for waste-water treatment. In this work, ZnAl layered double oxide nanosheets uniformly coated with ultra-thin amorphous carbon shells (ZnAl-LDO@C) were fabricated by modifying ZnAl layered double hydroxides (LDHs) with molecular ligands followed by calcination. Compared with their counterparts derived from the pristine ZnAl-LDH, ZnAl-LDO@C nanosheets exhibit higher specific surface area with abundant and highly accessible active sites. The adsorption performance of the ZnAl-LDO@C nanosheets for methyl orange (MO) and hexavalent chromium [Cr(VI)] ions was investigated in detail. It is found that the channel-like hydrophilic carbon shells facilitate the diffusion of water molecules and ions, leading to the fast adsorption rate. In addition, the rich oxygen-containing functional groups in the amorphous carbon shells can efficiently improve the adsorption capacity through multiple interactions. As a result, ZnAl-LDO@C nanosheets exhibit superior adsorption performance for MO and Cr(VI), outperforming most LDH- or LDO-based adsorbents reported previously. Meanwhile, a new oriented overlapping intercalation mechanism for MO adsorption was proposed for the first time to clarify how MO molecules arrange at the interlayer space.