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

Abstract

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.