Sulfate-loaded layered double oxide: A bifunctional adsorbent for simultaneous purification of metal ion and anionic dye

The design of bifunctional materials based on layered double oxides (LDO) with unique properties for the simultaneous removal of metals and dyes is necessary under the background of water sustainable development, yet remains hugely challenges. Herein, sulfate groups decorated on LDO (S-LDO) derived from LDH containing sodium dodecyl sulfate (SDS) were readily prepared via one-step calcination method, which exhibited favorable removal performance toward acid orange 7 (AO7, 4947.22 mg/g) and Cu(II) (181.80 mg/g) in the single system. In AO7-Cu(II) binary system, the removal capacity of Cu(II) was markedly enhanced, but slightly inhibited for AO7 removal owing to competitive adsorption. Additionally, the environmental condition (e.g., pH and ionic strength) had no influence on both contaminants removal. Multiple adsorption-desorption experiments unveiled the well sustainability of S-LDO. Such excellent removal performance was detailly explained by elemental mapping, XRD, and FT-IR. Memory effect, complexation and surface adsorption contributed to AO7 removal. While for Cu(II) removal, the synergistic effect between LDO and SO42- via chemical precipitation as well as the strong affinity of SO42- groups via chemisorption played crucial roles. Besides, the electrostatic interactions and additional N-containing adsorption sites offered by the adsorbed AO7 were responsible for the enhanced Cu(II) removal in the binary system. Overall, this work provides valuable information for designing bifunctional adsorbents based on LDO, with the promising application for simultaneous purification of metal ions and anionic dyes.

Automated summary

This study presents the preparation of sulfate-modified LDO through a simple method, showing good performance in the removal of Acid Orange 7 and Cu(II). In the binary system of AO7-Cu(II), the removal capacity of Cu(II) was significantly enhanced, while slightly inhibited for AO7 due to competitive adsorption.