Hierarchical Fe3O4 Core-Shell Layered Double Hydroxide Composites as Magnetic Adsorbents for Anionic Dye Removal from Wastewater

Hierarchical core-shell Fe3O4@Mg3Al-CO3 layered double hydroxide (LDH) as an efficient magnetic adsorbent was prepared and investigated for the adsorption of anionic dye under ambient conditions. The material was thoroughly characterized by a variety of spectroscopic methods, which indicate that it was composed of spherical Fe3O4 (ca. 330 nm) core with a vertically aligned Mg3Al-CO3 layered double hydroxide shell coating. Calcination of Fe3O4@Mg3Al-CO3 LDH at 400 degrees C gives a layered double oxide coated Fe3O4 nanoparticles (Fe3O4@Mg3Al-CO3 CLDH), which is shown to be an efficient magnetic adsorbent for removal of the anionic dye, C.I. Acid Yellow 219 (AY219) from aqueous solution under ambient conditions. The adsorption of AY219 from aqueous solution utilizes the "memory effect" of LDHs by which the calcined LDH can be reconstructed by intercalation of AY219 in water. During the multi-cycling tests, a stable adsorption capacity of 1024 mg/g was achieved after 3 cycles, which is the highest value among all reported magnetic dye adsorbents. We also demonstrate that the core-shell structure played a great role for the superior performance of Fe3O4@Mg3Al-CO3 CLDH, as its performance was much better than a control hybrid mixed phase Fe3O4/Mg3Al-CO3 LDH. This research suggests that Fe3O4@Mg3Al-CO3 LDH adsorbent is a promising candidate for the treatment of wastewater contaminated by anionic dyes.